2012 IR&D Annual Report

Analytical Methods and Concentrations of Exposure Biomarker Chemicals
in Deciduous Teeth, Quick-Look, 01-R8235

Principal Investigators
David E. Camann
Alice Y. Yau

Inclusive Dates:  06/27/11 – 12/28/11

Background — The developing fetus is particularly vulnerable to adverse effects from pharmaceutical and exogenous chemical exposure. No biomarkers exist to retrospectively assess prenatal and early post-natal exposure to many chemicals, including analgesics, organophosphate (OP) insecticides, and diester phthalates because the parent compound is rapidly metabolized and the metabolites are quickly excreted. An urgent need exists to identify perinatal exposure biomarkers of such chemicals for use in assessing their contribution to risk for epidemic pediatric neurodevelopmental disorders such as autism. The enamel and primary dentin of the crown of each deciduous tooth form during a specific period from initial dentin calcification within the second trimester in utero through crown completion within the first year after birth. Tooth concentrations of sequestered substances may provide useful biomarkers of exposure during its formation. It was hypothesized that organic chemicals or their metabolites circulating in the bloodstream during deciduous tooth formation may sorb along with calcium and other nutrients and remain sequestered when the tooth is shed.

Approach — The objectives were to devise analytical and preparation methods for potentially toxic or beneficial organic chemicals or metabolites in deciduous teeth, to discover if some were stored in teeth, and to estimate their detection frequency in deciduous molars. Tooth preparation, extraction, and analytical methods were developed for analgesics and specific and non-specific metabolites of OP insecticides and phthalates by tandem liquid chromatography/mass spectrometry, and for polyunsaturated fatty acids and insecticides by gas chromatography/mass spectrometry.

Accomplishments — The analgesic acetaminophen was stored at greater concentration in a child's second molar than a first molar, consistent with intake, suggesting that acetaminophen concentration in molars may be a biomarker of acetaminophen exposure during molar formation. Chemicals detected by liquid chromatography/tandem mass spectrometry in molars of 21 typically developing children include the endocannabinoid anandamide (86 percent of children), the analgesic acetaminophen (43 percent), and the specific metabolites mono-2-ethylhexyl phthalate (MEHP, of plasticizer di-2-ethylhexyl phthalate, 29 percent), 3,5,6-trichloro-2-pyridinol (TCPy, of OP insecticide chlorpyrifos, 10 percent), and 2-isopropyl-6-methyl-4-pyrimidinol (IMPy, of OP insecticide diazinon, 10 percent). None of these chemicals has previously been detected in human teeth. Molars from the two oldest subjects contained the largest concentrations of MEHP, TCPy, and IMPy. Potentially protective fatty acids detected by gas chromatography/mass spectrometry after derivatization include docosahexaenoic (19 percent), arachidonic (100 percent), and linoleic (100 percent). Validation studies are necessary to verify that each detected chemical in molars provides a biomarker of perinatal exposure.

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