Determinants of polybrominated biphenyl serum decay among women in the Michigan PBB cohort

Accidental contamination of the food chain in Michigan in 1973 with polybro minated biphenyls (PBBs) led to the establishment of a registry of exposed individuals in 1976. Serum was collected and analyzed for PBB at the time o f enrollment and for targeted studies in the following years. We used the a rchived PBB data to study the elimination of PBB and to identify factors as sociated with elimination. A total of 380 women greater than or equal to 16 years of age who had an initial PBB level of 2 ppb and at least two serum samples drawn when they were not pregnant were included in the analysis. Th e mean initial PBB level was 20.9 ppb (median 4) and mean time between the first and last measurement was 4.2 years (range 0.5-11.1). PBB was assumed to reach equilibrium in the body before substantial amounts were eliminated and before the first serum measurements were taken; therefore, the entire body was modeled as a single compartment for PBB with exponential decay. Su bject-specific decay rate estimates were regressed on predictor variables i ncluding initial age, body mass index (BMI), smoking history, breast-feedin g duration, and parity. In women with an initial PBB level < 10 ppb, the me dian half-life was 12.9 years; in those with > 10 ppb, the median half-life was 28.7 years. Decay was significantly slower among women with an initial BMI at or above the median (BMI greater than or equal to 23). The calculat ed half-life values are estimates of decay and can be used to estimate body burden of PBB at various points in time other than at the time of serum co llection.