Calibration of the SPEARpesticides bioindicator for cost-efective pesticide monitoring in East African streams

Background: Pesticides are washed from agricultural felds into adjacent streams, where even short-term exposure causes long-term ecological damage. Detecting pesticide pollution in streams thus requires the expensive monitor ing of peak concentrations during run-of events. Alternatively, exposure and ecological efects can be assessed using the SPEARpesticides bioindicator that quantifes pesticide-related changes in the macroinvertebrate community compo sition. PEARpesticides has been developed in Central Europe and validated in other parts of Europe, Australia and South America; here we investigated its performance in East African streams.Results: With minimal adaptations of the SPEARpesticdes index, we successfully characterized pesticide pollution in 13 streams located in Western Kenya. The East African SPEARpesticides index correlated well with the overall toxicity of 30 pesticides (maximum toxic unit=maximum environmental vs. median lethal concentration) measured in stream water (R2=0.53). Similarly, the SPEARpesticides index correlated with the risk of surface run-of from agricultural felds (as identifed based on ground slope in the catchment area and the width of protective riparian strips, R2=0.45). Unlike other bioindicators designed to indicate general water pollution, SPEARpesticides was independent of organic pollution and highly specifc to pesticides. In 23% of the streams, pesticides exceeded concentrations considered environmen tally safe based on European frst tiered risk assessment. Conclusions: Increasing contamination was associated with considerable changes in the macroinvertebrate community composition. We conclude that pesticides need to be better regulated also in developing countries. SPEARpesticides provides a straightforward and cost-efcient tool for the required monitoring of pesticide exposure in small to medium streams.