Abstract:
Background: Pesticides are washed from agricultural fields 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-off events. Alternatively, exposure and ecological effects can be assessed using
the SPEAR pesticides bioindicator that quantifies pesticide-related changes in the macroinvertebrate community compo-
sition. SPEAR pesticides 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 SPEAR pesticides index correlated with the risk of surface run-off from agricultural fields (as
identified based on ground slope in the catchment area and the width of protective riparian strips, R 2 = 0.45). Unlike
other bioindicators designed to indicate general water pollution, SPEARpesticides was independent of organic pollution
and highly specific to pesticides. In 23% of the streams, pesticides exceeded concentrations considered environmen-
tally safe based on European first 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.
SPEAR pesticides provides a straightforward and cost-efficient tool for the required monitoring of pesticide exposure in
small to medium streams.