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

Abstract

Accidental contamination of the food chain in Michigan in 1973 with polybrominated biphenyls (PBBs) led to the establishment of a registry of exposed individuals in 1976. Seram was collected and analyzed for PBB at the time of enrollment and for targeted studies in the following years. We used the archived PBB data to study the elimination ofPBB and to identify factors associated with elimination. A total of 380 women 2 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 induded in the analysis.The 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.Subject-specific decay rate estimates were regressed on predictor variables icluding initial age, body mass index (BMI), smoking history, breast-feeding duration, and parity. In women with an initial PBB level < 10 ppb, the median half-life was 12.9 years; in those with > 10 ppb, the medi- (91; there-fore, the Michigan individuals were mainly exposed to virtually unchanged PBB153. In the absence of metabolism, elimination is a slow process. Some PBB is eliminated through feces and hair. In women, PBB can be eliminated through lactation. There is also evidence that some PBB is transferred to offspring during pregnancy (4,10,11). The highest PBB concentrations in the body are found in adipose tissue, but it can also be detected at lower concentrations in serum and other lipid-rich tissues, such as the skin and liver.There are two previous reports of serum PBB half-life in women. Both of these studies were conducted using data from the Michigan PBB cohort (12,13

Likelihood‐based methods for estimating the association between a health outcome and left‐ or interval‐censored longitudinal exposure data

“…In the second stage it treats the estimated ${\hat{Y}}_i^{*}=y_{i1}+(\text{adj slope})t_i^{*}$, as if measured without error. This method parallels that by Blanck et al [6]. …”

“…The research of Blanck et al [6] assumed a linear one-compartment model for PBB elimination such that the initial PBB serum level ( C 0 ) and subsequent concentrations ( C ( t )) at time t are related by the following formula: $$C(t)=C_0{\mathrm{normale}}^{-\lambda t},$$ where λ is the rate of decay. Taking the natural log of the above equation gives a linear relationship: ln( C ( t )) = ln( C 0 )−λ t , that allows one to estimate the rate of decay from the slope of a linear regression model given the repeated PBB serum levels taken over time.…”

“…In 1997–1998, the Michigan Female Health Study (MFHS) was conducted within the cohort of exposed women with the goal of associating reproductive health outcomes with exposure. Details of this follow-up study are provided by Blanck et al [6, 20]. …”

“…[4] and Thurigen et al [5] provide extensive coverage of conceptual and analytic issues related to measurement error. Studies dealing with longitudinal data to monitor exposure trends over time often seek to estimate an unmeasured exposure at critical time points [6]. These studies often rely on estimating exposure trends based on separate ordinary least-squares (OLS) fits to the longitudinal exposure measurements for each subject.…”

Breast cancer among women in Michigan following exposure to brominated flame retardants: Table 1

“…The estimated half-life of PBB ranges from 13 to 29 years in females. 3 Exposure to endocrine disruptors may increase the risk of hormone-dependent cancers, because they mimic or block natural hormones in the body, such as oestrogen. In animal studies, PBB has induced tumours in mice and rats.…”