RESUMO
Pesticides are transported from crop fields to adjacent streams via surface run-off, drains, groundwater, wind drift and atmospheric deposition and give rise to transient pulse contamination. Although the concentrations observed, typically <10 microg L(-1), cannot be expected to be acutely lethal, effects in streams at the population and ecosystem level have been reported. One of the most conspicuous phenomena associated with these transient pesticide pulses is drift, where large numbers of freshwater invertebrates are carried along by the current and disappear from the contaminated stretch of the stream. The aim of the present study was to evaluate the feasibility of linking laboratory studies of the sublethal effects of pulse exposure to the pyrethroid lambda-cyhalothrin on the locomotory behaviour of stream invertebrates with effects on drift behaviour under more environmentally realistic conditions in stream microcosms. In the laboratory as well as in the microcosms, the order of sensitivities of the three species tested was (with Leuctra nigra being the most sensitive): L. nigra>Gammarus pulex>Heptagenia sulphurea. The LOECs determined for L. nigra (1 ng L(-1)), G. pulex (10 ng L(-1)) and H. sulphurea (100 ng L(-1)) are all within expected environmental concentrations. For the species of invertebrates investigated, it was possible to extrapolate directly from pyrethroid-induced behavioural changes observed in the laboratory to drift under more realistic conditions in stream microcosms. Consequently, the fast and cost-effective video tracking methodology may be applied for screening for potential effects of a wider range of pesticides and other stressors on the locomotory behaviour of freshwater invertebrates. The results indicate that such behavioural changes may be predictive of effects at the ecosystem level.
