23
Mar
New Modeling Techniques Reveal Exposure Pathways to Pesticides
(Beyond Pesticides, March 23, 2007) Using advanced risk assessment techniques, researchers have shown pesticide usage in the Salinas Valley, California, exposes pregnant women to pesticides through air, water, and soil. The study tracks how agricultural pesticides can travel from the field into the body.
A team of scientists investigating whether there is a correlation between the high levels of pesticides in pregnant women in the Salinas Valley and the high pesticide usage in the surrounding farmland has discovered important pathways of exposure that greatly inform traditional risk assessment. At first, applying a simple statistical model suggested no direct correlation, but upon applying advanced modeling techniques that combine multiple fate and exposure models with biomonitoring data they found that the study population of 600 Latina women have a significantly higher intake of organophosphorus (OP) pesticides from exposure to the surrounding air, water, and soil, but not food.
The study, part of a larger study on women and children’s environmental health called the Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS) project, is conducted by Thomas McKone, Ph.D., and his colleagues at Lawrence Berkeley National Laboratory and the University of California, Berkeley. Results are published in Environmental Science and Technology (ES&T, March 21, 2007).
Originally, Dr. McKone and his team studied OP pesticide exposure in about 600 pregnant Latina women in the Salinas Valley. The concentration of pesticide metabolites in the CHAMACOS population was compared with the average levels in women from across the U.S. (from data collected by the National Health and Nutrition Examination Survey, or NHANES, in 1999—2000). This revealed that the Salinas Valley women are being exposed to “significantly higher” levels of the pesticides, says Dr. McKone. The next step was to determine how these women are being exposed.
This new study is very informative in terms of understanding the fate of pesticides, says Don MacKay, Ph.D., of the Canadian Environmental Modeling Center at Trent University. Most environmental models merely predict “that if you use this amount of chemicals in this area you probably get this concentration in air, and this in water, and that in fish, and that’s about as far as they go,” he says. Dr. McKone’s work goes beyond that and “quantifies the whole journey [of pesticides] from sources into the environments . . . into outdoors, indoors, into human body,” he says.
The scientists used more sophisticated methods in determining how much each route or source of pesticides was contributing to the measured levels of pesticide metabolites in the women. In this way they were able to track how pesticides travel from the fields through different channels into the human body. Few studies “include how much [of a contaminant] is actually reaching us and how this results in concentrations in our tissue and fluids,” adds Dr. MacKay. This study provides “a shining example of the approach that should be taken for more substances, including pesticides and industrial chemicals. If that can be done, it will help the whole risk assessment process enormously.”
Farmers use large amounts of pesticides in the Salinas Valley, an important agricultural region of California. Environmental Science and Technology Online reports that in 2001, 240,000 kilograms of OP pesticides were applied in and around the valley. Humans metabolize commonly used OP pesticides, such as chlorpyrifos, diazinon, and malathion, into simpler compounds that eventually are excreted. Researchers can monitor levels of exposure by analyzing the levels of these metabolites in urine. Understanding the routes of exposure, however, is trickier.
Interpreting biomonitoring data on chemicals like OP pesticides is also difficult because most of the chemicals don’t persist in the environment for very long and the data have an “inherent uncertainty and variability,” says Dana Barr, the chief of the pesticides laboratory at the Centers for Disease Control and Prevention’s National Center for Environmental Health. “If you take one spot, you may get no exposure where you’ve been exposed previously, and another time you can get peak exposure,” she says. Dr. McKone’s approach provides a unique way of getting at the complex mechanism of exposure to pesticides, Ms. Barr comments.
This analysis only shows how more information is needed. What this and the NHANES study has not shown yet .. is that by measuring the potential metabolites of OP pesticides in urine .. one still does not know whether the person was exposed to the pesticide .. or the less-toxic metabolite. Too many people think that these data clearly show that people are being exposed to significant levels of pesticides. If you want to find that out .. analyze for the pesticides .. not just the metabolites. Possibly .. this has already been done .. but didn’t make such an interesting news story?
March 23rd, 2007 at 8:34 am