Environmental fate of pesticides used as seed dressing : transport behaviour and occurrence in watercourses

Sammanfattning: Residues of chemical substances contained in pesticides (plant protection products) have been found in streams in four agricultural areas in Sweden despite no reported direct use. This report investigated whether these residues originated from seed dressing preparations used in the areas or some other source. Nine substances, two insecticides and seven fungicides included in the Swedish Pesticide Monitoring Programme, were investigated. Time-proportional water samples were collected from the streams in the four areas during 2002-2006. Mainly pesticides used within agriculture (plant protection products) were analysed. Data on the water samples together with information on crops, sowing dates and use of pesticides etc. obtained from the farmers in the four monitoring areas were analysed. Interviews with farmers about handling of treated seed and a field experiment were carried out in order to investigate potential transport pathways of seed dressing preparations into the environment. In the field experiment, a test plot in southern Sweden equipped with artificial drainage was sown with treated rape seed. Substance concentrations reported in the database are low, and only two substances (betacyfluthrin and bitertanol) have been detected above the Swedish guideline value for sur-face water, on one occasion each. However, analysis of the database showed that two of the substances detected, metalaxyl and bitertanol, could be linked to sowing treated seed of a specific crop, processing peas and winter wheat respectively. The interview responses indicated that handling of treated seed was not the source of the residues detected in the four streams. However, washing of seed drills could be an exception and is a poten-tial source worth further investigation. None of the farmers interviewed had considered seed dressing preparations as a potential source of environmental contamination. In the field experiment, two of the substances present in the rape seed dressing preparation were detected in water samples about two weeks after sowing, confirming that seed dressing preparations can leach from the soil. The conclusion is that some of the chemical residues detected in streams can be linked to seed dressing preparations. For other substances, point sources from some other use are the most likely cause, while for yet others, both are possible sources.