Organophosphate Pesticide Aquatic Life Toxicity as a
National Water Quality Problem

G. Fred Lee & Associates
27298 E. El Macero Dr.
El Macero, California 95618-1005
Tel. (530) 753-9630 Fax (530) 753-9956
web site:

June 30, 1998

Robert Perciasepe
Assistant Administrator
Office of Water
401 M Street
Washington, D.C. 20460

Dear Mr. Perciasepe:

Periodically, I have brought to your attention the problems with the organophosphate pesticides, diazinon and chlorpyrifos, causing aquatic life toxicity associated with urban area and, in some instances, agricultural area stormwater runoff. Recently, in connection with the Northern California Society for Environmental Toxicology and Chemistry annual meeting that was held in Reno, Nevada I prepared a discussion of regulatory issues for presentation at that meeting. Enclosed is a copy of the abstract, slides and discussion of these issues which summarize the current situation in California. In my previous discussions of the issues, I have raised the question about whether this is a national problem that the US EPA should be addressing. I never received a response to that inquiry. Since then, I have obtained sufficient information to know that this is a national problem, in that there is widespread urban and, in cases, rural stormwater runoff-associated toxicity to Ceriodaphnia and to some other organisms arising from the use of diazinon and chlorpyrifos as chemicals for structural, home and garden and agricultural pest control.

In my original contact I mentioned that we were just starting a major effort to define this problem as it relates to stormwater runoff to Upper Newport Bay in Orange County, California. We now have two years of data and have convincingly demonstrated that chlorpyrifos and diazinon used in urban areas by homeowners and commercial applicators is causing San Diego Creek, the primary tributary of Upper Newport Bay, to be toxic to Ceriodaphnia and mysids with each stormwater runoff event.

The key issue that has to be resolved is what it means to have toxic pulses of OP pesticide-caused toxicity enter a waterbody with each stormwater runoff event to the beneficial uses of that waterbody. It is clear to me that this country is not likely going to regulate urban or rural stormwater runoff-associated toxicity caused by OP pesticides based on the no toxics in toxic amounts approach used in regulating domestic and industrial waste water discharges. Instead, an approach similar to that advocated in my enclosed suggested regulatory approach of a watershed-based consensus of what constitutes excessive toxicity to a selected group of organisms which may or may not be important in the aquatic food web for higher tropic level organisms, such as game fish and shellfish, that are of greater importance to people than zooplankton. While I believe it should be the US EPA that convenes an expert panel to establish a national policy on this issue, it appears that this issue is too politically sensitive to be addressed at this time at the national level and therefore there will likely be a piecemeal policy across the country as various areas discover the OP pesticide toxicity problem associated with urban stormwater runoff.

If you or others to whom I am sending a copy of this have questions or comments or wish further information on our Orange County studies, my suggested regulatory approach in which a watershed-based, technical stake holder driven executive committee formulates an assessment of what constitutes excessive toxicity for various types of waterbodies of concern, please contact me.

If I can be of assistance in helping the US EPA address this national problem, please let me know.

Sincerely yours,


G. Fred Lee, PhD, PE, DEE


Copy to: F. Marcus

Reference as: "Lee, G.F., 'Organophosphate Pesticide Aquatic Life Toxicity as a National Water Quality Problem,' letter to R. Perciasepe, Office of Water, US EPA, Washington, D.C., June (1998)."

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