Aquatic toxicology of cypermethrin. III. Fate and biological effects of spray drift deposits in fresh water adjacent to agricultural land

Abstract

Fields of sugar beet and potatoes in the U.K. were treated with cypermethrin at a dosage of 70 g · ha −1 using tractor-mounted sprayers. Deposits of spray drift on three adjacent pond surfaces were very small and concentrations in subsurface water were near to or below the limits of detection. There were no detectable residues in fish and there were no effects on (he aquatic fauna except on the surface of one corner of one of the ponds where knockdown, but no mortality, was observed among a few individuals belonging to certain species of air-breathing insects. Vineyards in France were treated at dosages of 30 or 45 g · ha −1 using mistblowers. Deposits of cypermethrin on the surfase of three adjacent streams were in the range 0.04–0.45 mg · m −2 and concentrations in subsurface water were in the range 0.4–1.7 μg · l −1 soon after spraying, decreasing to < 0.1 μg · l −1 within a few hours. The resulting concentration-time profiles for cypermethrin in the stream water were considerably less than those required to cause mortalities of invertebrates. There was a marked increase in the numbers of live arthropods in the stream drift during the first few hours after spraying but 24 h later their numbers were similar to those in pre-treatment samples. Enhanced invertebrate drift had no detectable effect on population densities of benthic invertebrates. The choice of triansites, the conditions of spraying and the dosages used were all designed to increase the risk of contamination of natural waterbodies with cypermethrin to a higher level than would be expected to occur under normal conditions of agricultural use. Even so, only very low concentrations of cypermethrin could be detected in adjacent waterbodies and biological effects were insignificant. It was concluded that spray drift from ground-based applications of cypermethrin is unlikely to be a significant hazard to aquatic organisms, despite the high toxicity ot cypermethrin to such organisms in the laboratory.