Pesticides in San Diego's Water

We don’t want insects in our homes, in our food or on our flowers, so we rely on very toxic chemicals to kill them.

Unfortunately, these chemicals kill other invertebrates as well. Just because government agencies approve pesticides doesn’t mean they are safe for the wider environment. Research definitively shows two popular and widely used pesticides, diazinon and chlorpyrifos, to be lethal or cause harm to organisms living in creeks and rivers. Monitoring in the late 1990s found that Chollas Creek, a local waterway draining into San Diego Bay, had consistent and high levels of toxicity.  Further research demonstrated that the toxicity was due to concentrations of diazinon that was flowing into the creek in urban runoff, particularly during rain events.  

Due to the mounting evidence that diazinon was causing widespread toxicity in water bodies, the US EPA created a phase-out and elimination program in 2001. Diazinon is no longer available for sale for any indoor or outdoor residential use. Similarly, in 2000, EPA began the phase-out of almost all over-the-counter sales of chlorpyrifos.

Chollas Creek was deemed impaired due to toxicity from diazinon (as well as metals) and was placed on the 303(d) list. To address this problem, the Regional Water Quality Control Board developed a Total Maximum Daily Load (TMDL) with input from San Diego Coastkeeper and other municipal stakeholders. The TMDL largely rests on the effectiveness of the diazinon ban. In addition, municipalities must ensure that concentrations in runoff do not exceed certain limits.

Unfortunately, the banning of specific pesticides like chlorpyrifos and diazinon has led to an unintended consequence. Without the availability of these two pesticides, residential users largely turned to a new class of pesticides called pyrethroids.  Pyrethroids are now detected in creeks and rivers throughout California. Recent research has also determined that pyrethroids cause toxicity detected in creeks and rivers in California. The widespread problems caused by pyrethroids have led the California Department of Pesticide Regulation’s to re-evaluate some 600 pyrethroid products on the market in August 2006. This process has not yet been completed.