Pyrethroid insecticides are a class of chemicals that have been identified as pesticides of concern in California surface waters due to their potential toxicity to aquatic invertebrates such as the amphipod <i>Hyalella azteca</i>.  The California Department of Pesticide Regulation (CDPR) Surface Water Monitoring Program has been monitoring pyrethroids in California waterways since 2008.  Pyrethroids have been detected frequently throughout the state, with concentrations often exceeding toxicity thresholds.  To address this concern, CDPR implemented surface water regulations in June, 2012.  The regulations restrict outdoor applications made by professional applicators of products containing one or more of seventeen pyrethroid active ingredients.  CDPR has a large dataset to evaluate the effectiveness of the regulations at lowering pyrethroid concentrations in surface waters.   With approximately half of the 650 water samples collected prior to the regulations were implemented, there is a substantial baseline to detect a response.  The dataset also represents a large spatial distribution, with samples collected within twenty-one watersheds located in eight counties.  Samples were collected at both storm drain outfalls and within receiving waters, allowing for both source identification and stream health determinations.  Statewide temporal and spatial trends in pyrethroid concentrations will be evaluated for this presentation. In addition, flow gauging stations at select monitoring locations allow for mass transport calculations, which will aid in determining seasonality effects on contaminant transport.

Effectiveness of California’s surface water regulations at lowering pyrethroid concentrations in surface waters

253rd National Meeting (2017)

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