Saliva Spits Out Information On Chemical Exposure

Using sophisticated mass spectrometry equipment at PNNL, researchers have been able to identify breakdown products of a common pesticide in the saliva of rats exposed to known amounts of the pesticide. The researchers are working now to develop a simpler, portable microanalytical sensor system to quickly diagnose pesticide exposure in humans and a modeling method than can estimate the dose. Researchers say the technology could be adapted to test for a variety of contaminants, including chemical warfare agents.

The research project began with an Environmental Protection Agency grant to study pesticide exposure in adults and children working or living near farms. The research team exposed rats to a common agricultural chemical and found traces in the saliva shortly after exposure.

"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," said Jim Campbell, an analytical chemist working with mass spectrometers at PNNL.

Researchers believe saliva monitoring may be able to detect a broad range of chemical contaminants from ongoing occupational exposure, accidents or even acts of war and terrorism.

"The class of pesticides we are studying, organophosphates, are chemically similar and work on the same general principal as nerve gas," said Charles Timchalk, a Battelle toxicologist at PNNL. "Both pesticides and nerve gases inhibit an enzyme called acetylcholinesterase. Without acetylcholinesterase, nerves, including those responsible for breathing, stop functioning."

Chemical nerve agents also bind to and disrupt other enzymes, including one called butyrylcholnesterase. "Researchers at the laboratory have demonstrated that rat saliva contains a nearly pure population of this enzyme," said Campbell. "This data strongly suggests that it's possible to develop a portable device to yield immediate results from a small amount of saliva. Such a device might save lives in the event of a military or terrorist attack."

Real-time diagnosis is the key, as some treatments for nerve gas poisoning are effective, if initiated in time. Typically, however, testing for chemical exposure requires drawing blood or collecting urine samples, which must then be sent to a laboratory. Results may be days or weeks away.

"If expanded to identify chemical warfare agents, saliva analysis would not only identify those who need medical treatment, but might also offer up forensic evidence against the attackers," said Timchalk. "It might be possible to detect trace levels of the chemical agents in the saliva of a terrorist who handled the poisons before releasing them."

The saliva monitoring technology under development at PNNL is being designed to provide immediate results and be simple enough to be operated in the field by technicians with little training.

"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 Battelle analytical chemist at PNNL. "The biosensor consists of electrodes coated with carbon nanotubes. The carbon nantotubes hold the enzymes, which are targeted to the organophosphate chemicals, and electricity is applied. If organophophates are present, there is a decrease in the electrical current that can be correlated to the amount of chemical present. The hand-held biosensor detection system will facilitate the on-site saliva monitoring of exposures to these pesticides."

The Battelle team hopes to secure additional funding to study saliva testing and monitoring for nerve agents. Meanwhile they continue to develop the technology to assess exposure to agricultural pesticides.