Applicability of Ecotoxicological Methodologies Developed in Temperate Regions for the Risk Assessment of Pesticides in Tropical Thailand: From Laboratory to (Semi-) Field

The intensification of agricultural practices in developing countries located in the tropical zone has led to an increase in pesticide-use over the past decades. Pesticides have been detected in water, sediment and biota of agricultural areas and surrounding waterways in many tropical countries. Ecotoxicological research into the fate and side-effects of agrochemicals on aquatic ecosystems surrounding agricultural fields, however, has focused almost exclusively on temperate regions. Hence, aquatic risk assessments in tropical countries often rely on toxicity data derived from tests conducted with temperate organisms and communities. The present chapter describes the development of ecotoxicological tools to assess side-effects of pesticides on aquatic ecosystems in tropical Thailand. The developed tools covered various levels of ecological complexity and ranged from single-species laboratory toxicity tests to field studies. Local test species used for laboratory and in situ bioassays were the cladoceran Moina macrocopa and yolk-sac fry of the teleost Oreochromis niloticus. In situ bioassays were deployed in a reference canal as well as two farm canals at different time-intervals after pesticide application. Field pesticide concentrations in the water column and zooplankton communities were monitored at deployment moments to evaluate correlations between pesticide exposure and toxic effects observed on the deployed organisms, and correspondence of effects observed on caged M. micrura with the natural zooplankton community. In addition, an outdoor microcosm experiment was conducted in Thailand evaluating the fungicide carbendazim, allowing a comparison of effects noted on M. macrocopa and the microcosm zooplankton community. Indications for future research, shortcomings and possible improvements of the experimental approaches developed are discussed.