DEVELOPMENT OF TMDL GOALS FOR CONTROL OF ORGANOPHOSPHATE PESTICIDE–CAUSED AQUATIC LIFE TOXICITY IN URBAN STORMWATER RUNOFF

Urban stormwater runoff in several municipalities in California has been found to be toxic to Ceriodaphnia dubia. This toxicity is due to residential use of the organophosphate (OP) pesticides, diazinon and chlorpyrifos, for termite, ant, lawn and garden pest control. This toxicity has caused regulatory agencies to list the receiving waters for the urban stormwater runoff as 303(d) “impaired” waterbodies. This listing requires that a TMDL be developed to control the concentrations of diazinon and chlorpyrifos so that they do not cause aquatic life toxicity in the runoff waters. This paper provides guidance on an approach that can be used to develop an appropriate TMDL goal to control aquatic life toxicity due to the OP pesticides used in residential areas. While the paper focuses on residential use of these pesticides, many of the same issues and approaches are applicable to runoff from agricultural areas where the pesticides are used.