"Intrinsic" elimination rate and dietary intake estimates for selected indicator PCBs: toxicokinetic modeling using serial sampling data in US subjects, 2005-2010

Polychlorinated biphenyl (PCB) half-lives in humans: A systematic review

This manuscript presents a systematic review of PCB half-lives reported in the scientific literature. The review was completed in accordance with PRISMA guidelines and included a review of almost 1000 peer-reviewed publications. In total, 26 articles were found to report half-lives in humans, with the majority of data coming from studies performed in North America on individuals suspected to have been exposed to PCBs. Terminology for reporting PCB half-lives was inconsistent, so we have attempted to consolidate this and recommend using either "apparent half-life" or "intrinsic half-life" in future studies. Within the literature, values for reported half-lives varied considerably for different PCBs. Less chlorinated PCBs generally have shorter half-lives than more chlorinated PCBs. It was interesting to note the large variability of half-lives reported for the same PCB. For example, the reported half-life for PCB 180 varied by nearly 3 orders of magnitude (0.34 years-300 years). Our review identified that the half-lives estimated were largely dependent on the studied cohort. We discuss the importance of PCB body burden, degree of chlorination and PCB structure, gender, age, breastfeeding, BMI, and smoking status on half-life estimations. We also identified significantly shorter half-lives for some PCBs in occupationally exposed individuals compared to results reported from the general population. PCB half-lives are not the same for every PCB or every individual. Therefore, careful consideration is needed when these values are used in human exposure studies.

Ten years after: findings from the medical surveillance program on Health Effects in High-Level Exposure to PCB (HELPcB)

After the detection of high environmental and occupational exposure to polychlorinated biphenyls (PCBs) in a German recycling company for transformers and capacitors in 2010, the multidisciplinary medical surveillance program "HELPcB" (Health Effects in High-Level Exposure to PCB) was established for former PCB-exposed workers of the company, their family members, employees of surrounding companies, and area residents to investigate potential adverse health effects by PCB exposure in a longitudinal study approach with up to seven examination time points between 2010 and 2019. More than 300 individuals were enrolled into the program. Assessments particularly included plasma and urine concentrations of PCB congeners and their metabolites, clinical laboratory parameters, Comet assay, analysis of telomere length, neuropsychological examinations, psychological screening, abdominal and thyroid ultrasound examination. This review summarizes the main results of the studies conducted in the HELPcB program yielding relevant new data on potential adverse effects of PCB exposure in humans and potential mechanisms that underlie these effects. Even larger studies in PCB-exposed individuals are warranted to confirm the results of this program and to further establish causality between PCB exposure and clinical effects in humans.

Inhalation and dermal absorption as dominant pathways of PCB exposure for residents of contaminated apartment buildings

Applications of polychlorinated biphenyls (PCBs) in buildings and their persistence in indoor environments have led to cases of current and highly elevated exposure in humans, despite the global cease of production decades ago. Personal exposure to PCBs was assessed among residents in a social housing estate in Denmark containing both contaminated (n = 67) and non-contaminated (n = 23) apartments. Samples and estimated daily intakes (EDIs) were assessed for 15 PCB congeners, and body burden, which was limited by the dietary data availability, was compared across 7 indicator PCBs, with its sum (PCB_sum7) often applied in European regulation of PCBs. Median PCB_sum7 EDI across measured pathways for exposed residents was 101 ng· (kg bodyweight)^-1· day^-1, with the majority of exposure (60%) coming from inhalation of contaminated indoor air. Calculated from both PCBs measured in indoor air and on hand wipes, dermal absorption estimates showed comparable results and served as a secondary exposure pathway, accounting for 35% of personal exposure and considering selected assumptions and sources of physical-chemical parameters. Estimates revealed that diet was the primary PCB source among the reference group, accounting for over 75% of the PCB_sum7 EDI across exposure routes. When evaluating overall EDIs across the two study groups and including dietary estimates, PCB exposure among exposed residents was around 10 times higher than the reference group. Solely within the exposed population, pathway-specific body burdens were calculated to account for exposure across years of residence in contaminated apartments, where lower chlorinated PCBs were dominant in indoor air. Among these dominant congeners, estimated body burdens of PCB-28 and -52 were significantly correlated with measured serum (r_s = 0.49, 0.45; p < 0.001). This study demonstrates that inhalation and dermal absorption serve as dominant exposure pathways for residents of apartments contaminated with predominantly lower chlorinated PCBs and suggest that predictions of body burden from indoor environment measurements may be comparable to measured serum PCBs.

Modelling past human internal exposure to lower chlorinated indicator PCBs using proxies - A calculation based on multiple longitudinal PCB analyses

Polychlorinated biphenyls (PCBs) are persistent organic pollutants with former applications in electric transformers, capacitors, hydraulic fluids or joint sealants. While current internal exposure to PCBs can be readily assessed by human biomonitoring, the evaluation of longgone past exposures, in particular the estimation of past exposure to lower chlorinated non-dioxin-like PCB 28, 52 or 101 is limited due to the relatively short biological half-life of these PCB-congeners. This study was aimed to find a proxy that would allow an estimation of the former plasma level for these congeners even several years after exposure cessation. We used biomonitoring data of the German HELPcB cohort with six consecutive follow-up investigations and identified the congeners PCB 66, 74 and 99 as suitable proxies for the congeners of interest. The biological half-lives of the proxies as well as their individual correlation with the plasma levels of PCB 28, 52 and 101 was considered in the calculation models. The correlation coefficients and the inter correlation coefficient 3 (ICC3) between measured and calculated initial values were applied for validation. For external validation purposes we used longitudinal biomonitoring data from two different cohorts with indoor exposure to lower chlorinated PCBs. The backward estimation from current PCB 74 levels to former PCB 28 levels led to an ICC3 of 0.682 and a correlation of rho = 0.724 within the HELPcB cohort. The external validation revealed an ICC3 of 0.723 and a correlation of rho = 0.654. The external validation for PCB 101 was feasible, but measures were not comparably good (ICC3 = 0.460; Rho = 0.516). External validation for PCB 52 was not successful, maybe due to the lower level of burden. Our model shows that a rough estimation of former plasma levels of lower chlorinated PCBs is possible even years after exposure cessation using current measurements of PCB74.

Estimating plasma half-lives of dioxin like and non-dioxin like polychlorinated biphenyls after occupational exposure in the German HELPcB cohort

Polychlorinated biphenyls (PCBs) are carcinogenic persistent organic pollutants that have been used as mixtures in transformers, electrical capacitors or hydraulic oils in underground mining until their ban in the late 1980s in Germany. The widespread use of PCBs has led to an age-dependent body burden in the general population. In order to determine the human half-lives of different PCB-congeners, we have used data collected between 2010 and 2017 from the prospective investigation of the German HELPcB-cohort with high initial occupational exposure to PCBs from a transformer recycling company. PCBs were quantified in plasma of the study participants in six cross-sectional investigations using gas-chromatography coupled to mass-spectrometry. Applying logistic regression on the individual plasma levels after statistical elimination of outliers, the elimination half-lives of 18 PCB-congeners were determined. Further stratifications were performed using adjustment for blood lipids, calculation of the total amount of PCB in the body and by using a statistical model taking into account the individual age-dependent background burden. The calculated plasma half-lives ranged from 0.8 years for PCB 52 until a maximum of 28.9 years for PCB 189, depending on the model applied. E.g. the total body amount related half-live for PCB 28 is 2.41 years, for PCB 74 it is 12.81 years, for PCB 118 it is 6.65 years and for PCB 153 = 10.75 years. The model with adjustment for age dependent background burden led to shorter half-lives. The analysis revealed structure-related differences in the kinetics for the PCB-congeners examined. Congeners with a chlorine substitution in 2,4,(5)- and 4'-position showed longer half-lives than other isomers with one (or two) free 4-positions. Due to the high number of included cases and repeated measurements, our results provide valid half-live data for a large number of PCB congeners. Using these data, a rough estimation of former occupational exposures from current PCB-levels seems feasible.

Quantitative bias analysis of the association of type 2 diabetes mellitus with 2,2',4,4',5,5'-hexachlorobiphenyl (PCB-153)

An association between serum concentrations of persistent organic pollutants (POPs), such as 2,2',4,4',5,5'-hexachlorobiphenyl (PCB-153), and risk of type 2 diabetes mellitus (T2DM) has been reported. Conditional on body mass index (BMI) and waist circumference (WC), a higher serum PCB-153 concentration may be a marker of T2DM risk because it reflects other aspects of obesity that are related to T2DM risk and to PCB-153 clearance. To estimate the amount of residual confounding by other aspects of obesity, we performed a quantitative bias analysis on the results of a specific study. A physiologically-based pharmacokinetic (PBPK) model was developed to predict serum levels of PCB-153 for a simulated population. T2DM status was assigned to simulated subjects based on age, sex, BMI, WC, and visceral adipose tissue mass. The distributions of age, BMI, WC, and T2DM prevalence of the simulated population were tailored to closely match the target population. Analysis of the simulated data showed that a small part of the observed association appeared to be due to residual confounding. For example, the predicted odds ratio of T2DM that would have been obtained had the results been adjusted for visceral adipose tissue mass, for the ≥90th percentile of PCB-153 serum concentration, was 6.60 (95% CI 2.46-17.74), compared with an observed odds ratio of 7.13 (95% CI 2.65-19.13). Our results predict that the association between PCB-153 and risk of type 2 diabetes mellitus would not be substantially changed by additional adjustment for visceral adipose tissue mass in epidemiologic analyses. Confirmation of these predictions with longitudinal data would be reassuring.

Polychlorobiphenyl levels in the serum of cats from residential flats in Italy: Role of the indoor environment

The domestic cat (Felis catus) was used as a sentinel of exposure to polychlorobiphenyls (PCBs) in indoor urban environments y. Sera from 120 cats were pooled to form 30 different groups selected by age (<2 years; > 2 ≤ 8 years; > 8 years), sex, municipality (Bologna and Turin) and environment (indoor vs. outdoor). Test portions of 1 mL were analyzed by means of gas chromatography coupled to high-resolution mass spectrometry (GC-HRMS) for six selected indicators non-dioxin-like PCBs (∑6 PCBs: congeners #28, #52, #101, #132, #153 and #180) and the results were computed in the upper-bound mode. The internal dose of PCBs attributable to the cats' alimentary lipid intake ranged from 32.4 to 1,446 ng/g (P50 165; mean 258). The Wilcoxon test revealed significantly lower PCB burden in "outdoor" groups than in "indoor" groups. Age correlated well with the heptachlorinated and most bio-accumulative congener, PCB #180, and slightly with hexachlorinated PCBs #138 and #153. Contamination attributable to house dust collected in 15 living-rooms ranged from 10.0 to 279 ng/g dry weight (P50 97.4; mean 94.4). Exposure estimates indicated a 0.6-16 ng/kg bw range of daily ∑6 PCB intake from a default value of 200 mg/cat of dust ingestion. The intake of PCBs due to dust ingestion fell within the same order of magnitude as that computed from a 60 g daily intake of commercial dry pet foods, while inhalation accounted for 0.21-8.2 ng/kg bw/day, on setting the nominal ∑6 PCB contamination in outdoor and indoor air at 0.37 and 15 ng/m³, respectively. Italian indoor cats could be exposed to higher levels of ∑6 PCBs than the Reference Dose (RfD) of 10 ng/kg/bw/day; this supports the World Health Organization's statement that the quality of the indoor environment is a major determinant of health.

Polybrominated Diphenyl Ethers, Polychlorinated Biphenyls, and 2,2-Bis(4-chlorophenyl)-1,1-dichloroethene in 7- and 9-Year-Old Children and Their Mothers in the Center for the Health Assessment of Mothers and Children of Salinas Cohort

We report longitudinal serum concentrations of select persistent organic pollutants (POPs) in children at ages 7 and 9 years and in their mothers prenatally and again when the children were 9 years old. The participating families were enrolled in the Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS), a longitudinal birth cohort study of low-income Hispanic families residing in the Salinas Valley, California. We observed decreasing concentrations in the mothers with year of serum collection (2009 vs 2011) for six out of seven polybrominated diphenyl ether (PBDE) congeners and for 2,2',4,4',5-pentachlorobiphenyl (CB-99; p < 0.05). The 9-year-old children had similarly decreasing serum concentrations of all seven PBDE congeners, CB-99, and 2,2',3,4,4',5'- and 2,3,3',4,4',6-hexachlorobiphenyl (CB-138/158) with year of serum collection (2009 vs 2011; p < 0.05). In mixed effect models accounting for weight gain as the children aged from 7 to 9 years, we observed an annual decrease (-8.3% to -13.4%) in tri- to hexaBDE concentrations (p < 0.001), except for 2,2',3,4,4'-tetrabromodiphenyl ether (BDE-85) and 2,2',4,4',5,5'-hexabromodiphenyl ether (BDE-153). The concentrations of these congeners were not associated with time of serum collection and instead showed an -0.9% to -2.6% decrease per kilogram of weight gain during the study period (p < 0.05). In the case of tetra- to heptachlorobiphenyls, we observed -0.5% to -0.7% decrease in serum concentration per kilogram of weight gain (p < 0.05) and -3.0% to -3.7% decrease in serum concentration per year of aging (p < 0.05), except for 2,3',4,4',5-pentachlorobiphenyl (CB-118) and 2,2',4,4',5,5'-hexachlorobiphenyl (CB-153), which were not associated with time of serum draw. 2,2-Bis(4-chlorophenyl)-1,1-dichloroethene (p,p'-DDE) decreased -2.4%/kg of weight gain between the two sampling points (p < 0.001). These findings suggest that as children grow, dilution in a larger body size plays an important role in explaining reductions in body burden in the case of traditional POPs such as PCBs and p,p'-DDE. By contrast, in the case of PBDEs, reductions are likely explained by reduction in exposure, as illustrated by decreased concentrations in more recent years, possibly amplified by presumed shorter biological half-life than other POPs.

Long-term time trends in human intake of POPs in the Czech Republic indicate a need for continuous monitoring

Polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) from the group of persistent organic pollutants are detected in human tissues years or even decades after their ban. Exposure to PCBs and OCPs can pose risks to human health. In the present study, we calculated the daily intakes of PCBs and OCPs in the Czech population and investigated the long-term trends of human exposure to POPs. Data on POP concentrations from a 16-year period of breast-milk monitoring were used. A toxicokinetic model with consideration of compound-specific elimination half-lives was used to calculate the mothers' daily intake of PCBs and OCPs representing the intake of POPs by all exposure routes. The calculated intakes were compared with dietary intakes calculated by the Czech National Institute of Public Health. The comparison shows good agreement of both intake estimates with decreasing intake trends of POPs in the Czech population in the time period studied. However, several fluctuations with peaks of higher levels were observed in both datasets which are not typical for the period after the ban of use and production of POPs. The available evidence suggests that the increases in chemical concentrations might be caused by food contamination. The calculated intakes of compounds with longer elimination half-lives, such as higher-chlorinated PCBs, were higher in older mothers. This "memory effect" was already observed in other studies and indicates higher exposure in earlier life periods of the mother. Our results suggest that exposure to POPs is still relevant for the Czech population in the period after the ban of the use and production of POPs (post-ban period), especially via food ingestion, though the intake trends are decreasing. Possible food contamination by POPs in the post-ban period requires further assessment.

Polychlorinated biphenyls: New evidence from the last decade

Millions of pounds of polychlorinated biphenyl (PCB) compounds have been produced in multiple countries for industrial applications over the last several decades. PCB exposure induces various adverse health effects in animals and humans. Environmental and occupational exposures to PCBs have been associated with liver, kidney, endocrine, and neurodevelopmental adverse effects. We have collected and reviewed animal and human data cited in the US National Library of Medicine from 2000 to 2010. In brief, our review shows new evidence, that is, in animal studies, exposure to one of the PCBs, A1221, induces a significant alteration of serum luteinizing hormone. The effects were more profound in the F2 generation, particularly with respect to fluctuations in hormones and reproductive tract tissues across the estrous cycle. Morphological analyses of brain tissue from rats exposed to A1254 confirmed the results of an earlier work which showed that the relative size of the intra- and infrapyramidal (II-P) mossy fibers was smaller than that in the controls and also reduction in growth was selective for the II-P mossy fibers. PCB exposure increased anogenital distance and prostate size but decreased epididymal weight, epididymal sperm count, and motile epididymal sperm count. No effects were observed on testicular weight or size. The epidemiological data showed an association between diabetes mellitus prevalence and elevated concentrations of PCB 153. Additionally, prenatal PCB exposure studies were associated with a smaller thymic index at birth and could adversely affect immune responses to childhood vaccinations and resistance to respiratory infections. PCB exposure was also reported to adversely affect enamel development in children in a dose-dependent manner. Because PCBs and their metabolites are potential health hazards, understanding the risk factors associated with individual PCBs, PCB mixtures, and PCB metabolites is important. PCB exposures of vulnerable populations (pregnant women, fetuses, infants, and children) are of particular concern because of heightened sensitivity during this period of brain development.

Deterministic modeling of the exposure of individual participants in the National Health and Nutrition Examination Survey (NHANES) to polychlorinated biphenyls

A population's exposure to persistent organic pollutants, e.g., polychlorinated biphenyls (PCBs), is typically assessed through national biomonitoring programs, such as the United States National Health and Nutrition Examination Survey (NHANES). To complement statistical methods, we use a deterministic modeling approach to establish mechanistic links between human contaminant concentrations and factors (e.g. age, diet, lipid mass) deemed responsible for the often considerable variability in these concentrations. Lifetime exposures to four PCB congeners in 6128 participants from NHANES 1999-2004 are simulated using the ACC-Human model supplied with individualized input parameters obtained from NHANES questionnaires (e.g., birth year, sex, body mass index, dietary composition, reproductive behavior). Modeled and measured geometric mean PCB-153 concentrations in NHANES participants of 13.3 and 22.0 ng g^-1 lipid, respectively, agree remarkably well, although lower model-measurement agreement for air, water, and food suggests that this is partially due to fortuitous error cancellation. The model also reproduces trends in the measured data with key factors such as age, parity and sex. On an individual level, 62% of all modeled concentrations are within a factor of three of their corresponding measured values (Spearman r_s = 0.44). However, the model attributes more of the inter-individual variability to differences in dietary lipid intake than is indicated by the measured data. While the model succeeds in predicting levels and trends on the population level, the accuracy of individual-specific predictions would need to be improved for refined exposure characterization in epidemiological studies.

Change in decay rates of dioxin-like compounds in Yusho patients

BACKGROUND

Once ingested, dioxins and dioxin-like compounds are excreted extremely slowly. Excretion can be evaluated by its half-life. Half-lives estimated from observed concentrations are affected by excretion and ongoing exposure. We investigated the change in apparent half-life using a theoretical model based on exposure to dioxin and dioxin-like compounds.

METHODS

We carried out longitudinal measurements of the blood concentration of dioxins and dioxin-like compounds in a Yusho cohort during 2002 to 2010. We estimated the change in decay rates of 2,3,4,7,8-PeCDF and octachlorodibenzodioxin (OCDD) using a second-order equation.

RESULTS

We found that the decay rate of OCDD increased, whereas the decay rate of 2,3,4,7,8-PeCDF of patients with a relatively high concentration of 2,3,4,7,8-PeCDF decreased. OCDD results were in accordance with decreasing levels of dioxin and dioxin-like compounds in the environment. The decay rate of OCDD in the body was affected by the decay rate of OCDD in the environment by ingestion because it was near the steady-state. In contrast, the decay rate of 2,3,4,7,8-PeCDF in the body was affected less by ingestion from the environment because it was far higher than in the steady-state.

CONCLUSION

We demonstrated that the level of 2,3,4,7,8-PeCDF in the environment is decreasing. The excretion half-life is longer than the environmental half-life, thus the excretion half-life in a Yusho patient is increased.

Recommendations for Evaluating Temporal Trends of Persistent Organic Pollutants in Breast Milk

BACKGROUND

Biomonitoring data of persistent organic pollutants (POPs) in breast milk are increasingly collected and available for quantitative analysis of levels and time trends. A common approach is to apply log-linear regression to calculate doubling and halving times of the POP concentrations based on the temporal trend observed in breast milk. However, there are different, sometimes conflicting interpretations of these doubling and halving times.

OBJECTIVES

We provide a mechanistic understanding of doubling and halving times where possible. Five recommendations are proposed for dealing with POP concentration trends in breast milk during three distinct periods (pre-ban, transition, post-ban period).

DISCUSSION

Using temporal trends of BDE-47 and PCB-153 in breast milk data, we show which information can be gained from the time-trend data. To this end, we analyzed time trends of hypothetical POPs for different periods with time-variant exposure and different intrinsic elimination half-lives, using a dynamic population-based pharmacokinetic model. Different pieces of information can be extracted from time-trend data from different periods. The analysis of trends of short-lived POPs is rather straightforward and facilitates extraction of the intrinsic elimination half-lives from the breast milk data. However, trends of slowly eliminated POPs only provide indications for the exposure time trend.

CONCLUSIONS

Time-trend data of rapidly eliminated POPs provide information on exposure time trends and elimination half-lives. Temporal trends of slowly eliminated POPs are more complicated to interpret, and the extraction of exposure time trends and elimination half-lives require data sets covering several decades.

CITATION

Gyalpo T, Scheringer M, Hungerbühler K. 2016. Recommendations for evaluating temporal trends of persistent organic pollutants in breast milk. Environ Health Perspect 124:881-885; http://dx.doi.org/10.1289/ehp.1510219.