Legacy Persistent Organic Pollutants in Human Placental Tissue from the United States

Polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDT) are persistent environmental pollutants that accumulate in biological tissues. Dichlorodiphenyldichloroethylene (DDE) is a common degradation product of DDT that is often found in higher concentrations than DDT. These pollutants are commonly found in maternal blood, cord blood, and breast milk of humans, indicating that prenatal exposure to these chemicals is occurring. The purpose of this study was to determine the levels of select PCBs and DDE concentrations in human placental tissue specimens, compare pollutant levels among three collection locations across the United States, and evaluate the potential change of pollutant levels with the time between the initial tissue collection after child delivery and tissue collection at times thereafter. Tissue samples were collected in conjunction with the National Children’s Study (NCS) and extracted using matrix solid phase dispersion (MSPD) method optimized for placental tissue analysis. The extract was cleaned using a multi–layer silica gel column. Concentrations were determined using a gas chromatograph, coupled with a triple quadruple mass spectrometer (GC/QQQMS). The individual compound with the overall highest concentration in the tissue was DDE with concentrations ranging from 9.8 to 3,220 pg/g wet tissue weight, a median of 82.2 pg/g and an average of 208 pg/g. The sum of the 32 PCBs analyzed ranged from 76 to 1570 pg/g wet tissue weight. The average Σ32 PCB was 442 pg/g and the median was 395 pg/g. Placenta samples collected in Wisconsin had significantly lower PCB concentrations than those collected in California indicating regional differences in exposures. There were not statistically significant differences in chemical concentration among tissues collected at different times up to 96 h from the same placenta after the child delivery, although paired t–tests indicated that comparisons between initial collection and collection 72 h after delivery may be significant. The tissues had higher levels of lighter PCB congeners with PCB 52 and PCB 28 being the most abundant (medians were 45.6 and 39.2 pg/g wwt respectively). The least detected congener was PCB 126, which also had the overall lowest concentration in the samples ranging from below the detection limit to 0.1 pg/g wwt.