May 26, 1995
Pesticides in California Groundwater
According to a report just released by the School of Public
Health at the University of California, Berkeley, pesticide
contamination of drinking water poses a significant health
risk in agricultural areas of the largest agricultural state
of the U.S. The report, "Pesticide Contamination of
Groundwater in California," assesses the role that pesticide
use plays in degrading California's groundwater resources and
evaluates the adequacy of current efforts to protect
groundwater. Groundwater supplies a significant proportion of
California's drinking water: 60% of large public drinking
water systems and 80% of small water systems use groundwater
sources. In rural areas, 90% of the population relies on
groundwater as their only supply of drinking water.
Using data generated by California's pesticide monitoring
programs, the report examines the extent of pesticide-related
contamination and resulting environmental health risks. The
report found that over the last 15 years of monitoring,
pesticides or their breakdown products have been detected in
2,198 domestic wells and over 1,200 wells serving large and
small public water systems. The following ten pesticides
account for over 92% of the contaminated wells: DBCP
(dibromochloropropane), simazine, diuron, atrazine, 1,2-
dichloropropane (1,2-DCP), bromacil, EDB, bentazon, chlorthal
dimethyl and aldicarb sulfone. Although DBCP, EDB and 1,2-DCP
are no longer used, they continue to contribute significantly
to the health risks associated with groundwater
contamination.
The report states that DBCP is responsible for contaminating
more California wells than any other pesticide (over 70% of
the wells with detections), and now exceeds federal standards
for safe exposure in about 1,700 wells throughout the state,
affecting more than more than 200,000 people. DBCP, once
widely used in the U.S. as a fumigant to kill nematodes
(small worms in the soil) and one of PAN International's
Dirty Dozen pesticides, was virtually banned in 1979
following revelations that 35 workers in an Occidental
formulation plant had been sterilized by exposure to the
chemical. Dow and Shell company scientists had known, at
least since the 1960s, that the pesticide was a testicular
toxin, but had suppressed the information. DBCP is also a
potent carcinogen and can cause numerous acute and chronic
health effects.
On May 15, 1995, the city of Fresno announced that Shell Oil
Co., Dow Chemical Co. and Occidental Chemical Corp, all
former manufacturers of DBCP, will pay the city $21 million
to help clean up wells contaminated with the pesticide. At
least half of the wells supplying the city's water are
contaminated with DBCP. As part of the agreement, the three
chemical companies have agreed to make annual payments for 40
years to operate 24 municipal wells that are contaminated
with DBCP. They also will pay operation and maintenance costs
for five water treatment units. Approximately $30 million has
already been paid by the companies to other towns in the
affected areas of California's Central Valley.
The new report states that groundwater in Northern California
has not been affected by pesticide use, nor have water
systems that rely on diversion from the Sierra Nevada
Mountains. However, according to William Pease, a
toxicologist at the School of Public Health and lead author
of the report, cities and towns in the Central Valley and
several Southern California counties, as well as people using
private wells in those areas are "getting a cocktail of
chemicals in their drinking water, and no one can say whether
or not it is safe."
In terms of the number of cancers that might be caused by
drinking water, the authors found that, overall, pesticides
constitute a "moderate risk" when compared with naturally
occurring chemicals, particularly arsenic and radon. The
authors calculated for every 1,000 cases of cancer caused by
natural arsenic in the water, pesticides might cause five.
"But those five are caused by human action and they are
avoidable," stresses Pease.
Sources: Pesticide Contamination of Groundwater in
California, UC Berkeley School of Public Health, 1995; Office
of Public Information, UC Berkeley press release, May 18,
1995; San Francisco Examiner, May 16, 1995; PANUPS, March 5,
1993.
Contact: William Pease, California Policy Seminar, 2020
Milvia St., Suite 412, Berkeley, CA 04704; phone (510) 642-
9103.
Copies of the report are available from the California Policy
Seminar.
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