Monitoring results May 1999 - July 2000
The Danish Pesticide Leaching Assessment Programme
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Geological Survey of Denmark and Greenland
Øster Voldgade 10, DK-1350 Copenhagen, Denmark
Phone: +45 38 14 20 00, fax +45 38 20 50
Table of contents
1 INTRODUCTION 1
1.2 STRUCTURE OF THE PLAP PROGRAMME
2 PESTICIDE LEACHING AT TYLSTRUP
2.1 MATERIALS AND METHODS
2.1.1 Site description
2.1.2 Agricultural management
2.1.3 Monitoring strategy
2.2 RESULTS AND DISCUSSION
2.2.1 Bromide leaching
2.2.2 Pesticide leaching
3 PESTICIDE LEACHING AT JYNDEVAD
3.1 MATERIALS AND METHODS
3.1.1 Site description
3.1.2 Agricultural management
3.1.3 Monitoring strategy
3.2 RESULTS AND DISCUSSION
3.2.1 Bromide leaching
3.2.2 Pesticide leaching
4 PESTICIDE LEACHING AT FAARDRUP
4.1 MATERIALS AND METHODS
4.1.1 Site description
4.1.2 Agricultural management
4.1.3 Monitoring strategy
4.1.5 Drainage runoff
4.2 RESULTS AND DISCUSSION
4.2.1 Bromide leaching
4.2.2 Pesticide leaching
5 DEGRADATION AND SORPTION PARAMETERS
5.1 MATERIALS AND METHODS
5.1.1 Sampling of soil
5.1.2 Degradation rate
5.1.3 Determination of sorption
5.1.4 Microbial activity
5.2 RESULTS AND DISCUSSION
5.2.3 Microbial activity
6 PESTICIDE ANALYSIS QUALITY ASSURANCE
6.1 MATERIALS AND METHODS
6.1.1 Internal QA
6.1.2 External QA
6.2 RESULTS AND DISCUSSION
6.2.1 Internal QA
6.2.2 External QA
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 assessment of pesticides for registration 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.
Under the PLAP, the leaching risk of 24 pesticides was evaluated at six agricultural sites (ranging from 1.1 to 2.4 ha) representing a wide range of Danish soil and climate conditions. The pesticides were all applied using the maximum permitted dosage. Bromide tracer was applied concomitantly with the pesticides and the concentrations of the bromide and pesticides measured monthly in both the unsaturated and the saturated zone. This report presents the monitoring results for three of the six agricultural sites during the first monitoring period (May 1999 to June 2000).
The findings indicate that transport of the bromide tracer will continue throughout the subsequent monitoring period. Although no final conclusion can thus be drawn concerning bromide transport and pesticide leaching risk until the results of the subsequent monitoring period are available, the findings hitherto suggest that:
The field monitoring was supported by site-specific determination of sorption and degradation parameters. These determinations were performed on various combinations of pesticides and soil types representative of the PLAP programme. The results verified the low microbial activity, sorption and degradation rates that are generally found in subsoil. The findings also demonstrated the importance of the availability of site-specific parameters when carrying out root zone modelling. Thus, the determined sorption and degradation parameters (DT50 values) were all in the lower end of the literature values, particularly in the case of bromoxynil, the DT50 of which was remarkably low, ranging from <1 day in the plough layer to <5 days in the subsoil. ioxynil also degraded very fast, dt50 ranging from <1 day in the plough layer to 12 days in the subsoil. finally, the koc of bromoxynil and ioxynil only reached 85 ml/g in the plough layer and 52 ml/g in the subsoil.
- The monitoring system in terms of instrumentation, sampling procedure etc. is suitable for describing the transport of pesticides through the root zone down to the upper aquifer. The tracer application studies thus provide a good indication of the water transport occurring during the monitoring period and revealed a marked breakthrough of bromide in various parts of the hydrological cycle. In addition, they provide a good indication of the heterogeneity occurring at field level.
- The leaching risk could not yet be evaluated for linuron, glyphosate, fenpropimorph, propiconazol, pirimicarb, fluroxypyr and tribenuron-methyl since the monitoring period did not fully cover the potential leaching period. The results obtained so far provide no evidence that these pesticides or their degradation products AMPA, fenpropimorphic acid and triazinamin-methyl leach out of the topsoil.
- With ioxynil, bromoxynil and ETU (degradation product of mancozeb) the leaching risk was found to be negligible – none of the substances were detected in the analysed water samples, thus suggesting that they had already degraded.
- Two degradation products of metribuzin (desamino-diketo-metribuzin and diketo-metribuzin) were found to leach from the root zone in concentrations exceeding the maximum permitted concentration of 0.1 µg/l. Leaching was most pronounced with desamino-diketo-metribuzin, which was detected in concentrations as high as 2.1 µg/l 1 m b.g.s. and 1.4 µg/l 2 m b.g.s. As these degradation products have not yet reached the downstream monitoring wells, their impact on groundwater quality cannot yet be assessed.
- At the two sandy sites, previous application of pesticides has caused marked groundwater contamination with the degradation products of metribuzin, particularly diketo-metribuzin, which was detected at a maximum concentration of 0.33 µg/l at the Tylstrup site and 0.5 µg/l at the Jyndevad site.
The quality of the pesticide analyses was evaluated continuously using an intensive quality assurance (QA) system consisting 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, the QA system showing that:
- Reproducibility of all the analyses was good and the internal control samples were acceptably close to the nominal concentrations.
- No contamination of the samples took place at the laboratories.
- All the pesticides in the spiked samples were detected, although the observed concentrations were low compared to the nominal concentrations, with recovery ranging from 25–85%. It is difficult to find an unambiguous explanation for the low recovery rate, which is most likely due to uncertainty in the spiking procedure in the field. A new spiking procedure has already been introduced that is expected to improve the results.