Toxicity of copper/dimethomorph combination for Lemna minor and depuration of the fungicides by aquatic plant.

Runoff-water of Champagne vineyards is often collected in decantation ponds where pesticides may be eliminated before the water is transferred to rivers. In order to accelerate this process, Lemna minor was tested for its phytoremediation capacity. In the ponds several pesticides coexist. Therefore, the cross-influence of copper and dimethomorph, two pesticides frequently used on grape to control fungal diseases, was studied on toxicity and their removal by L. minor. The toxicity of copper and dimethomorph alone and in combination, was assessed by growth inhibition of L. minor cultures after 96 h and 168 h. Copper had a severe impact on growth (maximum inhibition: 90% at 1000 microg/L) while dimethomorph (as pure ingredient DMM(P) or formulated as Forum DMM(F)) did not (inhibition < 45% at 1000 microg/L) after 168 h of treatment. When both chemicals were combined, a synergistic effect was detected after 96 h of exposure to copper and DMM(F). However, this interaction tended towards additivity after 168 h. Additivity was also observed when DMM(P) replaced DMM(F) in the mixture of copper and dimethomorph at 96h00 and 168h00. The removal of copper depended on DMM(F) concentration. For example, with 250 microg/L of dimethomorph as Forum, removal of copper increased from 36 to 41%. Depuration of DMM(F) by L. minor varied between 10 and 40% after 96 h. This depuration decreased in the presence of copper possibly due to the metal toxicity.