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Breakthrough On The Horizon in Chemical Exposure Testing
(Beyond Pesticides, November 6, 2003)
Scientists at the Department of Energy's Pacific Northwest National Laboratory (PNNL) have found a way to identify breakdown products of pesticides in the saliva of rats. They believe that a broad range of pesticides will eventually be detected through saliva monitoring and envision a day when such testing will be fast, easy, and cost-effective for humans with almost immediate results.

Biomonitoring - or the testing for chemical residues in a person's body - is a vital way to determine the presence of chemicals within a given population and find trends or make informed decisions. Determining the build up of chemicals in the body (the body burden) can be used by health care providers to treat patients, health departments to track chronic diseases, policymakers to enforce and create regulations, or by citizens to take action to stop contamination in a local community.

Currently, biomonitoring is done by collecting samples of bodily fluids, usually blood or urine, and having the samples analyzed in a laboratory. Yet, collecting these samples can be complicated, costly and time-consuming - especially from children. Lab costs are also high and results can sometimes days or weeks to receive. In many cases antidotes to pesticide poisonings, like antidotes to nerve agents, are only effective if administered quickly.

"We wanted something less invasive and easier for us to get," says Charles Timchalk, one of the scientists working on the controlled experiments at PNNL. Researchers are using chlorpyrifos, known by its trade name Dursban, one of the main organophosphate pesticides used in agriculture, along with a modeling method to make extrapolations and estimate dosage.

"The fact that we were able to find the chemical in very low concentrations confirms that saliva can be a reliable, non-invasive method to monitor farm or industrial workers who are exposed routinely to potentially harmful pesticides," says PNNL chemist Jim Campbell.

Although making great achievements, Timchalk admits "we're not ready for prime time", as it will be some time before the tests are ready to come out of the laboratory and even longer before saliva testing is considered as effective as blood or urine samples.

Funding for the project is coming from an Environmental Protection Agency (EPA) Science to Achieve Results (STAR) grant but, says Timchalk, the project actually grew out of a National Institutes of Health (NIH) grant on the issue of children and lead poisoning. Funding for such research projects has been influenced by the 1999 lawsuit against the EPA filed by the National Resources Defense Council (NRDC) for failing to implement a provision of the 1996 Food Quality Protection Act that requires EPA to set a margin of safety ten times higher for children than adults on chemicals that EPA does not have complete health data.

The EPA is particularly interested in organophosphates as children have been found to be especially vulnerable to their effects. Organophosphate chemicals bind irreversibly to acetylcholine esterase (AchE), an essential enzyme for normal nerve impulse transmission and can seriously affect the nervous system, cardiovascular system, and respiratory system. In 1997, EPA's Office of Pesticide Programs, Health Effects Division reported that chlorpyrifos is one of the leading causes of acute insecticide poisoning incidents in the U.S.

Researchers claim that there is a definite possibility to develop a portable device that can test pesticide exposure on-site and deliver results almost immediately. "We have demonstrated that a biosensor linked to a hand-held electrochemical detector can identify the organophosphates in solution with a high degree of sensitivity," said Yuehe Lin, a PNNL chemist.

Once developed, PNNL scientists and researchers say that the new technology could be adapted to test for a variety of contaminants and foresee its usefulness in the case of a bioterrorist attack. Regardless of adaptations, developing the technology to assess exposure to agricultural pesticides means that it may very well be put to use on a daily basis wherever pesticides are found - in agricultural and non-agricultural lands throughout the country.