More than 12 years after it was banned, the potent pesticide DDT persists in soil throughout the state, and detectable--but reportedly safe--levels are continuing to show up in vegetables, the state Department of Food and Agriculture said Monday.
But the department said there was no evidence that DDT is being used illegally, as some had suspected.
"Based on all available evidence, the California Department of Food and Agriculture concluded that long-lived residues from previous applications are the apparent source of DDT residues in produce and in the environment," the report said.
DDT was detected in crops in which an edible portion grows in, or close to, the ground, such as carrots, beets, lettuce and spinach. The department said that "in most cases" the contamination was well within acceptable levels. What contamination that was found was believed to be caused in large part by DDT-laced soil on the plant's surface, not within the plant's system.
Rinsing the produce with water may further reduce DDT levels, the department said.
In a yearlong study ordered by the Assembly, in part because of suspicions of clandestine use of DDT by some growers, the department found widespread DDT levels throughout California's principal agricultural areas.
Indeed, the report said, DDT was detected in all 99 soil samples taken in 32 counties. The department concluded that half of the DDT used before it was prohibited at the end of 1972 is still in the environment and may remain in California soil for 12 to 15 more years.
"The important role that DDT has played in California agriculture cannot be diminished or denied. Equally important, however, is the legacy of long-term, widespread environmental contamination which the usage of DDT has left us," the report said.
The report was generally applauded Monday by the office of Assemblyman Lloyd Connelly (D-Sacramento) and by a scientist with the Natural Resource Defense Council in San Francisco. Connelly authored the resolution calling for the study.
However, both Connelly's office and the environmental group noted that DDT principally accumulates in fatty tissue of fish and animals rather than in leafy crops but that the department study failed to list what, if any, DDT levels were found in feed grain that is eaten by beef cattle and milk-producing cows.
Lawrie Mott, a senior project scientist with the Natural Resource Defense Council, added that the report failed to adequately examine the role of a DDT substitute known as dicofol in possibly adding new levels of DDT to the environment. The federal Environmental Protection Agency has found that the level of DDT in dicofol to be 10% before it is formulated into commercial pesticides.
The department report concluded that dicofol use in California "is not a significant source of DDT residues." However, the finding was based on only a limited sampling. Dicofol is used on cotton, fruits and vegetables, as well as lawns.
DDT usage in California began about 1944 and reached a peak in 1970, the last year in which substantial amounts were applied to crops. DDT is still widely used in developing countries.
The study investigated three possible sources in an attempt to explain the continued presence of DDT: new illegal use, use of other pesticides containing DDT, and long-lived residues from previous legal use of DDT.
In addition to taking soil samples, investigators also reviewed a 1984 study of DDT residue levels in fish and mussels in Monterey County's Salinas River as well as the state's existing pesticide monitoring program.