Aquatic Fate and Effects of Lambda-Cyhalothrin in Model Ecosystem Experiments

The fate and effects of the synthetic pyrethroid lambda-cyhalothrin in aquatic model ecosystem experiments are reviewed. In laboratory studies, lambda-cyhalothrin is highly toxic to fish and invertebrates. Its physico-chemical and laboratory fate properties indicate that it will dissipate rapidly from the water phase, reducing exposure for organisms in the water-column. For European aquatic risk assessments, where exposure models predict that spray drift is the main entry route from agricultural uses, this has been a key factor in refining higher-tier risk assessments for water-column organisms. Modified exposure studies in the laboratory confirmed that rapidly reduced exposure mitigates effects on fish and invertebrates. Eight aquatic model ecosystem experiments have been conducted with lambda-cyhalothrin in a variety of indoor and outdoor test systems. These were of differing trophic status, and ranged in size from 0.43 to 450 m 3 . The timing of application of test substance also varied between studies. The fate of the compound in the various experiments was consistent, typified by rapid dissipation (and degradation) in the water phase with median dissipation times (DT 50 ) of typically a day or less. Only 5-22% (where quantifiable) of the chemical applied to the water column reached the sediment, and it was not possible to calculate sediment DT 50 values. Effects in the studies were driven by population responses of macrocrustacea and certain insects, along with zooplanktonic microcrustacea. Considering the range of test systems, the variety of locations, different trophic status of the test systems, differences in season of application, and differences in numbers of applications, the effects thresholds observed in the studies were remarkably consistent, with no to slight effects occurring consistently at initial nominal treatment concentrations up to 10 ng/L. The effects threshold values for clear effects with recovery were more variable than the no to slight effects, but still reasonably consistent, with thresholds between initial nominal treatment concentrations of 16 and 50 ng/L. This gives considerable confidence in the potential to extrapolate the effects observed in one study to a different situation, at least in this case where effects tend to be of an acute nature, and the dissipation and degradation of the compound is rapid.