Serial PBB levels, PCB levels, and clinical chemistries in Michigan's PBB cohort.

Half of a cohort of 3683 Michigan residents exposed to polybrominated biphenyls (PBBs) in 1973 and 1974 had 2 serum PBB determinations at a 1- or 2-yr interval. The median decrease in serum PBB levels during both 1- and 2-yr intervals was 1 microgram/L. The geometric mean serum polychlorinated biphenyl (PCB) level (6.3 microgram/L) exceeded that of PBB (4.1 micrograms/L), although the range of PCB levels (smaller than 1-57 microgram/L) was narrower than that of PBB levels (smaller than 1-3150 micrograms/L). Mean PCB and PBB levels were higher for males, and mean PCB levels increased with age. In a subgroup with higher-than-average PBB levels, serial clinical chemistry tests during 4 different years showed no consistent significant correlation with serum PBB levels. Tests with greater sensitivity and specificity for hepatic microsomal enzyme induction and thyroid status are needed in future evaluations of the most highly exposed subgroup of the cohort.