REGIONAL WATER QUALITY CONTROL BOARD
SAN FRANCISCO BAY REGION
STAFF SUMMARY REPORT (Bill Johnson)
MEETING DATE: September 18, 2002
SUBJECT: TMDL FOR DIAZINON AND PESTICIDE-RELATED TOXICITY IN
SAN FRANCISCO BAY AREA URBAN CREEKS
CHRONOLOGY: A status report, including drafts of the problem statement and source analysis elements of the TMDL, was presented to the Board on January 17, 2001.
DISCUSSION: We have prepared a Preliminary Project Report for the Total Maximum Daily Load (TMDL) for Diazinon and Pesticide-Related Toxicity in San Francisco Bay Area Urban Creeks. The report represents a significant milestone in the TMDL development process. It contains the results of our efforts to date, including a problem assessment, source analysis, and preliminary implementation strategy. Publication of the report provides an opportunity for stakeholders to provide feedback on technical TMDL issues and the preliminary implementation strategy.
Urban creeks support beneficial uses related to aquatic habitats, fish spawning and migration, and rare and endangered species, but Bay Area urban creek water is often toxic to test organisms. Diazinon, a common insecticide, is responsible for most of the toxicity. Diazinon concentrations in Bay Area urban creeks often exceed water quality criteria developed by the California Department of Fish and Game. The presence of toxic substances in urban creeks in concentrations that are toxic to aquatic life is inconsistent with the Basin Plan’s water quality objective for toxicity. Therefore, 35 urban creeks have been placed on the 303(d) list of impaired water bodies as a result of diazinon. The listed creeks include those specifically named in the Basin Plan, but essentially all Bay Area urban creeks receive similar discharges and are similarly impaired.
The sources of diazinon and pesticide-related toxicity in urban creeks are storm drains that convey urban runoff. Each year, the Bay Area uses about 85 tons of diazinon. Pest management professionals apply diazinon for structural pest control, agriculture, and landscape maintenance. Private individuals purchase diazinon over-the-counter for a variety of pest problems. Urban runoff transports pesticides from application sites to storm drains during rain and irrigation events. Storm drains discharge pesticide-laden runoff into urban creeks. About 0.25% of the diazinon applied outdoors is discharged to urban creeks. This small fraction results in diazinon concentrations in urban creeks at the parts per trillion level, and these low concentrations are sufficient to cause the observed toxicity.
Several factors contribute to the amount of pesticides in runoff. In the Bay Area, ants are the most commonly reported insect pest, and pesticides such as diazinon are common choices for ant control. Many pesticides, including diazinon, are applied to paved surfaces like building perimeters, where the potential for runoff is great. Common pesticide formulations are often designed to disperse readily in water, increasing their potential to run off. Moreover, pesticides sold over-the-counter are applied with essentially no supervision. Focusing on these factors can help us optimize our implementation efforts.
Since storm drains are the only significant source of pesticides in Bay Area urban creeks, those contributing to urban runoff share responsibilities for meeting diazinon and pesticide-related toxicity targets. However, many parties contribute to pesticide runoff, including pesticide manufacturers, formulators, distributors, retailers, and users. In addition, many organizations oversee these parties’ activities.
The U.S. Environmental Protection Agency (EPA) Office of Pesticide Programs and the California Department of Pesticide Regulation are the primary agencies that regulate pesticides. Their pesticide regulations, however, do not ensure compliance water quality laws and regulations overseen by the U.S. EPA Office of Water and the State and Regional Boards. The separation of these regulatory programs among different agencies has resulted in regulatory gaps that have allowed the impairment of Bay Area urban creeks. Municipalities are caught in the middle because they are responsible for pesticide discharges through their storm water permits, but federal and state laws withhold authority to regulate pesticide sales or use from local governments.
As a result of a re-assessment of diazinon risks pursuant to the Food Quality Protection Act, diazinon manufacturers and U.S. EPA have agreed to phase out most urban diazinon uses by the end of 2004. These actions will likely result in the attainment of diazinon concentration targets. However, the pesticides replacing diazinon in the marketplace pose new challenges. Like diazinon, many are toxic to aquatic organisms at ecologically relevant concentrations. Many of the newer pesticides strongly bind to sediment, and their potential to contribute to sediment toxicity is unknown. Because the foreseeable diazinon replacements may pose their own toxicity risks, this TMDL focuses on the underlying causes of pesticide-related toxicity, and not just diazinon in particular.
Our over-arching strategy for implementing this TMDL is to discourage the use of conventional pesticides that threaten water quality. One way to do this is to practice Integrated Pest Management (IPM). IPM is an ecosystem-based approach to pest management that focuses on long-term pest prevention through a combination of biological control, habitat manipulation, modification of cultural practices, and use of pest resistant plant varieties. Conventional pesticides are used only after monitoring indicates that they are needed, and treatments are made with the goal of removing only the target organism. This strategy prevents pesticide pollution at its source.
In conclusion, our proposed approach to TMDL implementation involves (1) working with U.S. EPA and the California Department of Pesticide Regulation to better integrate pesticide and water quality regulations, (2) working with storm water programs and other parties to undertake education and outreach programs that reduce pesticide use that threatens water quality, and (3) following-up with monitoring to demonstrate that diazinon and pesticide-related toxicity no longer impair urban creeks. We plan to complete a final project report for this TMDL in early 2003 and propose Basin Plan amendments to formally establish this TMDL about a year from now.
RECOMMEN- No action is necessary at this time.
Appendix A Total Maximum Daily Load (TMDL) for Diazinon and Pesticide-Related Toxicity in San Francisco Bay Area Urban Creeks—Preliminary Project Report