Water Quality Control TMDL Goals for Urban Stormwater Runoff OP Pesticide-Caused Aquatic Life Toxicity

The finding of widespread urban stormwater runoff aquatic life toxicity and the listing of waterbodies experiencing this toxicity as 303(d) listed impaired waterbodies has established the total maximum daily load (TMDL) process to control this toxicity in several areas of California. Since the toxicity is typically associated with the organophosphate pesticides (OP pesticides) diazinon and chlorpyrifos, often these chemicals are targeted as the constituents that must be controlled in the TMDL process. However, considerable confusion exists today on the appropriate goal for the OP pesticide aquatic life toxicity control TMDL process. This paper reviews some of the issues that are pertinent to establishing TMDL goals for OP pesticide-caused aquatic life toxicity. A discussion is presented on some of the aspects of establishing appropriate TMDL goals that need to be considered in appropriately regulating OP pesticide-caused aquatic life toxicity in urban stormwater runoff. While the focus of this paper is urban stormwater runoff, the same issues apply to agricultural stormwater runoff where the toxicity is due to the use of OP pesticides. Additional background information on the issues discussed in this paper are available from Lee and Jones-Lee (1999a,b). Elimination of Pesticide Us