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

Akbar A Ganatra,Ulrike Fillinger,Werner Brack,Baldwyn Torto,Jeremias M Becker,Francis Mcodimba,Matthias Liess,Faith Jebiwot Kandie,Henner Hollert

doi:10.1186/s12302-021-00497-9

Abstract

BackgroundPesticides 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 monitoring of peak concentrations during run-off events. Alternatively, exposure and ecological effects can be assessed using the SPEARpesticides bioindicator that quantifies pesticide-related changes in the macroinvertebrate community composition. SPEARpesticides 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.ResultsWith 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-off from agricultural fields (as identified 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 specific to pesticides. In 23% of the streams, pesticides exceeded concentrations considered environmentally safe based on European first tiered risk assessment.ConclusionsIncreasing 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-efficient tool for the required monitoring of pesticide exposure in small to medium streams.

Highlights

Pesticides are washed from agricultural fields into adjacent streams, where even short-term exposure causes long-term ecological damage
Pesticide pollution and effects on the macroinvertebrate community We observed considerable pesticide toxicity to freshwater macroinvertebrates in our 16 study sites from 13 streams, quantified as the maximum toxic unit derived from chemical water analyses (TUmax, see methods). TUmax exceeded the threshold range for environmental effects of 1 0–4 to 10–3 [36] in nine and eight streams, respectively
The results indicate that pesticide pollution was a relevant environmental stressor in the study area

Summary

Introduction

Pesticides are washed from agricultural fields into adjacent streams, where even short-term exposure causes long-term ecological damage. The detection and quantification of pesticides in streams is challenging, as exposure occurs typically in short pulses due to spray drift and due to surface run-off from agricultural fields following heavy rainfall [15]. Such short-term exposure peaks (in the range of hours) drive long-term effects on the macroinvertebrate community for months [16,17,18]. In addition to the chemical analysis of samples for many compounds, samplers need to be installed, protected and regularly accessed in remote areas These challenges limit the feasibility of monitoring pesticide pollution based on chemical analyses, in developing countries

Methods

Results

Discussion

Conclusion