Pesticide contamination of fish ponds in relation to crop area in a mixed farmland-pond landscape (Dombes area, France)

Pesticides are still widely used by agriculture, leading to the exposure of surface water. This may be the case for fish ponds located in farmland landscapes. To address this issue, the present study investigated the contamination by pesticides of fish ponds located in the mixed agriculture-pond landscape of the Dombes area, France. Ten ponds were selected in water catchments with a gradient of 3-57 ha of cropland with maize and winter cereals as the dominant crops. A total of 197 water samples were collected in the ponds during the fish production season over 3 years. Recently used pesticides were the most frequent residues occurring. Occurrences greater than 0.1 µgL^-1 particularly concerned chlorotoluron and S-metolachlor. Maximum observed concentrations were slightly above 3 µgL^-1 for S-metolachlor, acetochlor, and dimethenamide, all herbicides allowed for maize cultivation. Isoproturon and chlorotoluron, herbicides allowed in cereal crops, reached up to 1.2 and 1.0 µgL^-1, respectively. We found a significant positive effect of crop area in catchments on the pond contamination frequency by pesticides and more significantly on the contamination frequency by broad-spectrum herbicides (glyphosate and AMPA residues). The cumulative antecedent rainfall was best correlated to the frequency of highest contaminations (> 0.5 µgL^-1). In such a hydrological context, the crop area within catchment was identified as a good indicator of fish pond exposure to pesticide residues. Finally, we proposed to adapt some mitigation measures to reduce fish pond contamination.