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The fate of pesticides mapped

Scientists from Aarhus University have mapped the methods that can be used to study what happens to pesticides in agricultural soil. The focus is on adsorption, degradation and transport of pesticides to the aquatic environment.

[Translate to English:] Forskere fra Aarhus Universitet har kortlagt de modeller, der bruges til at følge pesticiders skæbne på landbrugsjorden, med fokus på danske forhold. Foto: Janne Hansen

What happens to pesticides on farmland? Do the various pesticides leave residues after they have had their intended effect in the field? Can you find metabolites of pesticides in groundwater or do they disappear somewhere else?


To find answers to these questions, it is important to have effective methods of analysis and simulation models for the fate of pesticides. Scientists from Aarhus University have reviewed the models used to follow the fate of pesticides on farmland, with focus on Danish conditions. The results have been published in a report by DCA - Danish Centre for Food and Agriculture.


The scientists have also developed a method that can estimate the current average use of pesticides at regional level based on knowledge of land use. Based on the methodology, the scientists have compiled maps showing the consumption of 43 different pesticides in the period 2007-2009 in Denmark. These maps can be used to assess where in the country there is the highest risk of leaching of certain pesticides.


The fate of pesticides in soil

If pesticides or their breakdown products find their way from the field to the aquatic environment this is initially through contact with soil particles or water molecules. They can subsequently be degraded into new compounds, followed by transport to the aquatic environment. A number of factors affect the pathway of pesticides from the field to the aquatic environment.


Both soil type and pesticide properties are important for the extent to which the pesticide or its metabolite attaches to soil particles or travels with soil water molecules to water bodies.


The millions of microorganisms on our planet are essential for the breakdown of the chemicals. In some cases, the degradation process may be chemical or it may be a combination of chemical and microbiological processes. A variety of factors affect the rate of degradation of pesticides in the soil, including pesticide properties, the soil and its properties, the climate and the quantity and method of pesticide use.


Upscaling of models to regional level

In order to calculate the risk of leaching of a given pesticide to the groundwater there are, as you can see, many processes and factors that need to be taken into account in the simulation models. The models must be able to both represent the field scale at which the pesticides are actually applied and form the basis for upscaling to entire regions. This means that you need to incorporate knowledge about the landscapes in addition to the above factors on soil, climate and pesticides.


Another factor that is important for a realistic picture of the risk of loss of pesticides on a larger scale is the actual use of pesticides in the field.


- When only limited quantities of a particular pesticide are used in an area, the risk of leaching is less than when using large amounts. Many pesticides are crop-specific and used only in specific crop rotations. Special crops such as potatoes, vegetables and beets are grown intensively in certain parts of Denmark, which means that the risk of leaching is greater here, explains Senior Scientist Christen Duus Børgesen from the Department of Agroecology at Aarhus University.


The scientists have developed a method that can estimate the average use of pesticides at regional level. It has enabled them to draw up maps showing the use of 43 individual pesticides at national level in 2007-2009. These maps can enable a better assessment of the risk of leaching of certain pesticides in different regions in Denmark.


In addition to the review of different assessment methods for the fate of pesticides in agricultural soils, the published report also contains a catalogue of ideas for new research in the area.


- There is a need for more research and development in order to better understand: 1. The degradation processes of pesticides in the soil; 2. the processes of adsorption and desorption to soil particles and 3. transport processes in the soil at different scales and soil types. These studies can form the basis for improvements to current models and also provide new knowledge for the benefit of agriculture and the environment, says Christen Duus Børgesen.


The report "Fate of pesticides in Agricultural soils", DCA report no. 62, June 2015 can be downloaded here.


For further information please contact:

Senior Scientist Christen Duus Børgesen, Department of Agroecology, e-mail: christen.borgesen@agro.au.dk, telephone: +45 8715 7745, mobile: +45 2169 4138


Associate Professor Inge S. Fomsgaard, Department of Agroecology, e-mail: inge.fomsgaard@agro.au.dk, telephone: +45 8715 8212, mobile: +45 2228 3399