Effect Measure

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.


  1. #1 marquer
    March 23, 2007

    It would seem fairly obvious that people who live, work, eat and drink in close proximity to where spray-applied toxins are used are going to end up directly ingesting (if not breathing) a lot of the stuff.

    I’m still myself trying to figure out how the heck PDBE flame retardants are escaping their incorporation into household objects and finding their way into women’s breast tissue. It’s not as though the appliances have PDBE spray nozzles on them.

    The leading theory I had heard was that it was seating foam in furniture, oxidizing to dust and then being inhaled. Roughly plausible. One wonders what else is in that dust…

  2. #2 revere
    March 24, 2007

    marquer: It’s actually not that obvious. The fields are not in their living rooms and you can’t measure the pesticides in the air. As for PBDE, no on knows but household dust is shaping up to be one place where they reside in ways that can cause potential exposure.

  3. #3 Pogie's Mom
    March 26, 2007

    Perhaps even though the women don’t work in the fields, it may be likely that others in their families do, picking up pesticides on their clothing and shoes, which brings it all home to the families.
    Just in the normal routines of family life, hugging, bathing kids, feeding, laundering clothing, sweeping the floor the women could end up having just as much exposure to pesticides as the out of the home working people in the house. Does she ride around in the same car that Dad and the uncles take to and from work? Shower in the same bathroom? Shake out clothing before it’s dropped in the washing machine? Or worse, wash the laundry by hand?
    In my experience, pesticides seem to have an oily residue that doesn’t evaporate, but tends to smear onto anything that it touches. Might be time to do a study similar to the ‘glow in the dark’ bacteria tracing done to show how germs spread in offices in people’s homes.

  4. #4 Greg
    March 26, 2007

    Where does it say the women do not work in the fields?

  5. #5 revere
    March 26, 2007

    Pogie, Greg: There are many possibilities here. McKone’s group narrowed them down. The results indicate that the exposure is not primarily occupational, so we learned something.

  6. #6 Greg
    March 26, 2007

    Oh!, he says, taken aback.

    Yes, an important something. Very important.

    The pushers always sing, “Safe when Properly Applied”, in multipart harmony; then assure that evidence circulates of improper application, to explain away the evidence of unsafety.

  7. #7 Ground Zero Homeboy
    March 27, 2007

    Organic food is its own scandal: big-O food in your supermarket has no bug damage because it is grown with organic pesticides. These break down very quickly and leave no residues. Here is a list of such things.

    These substances are more toxic to the applicators. The poor farmworkers are hit with nastier stuff than the guys working on conventional farms.

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