Environmental Risk Assessment of Pesticides in Nepal and Hindukush-Himalayan Region

Abstract

An environmental risk assessment, uncommon since focusing only on the pollution risk of soil and groundwater through pesticides, for a site in the Mid-Hills of Nepal will be introduced and discussed.

It will be shown, that model fits which have been developed for the three compounds Metalaxyl, Dimethoate and Fenvalerate, show satisfying results for the further application on risk assessment for the first two, as they account for the general trend of the transport mechanism. For the latter one, the applied model failed due to unidentified transport and degradation processes. Furthermore, the assessment profiles show phenomena in the data which cannot be explained with the applied model, i.e. higher concentrations of pesticides in greater depths than in medium depths. Field studies conducted as combined tracing experiments with the respective pesticides and Vitasin Blue FCF 90 and Deuterium (as a conservative tracer) are used to investigate these phenomena. Results show a leading role of preferential flow paths and free soil water in the transport of pesticides into the deeper soil and into the groundwater system under the given agricultural system (ponding and furrow irrigation), climate and soil type. These additional field studies were necessary in order to reach a sound environmental risk assessment.