| Large quantities of organophosphorus ester insecticides are used in commercial agriculture to control arthropod and nematode pests. Surface runoff represents an important route for the inadvertent introduction of these compounds into aquatic ecosystems. Dissolved organophosphorus insecticide concentrations were measured in surface runoff from four irrigated crop, one orchard and two residential sites during irrigation and rainfall events in a coastal watershed in southern California. Organophosphorus insecticides occurred as mixtures, with chlorpyrifos, diazinon, dimethoate and malathion being most frequently detected. Dissolved chlorpyrifos and dimethoate levels were frequently higher than published LC50 values for sensitive aquatic invertebrates. Event mean concentrations varied between two and four orders of magnitude for most organophosphorus insecticides in agricultural runoff, and less than tenfold in residential storm runoff. Higher EMCs and event loads were observed for runoff events occurring subsequent to reported insecticide applications. Median EMCs did not differ significantly between agricultural and residential storm runoff for chlorpyrifos, diazinon or malathion. This finding strongly suggests that residential land use warrants consideration in TMDL development and implementation. No consistent first flush effect was discernable for any dissolved organophosphorus insecticide in storm or irrigation runoff.;Investigations of agricultural chemicals in surface runoff typically target nutrients or specific pesticides; however, numerous other organic compounds are regularly applied to agricultural fields in pesticide formulations, irrigation water, soil amendments and fertilizers. A broad spectrum analysis of surface runoff from individual irrigated agricultural fields in coastal southern California was conducted to characterize organic compounds amenable to analysis by gas chromatography-mass spectrometry. Aqueous phase extracts contained numerous compounds of potential toxicological significance. A variety of insecticides, herbicides and fungicides, as well as pesticide transformation products were also present. Several compounds associated with pesticide adjuvants were identified. A suite of compounds associated with runoff from fields irrigated with treated wastewater was identified including pharmaceuticals, polycyclic musks and alkyl phosphate flame retardants. Although these compounds were not present at levels likely to cause acute effects (e.g., lethality), pharmaceuticals and personal care products have the potential to elicit more subtle effects (e.g., modulation of endocrine function, chemosensitization). |
