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Establishment of a basis for administrative use of PestSurf

Annex 1

1 Comparison of risk assessment data produced by spray drift assessments, FOCUS SW and PestSurf

1.1 Chemical characteristics of the compound

Table 1.1. Overview of chemical properties of alpha-cypermethrin and the parameters used in the simulations.

Tabel 1.1. Oversigt over alpha-cypermethrins kemiske egenskaber og parametrene brugt i simuleringerne.

1.2 Concentration generated by spray

1.3 Concentrations generated by FOCUS SW

1.3.1 D3 - Ditch

1.3.2 D4 – Pond

1.3.3 D4 – Stream

1.3.4 Conclusion – FOCUS SW

The highest concentration is generated in the ditch (D3). It is caused by wind drift and the concentration becomes 0.093 µg/l. The same scenario shows the highest concentration in the sediment, 0.223 µg/kg. For all scenarios, the concentrations are lower than what is generated by the simpler assessments.

1.4 PestSurf

1.4.1 Sandy catchment, stream

The distribution of concentrations were assessed in several steps. First, the maximum concentrations at each calculation point were listed, and the dates for the occurrence of the maximum was assessed. The points, for which the maximum value also represents a local maximum were selected for further analysis. The relevant values are listed in Table 1.2.

Table 1.2. Maximum concentrations (ng/l) of alpha-cypermethrin simulated for each calculation point in the sandy catchment.

Tabel 1.2. Maximumskoncentrationer (ng/l) af alpha-cypermethrin simuleret for hvert beregningspunkt i det sandede opland.

The pattern over time was the same for all calculation points. The peak values are generated by wind drift, see Figure 1.1.

Each of the events generated an almost identical pattern along the stream, see Figure 1.2, Figure 1.3 and Figure 1.4. The thin black line represents the concentration, while the full black line shows the maximum concentrations obtained during the simulations. In addition, the outline of the stream is shown. In the middle of the catchment, the stream is protected by unsprayed areas. The maximum values at the center of the catchment are obtained when the peak from upstream move through the catchment during the hour following spraying.

In order to present the data in a similar fashion to the FOCUS SW-results, data were extracted and recalculated for the time series marked in
Table 1.2. The global maxima and time weighted concentrations (up to 7 days) were extracted and are reported in Table 1.3 for actual and time weighted concentrations, respectively. Note that the unit is ng/l.

The amount of alpha-cypermethrin sorbed on macrophytes is shown in Figure 1.5. The amount is within a factor 6-7 of the concentration in the water phase. An example of pore water concentration is shown in Figure 1.6. The concentration level is very low (2.08*10^-6 µg/l) and the highest adsorption to sediment is 0.155 ng/kg (Figure 1.7).

Figure 1.1. Concentration pattern over time for alphacypermethrin in the sandy catchment.
Figur 1.1. Koncentrationsmønster som funktion af tid for alpha-cypermethrin i det sandede opland.

Figure 1.2. Concentrations of alpha-cypermethrin in the sandy catchment on the day of spraying 1998, just at the end of the spraying period.
Figur 1.2. Koncentrationer af alpha-cypermethrin i det sandede opland på sprøjtedagen i 1998 lige efter endt sprøjtning.

Figure 1.3. Concentrations of alpha-cypermethrin in the sandy catchment on the day of spraying 2004.
Figur 1.3. Koncentrationer af alpha-cypermethrin i det sandede opland på sprøjtedagen i 2004.

Figure 1.4. Concentrations of alpha-cypermethrin in the sandy catchment on the day of spraying 2005.
Figur 1.4. Koncentrationer af alpha-cypermethrin i det sandede opland på sprøjtedagen i 2005 lige efter endt sprøjtning.

Figure 1.5. Concentration of alpha-cypermethrin on macrophytes in the point of maximum concentration in the water phase in the sandy catchment. The absolute maximum for macrophyte concentration, 59.8 ng/l, was reached further downstream (1421).
Figur 1.5. Koncentration af alpha-cypermethrin på makrofytter på lokaliteten med maximumskoncentration i vandfasen i det sandede opland. Det absolutte maximum for makrofytkoncentration, 59.8 ng/l fandtes længere nedstrøms (1421).

Figure 1.6. Pore water concentration for alpha-cypermethrin at the point of maximum concentration in the sandy catchment.
Figur 1.6. Porevandskoncentration for alpha-cypermethrin på lokaliteten med maximumskoncentration i det sandede opland.

Figure 1.7. Sediment concentration for alpha-cypermethrin at the point of maximum concentration in the sandy catchment. Note that the concentration is in µg/g and not µg/m³ as stated.
Figur 1.7. Sedimentkoncentration for alpha-cypermethrin på lokaliteten med maximumskoncentration I det sandede opland. Bemærk at koncentrationen er i µg/g og ikke i µg/m³ som angivet.

Table 1.3. Actual and time-weighted concentration of alpha-cypermethrin, ng/l, at selected points in the sandy stream.
Tabel 1.3. Beregnet og tidsvægtet koncentration af alpha-cypermetrhin, ng/l, på udvalgte lokaliteter i det sandede vandløb.

Click here to see Figure 1.8.

Figure 1.8. Overview for alpha cypermethrin in the sandy catchment generated by the PestSurf excel template. The max concentrations generated over 24 hours are similar to the overviews in Figure 1.2, Figure 1.3 and Figure 1.4. The graph to the lower right shows how many events have concentrations higher than a given value for the selected monitoring point. Detection value was set to 1 ng/l.
Figur 1.8. Oversigt for alpha-cypermethrin i det sandede opland genereret med PestSurf-excel-skabelonen. Den maximale koncentration genereret over 24 timer svarer til oversigterne i Figur 1.2, Figur 1.3 og Figur 1.4. Grafen nederst til højre viser hvor mange hændelser, der har koncentrationer højere end en given værdi i et udvalgt punkt. Detektionsgrænsen var sat til 1 ng/l.

Click here to see Figure 1.9.

Figure 1.9. Same as Figure 1.8, but with a limiting value of 10 ng/l. The graph to the lower right shows how many events (above 10 ng/l) have a duration longer than the value on the Y-axis for the selected monitoring points.
Figur 1.9. Mage til figure Figur 1.8, men med en begrænsende værdi på 10 ng/l. Grafen nederst til højre viser hvor mange hændelser (over 10 ng/l) med længere varighed end værdien på Y-aksen, der er for udvalgte lokaliteter.

Table 1.4. Part of the result sheet generated by the PestSurf Excel sheet. The selected table shows the Pre-defined point along the stream with the highest concentration recorded. The lowest detection concentration is set to 1, while the toxicity values for fish, daphnies and algae are set to 10, 100 and 1000 ng/l, respectively.
Tabel 1.4. Uddrag af resultatpresentationen genereret af PestSurf-Excel-arket. Den udvalgte tabel viser det fordefinerede punkt langs med åen med højest koncentration. Detektionsgrænsen er sat til 1 mens toxicitetsværdierne for fisk, dafnier og alger er henholdsvis 10, 100 og 1000 ng/l.

Click here to see Table 1.4.

The global maximum value calculated by PestSurf for the sandy catchment in the water phase is 409 ng/l. This is 4-5 times more than what is found in the D3-ditch scenario (91 ng/l). The pesticide was sorbed to macrophytes in the stream rather than to sediment.

Figure 1.8 shows the output of the PestSurf Excel template. The template works with pre-defined data extraction points. The plot requires specification of a “lowest detection value” (ldc), which defines when a pesticide occurrence is defined as an event. The time series plot is identical to the time series shown earlier, and the graph in the upper right corner resembles the plots in Figure 1.2, Figure 1.3 and Figure 1.4, but takes into account a longer period of time. A curve is generated when a downstream point reaches a concentration higher than the ldc. The programme then tracks the highest concentration for each calculation point in the stream within the last 24 hours. The plot in the lower right corner shows how many events have concentrations higher than a given toxicity value for the selected monitoring points. The curves are rather flat, showing little variation from year to year. Figure 1.9 shows the same picture, except that the figure to the lower right shows how many events have a duration longer than a given value for the selected monitoring points. In this case an event is defined by a concentration higher than 10 ng/l. Table 1.4 shows part of the result sheet generated by the PestSurf Excel sheet based on the ldc-value. The selected table shows the point along the stream (of the pre-defined points) with the highest concentration. This value was, however, only 226 ng/l. Thus, the pre-defined points have not caught the highest concentration of the simulation, which was 409 ng/l.

1.4.2 Sandy catchment, pond

The concentration pattern is evaluated in the middle of the pond only, see Figure 1.10. The pond receives drift and a contribution from groundwater. The drift peaks dominate in all years, however in the last two years, the dry and normal weather leads to significant concentrations through the baseflow contribution. The maximum concentration is still quite low, 2.1 ng/l.

In Table 1.5, global maxima and time weighted concentrations (up to 7 days) were extracted.

Figure 1.10. Concentrations of alpha-cypermethrin in the sandy pond.
Figur 1.10. Koncentration af alpha-cypermethrin i det sandede vandhul.

Table 1.5. Maximum actual and time-weighted concentrations of alpha-cypermethrin (ng/l) generated by drift and baseflow for the sandy pond.
Tabel 1.5. Beregnede og tidsvægtede maximumskoncentrationer af alpha-cypermethrin (ng/l) genereret af drift og grundvandstilstrømning for det sandede vandhul.

The sorption to macrophytes is shown in Figure 1.11. The pattern generally follows the concentration in the water. However, concentration patterns of longer duration seem to have greater impact on the sorbed amount than the drift peaks. The concentration is specified per m³ water column. To find the value in biomass, the concentration should be divided by 33 g/m³.

The concentration of alpha-cypermethrin in porewater is shown in Figure 1.12. Here both the drift peaks and more permanent concentration patterns are visible. The concentration in sediment is below 0.01 ng/kg. Values below 0.01 ng/kg are stored as “0” in the model.

Figure 1.11. Sorption of alpha-cypermethrin to macrophytes in the sandy pond.
Figur 1.11. Sorption af alpha-cypermethrin til makrofytter i det sandede vandhul.

Figure 1.12. Pore water concentration of alpha-cypermethrin in the sandy pond.
Figur 1.12. Porevandskoncentration af alpha/cypermetrin i det sandede vandhul.

Figure 1.12 shows the output of the PestSurf Excel template. The template works with one pre-defined data extraction point for the pond (center of the pond). The plot requires specification of a “lowest detection value” (ldc) which defines when a pesticide occurrence is defined as an event. The time series plot is identical to the time series shown earlier. The plot to the right shows how many events have concentrations higher than a given toxicity value for the selected monitoring points.

Table 1.6 shows part of the result sheet generated by the PestSurf Excel sheet based on the ldc-value.

Click here to see Figure 1.13.

Figure 1.13. Overview for alpha cypermethrin in the sandy pond generated by the PestSurf excel template. The time series shown is identical to the one in Figure 1.10. Lowest detection value is set to 0.05 ng/l.
Figur 1.13. Oversigt for alpha-cypermethrin i det sandede vandhul genereret med PestSurf-excel-skabelonen. Den viste tidsserie er mage til den i Figur 1.10 Detektionsgrænsen er sat til 0.05 ng/l.

Table 1.6. Part of the result sheet generated by the PestSurf Excel sheet. The lowest detection value is 0.05 ng/l, toxicity to fish, daphnies and algae are 1, 10 and 100 ng/, respectively. The recorded peaks are shown in Figure 1.13.
Tabel 1.6. Uddrag af resultatpresentationen genereret af PestSurf-Excel-arket. Detektionsgrænsen er sat til 0.05 ng/l mens toxicitetsværdierne for fisk, dafnier og alger er henholdsvis 10, 100 og 1000 ng/l. De tabellerede hændelser er vist i Figur 1.13.

Click here to see Table 1.6.

1.4.3 Sandy Loam catchment, stream

The distribution of concentrations were assessed in several steps. First, the maximum concentrations at each calculation point were listed, and the dates for the occurrence of the maximum was assessed (Table 1.7). The points, for which the maximum value also represents a local maximum, were selected for further analysis.

Table 1.7. Maximum concentrations (ng/l) of alpha-cypermethrin simulated for each calculation point in the Sandy loam catchment.
Tabel 1.7. Maximumskoncentrationer (ng/l) af alpha-cypermethrin simuleret for hvert beregningspunkt i morænelersoplandet.

All over the catchment, the wind drift contribution dominates. In the upper part of the catchment, only drift peaks are visible on Figure 1.14. In the downstream part of the system (Figure 1.15), winddrift still dominates, but a contribution through the groundwater (reaching the stream system via drains) can be seen. The concentrations build up over the 8 years simulated and become significant at the end of the summer of 2000 and 2001 (corresponding to a very dry year and a normal year, respectively). During these periods, the flow in the stream consists of base flow contributions through drain only. The downstream tributaries, Fredligbaek and Groeftebaek show exactly the same picture as the downstream part of stream with respect to groundwater buildup.

Figure 1.14. Typical concentration pattern as a function of time for alpha-cypermethrin in the upstream end of the sandy loam catchment.
Figur 1.14. Typisk koncentrationsmønster som funktion af tid for alpha-cypermethrin i den opstrøms ende af morænelersoplandet.

Figure 1.15. Typical concentration pattern in the downstream end of the sandy loam catchment. The wind drift events dominates, but a groundwater contribution is visible.
Figur 1.15. Typisk koncentrationsmønster i den nedstrøms ende af morænelersoplandet. Vinddriften dominerer, men grundvandstilstrømning kan ses.

Longitudinal concentration profiles for the sandy loam catchment are shown in Figure 1.16 and  Figure 1.17 for 31. May 2000 and 27^th August 2000, respectively. The thin black line represents the concentration, while full black line shows the maximum concentrations obtained during the simulations. In addition, the outline of the stream is shown.

Figure 1.16. Concentrations in the sandy loam catchment on 31 May-2000. The concentrations are generated by wind drift. Note that the actual concentrations are shown with a thin black line  and the maximum concentrations with a thicker black line.
Figur 1.16. Koncentrationer i morænelersoplandet den 31 maj-2000. Koncentrationerne genereres af vinddrift. Bemærk at den beregnede koncentration er vist med en tynd sort linie og maximumskoncentrationen med en tykkere sort linie.

Figure 1.17. Concentrations caused by an increase of alpha-cypermethrin in the groundwater in  the sandy loam catchment on 22.8-2000 (dry year).
Figur 1.17. Koncentrationer begrundet af alpha-cypermetrin i grundvandet i morænelersoplandet den 22.8-2000 (tørt år).

It is generally thought that the model overestimates the transport to groundwater, and, as a consequence of this, it overestimates the contribution through groundwater flow. The particularly high level of baseflow in the lower part of this catchment is due to occurrence of a sandy layer that transports solute horizontally through the catchment to the lower part of the stream.

To be able to extract comparable values to FOCUS SW, the global maxima and time weighted concentrations (up to 7 days) were extracted when these were meaningful (Table 1.8).

Figure 1.18 and Figure 1.19 shows the concentrations sorbed to macrophytes in the upper and lower section of the stream. The pattern follows the pattern of the water concentrations, but the more permanent patterns seem to have the largest influence on the macrophyt concentration. The concentrations are very high compared to the concentration in the water phase, particularly in the lower end of the catchment. The maximum value obtained in the upstream part is 617 ng/l, comparable to the maximum water concentration of 607 ng/l, and in the lower part, the concentration reaches 6.2 µg/l (Nedrelillebaek 847, with a maximum water concentration of 1.07 µg/l). This value is caused by the unrealistic buildup in the groundwater downstream. Macrophytes thus strongly regulate the concentration in the stream.

The concentration of alpha-cypermethrin in porewater is plotted in Figure 1.20 for the site of maximum concentration, and the concentration in sediment is shown in Figure 1.21. The maximum value reached in the upstream part of the catchment is from below 0.01 ng/kg to 0.12 ng/kg. In the downstream part a maximum value of 1.36 ng/kg is reached.

Compared to the FOCUS SW-stream-scenario for D4, the concentration level in the upper part of the stream is considerably higher (583 ng/l compared to 79 ng/l). Both concentrations are generated by drift. The high value of PestSurf is directly caused by the assumption that the total agricultural area is sprayed within 30 minutes. The stream has received drift along a stretch of 855 meter at this point. Concentrations decrease along the following stretch due to presence of buffer zones and drain contributions, but increases again at the end of the catchment due to direct drift, reaching a maximum value of 1.4 µg/l.

With respect to sediment concentrations, the concentration vary over the catchment - in the upstream part (<0.01 ng/kg-0.14 ng/kg compared to 0.119 µg/kg in the D4-scenario), and in the lower part of the catchment (1.36 ng/kg compared to 0.119 µg/kg). All sediment concentrations generated by PestSurf are lower than the concentrations generated by FOCUS.

Figure 1.18. Concentration of alpha-cypermethrin on macrophytes in ng/l at 1425 m from the upstream point. The pattern is representative of the upper part of the sandy loam catchment.
Figur 1.18. Koncentration af alpha-cypermethrin på makrofytter 1425 m fra opstrøms ende. Mønsteret er repræsentativt for den øvre del af morænelersoplandet.

Figure 1.19. Concentration on macrophytes (ng/l) the lower part of the sandy loam stream. The pattern is representative of the lower part of the sandy loam catchment. The highest value reached is 6157 ng/l.
Figur 1.19. Koncentration på makrofytter i den nedstrøms del af morænelersoplandet. Mønsteret er repræsentativt for den nedstrøms del af oplandet. Den højest opnåede værdi er 6157 ng/l.

Figure 1.20. Pore water concentration in the downstream part of the sandy loam catchment.
Figur 1.20. Porevandskoncentration i den nedstrøms del af morænelersoplandet.

Figure 1.21. Concentration pattern of alpha cypermethrin sorbed to sediment at the downstream part of the sandy loam catchment. The concentration is in µg/g sediment and not µg/m³ as stated.
Figur 1.21. Koncentrationsmønster for alpha-cypermethrin sorberet til sediment i den nedstrøms ende af morænelersoplandet. Koncentrationen er i  µg/g sediment og ikke µg/m³ som angivet.

Table 1.8. Instantaneous and time weighted concentrations (ng/l) of alpha-cypermethrin in the sandy loam catchment.
Tabel 1.8. Beregnet og tidsvægtede koncentrationer (ng/l) af alpha-cypermethrin i morænelersoplandet.

Table 1.8. continued. Instantaneous and time weighted concentrations (ng/l) of alpha-cypermethrin in the sandy loam catchment.
Tabel 1.8. fortsat. Beregnet og tidsvægtede koncentrationer (ng/l) af alpha-cypermethrin i morænelersoplandet.

Click here to see Figure 1.22.

Figure 1.22. Overview for alpha-cypermethrin in the sandy loam catchment generated by the PestSurf excel template for the upstream part of the catchment. The limiting value was set to 1 ng/l.
Figur 1.22. Oversigt for alpha-cypermethrin i morænelersoplandet genereret med PestSurf-excel-skabelonen for den opstrøms del af oplandet. Detektionsgrænsen var sat til 1 ng/l.

Click here to see Figure 1.232.

Figure 1.23. Overview for alpha-cypermethrin in the sandy loam catchment generated by the PestSurf excel template for the downstream part of the catchment. The limiting value was set to 20 ng/l.
Figur 1.23. Oversigt for alpha-cypermethrin i morænelersoplandet genereret med PestSurf-excel-skabelonen for den opstrøms del af oplandet. Detektionsgrænsen var sat til 1 ng/l.

Click here to see Figure 1.24.

Figure 1.24. As Figure 1.23, but the lower right figure shows the duration of events above 50 ng/l.
Figur 1.24. Som Figur 1.23, men figuren nederst til højre viser varigheden af hændelser over 50 ng/l.

Table 1.9. Part of the result sheet generated by the PestSurf Excel sheet for the upstream part of the sandy loam catchment. 10 events above 1 ng/l are recorded, all with a very short duration. Toxicity to fish, daphnies and algae are 10, 100 and 1000 ng/, respectively. The peaks are shown in Figure 1.22.
Tabel 1.9. Uddrag af resultatpresentationen genereret af PestSurf-Excel-arket for den opstrøms del af morænelersoplandet. 10 hændelser over 1 ng/l er registreret, alle af kort varighed. Toxicitetsværdierne for fisk, dafnier og alger er henholdsvis 10, 100 og 1000 ng/l. Hændelserne er vist i Figur 1.22.

Click here to see Table 1.9.

Table 1.10. Part of the results generated by the PestSurf Excel sheet for the downstream part of the sandy loam catchment. The limiting value applied in the simulation is 20 ng/l, toxicity to fish, daphnies and algae are set to 50, 100 and 1000 ng/, respectively. The peaks are shown in Figure 1.23.
Tabel 1.10. Uddrag af resultatpresentationen genereret af PestSurf-Excel-arket for den nedstrøms del af morænelersoplandet. Den afgrænsende værdi anvendt i simuleringen er 20 ng/l, toxicitetsværdierne for fisk, dafnier og alger er henholdsvis 50, 100 og 1000 ng/l. Hændelserne er vist i Figur 1.22.

Click here to see Table 1.10.

Figure 1.22-Figure 1.24, and Table 1.9 and Table 1.10 show the results as generated by the PestSurf templates. For the upper part of the catchment, one of the standard points is close to the point of maximum value, reaching a value of 513 ng/l compared to the maximum value of 560 ng/l. For the lower part of the stream, one of the selected standard points reach the maximum value of 1.36 µg/l.

1.4.4 Sandy Loam catchment, pond

The concentration pattern is evaluated in the middle of the pond only, see Figure 1.25. The pond receives contributions mainly through drift, in good correspondence with the fact that it is situated in the upper part of the sandy loam catchment. The maximum concentration is quite low, 5 ng/l.

Figure 1.25. Concentrations of alpha-cypermethrin for the sandy loam pond.
Figur 1.25. Koncentration af alpha-cypermethrin i morænelersvandhullet.

Figure 1.26 shows that the macrophytes participate in the regulation of the concentrations in the pond. The concentration in macrophytes is expressed as concentration in the water phase and the concentration in the water phase and in the macrophytes are therefore comparable. About 2/3 of the alpha cypermethrin present above the sediment is present on the macrophytes. To obtain the concentration in the biomass, the figure has to be divided by 875 g/m³. Figure 1.27 shows the concentration in porewater. It is minute in comparison (1.32 *10^-5 ng/l), and the concentrations in the sediment is below 0.01 ng/kg.

Figure 1.26. Alpha-cypermethrin sorbed to the macrophytes in the sandy loam pond.
Figur 1.26. Alpha-cypermethrin sorberet til makrofytter i morænelers-vandhullet.

Figure 1.27. Pore water concentration of alpha-cypermethrin in the sandy loam pond.
Figur 1.27. Porevandskoncentration af alpha-cypermethrin i morænelersvandhullet.

In Table 1.11, global maxima and time weighted concentrations (up to 7 days) were extracted.

Table 1.11. Actual and time weighted concentrations (ng/l) of alpha-cypermethrin in the sandy loam pond.
Tabel 1.11. Beregnede og tidsvægtede koncentrationer (ng/l) af alpha-cypermethrin i morænelersvandhullet.

Figure 1.28 and Table 1.12 show the output from the PestSurf template (page- lowest detection limit), with a time series identical to Figure 1.25.

Compared to the FOCUS SW-scenario D4-pond the concentrations are rather similar. D4 generates a concentration of 0.003 µg/l while PestSurf reaches 0.005 µg/l. This is consistent with the fact that both concentrations are generated by drift and with that the PestSurf pond is smaller than the FOCUS SW-D4-pond (250 and 900 m², respectively).

The concentration in the sediment is 0.012 µg/kg for FOCUS SW –D4-pond and < 0.01 ng/kg for the PestSurf sandy loam pond.

Click here to see Figure 1.28.

Figure 1.28. Overview for alpha cypermethrin in the sandy loam pond generated by the PestSurf excel template. The time series shown is identical to the one in Figure 1.25. The lowest detection value used is 1 ng/l.
Figur 1.28. Oversigt for alpha-cypermethrin i morænelersoplandet genereret med PestSurf-excel-skabelonen. Den viste tidsserie er mage til den i Figur 1.25. Detektionsgrænsen er sat til 1 ng/l.

Table 1.12. Part of the result sheet generated by the PestSurf Excel sheet. Lowest detection value is set to 1.0 ng/l, toxicity to fish, daphnies and algae are set to 10, 100 and 1000 ng/, respectively. The peaks recorded are visible inFigure 1.28.
Tabel 1.12. Uddrag af resultatpresentationen genereret af PestSurf-Excel-arket. Detektionsgrænsen er sat til 1.0 ng/l mens toxicitetsværdierne for fisk, dafnier og alger er henholdsvis 10, 100 og 1000 ng/l. De tabellerede hændelser er vist i Figur 1.28.

Click here to see Table 1.12.

1.5 Summary of simulations

The maximum actual concentrations for all simulations are recorded in Table 1.14.

FOCUS SW and PestSurf generally agree that drift is an important source for alpha cypermethrin. However, groundwater contributes significantly to the concentration levels in the sandy pond and the sandy loam stream. The high groundwater table around the sandy pond in the undrained sandy soil leads to very fast transport from the surface to the top of the groundwater table, which again is in direct contact with the pond. For the sandy loam stream, the lower part of the stream is in contact with a sand layer that receives water from the upstream part of the catchment. A groundwater contribution is not included in FOCUS SW.

The sandy scenarios are not quite comparable for the two models. The concentrations generated by PestSurf for the two sandy scenarios are lower for the pond and higher for the stream than what is generated for the D3-ditch. As the pond is less exposed to drift than the ditch, the concentration difference is expected.

For the stream, the high concentration is caused by the fact that the whole catchment is sprayed within 30 minutes. This assumption is the determining factor for the result. The maximum concentration is reached about 1 km from the top end of the catchment. Further down dilution, and in some places presence of buffer zones, lead to lower concentrations.

For the point of maximum concentration, the following calculation was carried out: The dose is 15 g/ha, and the percentage calculated to enter the stream is 1.85 % of the dose. The resulting amount is 27.7 µg/m². The water depth at the time of spraying is 8.2 cm, but the cross section is triangular at this point, meaning that the average depth is 4.1 cm only. If the water was stationary and not flowing, the concentration would reach 0.68 µg/l. The maximum concentration reached is 0.41 µg/l. The resulting concentration ub a given location becomes a balance between concentration in the inflow and outflow, and the addition in the given point.

If the concentrations are extracted 112 m from the upstream end of the sandy catchment, the concentration only reaches 37 ng/l, which is about 1/3 of the concentration in the D3 ditch. However, the concentrations are not directly comparable. At this point, the stream is protected by a 20 m buffer zone. The dose is therefore about 14.7 times lower than in the D3-ditch. The water depth, however, is only about 5 cm.

The sandy loam pond may be compared to the D4-pond-scenario. The concentration levels are comparable. In the PestSurf sandy loam pond 2/3 of the active substance in the water phase is sorbed to macrophytes, but the higher amount of substance can be explained by the fact that the PestSurf pond is considerably smaller than the FOCUS SW-pond (250 m² against 900 m²) and therefore more exposed. A rough estimate of the exposure is to assume that 20 m is sprayed in PestSurf sandy loam pond and 30 m in a FOCUS SW-pond. The dosis is then diluted in 250 and 900 m³, respectively: 20/250/(30/900) = 2.4. When comparing the two systems, it should be noted that part of the load on microphytes appear to stay in the pond from year to year.

The concentration in sediment is low in both models, but considerably lower in PestSurf than in FOCUS SW.

For the upstream part of the sandy loam catchment, the concentration of 560 ng/l generated by PestSurf is considerably higher than the concentration generated for the FOCUS D4-stream (79 ng/l), particularly when taking into account that the concentration is halved by macrophytes. The reason is again the assumption that all agricultural land is sprayed within 30 minutes, with a wind direction perpendicular to the stream. The maximum concentration in the upper part of the catchment is reached after 1425 m of the stream. On the following stretch, the concentration is lowered by additions of drainage water and the presence of bufferzones, but even higher concentrations (1.36 µg/l) are reached towards the end of the catchment, along a stretch that is also susceptible to wind drift.

Because the concentrations in the sandy loam catchment are so much higher than in the D4-catchment, a detailed evaluation of the longitudinal pattern of high concentrations was carried out. Evaluating from the upstream end, the concentration first increases and then decreases twice due to the tributaries Albjergbaek and Steensbaek. The concentration increases again and drops strongly around 1000 m from the upstream end due to the tributary Elholt baek. Just after 1700 m, a buffer zone of 20 m is present, leading to a drop in concentrations. This is followed by buffer zones of 10 and 3 m. The tributary Fredligbaek enters around 2400 m from the upstream end and Groftebaek around 2600 m from the upstream end.

The maximum concentrations generated by drift were then evaluated. The maximum reachable concentration should be the concentration obtained if the water was standing in the river strech.

Table 1.13. Maximum concentrations for drift calculated by PestSurf and assuming stationary conditions.
Tabel 1.13. Maximum-koncentrationer for drift beregnet med PestSurf og under forudsætning af stationære forhold.

The high concentrations found at the end of the catchment become higher than the theoretical considerations allow. No good explanation could be found for the up-concentration found at the end of the catchment, see discussion in chapter 4.3 and 4.4.3.

The concentration 125 m from the upstream end of the sandy loam catchment becomes 518 ng/, and is still higher than the 79 ng/l generated in the FOCUS SW D4-stream scenario, especially when the presence of macrophytes are considered. However, the water depth at the time of maximum is only 4.3 cm, and this accounts for most of the difference between the models. The maximum concentration on the stretch, where the stream is permanent and upstream of the groundwater influence is 583 µg/l, 855 m from the upstream end.

Macrophytes are significant in all scenarios, but particularly in the sandy loam catchment. Macrophytes are not included in the FOCUS scenarios.

Assuming that the drift contribution to the stream is overestimated, drainage events may be of interest in the sandy loam catchment. The 20-year event causes concentration of about 1.4 ng/l in the upstream part of the catchment, and the (overestimated- see section 2.1) groundwater contribution causes concentrations around 136 ng/l in the downstream part of the catchment, about one 6^th of the maximum concentration caused by drift.

Table 1.14. Summary of simulation results for alpha-cypermethrin.
Tabel 1.14. Opsummerede resultater for alpha-cypermethrin.

Click here to see Table 1.14.

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Version 1.0 December 2006, © Danish Environmental Protection Agency