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A study that measured agricultural chemicals in the air near Washington State orchards did not find pesticides at levels considered harmful.

The $530,000 study, conducted by the Washington State Department of Health in 2008 in the Yakima Valley and in north central Washington, was designed to find out if off-target movement of organophosphate pesticides posed a potential risk to residents or bystanders.

Sampling was done in both regions in March and April for chlorpyrifos and in May to July in the Yakima area for azinphos-methyl, phosmet, and malathion.

In each region, at least three air samplers were located outside houses that were within 100 meters (330 feet) of an orchard. An additional sampler was located more than 1,000 meters (more than half a mile) from the nearest orchard to measure background levels of the pesticides. Samples were collected for 24-hour periods. Most of the air samples collected had detectable amounts of pesticides, but at very low levels.

None of the residential air samples exceeded screening levels for human health concern set by either the U.S. Environmental Protection Agency or the state of California.

The highest 24-hour average concentration of chorpyrifos detected was 607 nanograms per cubic meter of air, compared with an acute screening level of 1,200. A nanogram is one billionth of a gram, and a cubic meter of air is the amount of air in 500 empty two-liter soda bottles, according to the Department of Health.

The highest 24-hour azinphos-methyl concentration was 356 nanograms per cubic meter, compared with California’s acute screening level of 101,000 nanograms, and the EPA’s screening level of 5,000.

Levels of phosmet and malathion were very low—mostly less than one nanogram per cubic meter.

In addition, measurements were taken on the edge of orchards (within 25 feet) before, during, and soon after spraying. The highest azinphos-methyl concentration averaged over a 24-hour period was 2,372 nanograms per cubic meter, though higher levels were detected over shorter sampling periods.

The department concluded that agricultural spraying in those regions did not appear to pose a health risk to residents or bystanders through inhalation.


Carol Dansereau, executive director of the Farm Worker Pesticide Project based in Seattle, had lobbied for the study to show where pesticides are drifting and the kinds of exposure that children and adults experience. She said sound science on exposure and health risks was needed to ensure that farmworkers, growers, and others in agriculture were protected.

Kirk Mayer, manager of the Washington Growers Clearing House Association, found the results of the study encouraging and positive. “I think it does demonstrate that the growers are being careful in their applications and following proper procedures. It seems like the protections that are built into the labels by the various regulatory agencies have proven effective.”

Dr. Jay Brunner, director and entomologist at Washington State University’s Tree Fruit Research and Extension Center in Wenatchee, said the results probably reflect that while some Lorsban (chlorpyrifos) and Guthion (azinphos-methyl) are still used in orchards, the amount is much reduced. “I think it was an unanticipated result by some groups, but there’s not much there to get too excited about,” he said.

Since Guthion will be phased out completely by 2012, concerns about longer-term exposure to the pesticide should be minimized, he said.

At the same time that the state funded the air monitoring program, it also provided $550,000 in funding to WSU for a Pest Management Transition Project, to help the industry understand how to use newer pest controls in place of the old organophosphates, Brunner pointed out, and that appears to have been successful.

The funding covered the first two years of the project. WSU has just received a federal specialty crop grant of almost $250,000, through the Washington State Department of Agriculture, which will fund another year of the project, running through fall of 2010. Brunner said the university would apply for a fourth and final year of funding.