Patterns of uses of the organophosphorus insecticide, chlorpyrifos (CPY) in North America have changed over the past decade. This along with emerging issues and new knowledge were considered in reassessing the risks of CPY to terrestrial and aquatic wildlife. Based on the physical-chemical properties of CPY, it would not be classified as a persistent or bioaccumulative chemical. Results of a model developed to predict long-range atmospheric transport were consistent with measured concentrations in areas remote from sites of application. Results of refined models used to predict concentrations in surface waters under a number of scenarios of use were consistent with measured values in surface waters. Both predicted and measured concentrations of CPY in surface waters were less than the threshold concentration predicted to cause adverse effects on aquatic organisms, except for a few situations in drainage ditches which receive irrigation return water directly from agricultural fields. Results of simulations of exposures of birds to CPY, which predicted de minimus risks to a range of species are consistent with the lack of incident reports under current label uses. Risk to honeybees is minimal. CPY poses de minimus risk to terrestrial and aquatic organisms near sites of application and the risk to aquatic organisms at locations more remote are even less. Concentrations of the oxon of CPY have been reported for rain and surface waters, but the oxon is very reactive and not accumulated into organisms and thus does not pose risks beyond those predicted for CPY. When used under conditions specified on the current US label, CPY is predicted to have de minimus risks to aquatic and terrestrial wildlife as well as honeybees in North America.

Ecological risk assessment for chlorpyrifos in terrestrial and aquatic systems in North America: Overview and conclusions

246th National Meeting (2013)

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