Groundwater pesticide vulnerability: comparing simple assessment methods.

Abstract

Residues of pesticides are found in drinking water and groundwater, in fact all compartments of the water cycle. Should we protect our water sources better, and if so, how? Four methods have been applied to assess the vulnerability of a phreatic aquifer used for a local drinking water supply serving approximately 1000 people. Of the 24 compounds listed in the case study, a method based on labeled pesticide risk class accepted 14 (58%), a method based on data on pesticide soil-water partition values an very simplified local hydrogeological data also accepted 14 (58%), a method based on model simulation accepted 18 (75%) and e method based on tabulated values of pesticide half-life and soil adsorption values (the so called GUS-index) accepted 8 (35%) of 23 compounds. Taking probable values of high precipitaion into account, the accepted compounds based on model simulation were reduced to 10 (42%). None of the 4 methods used all relevant information about risk assessment and drinking water and groundwater protection. The disagreement in the conclusions between the methods is high, ranging from 35 to 60%. Since none of them are consistent, we cannot be confident that they will work under variable conditions. Decisions supported by site specific field or local variables like pesticide half-life in soil and water, soil pesticide adsorption, climatic conditions and others, are recommended.