Are the effects in the Faroes attributable to confounding by PCBs, PCDFs and PCDDs?
These organochlorines are contaminants of (inter alia) pilot whale blubber in the Faroe Island studies. PCBs may affect motor development, memory, and IQ. The appropriate measure of PCB exposure should capture prenatal exposure, such as maternal blood, breast milk, etc. The concentration in the child after birth is more closely related to transfer through breast milk, but so far the major associations between PCB exposure and development have been with some measure of maternal body burden at term. Although the level of PCBs in the umbilical cord is not a validated measure, it is plausible that cord concentrations, if adjusted for their fat content, would be a very reasonable index of transplacental exposure. While this would be the appropriate measure to be used as a covariate in statistical models, there is substantial correlation between PCBs and MeHg, and thus the possibility of bias in the regression coefficient for MeHg, arising from technical modeling issues as discussed by the D
