A new study published August 7, 2013 in the peer-reviewed scientific journal Proceedings of the Royal Society B suggests that the relative length of digits (digit ratios) at the paws of male rats may be a good biomarker for prenatal low dose exposure to endocrine disrupting chemicals (EDCs) (Auger et al. 2013). Digit ratios in humans and rodents differ between the sexes, and are understood to correlate with prenatal ratios of testosterone and estrogen. The researchers investigated the effects of prenatal low dose exposure to the estrogenic compound bisphenol A (BPA) (5µg/kg/day) alone, or in combination with the phytoestrogen genistein (1000 µg/kg/day) and/or the fungicide vinclozolin (10 µg/kg/day) on digit ratios in male rat offspring. Digit ratios were measured using X-ray combined with image analysis. Auger and colleagues found low dose exposure to feminize digit ratios in prenatally exposed Wistar rats. The feminization caused by the exposure to mixtures of BPA with genistein and vinclozolin persisted into the second, unexposed generation, suggesting epigenetic changes. Auger and colleagues were not able to associate anogenital distance (AGD), another commonly used and confirmed biomarker for prenatal exposure to EDCs, with digit ratios. Scientists use biomarkers as indicators of other, less easily measurable, but more substantial health effects caused by chemical exposures.

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Auger, J. et al. (2013). “Environmental levels of oestrogenic and antiandrogenic compounds feminize digit ratios in male rats and their unexposed male progeny.” Proceedings of the Royal Society B (published August 7, 2013).