Pesticides pathways

Pregnant Latina women in the Salinas Valley in CAlifornia have pesticides in their bodies. The surrounding farmland is loaded with pesticides. But how is it getting from the land to them? Or is it? Tom McKone and his colleagues at Lawrence Berkeley National Labs set out to find out. It turned out not to be that easy.

McKone and company concentrated on organophosphate pesticides (OPs). These are long acting nerve poisons for pests but can also affect humans and are of concern for neurodevelopmental effects on fetuses and children. When taken into the body they are metabolized to other chemicals and excreted in the urine, where they can be measured and an estimate of exposure done. They measured OP metabolites in 600 pregnant women and compared the levels with levels found in the general US population. The levels were described as "significantly higher." There is also a lot of pesticide use nearby, as the map shows.

Source: McKone et al. Map of the Salinas Valley showing average yearly pounds of OP pesticides applied per section (~1 square mile).

But how were the chemicals getting to the women, or were their body burdens from elsewhere? The most likely culprit would be food. To disentangle the multiple interacting pathways, McKone and his colleagues used some well validated physical fate and transport models. These are computer models that predict concentrations or amounts of chemicals as they move by physical processes through air, water and soil and may be chemically transformed along the way. Models are needed because the OPs themselves aren't very persistent in the various environmental media and they vary significantly over space and time. The models allow estimation of an average exposure over time.

First, they adapted the CalTOX fate and exposure model to estimate OP pesticide concentrations in outdoor air and soil near participants' homes. They then combined the results with an indoor mass-balance model to estimate indoor air, dust, and surface concentrations. The team modeled nondietary exposures through inhalation, nondietary ingestion, and skin contact, and they estimated dietary exposures using the U.S. Food and Drug Administration's Total Diet Study, which provides information on the levels of pesticide intake through "table-ready" foods.

When McKone and colleagues combined the results from the models with biomonitoring data, they found that the Salinas Valley population was receiving similar levels of the pesticides from their diet as women elsewhere in the U.S. The real culprit behind the higher levels of OP pesticide in this population was exposure through air, water, and soil. (Environmental Science and Technology, news release)

For other chemicals, like PCBs, diet is probably the main culprit. McKone and his team are top notch scientists and they have been doing this kind of fate and transport modeling for a long time. This is an important contribution to understanding how environmental chemicals are finding their way into our bodies. The Lawrence Berkeley Labs also do nuclear weapons research. Too bad more of their efforts aren't devoted to life sustaining work rather than life denying work. As for the publication, Environmental Science and Technology where this work appears (DOI: 10.1021/es0618447), it is one of the flagship publications of the American Chemical Society, a professional association lately best known for soiling itself in public with its attempts to kill Open Access scientific publishing. I can only read the news release because my own subscription lapsed when I couldn't justify the $150 annual rate.

Mea culpa, 3/25/07: Professor David Michaels of The Pump Handle pointed out to me that the weapons work is done at Livermore, not Lawrence Berkely Labs. He oughta know. He was Assistant Secretary at the Department of Energy in the Clinton Administration. My bad.