Evaluation of spot and passive sampling for monitoring, flux estimation and risk assessment of pesticides within the constraints of a typical regulatory monitoring scheme

In many agricultural catchments of Europe and North America, pesticides occur at generally low concentrations with significant temporal variation. This poses several challenges for both monitoring and understanding ecological risks/impacts of these chemicals. This study aimed to compare the performance of passive and spot sampling strategies given the constraints of typical regulatory monitoring. Nine pesticides were investigated in a river currently undergoing regulatory monitoring (River Ugie, Rolland). Within this regulalory framework, spot and passive sampling were undertaken to understand spaltolemporal occurrence, mass loads and ecological risks. All the target pesticides were detected in water by both sampling strategies. Chloroluluron was observed Lo be the clominant pesticide by both spot (maximum: 111.8 ng 1 mean: 9.35 ng/l) and passive sampling (maximum: 3924 ng/l, mean: 4.76 ng/l). The annual pesticide loads were estimated to be 2735 g and 1837 g based on the spot and passive sampling data, respectively. The spaltoLemporal trend suggested Thal agricultural activities were the primary source of the compounds with variability in loads explained in large by timing of pesticide applications and rainfall. The risk assessment showed chlorotoluron and chlorpyrifos posed the highest ecological risks with 23% of the chlorotoluron spot samples and 36% of the chlorpyrifos passive samples resulting in a Risk Quotient greater than 0.1. This suggests that mitigation measures might need to be taken to reduce the input of pestiddes into the river. The overall comparison of the two sampling strategies supported the hypothesis that passive sampling tends to integrate the contaminants over a period of exposure and allows quantification of contamination at low concentration. The results suggested that within a regulatory monitoring context passive sampling was more suitable for flux estimation and risk assessment of trace contaminants which cannot be diagnosed! by spot sampling and for determining if long-term average concentrations comply with specified standards. (C) 2016 Elsevier B.V. All rights reserved.