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Pesticides Research, 57

Pesticides in air and in precipitation and effects on plant communities

Pesticides in precipitation

Table of contents

Summary

Pesticides in precipitation

The concentration of pesticides in precipitation was investigated during the period May 1996 - December 1998 at three sites on Zealand in Denmark (Gadevang, Gisselfeld and Lorup). These sites had not been directly affected by local emissions. The samples were analysed for isoproturon (including 2 metabolites), the phenoxyalkanoic acid herbicides MCPA, mecoprop, and dichlorprop plus bentazone (including 2 metabolites), and DNOC.

Effects of pesticides

This project was part of a larger project, which studied the effects of pesticides in precipitation on plants and plant ecosystems. The highest measured concentrations were 0.9µg/L for isoproturon and 0.6µg/L for phenoxyalkanoic acid herbicides.

Pesticides in precipitation when applicated

In most cases the concentrations in precipitation were found at times when the pesticides were known to be applied to crops. Combined samples for these three sites for the period September 1996 - November 1997 were analysed for 44 compounds. Concentrations over the detection limit were only found for isoproturon, metamitron, DNOC (2-methyl-4,6-dinitrophenol), mecoprop, methabenzthiazuron, 2-hydroxyterbuthylazine, terbuthylazine and 2,4-D.

DNOC in precipitation caused by photochemical reactions

Unexpectedly high concentrations of DNOC (0.38 - 4.5µg/L) were found during the whole sampling period. Although DNOC has not been applied in Denmark since 1986, it has been detected in other investigations in the top layers of the ground water and in streams. Current literature indicates that DNOC is likely to be formed by photochemical reactions of toluene and nitrogen oxides in the atmosphere probably from traffic pollution. The atmospheric deposition of DNOC, mecoprop and isoproturon is respectively 7.5-, 0.3- and 0.3g/ha/year.

Generally, pesticides will be transported over distances of more than several hundred kilometers before they are deposited, unless they are (photochemically) degraded in the atmosphere at a high rate.

Dansk sammendrag

Den danske nedbørs eventuelle indhold af pesticider er undersøgt ved opsamling af regnvandsprøver fra lokaliteter, som er beliggende således, at et lokalt bidrag er minimeret.

Pesticider i nedbør fra skovlysninger

Der er udtaget nedbørsprøver fra lysninger i skove på 3 sjællandske lokaliteter Gadevang, Gisselfeld og Lorup, som i perioden 1996-1997 er blevet analyseret for phenoxysyrerne: MCPA, mechlorprop og dichlorprop samt for isoproturon. I 1998 er analyseprogrammet udvidet, idet bentazon og 2 metabolitter heraf, DNOC samt 2 metabolitter af isoproturon er medtaget.

Pesticider fundet i sprøjtesæsonen

Den højeste koncentration af phenoxysyrerne var på 0,6µg/L. For isoproturons vedkommende var den maksimale koncentration 0,9µg/L. I langt de fleste tilfælde var der sammenfald mellem det tidspunkt, hvor herbiciderne blev påvist i nedbøren og anvendelsestidspunktet. DNOC er påvist i alle de vandprøver, der er udtaget i 1998 i koncentrationsområdet fra 0,04µg/L til 0,87µg/L.Phenoxysyrerne forekommer på alle tre lokaliteter forår og efterår 1996. I 1997 er der kun fundet mechlorprop i en enkelt prøve i sprøjteperioden om efteråret og i 1998 er der ikke påvist phenoxysyrer. Isoproturon er påvist efterår 1996 og 1997 på alle tre lokaliteter og forår og efterår 1998 på alle tre lokaliteter. Det er ikke tilladt at anvende isoproturon om foråret i Danmark, så der kan være tale om langtransport fra lande, hvor sprøjtning er tilladt eller eventuelt sprøjtning i Danmark uden for efterårsperioden, hvor det har været tilladt.

DNOC i nedbør stammer fra atmosfæriske processer

Derudover er der i perioden september 1996 til november 1997 udtaget 13 prøver til analyse for de 44 stoffer, som indgår i DMU´s analysemetode, heraf er de 8 påvist. Det er følgende pesticidkemikalier: isoproturon, metamitron, DNOC (2-methyl-4,6-dinitrophenol), mechlorprop, methabenzthiazuron, 2-hydroxyterbuthylazin, terbuthylazin og 2,4-D. Det, der især overraskede, var indholdet af DNOC, som blev fundet igennem hele perioden og i et forholdsvis højt koncentrationsområde fra 0,38µg/l til 4,5µg/l. Stoffet har ikke været anvendt i Danmark de sidste 10 år, så her er formentlig tale om en mere global forurening, sandsynligvis stammende fra atmosfærekemiske processer forårsaget af traffikkens forurening. Beregnes belastningen i g pr. ha i ovennævnte periode, er belastningen af DNOC 7,5 g pr. ha, mechlorprop og isoproturon tilfører begge ca. 0,3 g pr. ha svarende til henholdsvis 88% og 8% af den totale belastning.

1. Introduction and background

Transport of pesticides in the atmosphere depends on atmospheric lifetime

Pesticides that evaporate can be transported in the atmosphere before they
are deposited on the surface again. How far a substance can be transported
depends on its atmospheric lifetime, which is determined by how fast the compound is removed from the atmosphere caused by reaction, dry deposition, and wet deposition.

In a co-operation project within the framework of Nordic Council of Ministers from 1992 to 1994, rainwater samples from 2 places in Denmark, respectively from Ulborg plantation 10 km from the Jutlandic west coast (56^o 17’ N , 8^o 26’ E) and from Gadevang in Gribskov were gathered. The content of the samples was analysed for the following 10 pesticides: propiconazole, prochloraz, lambda-cyhalothrin, cypermethrin, esfenvalerate, deltamethrin, atrazine, mecoprop, dichlorprop and MCPA. Only phenoxyalkanoic acid herbicides were found. The maximum concentrations were 0.4µg/L (Kirknel and Felding, 1995).

Lindane in precipitation

In 1990-1991, the National Environmental Institute in Denmark measured the contents of a -HCH and g -HCH (lindane) in rainwater on 2 localities in Denmark Husby (56^o 17’ N , 8^o 8’ E) and Ulborg in West Jutland respectively. Three localities, Ulborg, Bagenkop and Anholt, respectively were tested in 1992. The maximum concentration found was 0.1µg/L, The conclusion was, that findings of lindane was due to their use in countries South and West of Denmark (Cleemann et al., 1995).

Wet deposition of pesticides investigated

In the present study, wet deposition of pesticides was investigated.
Precipitation samples have been gathered over a period of 3 years from 1996-1998 from 3 localities on Zeeland: Gadevang, Gisselfeld and Lorup, which have been analysed for the phenoxyalkanoic acid herbicides: MCPA, mecoprop and dichlorprop together with isoproturon. In 1998 the program was expanded, when bentazone and 2 of its metabolites, DNOC, and 2 metabolites of isoproturon were included.

44 pesticides in analytical programme

13 water samples, taken in the period from September 1996 to November 1997, from the 3 above mentioned localities, were analysed for 44 different pesticide compounds.

2. International findings

A short summary about the findings of specific pesticides in precipitation in different countries is given below.

Chlorinated insecticides in USA

USA (U.S. Geological Survey, 1995). U.S. Geological Survey has gathered the results from 132 studies of pesticide findings in air and in precipitation in the United States during 30 years in a summary report. The studies show:

	that most of the pesticides being analysed for were found and that the findings represent many different chemical groups of pesticides,
	that pesticides have been found in the atmosphere in all regions in the United States,
	that the highest concentrations of pesticides are found in the spraying season,
	and that certain slowly degradable pesticides are found throughout the year in low concentrations in the atmosphere. The most frequently found pesticides are the insecticides; DDT, HCH, heptachlor and dieldrine. The annual wet deposition of pesticides is generally found to be less than 1% of the amount of pesticides used in the region concerned.

Phenoxyacid herbicides in Norway, Sweden and Finland

Norway (Lode et al., 1995). In Norway during 1992-1993, 520 tests of rainwater were conducted. Phenoxyalkanoic acid herbicides MCPA and dichlorprop were analysed among others. The maximum concentrations found were respectively 0.32 µg/L and 0.25 µg/L. Pesticides have been found in every tenth sample. Regarding phenoxyalkanoic acid herbicides a correlation was found between the findings of the pesticides in the precipitation and the spraying season.

Sweden (Kreuger et al., 1995). From 1990 to 1992, 18 pesticides were detected. Phenoxyalkanoic acid herbicides were found most frequently (MCPA in 35% of the samples, max. concentration 0.24 µg/L). For MCPA the load in g/ha/year was from 0.0001- 0.092.

Finland (Hirvi et al., 1995). From 1991-1992, the largest measured concentration of phenoxyalkanoic acid herbicides in 22 samples, were 0.19µg/L for dichlorprop.

Isoproturon, atrazine, lindane terbuthylazine and others in Germany

Germany (Hüskes and Levsen, 1997). In 1992, 40 samples were gathered
from the area around Hannover, and they were analysed for 59 pesticides, 11 pesticides were found in more than 10 of the samples. The highest concentrations were due to terbuthylazine. There is a correlation between the findings in the samples and the spraying season as demonstrated in other projects. In 1995, Bester et al. also detected terbuthylazine. In 1994, Siebers et al., published a study from North-Germany, where they analysed for 11 pesticides: isoproturon, atrazine, lindane and terbuthylazine, and others. The pesticides were mainly detected in the spraying season. The highest concentrations found were about 0.7µg/L. The load of isoproturon on the soil amounts to about 0.1g/ha/år. Jeaschke et al. also found IPU in samples taken in the area around Frankfurt in 1995.

MCPA in Italy

Italy (Trevisan et al.,1993). In 1988, 166 air and precipitation samples were gathered and analysed for 11 pesticides; MCPA among others, (max. concentration 0.3µg/L), in 49 of the 166 samples at least one of the 11 pesticides was present.

Lindane in India

India (Dua et al., 1994). In the period from January to September 1992, samples were analysed for HCH, which constitutes 55% of the pesticide consumption (1984 figures). The average concentration was 0.077µg/L. The largest concentrations were measured in the spraying season.

Japan (Suzuki 1996). From 1989-1992, samples were analysed for 9 pesticides, most of them were only found in the spraying season.

3. Materials and methods

The localities were chosen so they were at some distances from agricultural areas. They are all situated in a clearing in a forest.

Three localities away from agricultural areas

The Gadevang locality (12° 16.29´Ø, 55° 58.01´N) is placed about 1 km
West, 5 km South, 5 km East and more than 10 km North of the nearest agricultural area. The Lorup locality (11° 29.86´Ø, 55° 23.24´N) is situated about 0.5 km in all directions from smaller fields, but 2-3 km from larger connected agricultural areas in all directions. The Gisselfeld locality (11° 55.20´Ø,55° 15.50´N) is placed about 1 km West, 3 km East and 2,5 km North of sprayed areas. Samples were taken in March/April, when the first spraying is conducted and until November/December, when the last spraying is done before it begins to freeze.

3.1 Sampling and analysis of rainwater

2 weeks collection periods

The rainwater is sampled through a glass funnel (20 cm in diameter), which is placed about 2 meters above ground. From the funnel, the water runs through a Teflon tube into a 2 liter glass bottle, which is insulated to prevent fluctuations in the temperature and photochemical reactions. Four bottles were placed at each locality, each collects water from two funnels to get a sample that is large enough for analysis. The bottles were acidified to avoid/delay microbiological degradation of whatever pesticides, collected with the rainwater. The samples were normally collected after 2 weeks. In the laboratory the samples were kept at approximately –18^oC until sample preparation and analysis.

With the described experimental design it was not possible to avoid degradation of the pesticides from the time they were collected in the bottle to the time they arrived in the laboratory. Pesticide residues due to rainfall in the beginning of the collection period will result in lower concentrations due to degradation compared to pesticides from rainfall happening just before the samples are collected and brought to the laboratory.

Minimum concentrations depending on storage periodes on locations

Therefore the concentrations listed in the tables in the result section, are minimum concentrations. Stability tests were performed to study the keeping
qualities of the rainwater samples when they were frozen before extraction. The amount of pesticides being degraded at -18° C, is negligible compared to the amount degraded in the collection period.

Solid phase extraction followed by gas- or liquid chromatography with mass spectrometric detection

The method for analysing isoproturon in the samples is based on a pre-
concentration by solid phase extraction. The phenoxyalkanoic acid
herbicides in the samples are also determined by a concentration step with solid phase extraction followed by derivatization with
pentafluorobenzylbromide, which produces the corresponding pentafluorobenzylesters. The samples are analysed with GC-MS in SIM and SCAN mode (see appendix I-III). The water samples collected in 1998 are analysed with the use of LC-MS (see appendix IV). With this method it is not necessary to derivatize the phenoxyalkanoic acid herbicides. The detection limit in using the LC-MS has been 0.01m g/L. Together with the rainwater samples, samples spiked with the pesticides concerned, were analysed.

For the GC-MS-analysis, several water samples were spiked in the concentration range 0.05µg/L-1.00µg/L, r² values were ³ 0.95 and the detection limits differed from 0.01µg/L and 0.09µg/L. The detection limits were set (Miller and Miller, 1988), every time a set of samples was analysed by quantifying the spiked samples together with the collected rain water samples. The samples were scanned to identify, if it was isoproturon, mecoprop, MCPA or dichlorprop etc. The results from the tests were transferred to SAS, which calculates the detection limits and the concentrations of pesticides in the samples based on the calibration data.

3.2 The pesticides

MCPA, dichlorprop, mecoprop and

The phenoxyalkanoic acid herbicides; MCPA, dichlorprop and mecoprop
together with isoproturon were chosen in the beginning as model substances. isoproturon The phenoxyalkanoic acid herbicides were extensively used both in the spring and in the autumn when the project began in 1996. In the beginning of 1997 the Danish Environmental Protection Agency announced that products containing phenoxyalkanoic acid herbicides in general were prohibited for autumn use henceforward and only allowed for spring for a few applications.

In 1996, isoproturon was approved for use both in the spring and in the autumn, but from 1997 only the autumn application was permitted.

The substances have been found in precipitation from neighbouring countries (Kirknel and Felding, 1996)

DNOC in 1998

In 1998, the analysis program was extended to include bentazone and 2 of its metabolites, DNOC, and 2 metabolites of isoproturon. DNOC has not been used in Denmark during the last 10 years, but was included because it was found in the samples that were analysed at DMU in 1997.

4. Results

The results are from the period of May 1996 until December 1998. The samples from 1996 and 1997 are analysed with GC-MS, whereas the rainwater samples from 1998 have been analysed with LC-MS.

Table 1
Concentration in µg/L (95% confidence limit) of phenoxyalkanoic acids herbicides in rainwater from Gadevang 1996 and 1997.

Koncentration i m g/L (95% konfidensinterval) af phenoxysyrer i regnvand fra Gadevang 1996 og 1997.

Nr = no respons
¤ = only for IPU

Table 2
Concentration in µg/L of phenoxyalkanoic acid herbicides and other acidic herbicides in rain from Gadevang 1998.

Koncentration i m g/L af phenoxysyrer og andre sure herbicider i regnvand fra Gadevang 1998.

n.d.: Not detected. Detection limit is 0.01m g/L.

All phenoxyalkonic acid herbicides in 1996

Only mecoprop in 1997

The results for the phenoxyalkanoic acid herbicides and other acidic substances are listed in table 1-6. At the Gadevang locality only mecoprop was detected in the period from October 1996 until Mid-November 1996. At the Lorup and Gisselfeld localities, all 3 phenoxyalkanoic acid herbicides were detected in 1996. In 1997, only mecoprop was found in one sample from Lorup, the sample was collected during November.

The products available on the market in 1996 containing phenoxyalkanoic acid herbicides were prohibited the July 1^st 1997, but hereafter manufacturers could apply for new permits for other products containing phenoxyalkanoic acid herbicides. This is the reason why it is still possible to find a number of products containing phenoxyalkanoic acid herbicides, which are permitted for weed control in herbage seed, grass lawns, and for control of root weeds in cereals in the late spraying growth stages. The permits are based on the coverage of the crop, i.e. the demand of a maximum of a 100 g (for dichlorprop 60 g) depositing on the soil surface.

Table 3
Concentration in µg/L (95% Confidence limits) of phenoxyalkanoic acid herbicides in rainwater from Lorup 1996 and 1997.

Nr = No response
¤ = Only for IPU

Table 4
Concentrations in µg/L of phenoxyalkanoic acid herbicides and other acidic herbicides in rain water from Lorup 1998.

Koncentration i m g/L af phenoxysyrer og andre sure herbicider i regnvand fra Lorup 1998.

n.d.: not detected. The detection limit is 0.01m g/L

Table 5
Concentrations in µg/L (95% confidence limits) of phenoxyalkanoic acid herbicides in rainwater from Gisselfeld 1996 and 1997.

Koncentration i m g/L (95% konfidensinterval) af phenoxysyrer i regnvand fra Gisselfeld 1996 og 1997.

Nr = no response
¤ = Only for IPU

Table 6
Concentrations in µg/L of phenoxyalkanoic acid herbicides and other acidic herbicides in rainwater from Gisselfeld 1998

Koncentration i m g/L af phenoxysyrer og andre sure herbicider i regnvand fra Gisselfeld 1998.

n.d.: Not detected. The detection limit is 0.01m g/L
i.a.: not analysed

Up to 0.87 µg/L DNOC

The results for DNOC in table 2,4 and 6 are corrected for 60% recovery at the sample preparation. The rest of the data is not corrected, because the recovery rates were close to 100%. DNOC was detected in all the samples in concentrations ranging from 0.04 µg/L to 0.87m g/L.

In 1996, the phenoxyalkanoic acid herbicides; respectively; mecoprop, MCPA and dichlorprop, were detected in the following concentrations; from 0.02 µg/L to 0.15 µg/L, from 0.08 µg/L to 0.14 µg/L and from 0.11µg/L to 0.63 µg/L. There is an obvious connection between findings in the rainwater and the time of spraying (Felding, 1998).

No phenoxyalkanoic acid herbicides were detected in 1997 at the Gadevang locality, with exception of the period from the 15/10 to the 3/11 where no samples were collected. In Lorup, none of the samples from the period 15/9 to 3/11, were analysed for phenoxyalkanoic acid herbicides, but in the following period mecoprop was detected in the samples. At the Gisselfeld locality, no phenoxyalkanoic acid herbicides were found in 1997, however, here are 2 periods without samples, from the 15/9 to the 6/10 and again from the 15/10 to the 3/11.

No phenoxyalkanoic acid herbicides in 1998

In 1998, no phenoxyalkanoic acid herbicides were detected at the three locations, which show that the limitation in the use of the phenoxyalkanoic acid herbicides had a remarkably effect on the findings in precipitation. It also shows that it is not possible to trace transport of phenoxyalkanoic acid herbicides from other countries without limitations in the use of these specific pesticides.

DNOC in all samples

With the exception of two findings of trace amounts of hydroxybentazone, bentazone and hydroxy compounds were not detected in the samples taken in 1998. On top of that, DNOC was detected in all samples from 1998, and most of the samples contained DNOC in concentrations between 0.1 and 0.4µg/L.

Isoproturon detected on all localities

The results for isoproturon are listed in table 7-12, where the compound is detected in rainwater from all three localities in the autumn 1996, 1997 and 1998 as well as in the spring 1998 at all three localities. Concentrations of isoproturon vary from 0.01-to 0.86µg/L.

The concentrations of pesticides shown in the tables are to be regarded as minimum concentrations, because of the degradation of the pesticides that are certain to arise from the time the rain event has occurred, and until the sample is collected and brought to the laboratory about 2 weeks later, even though the water is preserved.

Table 7
Concentrations in µg/L (95% confidence limits) of isoproturon in the rainwater from Gadevang in 1996 and 1997.

Koncentration i m g/L (95% konfidensinterval) af isoproturon i regnvand fra Gadevang i 1996 og 1997.

Nr = No response * = Only for phenoxyalkanoic acid herbicides

Table 8
Concentrations in µg/L of isoproturon and 2 metabolites in rainwater from Gadevang 1998.

Koncentration i m g/L af isoproturon og 2 metabolitter i regnvand fra Gadevang 1998.

n.d.: Not detected. The detection limit is 0.01m g/L

Table 9
Concentrations in µg/L of isoproturon (95% confidence limits) in rainwater from Lorup 1996 and 1997.

Koncentration i m g/L (95% konfidensinterval) af isoproturon i regnvand fra Lorup i 1996 og 1997.

Nr = No response *= Only for phenoxyalkanoic acid herbicides

Table 10
Concentrations in µg/L of isoproturon and 2 metabolites in rainwater from Lorup 1998.

Koncentration i m g/L af isoproturon og 2 metabolitter i regnvand fra Lorup 1998.

n.d.: Not detected. The Detection limit is 0.01µg/L

Table 11
Concentrations in µg/L of isoproturon (95% confidence limits) in rainwater from Gisselfeld 1996 and 1997.

Koncentration i m g/L (95% konfidensinterval) af isoproturon i regnvand fra Gisselfeld i 1996 og 1997.

Nr = No response * = Only for phenoxyalkanoic acid herbicides

Table 12
Concentrations in µg/L of isoproturon and 2 metabolites in rainwater from Gisselfeld 1998.

Koncentration i m g/L af isoproturon og 2 metabolitter i regnvand fra Gisselfeld 1998.

n.d.: Not detected. The detection limit is 0.01µg/L

Isoproturon metabolites onlyi n 4 samples

The samples from 1998 were tested for isoproturon and two of its metabolites. Metabolites were only detected in four samples from Lorup, with a maximum concentration of isopropyl-phenylurea at 0.082 µg/L.

Samples analysed for 44 pesticides

During the autumn of 1997 it was possible to analyse some frozen samples for up to 44 different pesticides. Samples from September 1996 until November 1997 were defrosted and mixtures from the three localities were made. The analyses were performed by National Environmental Research Institute, Department for Environmental Chemistry. The pesticides analysed, are listed in table 13.

Table 13
List of pesticides and metabolites contained in the analysis program at DMU.

Liste over pesticider og nedbrydningsprodukter i DMU’s analyseprogram

8 different pesticides detected

In table 14 the concentrations of the 8 different pesticide chemicals whichwere found in the sample mixture are listed. In addition to herbicides mecoprop and isoproturon, which were also detected in the samples mentioned above, the following substances were detected in relatively low concentrations from 2 to 5 times during the period. These are; metamitron, methabenzthiazuron, 2-hydroxyterbuthylazine, terbuthylazine and 2,4-D. DNOC on the other hand, was found in rainwater during the entire sampling period in concentrations from 0.38- to 4.5µg/L.

Table 14
Concentrations of pesticides in rainwater samples collected in the period from September 1996 until November 1997. The samples are in most cases sample mixtures from Lorup, Gisselfeld and Gadevang, and they typically represent a period of 2-3 weeks which gives results once or twice a calendar month. All together there was analysed for 44 pesticide chemicals at DMU. Results in µg/L

Koncentration af pesticider i regnvandsprøver opsamlet fra september 1996 til november 1997. Prøverne er i de fleste tilfælde blandingsprøver fra Lorup, Gisselfeld ogGadevangog repræsenterer 2-3ugers nedbør, hvilket giver et eller to resultater per kalenermåned.. Alle er analyseret for 44 pesticidkemikalier af DMU. Resultater i mg/L.

In table 15 the measured concentration of pesticide chemicals -from table 14- are converted from µg/L to g/ha. As shown in the table, DNOC supplies the ground with roughly 90% of the total amount of pesticides (7,5g of 8,5g), detected by the extended analysis.

Table 15
Concentrations of pesticides and metabolites in g pr. ha.

Koncentration af pesticider og metabolitter i gram per ha.

5. Discussion and conclusion

Connection between spraying and findings

Especially in the case of the phenoxyalkanoic acid herbicides and isoproturon, there is an obvious connection between findings in the rainwater and the time of spraying. The same pattern is repeated in the foreign papers, that describe analysis of rainwater. From the previous European research it appears, that the load of pesticides is of the same magnitude as in Denmark. A compound as lindane is also frequently seen in foreign literature, here the compound is normally detected in precipitation all year around.

Limitations in use reduced content in precipitation

The highest measured concentrations were 0.9 µg/L for isoproturon and
0.6 µg/L for phenoxyalkanoic acid herbicides. Phenoxyherbicides were in 1996 detected in the spraying periods in spring and autumn (autumn only mecoprop, which is the only phenoxyherbicide used for autumn application). In 1997 only mecoprop was detected and solely on one location in November, while in 1998 no phenoxyalkanoic acid herbicides were detected on the three localities. This displays that the limitations in the use of these herbicides have greatly reduced their appearance in precipitation.

Isoproturon was from 1997 until 1999 only allowed for autumn application. The compound was detected on all the three localities in the spraying period in 1996 and 1997, while in 1998 it was detected in the spring as well as in the autumn. This might be a result of long term transport from other countries or illegal use of the pesticide in Denmark.

High DNOC concentrations

The concentration of DNOC is high, and the compound is also detected in rainwater collected in periods were spraying is normally not performed. This indicates that either there are other sources of DNOC, or that the half-life of DNOC is very long (months) so that it can be transported over long distances from areas where application is still allowed. DNOC has been detected in the rainwater from September 1996 to November 1997 and in all samples collected in 1998.

DNOC formation in the atmosphere

It is therefore most likely that the findings of DNOC are caused by formation of the compound in the atmosphere. Nojima and Isogami (1994), Grosjean (1985), Nojima et al., (1983) and Atkinson and Aschmann (1994) describe the formation of DNOC in the atmosphere probably from a reaction between toluene and nitrous oxides caused by the sunlight. The limiting factor is most likely toluene which might come from the traffic. The amount of DNOC, about 7,5g, added to the area, is a rather modest amount compared to the amount of DNOC which was used in the eighties, about 2 kg a.i. pr. ha.

DNOC measured abroad

DNOC has also been measured abroad. In cloud water in England concentrations at 0.26-2.13µg/L were found (Lüttke and Levsen, 1997), and in Germany at 0.9-12.5µg/L (Richartz et al., 1990). Results from Switzerland shows concentrations at 0.95-1.6µg/L for rainwater samples (Leuenberger et al., 1988). The concentrations detected in the rain in Denmark are of the same size as concentrations found in England, Germany and Switzerland.

10 years since DNOC used in Denmark

DNOC is the only one of the 8 detected pesticides, which is no longer used in Denmark, it is about 10 years since the compound was used. In 1996, DNOC was still used in a few countries in Europe and probably also outside Europe. DNOC has been detected in groundwater close to the soil surface and in streams in Denmark (Spliid et al., 1996).

Rainfalls in beginning of collection periods gave unstable samples

Analysis of control samples placed at the three localities have shown that the samples are not adequately stable especially in the summer season if the rain falls in the beginning of the collection period. In forthcoming rainwater projects it is therefore necessary to use more advanced sampling equipment where the samples for example are cooled during the collection period.

6. Acknowledgements

The laboratory technicians Bente Laursen and Hanne Krogh Bæk, both employed in the Department of Crop Protection, Research Centre Flakkebjerg, are thanked for incredible, independent and competent work, both in the field and in the laboratory. Office manager, Sonja Graugaard, is thanked for all her work with corrections in the manuscript etc.

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Appendix I

Gaschromatography Mass Spectrometry

Program for detection of phenoxyalkanoic acid herbicides SIM and SCAN

Appendix II

Method for analysis of isoproturon (IPU)

50 ml preservation solution is added to the rainwater pr. 2 L bottle before it is placed at the collection site. When the water samples arrive at the laboratory the pH value is checked. It is supposed to be 1.

The rainwater is filtered via büchner funnels through a glass micro fibre filter, this is done before a possible freezing of the water, which is parted into 1 L pr. bottle.

Extraction:

5 ml methanol / L water is added.

The RDX-tubes are pre-treated with:

1. 10 ml acetonitrile
2. 10 ml methanol
3. 20 ml milli-Q water

The fluid is sucked slowly through every time.
It is very important that the tubes are not running dry.

The water samples are fitted with a vacuum suction at about 8 mm Hg.

1 L sample is sucked through each column, 2 L from each locality is extracted and the two fractions are treated together (same registry number ).

The columns are air dried with maximum suction in further 20 minutes.

Each column is eluted with 5 ml methanol.

First 1 ml is eluted. Then 2 minutes standing and the rest of the methanol is passed through the column. The elution is repeated with further 5 ml methanol.

Preconcentration:

The methanol fraction is evaporated to dryness under a gentle stream of nitrogen at ambient temperature.

The residue is redissolved in 1 ml ethylacetate in an ultra sonication bath for 5 minutes.

The ethylacetate fraction is filtered through 0,2 µm filter and evaporated to exactly 300 µl and is now ready for analysis. The vial is kept at –18^oC until analysis.

Appendix III

Analysis of phenoxyalkanoic acid herbicides:

50 ml preservation solution is added to the rainwater pr. 2 L bottle before it is placed at the collection site. When the water samples arrive at the laboratory the pH value is checked. It is supposed to be 1.

The rainwater is filtered via büchner funnels through a glass micro fibre filter, this is done before a possible freezing of the water, which is parted into 1 L pr. bottle.

Extraction:

A C8- Empore-disc is placed on the glass filter for millipore filtration. The filter is treated with 10 mL CH₂Cl₂. After 3 minutes standing the solvent is slowly sucked through the filter. The filter is dried by further suction for one minute. The filter is then treated with 10 mL methanol. The filter must not go dry before the water sample is passed through the filter. The filter is air dried by further suction during 15 minutes. The C8-filter is eluted with 10 mL CH₂Cl₂, and the elution is repeated.

Further 10 ml CH₂Cl₂ is used for transfer of the solutes and rinsing of the flask. The extracts are transferred to a separation funnel.

50 mL 1% NaOH is added and the funnel is shaken for 2 minutes. After 10 minutes standing the CH₂Cl₂ fraction is discarded. 3 mL 24 % H₂SO₄ is added to the separation funnel, pH less than 1. The funnel is shaken 2 min with 20 mL CH₂Cl₂. The dichloromethane-fraction is after 10 minutes standing transferred to a round bottom flask equipped with a funnel with anhydrous sodium sulphate on glass wool. The extraction is repeated twice. Na₂SO₄ is washed with 5-10 mL dichloromethane. The dichloromethane is evaporated on a rotoevaporator at 38-40 ^oC at -0,4 bar. The evaporation is stopped when about 500µL is left and 2 ml acetone is added. The acetone fraction is filtered through a 0.2 µm filter into a 20 mL test tube. Further 2x2 mL acetone is used for rinsing of the flask and the filter.

Derivatisation:

25 µL 1% pentafluorbenzylbromide solution and 20 mg incinerated K₂CO₃ is added to the acetone fraction.

The test tube is closed an shaken for 5 sec. on a Whirley mixer and is then standing over night at ambient temperature. The liquid phase is transferred to a new test tube while the precipitate is cleaned with 1 mL acetone which is transferred to the test tube.

2 mL isooctane is added to the test tube and the volume is reduced to about 1 ml under a gentle stream of nitrogen. This step is repeated twice and the residual volume is transferred to an amber glass vial passing a 0,2 µm filter.

The test tube is rinsed twice with max. 6 drops of isooctane which is transferred to the vial. The volume is reduced to exactly 300 µL under a gentle stream of nitrogen. The vial is closed with a teflon coated cap and is kept at –18 ^oC until analysis.

Appendix IV

Principles for analysis of water samples collected in 1998:

The water sample is passed through a solid phase extraction column (SPE-column) and the retained compounds are eluted with an organic solvent. The solvent is evaporated in a vacuum centrifuge and the residue is redissolved in a suitable solvent for HPLC. The compounds are separated on a HPLC column and detected in a mass spectrometer after electrospray ionisation (ESI)

Chemicals, solutions and standards:

Methanol, HPLC grade ( Rathburn )
Acetonitril, gradient grade (Merck)
Acetic acid 100 %, p.a. (Merck),
1,2-propanediol (propylene glycol), (Sigma ),
Konc. HCl rauchend, 37 %, (Merck),
Precervation solution for rain water: 60,0 ml konc. HCl – op to 1000 ml with milli-Q-treated water.
Deionised water from central osmose plant further cleaned in Milli-Q system (Millipore). Ammonium acetate, p.a. (Merck).
Standards from Dr Ehrendorfer or Riedel de Häen.

Stock solutions, standards and internal standards:

Stock solutions are made by weighing of 50 mg standard, which is dissolved in 50 ml acetonitril. Stock solutions are stored in refrigerator and are registered in a stock solution record.

Standards are made by dilution in acetonitril and final dilution in A-eluent or in a solvent comparable to HPLC-start conditions. Standard concentrations should cover the concentration range for the samples after preconcentration, for instance 10, 50 ,100 and 200 m g/L.

¹³C- or ²H-labelled internal standards are recommended for adding to the samples before preconcentration to checking recovery.

HPLC-Eluents:

For analysis of isoproturon the following gradient system is used:

A1-eluent: methanol/10 mM Ammonium acetate in milliQ-water 10/990,
B1-eluent: methanol/10 mM ammonium acetate 90/10,

For phenoxyalkanoic acid herbicides and other acidic compounds:

A1-eluent: methanol/ 20 mM acetic acid 10/90,
B1-eluent: 20 mM acetic acid in methanol.

The eluents are filtered through 0.2 m m millipore filter (type Fluropore, FG), Millipore.

LC-conditions

The LC-MS system was composed by a Hewlett-Packard LC-MSD 1100 system with a binary gradient pump system.

The HPLC-column was a Hypersil BDS 250 x 2.1 mm column.

The same linear gradient profile were used for both acidic compounds and isoproturon compounds with different eluents, as described above:

Mass spectrometry:

Phenoxyalkanoic acid herbicides, bentazon and – metabolites together with DNOC was detected by MS with electrospray inlet (ESI), negative mode and selected ion monitoring (SIM):

Isoproturon and degradation products were detected by MS with electrospray inlet (ESI),positive mode and selected ion monitoring (SIM):

Sample preparation:

50 ml preservation solution is added to the sample flasks before they are placed on the locations.

The samples are stored at 4 ^oC if sample preparation takes places within a few days. Otherwise the samples are frozen at –18 ^oC until sample preparation will take place.

The sample volume is registered and eventually internal standard is added

The sample is passed through a glass fibre prefilter and a glass fibre filter and the filters are rinsed with 5 ml methanol.

The filtrate or 250 ml water sample ( + 1,25 ml Methanol ) (+ 6,25 ml preservation solution to recovery and blanks) are added to Porapak Rdx solid phase extraction columns, which are preconditioned with 10 ml acetonitril, 10 ml Methanol and 20 ml Milli-Q water. The water sample is applied under vacuum pressure with a flow about 10-20 ml/min. The columns must never run dry during the application.

Afterwards the columns are air dried with vacuum suction in further 20 min.

The columns are eluted with 5 ml methanol/acetonitril 1/1 in the following way: 1 ml is passed through the column, 2 minutes standing and the rest of the solvent is passing without vacuum into a vial with 50 m L propylene glycol as keeper.

The sample volume is reduced to 50 m l in a vacuum centrifuge. The propylene glycol residue is diluted with 500 µl 10% methanol and is ready for HPLC-analysis.