CERCH Scientists’ Response to Epidemiologic Critique of Gemmill et al. 2013

Tags: Birth Outcomes, CHAMACOS, methyl bromide, Pesticides

Recently, CERCH published a study on methyl bromide and birth outcomes among CHAMACOS participants. In the study, we used information about nearby use of methyl bromide as an indicator of exposure.  Studies from the state Department of Pesticide Regulation show that nearby use of methyl bromide is a good indicator of levels in the air.  We found that higher methyl bromide use near the homes of pregnant CHAMACOS mothers was associated with lower birth weight, birth length, and head circumference.  For more on that paper click here for the fact-sheet that summarizes the study, or you can see the complete study by clicking here.

The study was published in the peer-reviewed journal Environmental Health Perspectives.  Like any article that is published in a peer-reviewed journal, it was read and scrutinized by other scientists to check the methods of the study.

A public relations firm in Watsonville commissioned a review of an unpublished draft of our study by the consultant group Exponent.  Click here for a full copy of their critique. The Exponent reviewers raised concerns about exposure mis-classification, confounding, and whether the findings are meaningful for other populations.  Many of the points raised by Exponent were raised by us in the paper  and we addressed those issues.  And, of course, every study has limitations.  As we have said before, most studies in humans, like CHAMACOS, can only report on associations between exposures and health outcomes, and do not prove that the exposure actually causes the problem. More research is needed to see if the same results are found in other studies.  We have prepared a detailed response to the Exponent review and it has been posted on our website here.

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