REGIONAL WATER QUALITY CONTROL BOARD
SAN FRANCISCO BAY REGION
STAFF
SUMMARY REPORT (Bill Johnson)
MEETING
DATE: September 18, 2002
ITEM: 12
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.
DATION:
Appendix
A Total Maximum Daily Load
(TMDL) for Diazinon and Pesticide-Related Toxicity in San Francisco Bay Area
Urban Creeks—Preliminary Project Report
APPENDIX A