Fig. 4
Performance of the East African SPEARpesticides index. (a) Background pesticide toxicity (maximum toxic unit, TUmax) predicted with the East African SPEARpesticides index correlates with the measured background toxicity in Kenyan water samples. R2 = 0.54, F = 12.97, df = 1, res. df = 11, p = 0.004, intercept = − 0.41, slope = 0.80. TUmax was restricted to ≥ 10–4, because lower toxicity could not be measured due to detection limits for pesticides. TUmax has been log10-transformed, so that differences are presented in orders of magnitude. (b) Relation of the East African SPEARpesticides index with the estimated peak pesticide toxicity during run-off in Kenyan streams, as compared to the relation of the European SPEARpesticides index v. 219.11 with measured peak toxicity in German streams (data from [37]. Peak exposure in Kenyan streams was estimated by multiplying the measured background toxicity with a correction factor of 4 (see main text for justification)