Organophosphates found in Meconium

A Review of: Whyatt RM, Barr DB. Measurement of organophosphate metabolites in postpartum meconium as a potential biomarker of prenatal exposure: A validation study. Environmental Health Perspectives: 2001,109(4), 417-420

Organophosphate pesticides include chemicals such as malathion, diazinon, and chlorpyrifos (Dursban). Organophosphates are used as insecticides for a wide variety of purposes, including food use, mosquito control, household pest control, and flea control on pets. These insecticides were first used in the 1940s and act by deactivating an enzyme critical to the function of the nervous system. As a result, these chemicals are acutely toxic to humans. More recent evidence suggests that organophosphates may have subtle and delayed effects on the development of the brain in infants and children. Thus, it is very important to assess human exposures to these chemicals during periods of greatest vulnerability such as fetal life.

Prior research has identified organophosphate pesticide residues on hand wipe samples of toddlers and in urine samples from children. Because these pesticides are not long-lived in the body, studies of exposure tend to generate a 'snapsho'Õ of exposure during a short period of time. For this study, the researchers chose to investigate levels in meconium because meconium accumulates in the fetal bowel during the entire second and third trimester of pregnancy. It is therefore likely that the levels measured in meconium reflect several months of accumulated exposure, rather than several days. Meconium is also readily available from the diapers of newborn babies in hospital nurseries, so the collection is painless and easy.

The researchers collected meconium samples from 20 newborns in the hospital nursery without any information about the pesticide exposure of the mother. The diapers themselves were tested and found to be negative for pesticide residue. The samples were tested or six organophosphate metabolites. The six metabolites are common to one or more of 28 different organophosphate insecticides. Two of the metabolites, diethylthiophosphate (DETP), and diethylphosphate (DEP) were detected in every sample and 95% of samples respectively. These metabolites can derive from any of ten different pesticides, but only two of those ten (diazinon and chlorpyrifos) are widely used and are available for use in the home. Thus it is likely that the DETP and DEP detected came from exposure to these two chemicals. The other metabolites were detected rarely or not at all. Furthermore, the concentrations of the pesticide metabolites were much higher than levels previously reported in umbilical cord blood, and were similar to the levels reported in urine in studies of the general population. [See, for example, www.cdc.gov/nceh/dls/report/Highlights.htm CDC Environmental Health. National Report on Human Exposure to Environmental Chemicals. NCEH Pub. No. 01-0164, March 2001.]

From this study, it is clear that meconium can be a useful substance for measuring prenatal exposures to environmental chemicals. The preliminary data from this small sample indicate that a large proportion of fetuses may be exposed to significant levels of some organophosphate pesticides.

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