Half-life of polybrominated biphenyl in human sera.

Abstract

(12).The purpose of this study was to estimate the half-life of PBB in human blood sera in order to contribute to our understanding of how continued body burden relates to the possible adverse health consequences of exposure. We found only one previous report of the half-life of PBB in humans (13). This study gave a median estimate of 12 years with a range of 4.6-94.7 years. This estimate was determined by serum measurements from 15 females and 12 males; the half-life for females and males was similar. An experimental half-life determined in rats using a multicompartment model that was then extrapolated to humans was reported as 6.5 years (14); the elimination of PBB from rat serum has been shown to be first order (15). A linear relationship between PBB concentrations in adipose tissue and in serum with a ratio of approximately 300:1 has been demonstrated; the different congeners of PBB do not have significantly different partition ratios (16,17). MethodsWe used data and participants from the Michigan PBB prospective cohort project, which was started in 1975 and was previously described by Pirkle et al. (18). The Michigan investigators enrolled people in the study if they were residents of farms quarantined because of PBB in milk detected at 300 ppb, in eggs detected at 50 ppb (N = 2148), or if they were recipients of food products from quarantined farms (N = 1421). Participation was over 95%. Subjects answered a questionnaire, provided a blood sample, and were followed over time to contribute new blood samples and answer follow-up questionnaires.Participants from the cohort were eligible for inclusion in our analysis if they: 1) lived on a quarantined farm or consumed food products from such a farm; 2) had at least two PBB level determinations between 1976 and 1982 that were a minimum of 1 year apart; 3) were over 18 years of age at the time of their first PBB level measurement; and 4) had an initial PBB level determination of at least 20 pbb. We included the age requirement because continued growth may affect measured PBB levels and half-life (19,20 Ct represents concentration at later times, and k is the rate of decline (21). After taking logarithms and rearranging, this formula is equivalent to -k = Alog(C)/At, where Alog(C) is the change in the log of PBB measurements and At is the change in time between the measurements. The estimated half-life is then equal to log(2)/X. We estimated k for each individual using simple linear regression of eligible PBB measurements and the times between them. We estimated the half-life using two methods in order to better summarize the data. The first method used the median of the individual x values to estimate the halflife. Confidence intervals (CI) were calculated using distribution-free techniques (22). The second method used the mean of the individual X values. Weighting subjects according to the number of available PBB measurements for sensitivity analysis did not change the results. The SAS system was used for calculations

Determinants of Polybrominated Biphenyl Serum Decay among Women in the Michigan PBB Cohort

“…Rosen and colleagues (13) reported a mean half-life of 13.0 years (CI, 6.3-infinite) and median half-life of 18.5 years (CI 9.5-40.1). Differences in inclusion criteria may account for the differences in half-life found in this study as compared to that found by Rosen et al (13), who used only samples taken before 1983. Rosen et al (13) had a sample size of 51, with a maximum of four measurements for any one participant and a 6-year maximum time between measurements.…”

“…The unmetabolized PBB153 and its analogous PCB congener have an average half-life of at least 10 years (13,33). PBB, like other highly persistent chemicals, is therefore assumed to be in equilibrium among the organs and tissues before substantial amounts are eliminated (34) and was likely in equilibrium before the first serum measurements were taken in That longer half-lives were found with higher initial PBB levels suggests that PBB elimination may be a saturable process at higher exposures resulting in different distribution patterns or, more likely, that there are unmeasured sources of variability.…”

“…Rosen et al (13) study, the estimation of half-life differed in men (14.2 years) and women (infinite years) in the highest quartile of body mass index (BMI). Neither of these studies examined the effect of breast-feeding duration, pregnancy, or smoking history on PBB elimination.…”

“…These include changes in an individual's weight, the lack of lipid adjustment or the fact that the serum samples might not be fasting, continued exposure to PBB, medication use by participants, and age-related changes including lipid concentrations and hepatic enzyme induction. We cannot eliminate the possibility that some individuals received continued exposure to PBB despite public health interventions (e.g., manure from some of the exposed cows could have been left on the fields, leading to potential subsequent exposure of replacement herds).The unmetabolized PBB153 and its analogous PCB congener have an average half-life of at least 10 years (13,33). PBB, like other highly persistent chemicals, is therefore assumed to be in equilibrium among the organs and tissues before substantial amounts are eliminated (34) and was likely in equilibrium before the first serum measurements were taken in That longer half-lives were found with higher initial PBB levels suggests that PBB elimination may be a saturable process at higher exposures resulting in different distribution patterns or, more likely, that there are unmeasured sources of variability.…”

A decay model for assessing polybrominated biphenyl exposure among women in the Michigan Long-Term PBB Study

“…The weighted model did not show meaningful changes in the parameter estimates obtained in the unweighted decay model. This is in agreement with Blanck et al (2000a) and Rosen et al (1995) who reported minimal changes when they weighted their models in a similar manner.…”