The majority of pesticides have relatively low/moderate hydrophobicity and current exposure assessments and monitoring study designs have been tailored for such molecules.  However, extremely hydrophobic molecules have unique characteristics which require specialized techniques for study conduct and also make certain regulatory aquatic exposure model outputs misleading. Pyrethroid pesticides are highly hydrophobic and this, along with their facile degradation via de-esterification, dominates their sediment/water behaviors.  Their very strong but rapidly reversible adsorption means that great care must be taken in measuring and selecting appropriate adsorption coefficients for different model processes and for interpreting sediment eco-toxicity.  Furthermore, some aquatic exposure model algorithms in the standard aquatic exposure model (EXAMS) are unsuited to highly hydrophobic molecules and alternative approaches are needed to adequately predict measured field behavior. Finally, several other sediment adsorption related processes can significantly impact aquatic exposure but cannot be included in current models.  These have an impact on real-world aquatic exposures and mean that even refined exposure model outputs may be over-predicting potential pyrethroid concentrations by large margins.

Aspects of the sediment/water behavior of hydrophobic pesticides that require special consideration in monitoring and aquatic exposure assessment as exemplified by synthetic pyrethroids

248th National Meeting (2014)

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