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Monitoring results May 1999 - June 2001

The Danish Pesticide Leaching Assessment Programme

Authors
Jeanne Kjær, Marlene Ullum, Preben Olsen, Pia Sjelborg, Arne Helweg, Betty Mogensen, Finn Plauborg, Jørgen Ole Jørgensen, Bo Vangsøe Iversen, Inge Fomsgaard and Bo Lindhardt.
Editor : Jeanne Kjaer
Cover: Peter Moors
Lay-out and graphic production: Authors
Printed: May 2002

Institutions
Geological Survey of Denmark and Greenland
Ministry of the Environment

Danish Institute of Agricultural Sciences
Ministry of Food, Agriculture and Fisheries

National Environmental Research Institute
Ministry of the Environment


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Price: DKK 200.00
ISBN 87-7871-103-7
Available from
Geological Survey of Denmark and Greenland
Øster Voldgade 10, DK-1350 Copenhagen, Denmark
Phone: +45 38 14 20 00, fax +45 38 20 50
e-mail:

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Table of contents
PREFACE
SUMMARY
1 INTRODUCTION
1.1 OBJECTIVE
1.2 STRUCTURE OF THE PLAP PROGRAMME
2 PESTICIDE LEACHING AT TYLSTRUP
2.1 MATERIALS AND METHODS
2.1.1 Site description and monitoring design
2.1.2 Agricultural management
2.1.3 Model set-up and calibration
2.2 RESULTS AND DISCUSSION
2.2.1 Soil water dynamics and water balances
2.2.2 Bromide leaching
2.2.3 Pesticide leaching
2.3 SUMMARY
3 PESTICIDE LEACHING AT JYNDEVAD
3.1 MATERIALS AND METHODS
3.1.1 Site description and monitoring design
3.1.2 Agricultural management
3.1.3 Model set-up and calibration
3.2 RESULTS AND DISCUSSION
3.2.1 Soil water dynamics and water balances
3.2.2 Bromide leaching
3.2.3 Pesticide leaching
3.3 SUMMARY
4 PESTICIDE LEACHING AT SILSTRUP
4.1 MATERIALS AND METHODS
4.1.1 Site description and monitoring design
4.1.2 Agricultural management
4.1.3 Model set-up and calibration
4.2 RESULTS AND DISCUSSION
4.2.1 Soil water dynamics and water balances
4.2.2 Bromide leaching
4.2.3 Pesticide leaching
4.3 SUMMARY
5 PESTICIDE LEACHING AT ESTRUP
5.1 MATERIAL AND METHODS
5.1.1 Site description and monitoring design
5.1.2 Agricultural management
5.1.3 Model set-up and calibration
5.2 RESULTS AND DISCUSSION
5.2.1 Soil water dynamics and water balances
5.2.2 Bromide leaching
5.2.3 Pesticide leaching
5.3 SUMMARY
6 PESTICIDE LEACHING AT FAARDRUP
6.1 MATERIALS AND METHODS
6.1.1 Site description and monitoring design
6.1.2 Agricultural management
6.1.3 Model set-up and calibration
6.2 RESULT AND DISCUSSION
6.2.1 Soil water dynamics and water balances
6.2.2 Bromide leaching
6.2.3 Pesticide leaching
6.3 SUMMARY
7 PESTICIDE LEACHING AT SLAEGGERUP
7.1 MATERIALS AND METHODS
7.1.1 Site description and monitoring design
7.1.2 Agricultural management
7.1.3 Model set-up and calibration
7.2 RESULTS AND DISCUSSION
7.2.1 Soil water dynamics and water balances
7.2.2 Pesticide leaching
7.3 SUMMARY
8 DEGRADATION AND SORPTION PARAMETERS
8.1 MATERIALS AND METHODS
8.1.1 Soil sampling
8.1.2 Microbial biomass and activity
8.1.3 Incubation of soil
8.1.4 Analysis
8.1.5 Degradation kinetics
8.1.6 Determination of sorption
8.2 RESULTS AND DISCUSSION
8.2.1 Soil characteristics
8.2.2 Bromoxynil, ioxynil and metamitron
8.2.3 Fenpropimorph and propiconazole
8.2.4 Discussion of degradation kinetics
8.3 SUMMARY
9 PESTICIDE ANALYSIS QUALITY ASSURANCE
9.1 MATERIALS AND METHODS
9.1.1 Internal Q
9.1.2 External QA
9.1.3 Stability tests
9.2 RESULTS AND DISCUSSION
9.2.1 Internal Q
9.2.2 External QA
9.2.3 Stability tests
9.3 SUMMARY
10 SUMMARY OF MONITORING RESULTS
11 REFERENCES

Summary

In 1998, the Danish Government initiated the Pesticide Leaching Assessment Programme (PLAP), an intensive monitoring programme aimed at evaluating the leaching risk of pesticides under field conditions. The objective of the PLAP is to improve the scientific foundation for decision making in the registration procedures for pesticides in Denmark. The specific aim is to analyse whether pesticides applied in accordance with current regulations leach to the groundwater at levels exceeding the maximum allowable concentration of 0.1 µg/l.

The PLAP includes evaluation of the leaching risk of 24 pesticides at six agricultural sites (ranging from 1.1 to 2.4 ha) representing a wide range of Danish soil and climate conditions. The pesticides are all applied using the maximum permitted dosage. Initially, bromide tracer was applied and the concentrations of the bromide and pesticides are measured monthly in both the unsaturated and the saturated zones, and weekly in the drainage water. This report presents the monitoring results for the six agricultural sites during the monitoring period May 1999–June 2001. The report must be considered preliminary as the monitoring period is too short to fully evaluate the leaching risk of all applied pesticides. A more complete evaluation integrating the monitoring data with both sorption and degradation studies and modelling of pesticide transport will be made once a more comprehensive data set covering the entire leaching period becomes available. The results hitherto obtained nevertheless suggest that:

  • The majority of the applied pesticides (13 of 21) did not leach during the current monitoring period. It should be noted, though, that evaluation of the leaching risk of many of these pesticides is still preliminary as the potential leaching period extends beyond the current monitoring period.
  • The monitoring data indicate unacceptable leaching by two of the applied pesticides. Thus glyphosate and its degradation product AMPA and two degradation products of metribuzin leached from the root zone (1 m b.g.s.) in average concentrations exceeding the maximum allowable concentration of 0.1 µg/l.
  • At the two sandy sites, previous application of pesticides has caused marked ground-water contamination with the two degradation products of metribuzin. These appear to be relatively stable and both leached throughout the entire monitoring period, thus indi-cating continuation of leaching as long as two years after application. Evidence was provided that the degradation products may still be present in the groundwater four years after application.
  • Finally, the monitoring data indicate leaching of a further six pesticides, but it is too early to determine whether this will reach critical levels as the potential leaching period extends beyond the current monitoring period. The levels of leaching hitherto detected were not unacceptable, however. Although the concentration in several samples ex-ceeded 0.1 µg/l, the average concentration did not.
The monitoring data were supported by hydrological modelling (MACRO version 4.2) providing an overall water balance for each of the six sites. The model was parameterized using measured data or literature/default values, but – apart from at the Tylstrup site – it has not yet been calibrated. The uncalibrated models performed surprisingly well when com-paring simulated and observed time series for groundwater table, soil water content and drainage flow.

Sorption and degradation parameters were determined on various combinations of pesticides and soil types representative of the PLAP programme. The results confirmed the low microbial activity, sorption and degradation rates generally found in subsoil. The findings also demonstrated very large variation in both degradation rates and sorption among soils, thereby underlining the importance of having site-specific parameters when modelling pesticide leaching. The rates of degradation were always better described by a two-compartment 1 st + 1 st order model than by the usual 1 st order model, especially with fenpropimorph. Thus degradation usually involved an initial fast degradation rate with a short half-life followed by a slower degradation rate with a longer half-life. An error is thus introduced if the simple 1 st order half-life is used in the evaluation of pesticide persistence. Further analysis of the significance of the introduced error for risk assessment of pesticide leaching is thus required.

The quality of the pesticide analyses was evaluated continuously using an intensive quality assurance (QA) system. This consisted of internal control samples prepared by the analysis laboratory as part of their standard method of analysis and both blank and spiked samples prepared in the field and analysed in the laboratory together with the routine samples. The overall quality of the pesticide analysis was considered satisfactory:
  • Reproducibility of the pesticide analyses was good (SD 0.002–0.015 µg/l).
  • Reproducibility of the degradation products was poorer than that of the mother compounds (SD 0.009–0.032 µg/l).
  • Recovery of pesticides in both internal and external QA samples was acceptable for all pesticides detected in field samples.
  • Variation in the recovery of the same compound in spiked samples from all field sites indicates uncertainty in analysis caused by differences in matrix composition.
  • No contamination of samples generally occurred during collection, storage and analysis. However, two cases of 'false positive' were observed in blank or spiked samples.
  • Stability tests indicated that the majority of the analysed compounds did not exhibit stability problems. However, the occurrences of degradation products in some of the spiked samples indicates that a few of the compounds are unstable and that conditions during transport and storage are important.


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