Breathing fog in California's San Joaquin Valley may be more dangerous than inhaling polluted air because particles of pesticides, chemicals and vehicle exhaust fumes accumulate in much higher concentrations in fog, scientists reported today.
"There is a difference between inhaling vapors (in air) and inhaling concentrated particles (in fog). The particles stay in the lungs, whereas vapors can be exhaled," said James N. Seiber, an environmental toxicologist at the University of California, Davis.
"But we really weren't doing a health study," he added, "and somebody else will need to take this data and follow it up to see what the consequences are."
Some of the compounds Seiber found in fog collected in the San Joaquin Valley have caused headaches, neurological damage and even deaths among farm workers accidentally exposed to much higher concentrations than occurred in the fog.
The fact that the tule fog stays in one place for long periods, he said, allows ample time for the water particles to absorb the contaminants. In some cases, the concentrations of pesticides in fog were thousands of times as high as concentrations in the surrounding air.
"We found that the concentrations of organic materials were much higher than we had expected," Seiber said. "We don't know why."
Seiber worked with chemists Dwight E. Glotfelty and Louis A. Liljedahl of the U.S. Department of Agriculture's Agricultural Environmental Quality Institute in Beltsville, Md. Glotfelty and Liljedahl invented a device that can be mounted on the back of a pickup truck and driven through fog to collect the moisture.
"You wind up with a jar of fog water," Seiber said. "When we collected fog water in Maryland and California, we wound up with a bottle of dirty brown water."
The dirt came from dust particles in the air and, especially in Maryland, from soot expelled by fireplace chimneys.
The contaminants accounted for about 1% of the organic materials found in the fog. The majority of the materials were naturally occurring hydrocarbons and other chemicals produced by plants.
In California, the researchers collected fog in a cotton-growing area near Corcoran, in fruit and citrus orchards near Fresno and in vineyards near Lodi. They collected their samples during the winter months when tule fog can blanket the San Joaquin Valley for weeks at a time.
The three researchers report in today's issue of the British journal Nature that they had identified at least 16 different pesticides in the fog, most of them organophosphates. Organophosphates, which are used on most types of crops, are "very acutely toxic generally," according to Albert Meyerhoff, a pesticides expert for the Natural Resources Defense Council, "and this report raises some reasons for alarm."
Some of the pesticides probably evaporated from the leaves of plants, Seiber said, but most were undoubtedly carried into the air by dust particles.
High levels were also found in fog water collected in agricultural areas near Beltsville, a Washington suburb, even though those fogs persisted for only short periods.
The high levels were especially significant, Seiber said, because the fog was collected during the winter, when pesticide spraying is at a minimum. This might suggest that concentrations in fog may be higher in the spring, when most spraying occurs, but Seiber declined to speculate.
Scientists have had a difficult time in the past pinning down the health effects of pesticides. A recent National Academy of Sciences report said that data about health effects was lacking for 85% of pesticides.
According to a 1986 report from the National Cancer Institute, however, studies in Nebraska and Wisconsin have shown that farmers have up to twice the risk of contracting leukemia and another group of blood cancers called lymphomas, presumably as a result of exposure to farm chemicals.
A September, 1986, study of farmers in Kansas conducted by the National Cancer Institute and the University of Kansas showed a sixfold increase in non-Hodgkin's lymphoma among farmers who frequently used herbicides to control weeds.
A spokesman for the California Department of Health Services said the agency could not comment on the risks until its scientists had seen the report.