Fate and environmental impact of pesticides in plastic mulch production runoff: field and laboratory studies

Concentrations of copper, azinphosmethyl, chlorothalonil, and endosulfan sulfate ranged from less than 1 to greater than 1000 microg/L in runoff from tomato plastic mulch production. When this runoff entered local creeks, the copper concentration was as high as 22 microg/L, which exceeded the measured larval clam LC50 values of 21 and 12 microg/L Cu at 96 and 192 h, respectively. A greenhouse scale investigation of copper and toxicity demonstrated that sedimentation reduced total copper concentration in runoff by 90%, although the dissolved copper concentration was unchanged, averaging 139 +/- 55 microg/L. When runoff was applied to marine mesocosms containing grass shrimp and mummichog fish, unsettled runoff produced the greatest mortality, although even settled runoff caused more mortality than that in the control mesocosm receiving runoff without added copper. Desorption of soil-sorbed copper occurred quickly in saline water and contributed to toxicity. Copper toxicity in runoff can be reduced, but not eliminated, by sedimentation.