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Report of the sub-committee on the environment and health.

4. Occurrence of pesticides in the environment

Pesticides are distributed in the environment through spraying, spreading as granulate, with dressed seed, through swabbing, etc. During spraying, the pesticides can be carried by the wind over both short and long distances. Some chemicals can also evaporate from the surface of plants or soil. Atmospheric transport can be of considerable magnitude and is often far-reaching and transboundary. Pesticides can also be washed out from the atmosphere with rainwater or be deposited on surfaces by so-called dry deposition. Pesticides can spread with rainwater to the aquatic environment, where they occur in soil water, run-off water, drain water, watercourses and lakes. Lastly, pesticides can be conveyed to the environment by accident or through unlawful use.

This section describes the occurrence of pesticides in the different compartments, as shown in table 4.1. This table also shows the types of organism that are exposed to pesticides. Section 4.1.6 also describes how pesticides can be distributed in the environment and thus contribute to exposure of people and the environment. The possible effects of pesticides are described in section 4.2. The main effects occur in connection with the treatment with pesticides, when organisms are directly affected, but there are also indirect effects as a consequence of the impact on food chains. The report does not cover bioaccumulation of pesticides in organisms and possible concentration in food chains. The Danish Environmental Protection Agency’s assessment of the bioaccumulability of pesticides is certain to lead to such pesticides not being authorised in Denmark.

Table 4.1
Compartments in which pesticides occur and the types of organisms exposed to them. The table also shows the sections of the report in which the occurrence is described and the sections in which the potential effects of pesticides in the different compartments are described.

Systematic data are not available on the occurrence of pesticides in lakes and coastal waters, so the report does not include data from these compartments.

4.1 Pesticides in groundwater

Denmark’s water supply system is based on pure groundwater, which can be supplied to the consumers without treatment. In the last few decades, groundwater has been found to be contaminated with industrial chemicals, leachate from landfills, nitrate, heavy metals and, lately, pesticides. In 1994, contamination of the groundwater in Ejstrupholm with the herbicide atrazine led to splash headlines in the media. At the same time, countrywide analyses showed that pesticides were commonly found in the groundwater. New research results also show that even in clayey soil, fissures and cracks from the Ice Age enable pesticides to leach down to the groundwater relatively quickly.

Groundwater quality is one of the main elements of Denmark’s environmental legislation. For pesticides, Denmark uses the EU’s limit values of 0.1 microgramme per litre water for every substance and 0.5 microgramme per litre water for the sum of pesticides, irrespective of the nature of the substance. Since groundwater is regarded as a basic resource that must be kept free of pollution, these limit values have been set as "hygienic limit values". This is further supported by the fact that the groundwater used as drinking water forms over long periods of time. This means that by the time pollution can be measured in the aquifer itself, it is too late to avert it or control the extent of it.

Database

In Denmark, groundwater is analysed for pesticides and, in some cases, for degradation products in different contexts:

	The Aquatic Environment Plan’s National Groundwater Monitoring Programme, GRUMO
	The Aquatic Environment Plan’s Nationwide Monitoring Programme for Agricultural Catchments, LOOP
	The water companies’ raw-water monitoring system
	Expanded analytical programmes carried out for example by county authorities and water companies.

Groundewater monitoring programme GRUMO

The groundwater monitoring programme (GRUMO) covers 67 monitoring areas spread around the country. The areas have been chosen with a view to providing a representative picture of Denmark’s aquifers. In most cases, the monitoring areas are situated in regions in which land is predominantly used for farming. Most of the areas include an extraction well to a waterworks and 10-20 specially established monitoring wells that characterise the main flow pattern of the groundwater (Figure 4.1).

The samples of water are extracted from well screens. A "well screen" should be understood to mean a closed pipe placed at the lower end of the groundwater well shaft. The well screen is equipped with slots or similar openings, which, in interaction with a screen pack of filter gravel around the well screen, are intended to retain the fine particles in the soil. The length of the well screen can vary so that the pumped up water comes from the depth interval in which the well screen is placed. Three types of well screen are used in the groundwater monitoring programme: point, line and volume monitoring screens. The last-mentioned type is often a waterworks well. In the point-monitoring and line-monitoring screens, the water samples represent the chemistry of the water samples at a specific point at a specific time in the aquifers examined. The volume-monitoring screens, on the other hand, represent mixed water, cf. the section on raw-water monitoring.

Figure 4.1 Look here!
Types of monitoring in the monitoring programme. GVS = groundwater table

The Nationwide Monitoring Programme for Agricultural Catchments (LOOP)

The Nationwide Monitoring Programme for Agricultural Catchments (LOOP) is carried out in five well-defined run-off catchment areas in agricultural regions where farming practice is known. Among other things, groundwater near the surface is monitored, so it is possible to relate leached substances to the use of the land. However, there are only limited data concerning pesticides from LOOP.

The water companies’ raw water monitoring system

The raw water monitoring system includes monitoring the water from the water companies’ extraction wells. In many cases, the interval in the wells from which water is extracted is of considerable length, and the water can be extracted from several separate saturated sediments. A water sample from the raw water monitoring system is therefore often a "mixed sample" of different types of water of different age and containing different substances. Since a number of water companies have extraction wells near towns, pesticides detected in the raw water monitoring system often bear signs of non-agricultural use.

In its yearly reporting of the results from the groundwater monitoring programme, GEUS gives the results from GRUMO, LOOP and the water companies’ raw water monitoring system separately because they concern different types of water sample.

Detection of a pesticide, or a metabolite, is defined as detection of the substance in question above the current detection limit. The laboratories use different detection limits. For example, DMU specifies a detection limit of 0.005 microgramme per litre for some substances, while other laboratories specify a detection limit of 0.01 microgramme per litre for the same substances. The detected substances are then divided into two groups: one over the detection limit and one over or equal to the limit value (i.e. the latter is a subset of the first group).

Pesticides have been found in groundwater all over the country with the exception of some areas north of the Limfjord and in North Zealand. Table 4.3 shows the pesticides detected in the raw water monitoring system.

The groundwater monitoring programme, GRUMO

The national groundwater monitoring programme gives a complete picture of the state of the groundwater, including the situation with respect to pesticides (GEUS 1998). Under the groundwater monitoring programme, analyses were carried out for eight pesticides in 1,014 well screens in the period 1990-1997. The programme covers two triazines (atrazine, simazine), four phenoxyacetic acids (dichlorprop, mechlorprop, MCPA, 2,4-D) and two nitrophenols (dinoseb, DNOC). Of the eight GRUMO pesticides, three (atrazine, dinoseb and DNOC) are now banned, while five of the others are subject to restrictions with respect to dosage, crops, etc. In all, 4,230 analyses of water samples have been carried out for these eight substances. As a consequence of the county authorities’ expanded analytical programmes, data were reported in 1998 from 594 well screens in the monitoring system from which water samples were analysed for more pesticides and their degradation products.

One or more of the eight GRUMO pesticides were detected one or more times in 121 well screens. The screens came from 101 wells, in 16 of which pesticides were found in two or three screens. The 121 screens correspond to just over 12% of the screens analysed, while the limit value for drinking water (0.1 microgramme per litre) was exceeded in 35 screens, corresponding to just under 3.5%, see table 4.2. There is often an interval of three years between sampling, and as pesticides normally occur in pulses, they are often not detected again in subsequent samples.

In the 594 screens in which some of the county authorities have carried out expanded analytical programmes, pesticides or degradation products have been detected in 21% and the limit value has been exceeded in 13%, see table 4.2. However, data have usually only been reported on one set of water samples from the 594 screens.

Counties analyse samples from sensitive wells for BAM

In the case of 2,6-dichlorobenzamide (BAM), which has been detected in about 14% of the screens analysed, the data must be treated with caution because the county authorities selected sensitive screens for testing for this compound. Sensitive screens should be understood to mean screens in young groundwater near the surface or screens close to potential sources of pollution. BAM is a degradation product, the parent compound of which is dichlobenil. Dichlobenil has not been used for agricultural purposes and is no longer permitted in Denmark.

The triazine degradation products desethylatrazine, desisopropyl-atrazine and hydroxyatrazine have been detected in 6.6%, 5% and 2.8%, respectively. However, hydroxyatrazine has been analysed for in only a few screens, and experience from other countries does not normally reveal high detection percentages for this substance.

Table 4.2
Detection of pesticides related to the number of analysed screens in the groundwater monitoring programme (GEUS 1998).

m g/L = microgramme per litre

The extension of the monitoring programme in 1998 to approx. 50 pesticides and degradation products may reveal possible further occurrence of pesticides in groundwater, particularly as only a few of the 594 screens have been analysed for all 50 substances.

The depth distribution of the pesticides shows that the eight GRUMO pesticides occur in 22% of the high-lying and youngest groundwater in the interval 0-10 metres below ground level and that the frequency decreases with the depth. Where screens have been analysed for more than eight substances in the monitoring programme, pesticides have been detected in 34% of the groundwater samples in the interval 0-10 metres below ground level, see figure 4.2. Of these, 23% of the detections were over or equal to 0.1 microgramme per litre.

It can thus be concluded that pesticides and their degradation products occur particularly in young groundwater. This may be due partly to the fact that the substances are gradually degraded while being transported down through the aquifers and partly to the fact that they are transported horizontally with the groundwater to watercourses, lakes and groundwater wells. It is also possible that the pesticides are transported towards the groundwater so slowly that the increased occurrence and rising concentrations of the substances found today in young ground water will be found in the lower aquifers in the future. It will only be possible to assess this when there are longer time series in the monitoring programmes, dating of groundwater with CFC and results from research projects that are being carried out to elucidate this.

Figure 4.2
Detections of pesticides in % against depth in metres below ground level are shown as white bars. The youngest groundwater is presumably most often found in the interval 0-10 metres below ground level. In analyses for eight GRUMO pesticides in the depth interval 0-10 metres below ground level, pesticides have been detected in 22% of the screens. The detection percentage rises to 34% when analysing for more than eight pesticides. In the bar chart, the black, horizontal bars show the detection percentage for the number of detections over or equal to 0.1 microgramme per litre (GEUS).

(Figure texts:
fundprocent = detection percentage
dybde interval i meter under terræn = depth in metres below ground level
pesticider = pesticides
dybde i meter under terræn = depth in metres below ground level
udvidet analyseprogram = expanded analytical programme

The water companies’ raw water monitoring system

In the water companies’ raw water monitoring system, pesticides have been detected in 17% of 4,209 wells, and the limit value has been exceeded in 6%. These wells have mainly been analysed for the eight GRUMO pesticides.

The most frequently analysed substances are shown in table 4.3. The number of analyses does not reflect the number of analysed wells; for example, dichlorprop has been analysed in 5,714 water samples from 3,998 wells. Of the eight GRUMO pesticides, dichlorprop, mechlorprop and atrazine have been detected most frequently, while, in percentage terms, degradation products from triazines have been detected more frequently in the water samples than, for example, atrazine. The relatively frequent occurrence of hexazinone is surprising because this substance has only been detected in samples from groundwater monitoring wells even though it has been used frequently in forestry. One explanation could be that hexazinone has been used for treating urban areas.

The distribution of finds of pesticides in the water companies’ wells is very reminiscent of the distribution in the groundwater monitoring system. However, the analysed pesticides occur in 26% of the water samples taken from wells with "top screen" in the interval from 10 to 20 metres below ground level, compared with 13% in the groundwater monitoring programme. This may be because the water companies in some areas extract groundwater from high-lying, fractured limestone, where the groundwater is presumably younger and more affected by the use of pesticides on the surface of the earth.

As a consequence of the many detections of the degradation product BAM (2.6-dichlorobenzamide) in the last few years, some water companies have analysed for this substance in their routine monitoring. The water companies have carried out 2,310 BAM analyses of water samples from 1,656 wells and have detected BAM in 448 of them, corresponding to around 30%. The limit value for drinking water was exceeded in 187 wells, corresponding to about 11% of the analysed wells. Most of the detections of BAM in waterworks wells were made from ground level to a depth of 0-30 metres, where the highest concentrations were also measured. BAM’s parent compound is a herbicide, dichlobenil, which has primarily been used in urban areas. Because of the earlier widespread use of the now prohibited parent compound dichlobenil, BAM can thus be expected to occur both under built-up areas and under farmyards, gravel roads and other areas kept free of vegetation.

Expanded analytical programmes

In recent years, the county authorities, the water companies and DMU have carried out a number of expanded analytical programmes for groundwater and waterworks water. Results covering 108 pesticides and metabolites are available. Of these 108 substances, around 40 have been detected in Danish groundwater, 29 of them in concentrations above the limit value for drinking water, see table 4.4. DMU's expanded analytical programmes comprise mainly analyses of groundwater from the LOOP regions. The data in the table are from analyses carried out in 1997, from older analyses that were not reported to the groundwater database at GEUS, and from analyses that were partly or totally reported to the groundwater database at GEUS, e.g. analytical programmes carried out in LOOP and a few groundwater monitoring areas. The table does not include data from the general monitoring of the groundwater monitoring areas. Twenty of the pesticides detected in groundwater were in use in Denmark in 1996, but some of them have since had restrictions imposed on their use or have been banned. However, a few substances, e.g. the degradation product ETU, was found in both soil water and groundwater in a research project by Fladerne Bæk (river) and in an analysis carried out by Copenhagen County Council in 1997, in which ETU was detected in piezometric wells close to a landfill site.

Table 4.3 Look here!
Detections of pesticides analysed in connection with the water companies’ raw water monitoring system (Brüsch et al. 1998). Ranked by falling number of analyses. Consumption data from Bekæmpelsesmiddelstatistik (Pesticide Statistics) 1997 (Danish Environmental Protection Agency 1998a).

Table 4.4 Look here!
Pesticides detected in groundwater in county authorities, water companies and DMU’s expanded analytical programmes. The situation in March 1998 from GEUS (Brüsch et al. 1998). Consumption data from Bekæmpelsesmiddelstatistik (Pesticide Statistics) 1997 (Danish Environmental Protection Agency 1998a).

In connection with a search of the literature for analytical data from foreign monitoring programmes for pesticides in groundwater, a search was made for 544 pesticides and metabolites that have been or still are used in Denmark. Of these substances, data were gathered on 281 that have been analysed abroad, 159 of which have been found mainly in groundwater. About 55 of these were used in Denmark in 1996. However, for many of these substances, there have been only a few finds in groundwater.

Finds of pesticides under different types of area

Finds of pesticides in deep aquifers cannot be definitely related to specific fields or other areas within the individual catchment area boundaries.

Prompted by a dialogue with the Agricultural Advisory Centre, GEUS has calculated the impact of pesticides on groundwater close to the surface of the ground in rural areas (including forests, wetlands, etc.) on the basis of data from the groundwater monitoring programme. The data treatment is conducted in relation to permitted and banned pesticides and in relation to agricultural and non-agricultural pesticides. Hydroxy-terbuthylazine was not included in the calculation owing to too little data. All data from the City of Copenhagen, Frederiksberg Municipality and Copenhagen County were omitted. Only screens placed in the interval 0-10 metres below ground level were included because it is estimated that groundwater near the surface is often the youngest groundwater. However, the age of this groundwater can vary.

Tables 4.5-4.7 show that pesticides found in the groundwater monitoring programme in rural areas in groundwater close to the surface are equally distributed between agricultural and non-agricultural substances. Most of the substances found are now banned or regulated with restrictions on their use.

Table 4.5
Permitted and banned pesticides. Of the 4 phenoxy acids, only MCPA is included as permitted on account of a large consumption, while the other 3 are included as banned substances even though they are still sold in small quantities. Desisopropylatrazine is included with 50% in each group because the metabolite can come from pesticides permitted today.

m g/L = microgramme per litre

Table 4.6
Agricultural/non-agricultural pesticides. All triazines are equally distributed between agricultural and non-agricultural because these substances have also been used in both forestry and fruit growing and in urban areas. However, simazine and hexazinone have not been included as agricultural substances. In this calculation, GEUS has not differentiated between permitted and banned substances.

m g/L = microgramme per litre

Table 4.7 Look here!
Background data, groundwater close to ground level. Groundwater monitoring data. Urban areas omitted. Only screens 0-10 metres below ground level are included. P = permitted; R = permitted with restricted use or authorised with conditions; B = banned; A = agricultural use; NA = non-agricultural use; Fr = fruit, berries, forest, plantation, etc. "Number of screens ³ 0.1 m g/L" is a sub-set of "number of screens with finds" (m g/L = microgramme per litre).

Table 4.8 Look here!
Pesticides and metabolites found in ground water in the five nationwide monitoring catchment areas during the period 1990-1997. The median value has been calculated on the basis of median values at screen level. GRUMO pesticides are in bold (GEUS 1998) (m g/L = microgramme per litre).

Triazines (including atrazine) and their metabolites are included in the calculation as equally distributed between use in agriculture and in urban areas. However, since agricultural land predominates in the groundwater monitoring programme, these substances should presumably be weighted higher as agricultural use. This is supported by the available data on pesticide finds in groundwater near ground level in the LOOP areas, where only agricultural land with known cultivation practice is monitored. There, high find percentages are found, particularly in the case of triazines’ metabolites (Table 4.8).

4.1.2 Conclusions

In Denmark, extensive data are available on the distribution and occurrence of the 8 GRUMO pesticides in Danish groundwater. A smaller database covers other pesticides and metabolites. Together, these data show that pesticides and metabolites occur particularly in the uppermost and youngest aquifers. In these aquifers, pesticides have been found in 34% of analysed screens in an expanded analytical programme in the interval 0-10 metres below ground level. A planned future expansion of the monitoring system and the water companies’ expanded analytical programme (covering more substances) will show the extent to which groundwater near the surface contains pesticides and metabolites. The frequency of finds of metabolites from the now banned substances atrazine and dichlobenil is high both in the groundwater monitoring system and in the water companies’ raw-water monitoring. It should be noted that the water companies’ raw water often comes from wells in areas near towns, so the finds are characterised by non-agricultural use of pesticides.

The following specific conclusions can be drawn:

One or more of the 8 GRUMO pesticides (dichlorprop, mechlorprop, MCPA, 2,4-D, dinoseb, DNOC, atrazine and simazine), have been found in just over 12% of the analysed 1,014 screens in the groundwater monitoring areas. The limit value is exceeded in 3.5%. In 42 screens, a pesticide has been found more than once, corresponding to just over 4% of the analysed screens.

In 594 GRUMO screens analysed with expanded analytical programmes, pesticides or metabolites have been found in 21% and the limit value has been exceeded in 13%. With BAM omitted, pesticides have been found in approx. 16% of 551 screens analysed for more than the 8 GRUMO pesticides.

The depth distribution in the groundwater monitoring areas shows that the 8 GRUMO pesticides occur in 22% of the groundwater near the surface and that the frequency decreases with the depth. Where screens have been analysed for more substances than the 8 GRUMO pesticides, pesticides have been found in 34% of the groundwater near the surface. Of these finds, 23% are equal to or greater than 0.1 microgramme per litre.

In a number of expanded analytical programmes, about 40 pesticides and metabolites are at present found in groundwater, with 29 of them in concentrations above the limit value. In foreign monitoring programmes, 159 substances that have been or are still being used in Denmark have been detected.

In the water companies’ raw water monitoring, pesticides have been found in 17% of the wells tested, with the limit value exceeded in 6%. The distribution of finds of pesticides in the water companies’ wells is very reminiscent of the distribution in the groundwater monitoring system.

The water companies have found BAM, (2,6-dichlorobenzamide), in approx. 30% of 1,656 tested wells, with the limit value exceeded in around 11%.

In the groundwater monitoring areas it is not possible to relate finds of pesticides in aquifers to specific land use in fields and other areas.

A report on pesticides detected in groundwater near the surface in rural groundwater monitoring areas shows an equal distribution of agricultural and non-agricultural pesticides. Most of the substances found are now banned or regulated.

In the pesticide finds in groundwater, the limit value of 0.1 microgramme per litre for drinking water is exceeded in up to 13% of the samples. The metabolite BAM from the universal herbicide dichlobenil has been detected in 30% of the water companies’ wells, but a wide range of substances used by farmers for treating crops are also present in a relatively large number of wells. Larger amounts of pesticides were detected in drain water and soil water than in groundwater, and this may reflect concentrations that may similarly later move towards the groundwater, during which they may undergo degradation and possible formation of metabolites. In both watercourses and ponds, a number of pesticides have been detected in higher concentrations than the concentrations that have effected aquatic organisms in the laboratory.

4.2 Occurrence of pesticides in watercourses

In the following, the occurrence of pesticides in watercourses is described. The effects of their occurrence are described in section 5.3. These data have also been used in calibrating the models for calculating the consequences of a partial phase-out of pesticides.

Pesticides can reach watercourses through:

	spray drift
	spraying too close to watercourses
	deposition from the air through long-distance atmospheric transport
	leaching from treated fields and transport to watercourses via drainage pipes or groundwater
	surface run-off
	pollution from point sources, e.g. machine-washing sites.

The sources with the biggest implications for watercourses, quantitatively, are run-off from land treated with pesticides and leaching with transport in drain water. Direct spraying and leaching from washing sites are unlawful pollution events that imply a considerable risk of harmful effects in watercourses. Surface run-off from sloping fields can lead both water-soluble substances and substances that bind to particles of soil out into a watercourse. Particle-borne transport occurs during heavy run-off of rainwater or melt water and soil erosion.

Up to and including 1996, 32 different pesticides were detected in Danish watercourses, corresponding to approx. 30% of the pesticides tested for (see table 4.9). Several different pesticides can be found simultaneously in the individual watercourses. Pesticides are found in watercourses in all seasons, but most frequently in the spraying season and during increased run-off after rain. The frequency of pesticide finds and the concentration of pesticides are generally highest in agricultural catchment areas with clayey soil. Some of the pesticides are found in only a few per cent of the samples, while others are found in up to 64% of them.

The detection frequency is highest in the spraying periods and in connection with precipitation with increased run-off in watercourses. The highest value in the analyses up to and including 1996 was 10 microgramme per litre (bentazon). 12 of the pesticides were found in concentrations above 1 microgramme per litre and 31 substances were found in concentrations above 0.1 microgramme per litre. Glyphosate was tested for in 6 samples and found in all of them in concentrations from 0.02 to 0.21 microgramme per litre (Funen County 1997, Kronvang 1998; Spliid, Mogensen 1995).

Analyses of surface water in Funen County 1997

Since 1996 there have as yet been only a few reports from counties and municipalities. Funen County Council has published the results of analyses of 6 watercourses, 4 springs and 11 drains in agricultural areas (Funen County 1999). Samples were tested for 94 active ingredients and 5 metabolites. Of these, 33 different substances were found in concentrations up to 10 microgrammes per litre (the herbicide bentazon). Of these, 26 are authorised for use today. It should be noted that one of the substances found, metazachlor has never been authorised in Denmark. Most of the substances were found in concentrations above 0.1 microgramme per litre. Up to 18 different pesticides were found in individual watercourses within the same day. The substances found most frequently in 33 samples from watercourses in concentration of or over 0.1 microgramme per litre were the metabolite AMPA from glyphosate (79%), the metabolite BAM from the banned herbicide dichlobenil (48%), isoproturon (36%), glyphosate (31%), the banned herbicide hexazinone (30%), and diuron (24%). The substances and concentrations found largely correspond to earlier finds.

The study indicates that many of the pesticides occurring in the watercourses are transported to them via drains, particularly in the spraying season. It has also been established that there is some transport of pesticides via urban wastewater. Drift does not seem to be of any great significance to the occurrence of pesticides in the watercourses tested. On the basis of observations over a 10-year period, Funen County Council estimates that more than 200 km of watercourse, corresponding to around 20% of the watercourses tested, have been exposed to acute damage, since large numbers of crustaceans and aquatic insects have been killed.

Analyses of water from a watercourse in Kolding Municipality in 1998

In May-June 1998, Kolding Municipal Council tested 14 water samples from Dalby Møllebæk (a mill brook), situated in an agricultural catchment area consisting mainly of moraine clay (Kolding Municipality 1998). The analysis covered 33 pesticides or metabolites, of which 21 were found in concentrations of up to 11 microgramme per litre (simazine). Of these 21 pesticides, 14 are authorised for use today, while 5 are subject to restrictions. The 3 most frequently found substances were BAM, isoproturon and simazine, all of which were found in all the analysed water samples. Also found in at least half of the samples were the substances MCPA, mechlorprop, atrazine, bentazon, desisopropylatrazine, ethofumesate, metamitron, terbuthylazine, bromoxynil, propiconazole, dichlobenil, dichlorprop and ioxynil. The highest concentrations were found in connection with precipitation events. The frequent occurrence of atrazine (79% of the samples) and atrazine’s metabolites indicates that the occurrence came from use of the substance before it was banned in 1994 and thus from the groundwater.

The figures from Funen County for 1997 and those from Kolding Municipality for 1998 will be included in the overall survey for the years in question when the finds are reported. They therefore do not appear in the tables in this chapter as the data supplied are incomplete seen from a countrywide perspective.

Table 4.9
Occurrence of pesticides in Danish watercourses with indication of number of positive finds in relation to number of samples. H = herbicide, F = fungicide, I = insecticide. The samples were collected in the period 1989-1996 (Mogensen 1998).

Substances in italics are banned.
^a = permitted with restricted use/or authorised on special conditions
m g/L = microgramme per litre

Table 4.10 Look here!
Occurrence of pesticides in watercourses, with a breakdown in types of catchment area. The table shows the number of finds out of the total number of samples and the concentration range in microgramme per litre. The first study was carried out by DMU in 1989-1991. In 1994-1996 a major study was carried out in Funen County. In 1996, the table includes data from several counties (Mogensen 1998).

It will be seen from table 4.10 that the frequency of pesticide finds and the concentration of the pesticides are generally highest in agricultural catchment areas with clayey soils. That is presumably due to the fact that farmers on rich soil often farm more intensively and thus spray more often and to the fact that pesticides are quickly transported to watercourses via drains through cracks in the clayey soil. The fact that pesticides have been detected in springs indicates specifically that pesticides can be led to watercourses via groundwater. Fewer different pesticides have been found in forest watercourses, but the herbicides that are used in forests frequently occur in the watercourses. That applies particularly to hexazinone. Many different pesticides have been detected in urban watercourses, which cover both "urban watercourses" and "mixed catchment areas". Agricultural pesticides therefore also occur. Dichlobenil, which is used as a universal herbicide and particularly its metabolite, BAM (2,6-dichlorobenzamide), occur very frequently, both in urban areas, agricultural areas and forest watercourses, see table 4.11. Concerning BAM, readers are referred to section 4.1, where a similar frequency in groundwater is described.

In most of the watercourses, many different pesticides are found at the same time, which is of significance in the assessment of the effects on flora and fauna in the aquatic environment, see section 5.3.

Table 4.11 Look here!
Occurrence of metabolites (of a dichlobenil, b glyphosate, c atrazine) of pesticides in watercourses, with a breakdown by type of catchment area. The table shows the number of finds out of the total number of samples and the concentration range in microgramme per litre. Dichlobenil and atrazine may no longer be used in Denmark. The first studies were carried out by DMU in 1989-1991. In 1994-1996, a major study was carried out in Funen County. In 1996, the table includes data from several counties (Mogensen 1998).

4.2.1 Conclusions

32 different pesticides have been detected in Danish watercourses, corresponding to about 30% of the substances tested for, together with 4 metabolites. The frequency of finds is greatest in the spraying periods and in connection with precipitation events with increased run-off. The highest value of 10 microgrammes per litre was found for bentazon. 12 of the pesticides were found in concentrations above 1 microgramme per litre and 31 substances were found in concentrations above 0.1 microgramme per litre. Glyphosate was tested for in 6 samples and found in all of them in concentrations from 0.02 to 0.21 microgramme per litre (Funen County 1997, Kronvang 1998; Spliid, Mogensen 1995). The pesticides occur in all types of watercourse, but mostly in clayey agricultural catchment areas. Pesticides can be transported to lakes and watercourses with surface run-off. That applies both to water-soluble substances and to substances that bind to particles of soil and that are only transported with heavy run-off, which causes soil erosion. Therefore, both substances that are banned because of their mobility in soil (e.g. atrazine, dichlorprop and hexazinone) and substances that, as far as is known today, are only transported to the groundwater with leaching rainwater under extreme conditions (e.g. glyphosate, esfenvalerate and pirimicarb) have been detected. Also detected is DNOC, which can come from transboundary atmospheric transport and be synthesised from car emissions through atmospheric, chemical processes (see section 4.5).

The studies of watercourses are representative of Denmark

The first study was carried out in the period 1989-91, and the others in the period 1994-97. There are big differences in the sampling intensity and strategy in the various analyses. In some cases, sampling was done on predesignated dates; in some, it was concentrated in the spraying season, and in some, sampling extended over the whole year. Some sampling was done in connection with increased water flow in the watercourse. The analyses did not include samples taken because of suspected pollution from, for example, point sources. The watercourses analysed cover a number of counties and different types of catchment area and types of soil, and must generally be regarded as representative of Denmark. There are not as yet any long time series of measurements of pesticides in watercourses, but monitoring programmes in progress in the counties and countrywide studies will in time result in the necessary database for determining the development.

The following specific conclusions can be drawn:

32 pesticides have been detected in watercourses, corresponding to 30% of the substances tested for.

In many watercourses, several pesticides have been detected at the same time.

Detection of pesticides in springs indicates that pesticides can be carried to watercourses via groundwater.

The frequency of detection is highest in spraying periods and in connection with heavy precipitation, but pesticides have also been detected in watercourses outside the spraying periods.

The frequency of detection is highest in agricultural catchment areas with clayey soils.

There are not many different pesticides in forest watercourses, but pesticides that are or have been used in forests occur frequently (atrazine, hexazinone and dimethoate).

There are many different pesticides in urban watercourses.

The distance requirements made in connection with authorisation of pesticides are expected to reduce the frequency of detection in the future.

4.3 Pesticides in lakes and ponds

Pesticides enter lakes, coastal waters and ponds via watercourses, surface run-off from adjacent land, groundwater and atmospheric deposition, including spray drift. The effects of pesticides in stagnant water are described in section 5.3. There are as yet no systematic data on the occurrence of pesticides in Danish lakes and coastal waters. Data from these compartments are therefore not included in the report. In connection with Aquatic Environment Plan II, a measuring programme is being initiated, but results for lakes cannot be expected in the coming year.

The studies from stagnant water cover results from two projects. One includes samples from four ponds in the Køge district (Spliid, Mogensen 1995), while the other includes a number of ponds in South Funen and Avernakø (Briggs in press). In both districts, the ponds are in fields with clayey soil. Many field ponds have neither inflow nor outflow. It must therefore be expected that pesticides remain in them longer than in watercourses and that the risk to the aquatic organisms in them is greater. The results of these studies are given in table 4.12.

The concentration interval in the table indicates the lowest and highest concentration in the samples in which the pesticide in question was detected. Column 3 shows the number of samples analysed for the pesticide in question and the number of samples in which the substance was detected. All the substances for which the samples were analysed were detected, with the exception of bromoxynil and simazine. The highest concentration for an individual substance was 11 microgrammes per litre.

Table 4.12
Pesticides detected in ponds in Danish farmland in studies carried out by DMU in 1989-1991 and by Amphiconsult in 1994-1995 (Mogensen, Spliid 1997)

m g/L = microgramme per litre

4.3.1 Conclusions

There have been only a few analyses of stagnant water, and then only of ponds. Mechlorprop has been detected in concentrations up to 11 microgrammes per litre. In the case of 5 substances, the concentrations exceeded 1.0 microgramme per litre and in the case of 13 of the 15 substances tested for, the concentrations exceeded 0.1 microgramme per litre.

The ponds tested include several in the Køge region and on the island of Avernakø. The analyses were carried out at the beginning of the 1990s. Most of the sampling took place in the spraying season. The analyses of ponds were less extensive than those in watercourses and cannot be regarded as representative of Denmark as a whole.

The following specific conclusions can be drawn:

	15 pesticides have been detected in ponds.
	Danish analyses of pesticide concentrations in lakes and coastal waters are being initiated in connection with Aquatic Environment Plan II.
	Only a few analyses of pesticide concentrations in lakes and seawater have been carried out in Denmark.

4.4 Pesticides in drain and soil water

Soil water can be defined as water that is present in the uppermost part of the soil stratum. Soil water can be collected by installing ceramic or teflon suction cups in the soil to suck water out of the soil matrix. Drain water is water that runs freely through the soil to drainage pipes, which are typically placed at a depth of about 1 metre. Pesticides in drain water can thus, if mobile pesticides are used in periods with a lot of precipitation, have a retention time in the soil of just a few days or weeks. For pesticides that are bound in the soil or that are used in periods without downward movement of water in the soil, the retention time can be months or years.

Soil water samples containing pesticides generally indicate use of the pesticides in question on the surface of the ground directly over the sampling site or transport with rainwater. Pesticides spilled on the surface of the soil or pesticide waste buried near the sampling site can be detected in soil water or drain water, but if several suction cups are established under the same field, a point source occurrence near one of them can be detected.

Drain water samples represent water from the entire catchment area that is drained by the drainage system in question. The catchment area can include many fields with different uses, backfilled marlpits, buried waste, sites for filling and washing of spraying equipment, greenhouses, etc. To be able to interpret the result of a drain water sample it is important to know which catchment area the sample in question represents. By placing vertical drainpipes with screens at a depth of 1 metre one can extract drain water samples that represent the local area around the screen when the soil is saturated.

We have analyses of pesticides in soil and drain water from 10 different localities in Denmark. The samples analysed include samples from Højvands Rende and Bolbro Bæk, which are part of LOOP in Aquatic Environment Plan I. A number of samples have also been taken in special studies and research projects in the last 10 years. However, there have been no systematic analyses of pesticides in soil water and drain water of the kind carried out in groundwater.

The results of all analyses of pesticides and their metabolites in soil and drain water are shown in tables 4.13 and 4.14. Table 4.13 shows the occurrences in fields with sandy soil, and table 4.14 the occurrences in fields with clayey soil. These analyses do not include analyses of drain water from filling and washing sites, greenhouses, and other point sources, where high concentrations of pesticides have been found in special analyses.

The analyses cover 27 pesticides and metabolites. The number of analyses carried out is shown in the tables. The results are given as detections of less than 0.1 microgramme per litre, detections greater than 0.1 microgramme per litre and the highest concentration detected. It will be seen directly from a comparison of tables 4.13 and 4.14 that both the concentration levels and the frequency of detections are highest in localities with clayey soil. The substances detected in the highest concentrations are atrazine (7.8 microgrammes per litre), hexazinone (4.3 microgrammes per litre), dichlorprop (1.4 microgramme per litre) and 2,4-D (1.2 microgramme per litre). Concentrations greater than 0.1 microgramme per litre have also been found for the pesticides isoproturon, bentazon, MCPA, and mechlorprop, and for the degradation products desisopropylatrazine, 2,4-dichlorophenol and ETU.

Some of these detections can be correlated with pesticides used on experimental areas or stated to have been used on the land in question. For example, relatively high concentrations of both atrazine and hexazinone (herbicides) were detected under a Christmas tree plantation, where the substances had previously been used (Felding 1992). In some cases, low concentrations of pesticides have been detected in places where these substances have not been used for years. This could indicate that the retention time for the pesticides in question in the soil has been long in these cases. In a special analysis of the chlorophenoxy acids MCPA, dichlorprop, 2,4-D and mechlorprop, all the substances were detected after 3 years in soil water at a depth of one metre in concentrations that were in several cases greater than 0.1 microgramme per litre (Felding 1993). The detections of ETU are from a trial area treated many times with dithiocarbamate fungicides, which break down into ETU (Spliid 1998a).

As a test system between full-scale field analyses and simple laboratory analyses, lysimeter analyses with undisturbed columns of soil can be used to predict whether a pesticide or its degradation products can leach from a column of soil. Such lysimeter analyses now form part of the documentation material used as the basis for approving new pesticides. A lysimeter can consist of a block of soil sampled at the site in a steel frame without being disturbed. The lysimeter is moved to the test locality, where crops are grown in it and it is treated with the pesticide in the ordinary way. The naturally or artificially supplied water passing the block of soil is collected. Using a radioactively labelled pesticide, one can determine whether there is any breakthrough of radioactivity and thus of pesticide or degradation products. Where possible, the substances passing the soil column are identified by means of chromatographic methods and by comparison with reference substances. A lysimeter analysis is typically carried out several years after the pesticide has been applied. It can be used to determine the risk of a pesticide leaching in different types of soil, with different cultivation conditions and in different precipitation situations, with a surface area from 0.25 to 1 m².

To determine the mobility in columns of soil in the deeper soil layers, columns with a surface area of, for example, 0.25 m² can be sampled in a steel cylinder and taken to the laboratory, where the temperature and the groundwater’s movements can be simulated and controlled.

Table 4.13
Pesticides and metabolites detected in fields with sandy soil (Spliid 1998a)

n.d. = not detected
^M = metabolites
Italics = substances authorised in 1998, possibly with dispensation
m g/L = microgramme per litre

Table 4.14
Pesticides and metabolites detected in fields with clayey soil (Spliid 1998a)

n.d. = not detected
^M = metabolites
Italics = substances authorised in 1998, possibly with dispensation
m g/L = microgramme per litre

4.4.1 Conclusions

In a number of analyses, pesticides have been detected in soil water and drain water from fields that have been treated with pesticides. In the analyses described, there is information concerning the use of pesticides on the fields in several projects, while for a few localities, the figures cover the catchment area in general, and it is not possible to demonstrate a relationship between dosage and detections for the individual field. With the available data it is not deemed warranted to draw conclusions concerning relationships between dosage and concentration of pesticides in the water samples analysed.

The following specific conclusions can be drawn:

The pesticides detected in soil and drain water are often the same as are detected in the aquifers, see section 4.1.

The concentrations of pesticides detected in soil and drain water exceed the limit value for drinking water more frequently than in the groundwater analyses. Many of the pesticides detected are now banned in Denmark, but were permitted at the time of the analyses.

Owing to limited data, it is not deemed warranted to draw conclusions concerning relationships between dosage in the field and concentration of pesticides in drain and soil water.

Assuming that the extent of the catchment area is known and that the pesticides used in the area are known, a drain water analysis gives an idea of whether used pesticides or their degradation products can reach the groundwater. However, the results depend on the local conditions and the weather, and it is not possible to carry out a mass flow analysis that describes the fate of the pesticides in time and space.

Lysimeter studies and laboratory analyses of radioactively labelled pesticides and degradation products in undisturbed columns of soil can be suitable tools for judging the risk of leaching in connection with the use of pesticides in different soils.

Both the level of concentration and the frequency of detections are highest in clayey soils. However, the data are limited and can be improved with supplementary studies.

4.5 Pesticides in rainwater

As found by Felding (1998a), there have been relatively few studies in Denmark. In a cooperative project under the auspices of the Nordic Council of Ministers, rainwater samples were collected from 2 localities in Denmark – Ulfborg Plantation 10 km from the west coast of Jutland, and Gadevang near Gribskov, a forest in North Zealand – from 1992 to 1994. The analyses covered 10 pesticides: propiconazole, prochloraz, lambda-cyhalothrin, cypermethrin, esfenvalerate, deltamethrin, atrazine, mechlorprop, dichlorprop and MCPA. Only the phenoxy acids were detected, and the highest concentrations found were just under 0.4 microgramme per litre (Kirknel et al. 1997). The concentrations found were very small in relation to the dosage in field spraying. The effects of pesticides in rainwater are assessed in section 5.2.

In a current project, samples of precipitation are being collected from three Zealand localities: Gadevang, Gisselfeld and Lorup. The samples are analysed for the phenoxy acids: MCPA, mechlorprop and dichlorprop, and for the herbicide isoproturon. The highest concentrations found so far are just over 0.6 microgramme per litre for the phenoxy acids and just under 0.4 microgramme per litre for isoproturon. In most cases, the time when the herbicides were detected in the precipitation coincided with the time of use (Felding 1998a).

In autumn 1997, 13 mixed samples extracted from the above-mentioned 3 localities from September 1996 to November 1997 were analysed for 44 pesticide chemicals. Table 4.15 shows the content of the 13 samples. In all, 8 pesticide chemicals were detected: isoproturon, metamitron, DNOC, mechlorprop, methabenzthiazuron, 2-hydroxyterbuthylazine, terbuthylazine and 2,4-D. DNOC was found to be present during the entire period in a relatively high concentration range from 0.3 to 4.5 microgramme per litre. This substance has not been used in Denmark for the last 10 years. The substance can also be formed by atmospheric, chemical reactions, see section 4.5. There may thus be transboundary air pollution. DNOC has also been detected in groundwater near the surface and in watercourses (Spliid et al. 1996), see sections 4.1.1 and 4.1.2.

In 1990-1991, DMU measured the content of a -HCH and g -HCH (lindane) in rainwater in 2 localities in Denmark: Husby and Ulfborg in West Jutland. In 1992, analyses were carried out of samples from 3 localities: Ulborg, Bagenkorp and Anholt. The maximum concentration was found to be 0.1 microgramme per litre. The analysis indicated that the occurrence of lindane came from use in countries south and west of Denmark (Cleemann et al. 1995).

Table 4.15 Look here!
Pesticides and degradation products in rainwater samples collected in the period September 1996 to November 1997. In all, 13 samples were collected over a period of 2-3 weeks in Lorup, Gisselfeld and Gadevang on Zealand. DMU analysed the samples for 36 active ingredients and 8 metabolites. The concentrations are given in microgramme per litre. It will be seen that for isoproturon and DNOC, the concentration exceeds the drinking water limit of 0.1 microgramme per litre (marked in bold) (Felding 1998a).

Table 4.16 Look here!
Pesticides and degradation products in rainwater samples from Zealand. The table shows the figures from table 4.15 for the deposition of pesticides, calculated as g per hectare (Felding 1998a). The analysis covers 36 active ingredients and 8 metabolites.

In table 4.16, the measured concentration of pesticide chemicals from table 4.15 is converted from microgramme per litre to gramme per ha. In this analysis, which does not cover all volatile pesticides, DNOC (4,6-dinitro-2-methylphenol) constitutes just under 90% of the total quantity of pesticide chemicals in the atmospheric deposition with rainwater. The distribution of phenols and nitrophenols in clouds and the occurrence and formation of phenols in the atmosphere have been described by Lüttke and Levsen (1997) and Lüttke et al. (1997). It is concluded in these studies that DNOC occurs mainly in gaseous form rather than in liquid form in the atmosphere. Dinitrophenols are mainly formed through reactions in the atmosphere, unlike mononitrophenols, which are primarily formed in connection with exhaust fumes from cars.

Pesticide chemicals have been detected in precipitation collected in Denmark. The study was limited and covered only a few substances and not those with the highest potential for volatilisation. In most cases, there was a relationship between the spraying season and the time of detection. However, pesticides that are no longer used in Denmark were also detected. These substances were presumably transported here over long distances or originated from other sources than treatment with pesticides in agriculture. The prohibited substances found in the precipitation included DNOC, which was found in rainwater throughout the year and in by far the highest concentrations among the substances analysed for. It is therefore highly likely that its presence is due primarily to the formation of nitrophenols in the atmosphere. The international literature describes the formation of nitrophenols in the atmosphere as a reaction between benzene, toluene and NO_x. The exhaust fumes from cars contain mononitrophenols and other nitrophenols, which contribute to the atmosphere’s content of these substances. However, the use of DNOC as a pesticide outside Denmark may also contribute to the content of nitrophenol in the atmosphere.

The following specific conclusions can be drawn:

The insecticide lindane has been detected as an example of a presumed transboundary atmospheric transport of pesticides.

The existing national monitoring of the content of pesticide chemicals in precipitation is limited and there is a lack of data that can be combined with the meteorological data.

There are no Danish in situ measurements of the content of pesticide chemicals in the air in connection with spraying.

4.6 Exposure pathways

Exposure of both people and the environment can occur during handling of pesticides, during and immediately after treatment and as a consequence of dispersal in the environment. The extent to which pesticides are dispersed depends on their physical and chemical properties, environmental conditions, and the way they are used. A pesticide’s persistence should be understood to mean its durability in the environment: substances with a long degradation time are said to have high persistence. The environmental effects of pesticides are discussed in chapter 5. Human exposure from intake of pesticide residues is described in section 6.2. Exposure of the users of pesticides is dealt with in section 6.1. In the following we discuss the dispersal in the environment, which is of fundamental importance both for the environment and for the exposure of people. The following processes and dispersal pathways are described:

	surface run-off
	spray drift
	volatilisation
	degradation and leaching of pesticides
	filling and washing sites

4.6.1 Surface run-off

Pesticides can be transported with water running on the surface of the ground. Surface run-off from sloping fields can carry both water-soluble substances and substances that are adsorbed to particles of soil out into watercourses and lakes. Particle-borne transport occurs during heavy run-off of rainwater or melt water and soil erosion.

In a project in the Danish Environmental Protection Agency’s Pesticide Research Programme (Felding et al. 1997), the surface run-off of two relatively water-soluble herbicides (mechlorprop and dichlorprop) and a sparingly water-soluble insecticide (alfacypermethrin) was studied during two growth seasons (1992-1993). The field had an average gradient of 12% and was used for winter wheat in both years.

Table 4.17 shows the quantities of pesticide transported with surface run-off in the years mentioned. For both years, the quantities, stated in parts per thousand of the sprayed pesticide, were 0.08 for mechlorprop, 0.002 for dichlorprop and 0.001 for alphacypermethrin.

Mechlorprop and dichlorprop were detected particularly in the aqueous phase of the surface run-off, while alphacypermethrin was only detected in samples of water containing particles of soil, which accords with the fact that this substance adsorbs strongly to soil particles. It will be seen that the biggest run-off was of substances applied in the autumn.

Table 4.17 Look here!
Spraying of pesticides on the trial field and pesticides detected in surface run-off (Felding et al. 1997). The substances in question were authorised at the time of spraying.

Events with run-off occur only, and momentarily, when the precipitation within 24 hours exceeds 10 mm (DMU 1995); Groenendijk et al. 1994; Liess et al. 1999; Møhlenberg, Gustavson 1999). On average, this occurs three times a year in Denmark (Funen County, South Jutland County). During precipitation events of more than 10 mm, the surface run-off of pesticides make up 0.2 % of the pesticide pool from the nearest 2 ha in the field, which, according to Groenendijk et al 1994, is a good estimate in countryside with slight gradients. Swedish studies from 1990-1996 (Kreuger 1998; Kreuger, Tornqvist 1998) estimate correspondingly that 0.1-0.3% of the pesticide spread on fields in the catchment area are lost to the aquatic environment. Recent German studies carried out near Braunschweig, which has the same type of soil and field topography as Eastern Denmark, has shown that the run-off of fenvalerate, among other pesticides, occurred in pulses and was clearly associated with precipitation events of more than 10 mm per day (Liess et al. 1999). The total transport to a watercourse was calculated at between 0.012% and 0.068% of the total amount applied to a 9 ha field. Converting to a run-off area of 2 ha and taking account of the degradation as used in the model in section 10.3.3, that corresponds to a loss of 0.05-0.03% with surface run-off (Møhlenberg, Gustavson 1999). Møhlenberg, Gustavson use a loss of 0.2% from 2 ha as a conservative estimate in the model calculations in section 10.3.3.

The main measure used to try to prevent pollution of watercourses and lakes is the establishment of buffer zones along watercourses and lakes within which cultivation is not allowed. The buffer zone acts as a filter and reduces the amount of surface run-off.

4.6.2 Conclusions

The following specific conclusions can be drawn:

Pesticides can be transported to watercourses and lakes via surface run-off.

Surface run-off of pesticides occurs only in connection with precipitation events of more than 10 mm per day. The magnitude of the run-off depends on the run-off area and its gradient. In the scenario analyses in section 10.3.3, the run-off is estimated to be 0.2% of the amount of pesticide applied on the nearest 2 ha.

This applies both to water-soluble substances and to substances that adsorb to particles of soil.

Surface run-off is greatest for pesticides applied in the autumn.

The amount of pesticide that reaches watercourses and lakes can be reduced by establishing grass buffer zones between the field and the recipient.

4.6.3 Spray drift

"Spray drift" should be understood to mean the amount of pesticide that is not deposited on the field being sprayed. Pesticides can be transported via the atmosphere to land outside the sprayed area in the following two ways:

During field spraying, the spray liquid is relatively finely atomised in order to achieve a uniform distribution on the area and good deposition of the spray liquid on the crop and pests. During the droplets’ transport to the crop and its pests, loss can occur through the droplets being carried out of the sprayed area in particulate form as drift or in the form of vapour. The loss can occur both on the droplet’s way to the target and from the target of the spraying for a period after spraying. Drift, together with volatilisation of pesticides, explains why pesticides are detected in precipitation, surface water and on unsprayed areas. Drift is the reason why, with very low vapour pressure, pesticides can be measured in the atmosphere and in precipitation, because these substances can be transported as small particles that form from drops of spray fluid that are borne and dried in the air.

Several factors affect the extent of drift. Numerous measurements have shown that most of the spray liquid reaches the target in calm weather. In conditions with more wind or atmospheric instability, some of the spray liquid is transported out of the sprayed area. The proportion transported out of the area depends on the following factors (Jensen et al. 1998):

	the wind velocity and relative humidity
	the average droplet size and droplet size distribution, which depend on the type of and size of the nozzle, the hydraulic pressure and the surface tension and viscosity of the spray liquid
	the distance between the nozzle mouth and the spray target (boom height)
	the spraying equipment used (conventional, air-assisted, screening, size and design of the spraying equipment, electric charging of the drops, etc.).

The spraying techniques that can be used to reduce spray drift are discussed in section 9.6. In field spraying, for example, the farmer can influence the drift through his choice of spraying equipment and its setting, while the actual drift is heavily affected by the climatic conditions - particularly the wind. Also drift is far greater when spraying on bare soil or on soil with a low crop than when spraying in the later stages of the crop, when the crop is dense.

Droplet size, volatilisation and relative humidity

Volatilisation from such small droplets simply reduces the size of the droplets still further and produces very small droplets that are transported with wind over long distances. Droplets with a diameter of less than 50 micrometres have a critical size because they remain suspended in the air for a relatively long time. If the relative humidity is low, large droplets can also become smaller, whereby the risk of drift increases considerably. It has thus been calculated that the proportion of air-borne droplets at a distance of 500 metres from the sprayed areas increases more than tenfold if the relative humidity falls from 100% to 50% at 20^oC (Thomson, Ley 1982).

Height of spraying boom above the ground

The height of the spraying boom has a considerable effect on drift. It is primarily the small droplets – 100 micrometres or less – that are affected by changes in the height of the boom. Drift thus doubles when the boom height is increased from 50 cm to 70 cm with a traditional flat-spray nozzle (Miller 1988).

As mentioned in section 9.6, spraying equipment is undergoing further development that could help to reduce drift.

4.6.4 Conclusions

Drift to the surrounding areas implies a risk of exposure of hedgerows, dykes, dry stone walls and small biotopes in farmland and of natural terrestrial and aquatic areas. Drift, together with volatilisation of pesticides, explains why pesticides are detected in precipitation, surface water and on unsprayed areas. Drift depends particularly on the droplet size and wind velocity. The droplet size depends on the spraying equipment and spraying technique used.

The following specific conclusions can be drawn:

It is primarily droplets with a diameter of less than 100 micrometres that are transported with the wind.

Small droplets are formed when larger droplets evaporate in dry air.

Pesticides with a very low vapour pressure cannot be transported to the atmosphere by volatilisation. Even so, they are found in the atmosphere and in precipitation because they can be transported as small particles formed from droplets of spray liquid that are borne and dried in the air.

A low boom height reduces the quantity of small droplets that form through volatilisation.

In dry air, large droplets change into small droplets through volatilisation. Spraying in moist air reduces the volatilisation. The air is often moist and the wind velocity low in the morning hours, so the risk of drift is generally lowest then.

Little is known about the magnitude of drift and the exposure of terrestrial and aquatic biotopes. In current practice, terrestrial biotopes are protected by means of spray-free zones and aquatic environments are protected by means of substance-specific distance requirements in the authorisation of pesticides.

4.6.5 Volatilisation

Pesticides evaporate both during and, especially, after spraying. Together with drift, see section 4.6.2, volatilisation conveys relatively large quantities of pesticides to the atmosphere, which is thus, quantitatively, the principal transport path for pesticides away from the sprayed area. Lastly, it should be noted that considerable quantities of pesticides can be transported by wind erosion – for example, if there is a storm after spraying of crops in the spring, when the plant density is low. The volatilisation depends on the properties of the substance and, particularly, on its vapour pressure. The temperature, water solubility and adsorption to the soil and plant surfaces, the humidity of the soil, atmospheric turbulence, and the concentration of the pesticide, including its degradation, also play an important part. It is difficult to measure the volatilisation because of its great natural variability (Løkke 1998).

Models for volatilisation

Volatilisation of pesticides depends on the aforementioned factors and can be calculated by means of mathematical models that include the main factors governing the volatilisation. Jansma and Linders (1995) calculated the volatilisation from the surface of the earth by means of the so-called "Dow method", which takes account of the pesticides’ vapour pressure, water solubility and adsorption to soil as the factors governing the volatilisation. The method was validated by comparison with measured values. This method can thus be used for crops grown in rows, where the plant cover is small and most of the pesticides hit the surface of the earth. The calculated values generally lay within a factor of 7 from the measured values. However, this model has a tendency to overestimate the volatilisation. There are as yet no suitable models for estimating the volatilisation of pesticides that are mixed with the soil during harrowing and ploughing. It is also difficult to make a general model for the volatilisation of pesticides from the surface of the plants.

Volatilisation from soil

In the case of many pesticides, most of the pesticide that lands on the ground can in theory evaporate within a few days, depending on the climatic conditions. Volatilisation increases with rising temperature and wind velocity. If the relative humidity is low, the ground surface dries out, which reduces volatilisation.

Volatilisation from plants

Little is known about volatilisation of pesticides from plants. High relative humidity increases the volatilisation but can at the same time increase the absorption of a pesticide by the plant. Once the pesticide has penetrated the plant, 95% of it remains there. The volatilisation depends on the species of plant, the amount of foliage per unit of area and the nature of the surfaces of the plant. The spraying technique and the coformulants in the pesticide formulation also play a part. These substances are intended to ensure that pesticides are spread and attach to and penetrate the plant. The ancillary substances can thus help reduce volatilisation and thus increase the substances action time in and on the plant. Volatilisation is greatest from small droplets, which have the relatively largest surface, and least from large droplets, partly because absorption by the plant is greatest from large droplets. The Dutch authorities have estimated that about 20% of a sprayed pesticide evaporates from plant surfaces and is transported to the atmosphere (Ministerie van L.N.V. 1991).

Measurements of volatilisation in the laboratory and the field

There have been many foreign studies of the volatilisation of pesticides. Most of them were carried out more than 10 years ago with pesticides that are no longer used in Denmark. Jansma and Linders (1995) have reviewed data from the literature. It appears from their work that both the herbicide DNOC and the chlorinated insecticide lindane, which have been detected in rainwater in Denmark (see section 4.1.5), evaporate very quickly from plant surfaces. In German field tests with different crops, it was found, for example, that 45% of lindane evaporated from green beans within one hour of spraying, 50% from lettuce, 30% from kohlrabi and 25% from spring wheat (Boehncke et al.1990). After 3.1 days, 88% had evaporated from the spring wheat and more than 90% from the other crops. In several studies, measurements of the volatilisation of lindane from the ground showed a lower rate of volatilisation but still so much that most of the sprayed pesticide was transported to the atmosphere.

Measurements exist of the volatilisation of individual substances included in measurements of the content of pesticides in Danish rainwater. The substances include atrazine and simazine.

For atrazine, measurements in field studies in the USA have shown that up to 9% can evaporate from the ground surface in 35 days. In another study, 1.3% of simazine evaporated from the ground within 21 days. Measurements of volatilisation from the ground of substances now in use in Northern Europe, showed up to 49% of chlorpyrifos after 26 days, up to 52% of deltamethrin after 3.1 days and 90% of trifluralin after 2.5-7 days. Field tests in Germany of volatilisation of the insecticide deltamethrin after 3.1 days showed 72% from green beans, 34% from kohlrabi, 70% from lettuce and 24% from spring wheat (Boehncke et al. 1990). The same authors measured up to 100% volatilisation of mevinphos from plants after 3.1 days.

Calculation of the volatilisation from the surface of the ground

The simplest model for calculating volatilisation is a so-called 1st order model. In the "Dow model" it is assumed that the so-called rate constant for volatilisation is directly proportional to the vapour pressure and inversely proportional to the water solubility and the soil-adsorption constant (Jansma, Linders 1995). This model is used in the EU´s PC-based expert system for assessment of chemical substances, EUSES (EC 1996). The volatilisation according to this model is shown in table 4.18 for substances with high volatilisation that are also widely used. However, the model overestimates the volatilisation. Another model, developed recently in the Netherlands, includes the substances’ fate in the atmosphere, deposition and effects on plants. The results indicate that, with the pattern of use in the Netherlands in the period 1985-1995, in all 5.5% of the amount of herbicides applied evaporated. The atmospheric deposition corresponded to an average treatment frequency index on nature areas of 0.02 per year (Klepper et al. 1998).

Table 4.18
Calculated volatilisation of pesticides with potential volatilisation from ground surfaces (Jansma, Linders 1995; Løkke 1998).

Pesticide	Quantity sold	Percentage volatilisation after:
	in 1997 (1000 kg)	1 day	4 days
Chlorothalonil	39	1	6
Bentazone	79	7	24
Cypermethrinm	2	1	5
Dimethoate	35	1	6
Diuron	23	3	11
Fenpropimorph	278	11	38
Flamprop-M-isopropyl	13	1	6
Pendimethalin	358	99<	99<
Permethrin	2	31	77
Propyzamide	22	57	96
Prosulfocarb	75	26	69
Terbuthylazine	63	8	27

However, these calculations also showed that there is very little volatilisation from ground surfaces of most of the pesticides used in Denmark today. There is apparently considerable volatilisation of fenpropimorph, pendimethalin, permethrin, propyzamide and prosulfocarb. There is thus a risk of these substances being spread in the atmosphere and detected in rainwater and surface water. The fate and occurrence of these substances in the atmosphere over Denmark have not been investigated and are not covered by DMU’s analytical programme for rainwater (Løkke 1998).

4.6.6 Conclusions

Pesticides evaporate both during and, especially, after spraying. Together with drift, see section 4.6.2, and occasionally wind erosion of soil treated with pesticides, volatilisation transports relatively large quantities of pesticides to the atmosphere and is thus, quantitatively, the principal transport path for pesticides away from the sprayed area. The volatilisation depends on the properties of the substance and, particularly, on its vapour pressure. The temperature, water solubility and adsorption to the soil and plant surfaces, the humidity of the soil, atmospheric turbulence, and the concentration of the pesticide, including its degradation, also play an important part. It is possible to calculate the volatilisation from ground surfaces by means of simple mathematical models, whereas there are as yet no similar models for calculating the volatilisation from plant surfaces. According to model calculations, there can be considerable volatilisation from ground surfaces – theoretically right up to 100% within a few days in the case of some substances. In the Netherlands it is estimated that about 20% of the total amount placed of all types of pesticides evaporates.

Model calculations show that very little of most of the pesticides used in Denmark is transported from ground surfaces to the atmosphere through volatilisation, although some substances show a big potential for volatilisation.

The following specific conclusions can be drawn:

Calculations indicate that, quantitatively, considerable volatilisation of the substances fenpropimorph, pendimethalin, permethrin, propyzamide, prosulfocarb and trifluralin can occur. There is thus a risk of these substances being spread in the atmosphere and detected in rainwater and surface water. The fate and occurrence of these substances in the atmosphere over Denmark have not been investigated.

There is a need for studies of the actual volatilisation of the pesticides used in Denmark with a view to later modelling of the volatilisation.

In order to be able to estimate the importance of atmospheric deposition of pesticides in Denmark in relation to other sources, knowledge is needed about the rate of removal from the atmosphere through dry and wet deposition.

Knowledge is lacking about the fate of pesticides in the atmosphere – particularly their degradation, the rate of degradation and possible formation of environmentally xenobiotic reaction products.

4.6.7 Degradation and leaching of pesticides

Pesticides degrade in a stepwise process, often via the formation of metabolites, the chemical structure of which may be similar to the original pesticide. A pesticide’s metabolites can be more toxic and leach more easily than the original pesticides. This applies, for example, to the atrazine metabolites, deethylatrazine and desisopropylatrazine. It is therefore of great importance that studies of the persistence of pesticides in the soil and leaching from the soil include corresponding studies of metabolites (Fomsgaard 1998).

Degradation and sorption are key factors in the assessment of pesticides’ persistence in the soil. The time of application and the locality also affect the persistence of pesticides. The amount of organic matter in the soil can lead to greater sorption and thus slower degradation and slower leaching. Conversely, the organic matter can also increase the presence of microorganisms, which can in turn increase the rate of degradation. Extreme soil environments, such as the surface on railway lines, paths and car parks, are such poor environments for biological activity that herbicides used on these areas are degraded very slowly. Furthermore since these types of soil bind pesticides poorly, they have a high potential for pollution of groundwater.

Processes that remove pesticides from the soil

A wide range of processes – surface run-off, volatilisation, uptake in plants, leaching and degradation – help to remove pesticide residues from the soil after spraying. Degradation and metabolism in plants differ from the other processes by transforming the substance or removing it permanently from the environment. Surface run-off and leaching can carry the substance into surface water or groundwater; volatilisation can lead to the occurrence of pesticide residues in rainwater; and uptake by plants can lead to contaminated food if the pesticide is not broken down after uptake. Pesticide residues can also be bound in the soil without being degraded.

Persistent pesticides

Pesticides are generally either degraded abiotically, e.g. by photodegradation, or biologically, primarily through biological conversion by microorganisms. A persistent pesticide is characterised by remaining intact in its active form if it is not sensitive to physical and chemical factors or if the microorganisms cannot degrade it. In addition, metabolites, degradation products or reaction products that can be similarly persistent can be formed. The pesticide and/or these metabolites can be inaccessible to degradation if they are adsorbed on humus or clay minerals. The distribution of pesticides between the soil’s pore water and particles of soil is an equilibrium between free molecules and molecules bound to either dissolved organic matter or to attached soil particles. There is therefore a possibility that pesticides bound in the soil can later be released as a consequence of a change in the physical-chemical environment, e.g. acidification of the soil or degradation of humus or clay minerals.

Persistence analyses in the authorisation of pesticides

In connection with the authorisation of pesticides, laboratory tests are carried out as a basis for assessing the persistence. The active ingredient or its metabolites, degradation products or reaction products that are of environmental importance must not have a half-life of more than 3 months and not more than 10% of the amount applied must remain after one year. If only a small proportion of the active ingredient (i.e. less than 5% in 100 days) is completely broken down into CO₂, water and salts, there is a risk of it being bound unchanged in the soil. It is therefore a requirement that not more than 50% of the active ingredient may be bound in the soil after 30 days or max. 70% after 100 days. If these values are exceeded, an evaluation of the conditions for use is carried out and relevant field trials may also be included in the assessment. Active ingredients that have half-lives of more than 6 months and that imply a risk of exposure of the external environment are regarded as possessing unacceptable persistence. This means that the pesticide in question cannot be authorised.

In cases in which relatively large amounts of a persistent pesticide are bound in the soil after repeated application without being directly accessible, it is known that small amounts of the pesticide can be absorbed by plants, earthworms and microorganisms. With continuous accumulation of persistent pesticides in the soil, this absorption must be expected to increase. It is not known how such absorption will affect organisms in the soil in the longer term (the so-called chronic effects). In cases in which a pesticide is bound very strongly to the soil without breaking down, it will not be possible within the foreseeable future to carry out long-term trials to see whether the ingredient and its relevant metabolites, degradation products and reaction products are released and cause damage to the soil’s ecosystem. In such cases, the authorities may decide that an active ingredient must not be authorised due to unacceptable persistence. This authorisation practice is used in Denmark and the Netherlands, and Denmark is seeking to get it implemented in the EU.

Soil treatment

Soil treatment affects the chemical, physical and biological factors in the soil and thus has a major indirect effect on the persistence and leaching of pesticides. In the international literature, the relationship between leaching and soil treatment has been studied by Hatfield (1996), Locke and Harper (1991) and Gaston et al. (1996). If soil treatment is increased, some of the macropores would be destroyed. That means that the pesticides’ retention time would probably increase in the ploughing layer, where the potential for degradation is greatest, and leaching would be reduced. On the other hand, surface run-off might increase. If soil treatment were reduced or eliminated, transport in macropores would increase and thus also leaching of pesticides. Reduced soil treatment can also have the opposite effect, since volatilisation increases when the soil is not treated.

Metabolites

The degradation of a pesticide is a phased process that often proceeds via the formation of metabolites, the chemical structure of which is often similar to that of the original pesticide. Complete mineralisation leads to the formation of CO₂, salts and H₂O. Only some of the amount of pesticides that may end up in the soil after spraying will be fully mineralised (i.e. converted into water, CO₂ and salts). The rest of it will be leached or strongly bound or chemically incorporated in the soil’s humus and/or biomass. Both mineralisation and strong adsorption (non-desorbable) or chemical incorporation in, for example, humus remove the environmentally harmful effects of the pesticide/metabolites. The metabolites formed by degradation of pesticides can be not only more toxic to the environment but also more water-soluble and often leach more easily than the original pesticide. If the metabolite is more toxic or leaches more easily, it can present a bigger problem than the original pesticide. The detection of metabolites of dichlobenil and atrazine in groundwater illustrates this.

In the national groundwater monitoring programme (GEUS 1997), analyses were carried out in many Danish counties in 1997 for the metabolite 2,6-dichlorobenzamide (BAM), which is the degradation product of the herbicide dichlobenil, and for atrazine’s three primary degradation products deethylatrazine, desisopropylatrazine and hydroxyatrazine (see section 4.1). The occurrence in groundwater is an important indicator that future studies of the persistence of pesticides in the soil should include the persistence of metabolites with high water solubility and/or low sorption. The sorption can be expressed by the adsorption constant K_d. The value of K_d usually increases with the soil’s content of organic matter. The adsorption constant and solubility of atrazine and the three primary metabolites are shown in table 4.19. Deethylatrazine and desisopropylatrazine are less adsorbable than atrazine.

Table 4.19  Look here!
Water solubility and adsorption constants (K_d) for atrazine and primary atrazine metabolites. Atrazine is banned in Denmark.

DEPA has published a list of pesticides currently used in Denmark and the associated metabolites (DEPA 1997). Selected examples from this list are shown in table 4.20. It is just as important to determine the persistence of metabolites as the persistence of the pesticides themselves because, as mentioned, the metabolites are in some cases more toxic than the pesticides from which they are formed.

Table 4.20
Pesticides with associated metabolites. Selected from DEPA (1997).

Active ingredient	Metabolites
dichlorprop	2,4-dichlorophenol 3,5-dichlorocatechol
glyphosate	aminomethylphosphonic acid (AMPA) formaldehyde glycine methylphosphonic acid sarcosin (N-methylglycine)
mancozeb	ethylene thiouram disulphide ethylene thiouram monosulphide ethylene thiourea
terbuthylazine	2-chloro-4-ethylamino-6-amino- 1,3,5-triazine

Relationship between degradation and adsorption, transport, spraying time and locality

Most pesticides that are strongly bound in soil degrade slowly. This is because the adsorption reduces the contact between the pesticides and the microorganisms carrying out the degradation. The pesticides can be released again (desorbed). The rates of adsorption and desorption play an important role in leaching. The greater the adsorption and the slower the desorption, the lower the probability that the substances will be leached through the soil to the groundwater.

The presence of organic matter, on the other hand, can increase the rate of degradation if the organic matter supplies nutrition and thus growth for the microorganisms that break down the pesticide. This has been demonstrated by Mueller et al. (1992) for fluometuron, by Veeh et al. (1996) for 2,4-D and by Walker et al. (1983) for simazine. The amount of organic matter in the soil at the individual locality thus affects the rate of degradation, although it is not known exactly how.

The temperature can affect the metabolism of many herbicides. For example, on average, the rate of degradation is reduced 2.2 times with a temperature reduction from 20°C to 10°C (Walker et al. 1996). Metabolism of pesticides therefore takes place far more slowly in the wintertime. Application in the autumn with subsequent low temperatures and percolation of precipitation therefore has a much greater potential for pollution of groundwater than application of the same substance in the spring or summer.

4.6.8 Conclusions

The rate of degradation and the adsorption of pesticides are key factors in the assessment of the pesticides’ persistence in the soil. The rate of degradation is affected by a number of environmental factors. The effect of the temperature, the depth of the soil and the water content are of particular interest. Lower temperature and greater depth of soil generally reduce the rate of degradation. A very low water content reduces the possibilities of contact between the pesticide and microorganisms. A very high water content often reduces the rate of degradation because the supply of oxygen can be reduced. In recent studies it has been found that many other factors also influence the degradation of pesticides. For example, the initial concentration of a pesticide greatly affects the rate of degradation. With a high concentration of a pesticide, the degradation process is very slow.

A pesticide’s metabolites can be more toxic and leach more easily than the original pesticides. This applies, for example, to the atrazine metabolites, deethylatrazine and desisopropylatrazine. It is therefore very important for studies of the persistence of pesticides in the soil and leaching from the soil to include corresponding studies of metabolites.

Extreme soil environments, such as the surface on railway lines, paths and car parks, are such poor environments for biological activity that herbicides used on these areas are degraded very slowly. Furthermore since these types of soil bind pesticides poorly, they have a high potential for pollution of groundwater. For many substances, application in the autumn, with reduced temperature and bigger precipitation, can involve a higher risk of groundwater pollution than application in the summer and spring.

The following specific conclusions can be drawn:

	Lower temperature and increasing depth of soil generally reduce a pesticide’s degradation rate.
	A very low and a very high water content also reduces the degradation rate.
	A wide range of other factors influence degradation, including the initial concentration.

4.6.9 Pollution from filling and washing sites

No data are available on the extent of washing and filling sites as point sources of pollution of groundwater and surface water. There is thus no documentation showing whether this is a real problem, although there are indications that point sources with pesticides do pollute. For example, pesticides are sometimes detected in groundwater or watercourses in such high concentrations that it is unlikely that the source is application on fields. Point-source pollution can thus explain some local instances found today of limit values having been exceeded in groundwater and wells.

In one of the few studies carried out, Jørgensen and Spliid (1993) examined a washing and filling site in an orchard and found a very large content of phenoxy acids in the analysed soil samples.

Other studies have shown that farmers’ wells and boreholes can be seriously contaminated with pesticides (Anon 1995; Spliid 1998b) caused either by point sources or by use of herbicides on farmyard areas. Areas surfaced with gravel and stone present a special risk of leaching of pesticides compared with ordinary agricultural land. Areas of this type are found in farmyards (Jacobsen et al. 1998).

A German study by Fischer et al. (1996) showed that 98% of the considerable pollution of a watercourse was caused by discharge of isoproturon directly from yard areas via sewerage systems or drains.

Potential sources of pesticides in groundwater

Where pesticides are used and handled outside normal field spraying, there is a risk of pollution of the surrounding environment – of the groundwater, the farmer’s own well or borehole and watercourses – via drainage systems from the farm yard. Table 4.21 shows the potential water pollution from filling and washing sites.

There are no data showing whether washing water or pesticide spills cause serious groundwater pollution, nor is it known whether buried packaging is a serious problem. Before 1980. the authorities recommended burying empty packaging.

In directions from the Pesticide Board of the former Ministry of Agriculture from 1966 it was stated in a section entitled "Disposal of residual stocks of pesticides" that small remnants of pesticides and up to approx. 1 kg should be emptied into an 0.5 metre deep hole and that the packaging should be destroyed. The hole had to be at least 50 m from any well, watercourse, lake or drainage pipes. In the case of larger quantities, it was stated that these should be buried at a tip after permission for this had been obtained from the local health inspector.

Table 4.21
Potential sources of water pollution from filling and washing sites (Jensen et al. 1998).

Risk areas

Spilling of concentrated pesticide during filling, e.g. 100 ml IPU Overflow from the sprayer tank during filling, e.g. 10 l Express spray liquid Washing the outside of spraying equipment Controlling weeds in farmyard areas Storage and disposal of packaging and chemical waste Emptying residual spray liquid onto topsoil or gravel-surfaced areas

Can pollute 500,000 m3 water above the limit value Can pollute 5,000 m3 water above the limit value The IPU UK Task Force has estimated that washing the outside of a sprayer can pollute 2,500 m3 water and that washing of gloves can pollute 100 m3 water. The area load is generally high and there is a big risk of pollution of groundwater and well water. Just a few leaching ml can pollute large quantities of water. (see table 4.22)

IPU = Isoproturon.

A number of factors mean that the areas mentioned can be particularly critical. Pesticides from buried packaging and from filling and washing sites can affect the surroundings in a very concentrated form. They can also impede microbial activity, bringing degradation more or less to a standstill. Washing and filling sites are used regularly for many years. That means a big area load, compared with use of the pesticide for field spraying. In addition, washing and filling sites are often unsuitably sited on areas surfaced with gravel and stone but without any organic topsoil. This significantly increases the risk of pollution. When topsoil, with its content of humus, is removed, so are the microorganisms on which biological degradation of spilled pesticides mainly depends. And the big potential for sorption and retention is removed as well. That results in a relatively high rate of transport of water and pesticides. For the same reason, the use of herbicides in farmyard areas and lanes puts well water and groundwater at risk.

Another reason why pollution from filling and washing sites is particularly problematical is that the pesticides are led to the ground with a relatively large quantity of water, which increases the risk of leaching. The yards may also be connected with drains, so the pesticides can be led to watercourses or lakes. In addition, spraying equipment is often washed and filled close to wells, so leaching can occur directly in them unless special measures are taken to prevent it.

Table 4.22
Examples of pesticides in water used to wash spraying equipment. As the examples show, emptying even the diluted washing water out onto the ground can present a risk. The spray-liquid tank should be washed out several times with even small amounts of water. As the examples show, diluting 10 litres twice to 100 litres gives 100 times dilution. If the 10 litres are diluted to 50 litres in four goes, the water consumption will be only 160 litres, but the dilution will now be 625 times greater (Jensen et al. 1998).

Assumptions: The pesticide is mixed with 150 l water per ha. After spraying, the tank contains remaining spray liquid – normally 5-50 l. If 10 l is left and is diluted up to 100 l with clean water twice, a dilution of 100 times will be achieved.
	Active ingredient in spraying and washing water:	The limit of 0.1 µg/L can be exceeded in the following quantities of water:
Example 1: IPU dosage 1000 g active ingredient per ha:
- 10 l remaining spray liquid	67 g	670,000 m3
- 100 times diluted	0.7 g	6,700 m3
Example 2: Express dosage 7.5 g active ingredient per ha:
- 10 l remaining spray liquid	0.5 g	5,000 m3
- 100 times diluted	5 mg	50 m3

IPU = isoproturon.
m g/L = microgramme per litre

A model calculation by GEUS of the potential importance of point sources to groundwater pollution shows that only a minimal proportion of pesticide detections comes from point sources (GEUS 1996). The calculations are based on various assumptions – for example, that the size of the point source is only 0.3 x 0.3 m. Since washing sites and sprayed farmyard areas are usually much larger than that, the leaching could be much greater than calculated.

In an ongoing project in which DIAS, GEUS and DMU are participating, the extent of a pesticide plume from a washing and filling site is being studied. This will provide supplementary knowledge about the importance of point sources.

4.6.10 Conclusions

The use of pesticides and cleaning of tractors and sprayers near wells and the use of herbicides on farmyard areas and similar can lead to pollution of water supplies.

Filling and washing sites are serious but limited, potential sources of pollution because the concentration and area load are high.

Serious pollution can occur if a sprayer is filled directly from the water supply and the tube is left in the spray tank, since water can pollute the well by back-siphoning into the pipe.

It is assumed that point sources with pesticides pollute groundwater and surface water. In directions from 1966, farmers were advised to bury small remnants of pesticides, but despite later warnings and extensive information, pesticides are still sometimes detected in groundwater or watercourses in such high concentrations that the source is unlikely to be field application. It has not been proven that such point-source pollution is the cause of the cases found in which limit values are exceeded in groundwater and wells.

There is as yet no complete evaluation of filling and washing sites as sources of pollution.

4.7 The sub-committee’s conclusions and recommendations

1. There are studies of pesticides in the different compartments – groundwater, watercourses, drain water, soil water and rainwater. There are only a few measurements of pesticides in ponds and lakes. Only in the case of groundwater are there time series, but the measuring programmes have not been going on long enough to enable a description of the trends.
   
   
2. In the expanded analyses in the groundwater monitoring programme, pesticides or degradation products were detected in 34% of the screens examined in the interval 0 to 10 metres below soil surface. The limit value was exceeded in 23% of the screens. The detection frequency decreases with the depth, which may indicate that remnants of the last 50 years’ increasing use of pesticides are moving towards the deeper aquifers, with increasing future groundwater pollution as a consequence. Another possible explanation might be that degradation is taking place during the onward movement because the concentrations in the deeper soil strata have been exposed to biological and chemical degradation for a longer period of time than concentrations in the uppermost strata. Only when sufficiently long time series from the monitoring programmes are available – which means in 5 to 10 years time – will it be possible to test these hypotheses. The latest research indicates that the degradation of certain pesticides in the aquifers is very slow, while others show degradation.
   
   
3. In the expanded analyses in the groundwater monitoring programme, pesticides or degradation products were found in 21% of the screens examined. The limit value was exceeded in 13% of the screens. The degradation product BAM from the now banned herbicide dichlobenil was detected in about 30% of the wells analysed in connection with the water companies’ raw water monitoring system. However, a wide range of substances that are used in agriculture for treating crops are also present in relatively many wells analysed in connection with the water companies’ raw water monitoring system. Larger amounts of pesticides were detected in drain water and soil water than in groundwater, and this may reflect concentrations that may similarly later move towards the groundwater, during which they may undergo degradation and possible formation of metabolites. In both watercourses and ponds, a number of pesticides have been detected in higher concentrations than the concentrations that have effected aquatic organisms in the laboratory.
   
   
4. It is a condition of authorisation of pesticides that they degrade in the environment and are metabolised into water, carbon dioxide and salts or into harmless organic substances. However, the sub-committee has noted that, in the case of pesticides detected in the different compartments, it is often only a fraction of the quantities used that can be accounted for, apart from degradation. There is thus a lack of information concerning the total mass flows and the largest flows, including volatilisation and drift, and a lack of actual systematic measurements in the environment of degradation and metabolism as an element of the integrated mass flow analysis. It is thus not possible to make a real and complete description of the fate of the pesticides in relation to the environmental and health loads.
   
   
5. The detection of authorised pesticides above the limit value in both groundwater near the surface and in aquifers at greater depths indicates that the present authorisation scheme does not ensure completely against future pollution of the groundwater. As a safety measure, a warning system for pesticides has been established with a view to enabling fast evaluation and, if necessary, removal of authorised pesticides that are a threat to the groundwater.

At present, authorisation of pesticides in Denmark and the EU is based on analyses of research results and assessment of the consequences for health and the environment. This means, in particular, that the fate of the pesticides is not subject to an analysis of the uncertainties and actual variations that form part of an integrated mass flow analysis – in part because such an analysis would require data concerning the actual use, dispersal and degradation under Danish conditions. The sub-committee recommends that an actual mass flow analysis be carried out when pesticides are being reviewed for renewal of their authorisation in pursuance of section 33(4) of the Act on Chemical Substances and Products. This analysis must include both average and "worst-case" scenarios based on measurements taken and experience gained in the period in which the substance in question has been used. If, in this mass flow analysis, knowledge is lacking concerning the individual flows, the sub-committee recommends that the precautionary principle be applied in the assessment of the substances in order to counteract or prevent any consequences of the dispersal of the pesticides and exposure of people and the environment.

The sub-committee recommends that the gross list drawn up with a view to reexamining leaching of pesticides be included in recommendations concerning substitution with less dangerous substances. The sub-committee also recommends that new substances be assessed in relation to the gross list and in relation to non-chemical, alternative methods.

The sub-committee also recommends that volatilisation and chemical reactions of pesticides in the atmosphere be taken into account in connection with authorisation of the pesticides.

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