Synthetic Pyrethroids in Agricultural Surface Waters: Exposure, Effects, and Risk Mitigation

摘要

This book chapter gives an overview of synthetic pyrethroids in agricultural surface waters with particular emphasis on the aspects of exposure, effects and risk mitigation. Exposure from agricultural sources is largely short-term in nature and edge-of-field runoff appears to be a rather important source of entry for both aqueous-phase and particle-associated compounds. Concentrations of pyrethroids detected vary between a few nanograms in water up to several hundred micrograms in sediments or suspended particles. Three case studies on pyrethroid effects are included. Interspecific (predation) and intraspecific (cannibalism) interactions increased the susceptibility of model communities to pulse exposure with fenvalerate in artificial stream microcosms. Another stream microcosm study with cypermethrin that simulated agricultural runoff conditions with elevated turbidity levels indicated the importance of reduced bioavailability under field conditions in which there is naturally more suspended and dissolved material than in controlled laboratory studies. This study also suggested the behavioural reactions of mayfly nymphs as important, i.e. nymphs exposed to higher flow rates reduced their pyrethroid exposure by a flow avoidance behaviour. A third study used in situ bioassays with the amphipod species Gammarus pulex in a stream system receiving transient fenvalerate runoff. Here, an avoidance reaction was evident in　that the amphipods actively migrated from a site contaminated with fenvalerate into an uncontaminated tributary during the runoff event. Hence, under field conditions, avoidance reactions of mobile non-target organisms appear to be a relevant process which, if not considered, may lead to overestimation of real-world toxicity e.g. in in situ studies while there may be no manifest responses at the in-stream population level. Due to the relatively low water solubility of pyrethroids, in stream mitigation measures using aquatic plants such as vegetated ditches or constructed wetlands appear to be a valuable management tool. A case study is presented below, which demonstrates that 300-m stretches of vegetated ditches effectively mitigated concentrations of 666 μg/L bifenthrin or 375 μg/L lambda-cyhalothrin experimentally-added to simulate a storm runoff event. It may be concluded, that by incorporating vegetated drainage ditches or constructed wetlands into a watershed management program for pyrethroids, that agriculture can continue to decrease the potential impact of nonpoint-sources to downstream aquatic receiving systems.