In the 1990s, a nationwide groundwater monitoring program (GRUMO) recorded a worrying increase in the number of pesticide findings in the groundwater. On this background, the Danish Government launched in 1998 the Danish Alert System for Leaching of Pesticides to Groundwater (VAP), and it has now been in operation for 20 years. 

VAP consists of a variety of fields that are conventionally grown and sprayed with selected approved pesticides at maximum permissible dosages. Next, it is examined whether the pesticides and/or selected degradation products are leached to groundwater, drainage or soilwater below the fields. 

The six test fields

VAP has represented different types of climate, geology and soils in Denmark - including both sandy fields and cracked clay fields.

“The results from VAP provide unique knowledge about the transport of pesticides and their degradation products to the groundwater under realistic field conditions. This knowledge helps to protect the groundwater and such knowledge cannot be obtained solely through laboratory experiments or the models used in the EU regulation of pesticides. At VAP, we focus on investigating the risk of leaching from approved use of pesticides in agriculture,” says project Manager and Senior Researcher at GEUS, Annette E. Rosenbom.

What have we learned over 20 years?

Over the past 20 years, VAP has tested the leaching of 124 substances, of which 74 are degradation products derived from 39 pesticides. Among these, there have been a number of eye openers regarding the regulation of pesticides, which have been used not only in the Danish regulation of pesticides, but also in certain cases in the European regulation 

The following are examples of knowledge generated from VAP:

• More pesticides and/or their degradation products have been detected in the groundwater under the cracked clay fields than under the sandy fields. This appears to be caused by:
  • Precipitation on the fractured clay fields is often channeled quickly into wormholes and further down into crevices. This allows pulses of substances to move from the surface of the field to the groundwater relatively quickly, without soil bacteria or bonding to soil particles being able to reduce the concentration of the substances in the water.
  • The precipitation in the sandy fields seeps more evenly into the soil and not to the same extent in channels, whereby the substances come into contact with many more soil particle surfaces where they can be bonded or reacted by bacteria.
  
  
• Long-term leaching of degradation products on sandy soil with potato cultivation.
  When potatoes are combed, the soil is formed into ridges in which the potatoes are placed. Precipitation and any pesticides are easily transported down the sides of the potato combs and seep into the soil between the combs. Here, some pesticides can be hard bonded to the soil, but slowly released over several years and degraded. This binding of pesticides in the soil and their slow release and degradation is not possible in the laboratory and in the leaching models used in the regulation.

• Highly binding pesticides can be leached through the cracked clay soils.
  In the autumn, when it rains a lot, some of the pesticides that bind very hard to the soil can be washed out on the cracked clay fields. This may be because the precipitation on these soils and this season is primarily transported rapidly via the wormholes and crevices into the soil and to the groundwater, whereby the pesticides do not reach the ground or are already released.

• Quality assurance of analytical methods in relation to water type is essential for some substances.
  In VAP, there has always been a focus on quality assurance of the analytical methods based on reference standards from the manufacturers. The quality assurance made clear in 2010 that the laboratory was having trouble recovering measured amounts of glyphosate added to water samples from some of the fields. The problems were because the water from these fields had a high content of cations to which glyphosate hardened. Based on this quality assurance of analytical methods in VAP, the analysis method for glyphosate used in Denmark was improved from July 2010, and the recovery of glyphosate in water samples from the fields has now been optimized.
  
  
• Staining agents may also be a source of leaching.
  In 2014, on the basis of new data from the European Food Safety Authority (EFSA), the Danish EPA assessed that the degradation product 1,2,4-triazole from a group of pesticides called azoles could pose a greater risk of contamination of groundwater than previously assumed. For this reason, in the same year VAP decided to investigate the leaching of 1,2,4-triazole after spraying with azole agents. It was found that 1,2,4-triazole is leached from the VAP fields to an extent that varies from field to field. 1,2,4-Triazole was found both in water samples taken from the VAP fields before spraying with tebuconazole in 2014 and in wells upstream of the fields. This indicates that previous applications of the azole agents (before 2014) on the VAP fields, as well as sources other than pesticides sprayed on the VAP fields in 2014, contributed to the occurrences. A dialogue with the producers and a detailed literature study showed that azoles have been used in agriculture since 1958 in the form of either pesticides or herbicides (substances applied to seed) and as nitrification inhibitors in commercial and livestock manure. The sources were assessed in relation to VAP, and from 2017 it was decided to register all dressings used in VAP. The results from the latest VAP report show a possible coincidence in the use of azole dressings and 1,2,4-triazole in groundwater. Leaching of 1,2,4-triazole to groundwater - including from azole-stained seed - is currently being investigated more specifically in a research project funded by the Danish Environmental Protection Agency.

Read the summary and report here

VAP is funded through Pesticidstrategi 2017-2021. The results from VAP for the period 1999-2018 are described in a report series prepared by the National Geological Survey for Denmark and Greenland (GEUS) together with the Department of Agroecology and the Department of Bioscience at Aarhus University.

Read the full report 'Danish Pesticide Leaching Assessment Program: Monitoring Results May 1999 - June 2018'.

VAP reports from all years can be found here. http://pesticidvarsling.dk/

Contact

Project Manager and Senior Scientist Annette E. Rosenbom, The National Geological Survey for Denmark and Greenland (GEUS), tel.: 91333552. E-mail: aer@geus.dk 

Academic employee Preben Olsen, Department of Agroecology, University of Aarhus, tel.: 21730711. E-mail: preben.olsen@agro.au.dk