Polychlorinated biphenyls and thyroid hormones in adults: a systematic review appraisal of epidemiological studies

Prenatal exposure to 209 PCBs in mother-infant pairs from two cities in China: Levels, congener profiles, and transplacental transfer

Prenatal exposure to polychlorinated biphenyls (PCBs) has been well researched, but studies covering all 209 congeners are limited. Recent literature suggests a shift in the dominant congeners and increasing levels of unintentionally-produced PCBs (UP-PCBs) in environmental samples in China. To investigate the exposure levels and profiles of PCBs in pregnant women and newborns, as well as the characteristics of transplacental transfer, we measured 209 PCBs in 80 pairs of maternal serum (MS) and cord serum (CS) from Hangzhou and Mianyang, China. The levels of ∑PCBs of participants in this study were lower than those in developed countries and followed the order of (ng/g lw): Hangzhou-MS (148) > Hangzhou-CS (107) > Mianyang-MS (63.8) > Mianyang-CS (57.9). UP-PCBs (mainly PCB-11) contributed around 50% of ∑PCBs in serum, which is consistent with the environmental samples. Environmental burden and dietary intake may account for the differences in the exposure levels, while the historical production and release may have impacted the homologue profiles. Prenatal exposure to PCB-126 was associated with increased birth weight (n = 80, adjusted β = 0.270, p = 0.030). The body burden of dioxin-like PCBs of newborns in Hangzhou was 82.4 pg TEQ/kg bw, suggesting certain health risks under WHO tolerable daily intake of 1-4 pg TEQ/kg bw. Log₁₀ K_OW was negatively correlated with log₁₀-transformed transplacental transfer efficiency (R² = 0.36, p < 0.001), serving its importance for PCBs' transplacental transfer. This study is the first to investigate maternal and fetal exposure to PCBs in China based on their levels, congener and homologue profiles, and potential adverse effects. Our findings help to provide insights into the processes and factors influencing the transplacental transfer of PCBs.

Association between polychlorinated biphenyl exposure and thyroid hormones: a systematic review and meta-analysis

Purpose: To conduct a comprehensive meta-analysis investigating the association between polychlorinated biphenyl (PCB) exposure and serum thyroid hormone levels among adults. Methods: Eleven studies met inclusion criteria for analysis following systematic search of PubMed, Embase, and Scopus databases. Of these, 7 studies measured exposure by the total sum of PCB congeners (∑PCB), 1 study measured individual PCB congener levels, and 3 studies measured both ∑PCB levels and PCB congener levels. Correlation coefficients (r) were extracted from each study. Summary estimates were calculated for ∑PCB levels and PCB congeners reported by 2 or more studies: PCB 28, 52, 101, 105, 118, 138, 153, and 180, using random effects model. Results: Significant negative correlation was found between ∑PCBs and T3 (r: -0.09; 95% CI: -0.17, -0.02) and FT3 (r: -0.24; 95% CI: -0.36, -0.12). Congener-specific analysis found T3 to be negatively correlated with PCB-153 (r: -0.19; 95% CI: -0.34, -0.03) and PCB-180 (r: -0.14; 95% CI: -0.26, -0.01), whereas TSH was positively correlated with PCB-105 (r: 0.15; 95% CI: 0.02, 0.28). Conclusions: The present study is the first meta-analysis to investigate the association between PCB exposure and thyroid hormone dysfunction among adults. Results suggest a significant association between PCB exposure and thyroid hormone dysregulation.

Measurement of polychlorinated biphenyls with hand wipes and matched serum collected from Chinese E-waste dismantling workers: Exposure estimates and implications

To date, dermal/hand-to-mouth exposure to chemicals in the e-waste recycling environment has not been sufficiently understood, and the importance of dermal absorption of chemicals in e-waste dismantling workers remains controversial. In this study, we utilized hand wipes and matched sera to characterize dermal/hand-to-mouth exposure to PCBs for e-waste dismantling workers, and potential effects on thyroid hormones were also assessed. PCB loadings in hand wipes varied from 0.829-265 ng wipe^-1 (11.3-2850 ng m^-2 wipe^-1), with 37.2 ng wipe^-1 (432 ng m^-2 wipe^-1) as the median value. Serum concentrations of PCBs ranged from 32.3-3410 ng g^-1 lipid weight (lw) with 364 ng g^-1 lw as the median value. Between wipes and sera, lower-chlorinated congeners (e.g. CB-28, -66, -74, -99,-105 and -118) showed significant associations (p < 0.01), but higher-chlorinated congeners (e.g. CB-138, -153, -156, -170, and -180) did not. These lower-chlorinated CBs were the major contributors to estimated dermal/hand-to-mouth average daily doses (ADDs) and the hazard index (HI). Correspondingly, their estimated contributions to serum levels by dermal absorption were also significant, with the contribution of CB-28 being as high as 21.4%. As a consequence, dermal absorption of some low-chlorinated congeners was a non-negligible route for e-waste dismantling workers. Although insignificant association was shown between serum PCBs and thyroid hormones, the potential health risk should be of concern due to the high levels of PCBs observed in workers' sera.

Endocrine disrupting chemicals and thyroid hormone action

Thyroid hormones (predominantly thyroxine, T4, and triiodothyronine, T3) are essential for normal development and for adult physiology. There are several challenges, however, that make identifying chemicals that produce adverse effects by interfering with the thyroid system difficult. First, individual variability in serum concentrations of thyroid hormones represent only about 10% of the population reference range that is considered to be "normal." This means that populations studies evaluating the relationship between chemical exposure and serum thyroid hormones must be large enough to overcome this internal variance. In addition, we know that there are chemicals that do not produce changes in thyroid hormone levels, but nevertheless impact thyroid signaling in target tissues. A good example is that of polychlorinated biphenyls (PCBs). PCB exposure during development are clearly associated with cognitive deficits in humans. But PCB exposure isn't uniformly associated with a reduction in serum thyroid hormone in human populations despite mechanistic studies showing that PCBs reduce serum T4 in animals. In contrast, perchlorate is a chemical that inhibits iodide uptake, thereby reducing thyroid hormone synthesis and serum hormone levels. Human studies have been variable in identifying a relationship between thyroid hormone and perchlorate exposure, but studies also show that dietary iodine, cigarette smoking and other factors can modify this relationship. The conclusion is that identifying chemicals that interfere with thyroid hormone could depend on in vitro analysis of chemicals that interact with different proteins important for thyroid hormone to function properly.

Exposure to polychlorinated biphenyls and organochlorine pesticides and thyroid cancer in connecticut women

BACKGROUND

Thyroid cancer incidence has increased substantially over the past decades, and environmental risk factors have been suggested to play a role. Polychlorinated biphenyls (PCB) and organochlorine pesticides (OCP) are established thyroid hormone disruptors, but their relationship to thyroid cancer is not known.

METHODS

We investigated the relationship between serum PCB and OCP concentrations and papillary thyroid cancer (PTC) in 250 incident female PTC cases and 250 female controls frequency-matched on age, all residing in Connecticut. Interviews and serum samples were collected from 2010 to 2013. Samples were analyzed for 32 different chemicals using gas chromatography with isotope dilution high resolution mass spectrometry. We calculated odds ratios (OR) and 95% confidence intervals (CI) using single pollutant logistic regression models for concentrations (per interquartile range) of individual PCB/OCP and summed groups of structurally or biologically similar PCB/OCP, adjusted for education, family history of cancer, alcohol consumption, age, and body mass index. Sub-analyses included stratification by tumor size (≤ and >1 cm) and birth before or during peak PCB production (born in 1960 or earlier and born after 1960), as exposures during early life may be important. We also applied three multi-pollutant approaches (standard multi-pollutant regression, hierarchical Bayesian modeling, principal components regression analysis) to investigate associations with co-exposures to multiple PCB/OCPs.

RESULTS

No PCB/OCPs were positively associated with PTC in primary analyses. Statistically significant associations were observed for 9 of the 32 chemicals and 3 summed groups of similar chemicals in the those born during peak production based on single-pollutant models. Multi-pollutant analyses suggested null associations overall.

CONCLUSIONS

Our results using single and multi-pollutant modeling do not generally support an association between PCB or OCP exposure and PTC, but some associations in those born during peak production suggest that additional investigation into early-life exposures and subsequent thyroid cancer risk may be warranted.

Persistent Organic Pollutants in Human Breast Milk and Associations with Maternal Thyroid Hormone Homeostasis

Epidemiological studies have indicated the thyroid-disrupting effects of persistent organic pollutants (POPs). However, the association of low-exposure POPs with thyroid hormones (THs) remains unclear. Here, we aim to assess the association of low exposure of POPs, including polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs), and polybrominated dibenzo-p-dioxins and furans, with THs [total _L-thyroxine (TT₄), total 3,3',5-triiodo-_L-thyronine (TT₃), and total 3,3',5'-triiodo-_L-thyronine (TrT₃)] measured in human breast milk. Ninety-nine breast milk samples were collected from the LUPE cohort (2015-2016, Bavaria, Germany). Fourteen PBDEs, 17 PCBs, and 5 PCDD/Fs had quantification rates of >80%. Nonmonotonic associations were observed. In adjusted single-pollutant models, (1) TT₄ was inversely associated with BDE-99, -154, and -196; (2) TT₃ was inversely associated with BDE-47, -99, -100, -197, -203, -207, and OCDD; and (3) TrT₃ was inversely associated with BDE-47, -99, -183, and -203. Multipollutant analysis using principal component analysis and hierarchical clustering revealed inverse associations of PBDEs (BDE-28, -47, -99, -100, -154, -183, and -197) with TT₄ and TrT₃. These results indicate that POPs at low levels might be related to reduced THs. This study shows that human breast milk might be an appropriate specimen to evaluate the thyroid disruption of POPs.

Polychlorinated biphenyl serum levels, thyroid hormones and endocrine and metabolic diseases in people living in a highly polluted area in North Italy: A population-based study

Polychlorinated biphenyls (PCBs) are persistent organic pollutants produced until the 1980s, which they are still present worldwide. They have been associated with metabolic and endocrine diseases and hypertension in humans, but definite evidence is lacking. A chemical factory producing PCBs caused a heavy pollution in an urban area in Northern Italy. We aimed to evaluate present PCBs serum levels according to demographic and lifestyle variables and their associations with endocrine and metabolic diseases and hypertension in the resident general population. A random sample of 816 adults aged 20–79 years (mean ± SD: 49.1 ± 16.5 years) was enrolled in a cross-sectional population-based study. The participants provided a fasting blood sample for laboratory analysis and were face-to-face interviewed about the presence of chronic diseases. The serum level of total PCBs was computed as the sum of 33 PCB congeners. The median serum level of lipid-adjusted total PCBs was 435.2 and 95^th centile was 2154.9 ng/g lipid. Medium and high chlorinated PCBs with immunotoxic and endocrine disrupting activity contributed most to total PCB serum levels, particularly PCBs 138, 153, 170, 180 and 194. The serum levels of total PCBs and of PCB functional groups were positively associated with age and negatively with female gender, education, smoking habit and BMI, and not associated with serum levels of thyroid hormones and TSH and glycaemia and with presence of endocrine diseases, diabetes and hypertension by multivariable analysis. Subgroup analyses according to gender, age and BMI provided similar results. In conclusion, this study shows a long-term persistence of past exposure to PCBs and does not support the hypothesis of an association between PCB exposure and prevalence of endocrine and metabolic diseases and hypertension.

Polychlorinated biphenyls (PCBs) exposure and cardiovascular, endocrine and metabolic diseases: A population-based cohort study in a North Italian highly polluted area

BACKGROUND AND AIMS

Exposure to polychlorinated biphenyls (PCBs) has been linked to the onset of cardiovascular, endocrine, and metabolic diseases, but no conclusive evidence has been provided so far. A chemical factory produced PCBs from 1938 to 1984 in Brescia (North Italy) resulting in environmental contamination and human exposure. We aimed to evaluate the association between PCB serum levels and subsequent incidence of chronic diseases through a prospective cohort study design.

METHODS

Based on surveys conducted in Brescia province between 2001 and 2013, a cohort of 1331 subjects with at least one measure of PCB serum levels during the period was selected and followed longitudinally. Serum concentration of total PCBs was computed summing up the levels of 24 PCB congeners determined by gas chromatography. The data on incidence of hypertension, cardiovascular diseases, and endocrine and metabolic chronic diseases were retrieved from the Brescia Health Protection Agency database. Poisson regression models adjusted for age, level of education, BMI, cholesterol level, tobacco smoking and alcohol drinking were employed to calculate rate ratios (RRs).

RESULTS

1331 subjects were enrolled (45.7% males, mean age 50.6 years) contributing to 10,006 person-years of follow-up. A dose-response relationship was observed between PCB serum levels and the onset of hypertension (RR for 2nd and 3rd tertiles of serum PCB distribution: 2.07, 95% CI 1.18-3.63, and 2.41, 1.30-4.47, respectively). A possible, though not statistically significant, increase of the risk of cardiovascular disease was also found (RR for 2nd and 3rd tertiles of serum PCB distribution: 1.61, 0.72-3.64, and 1.96, 0.86-4.48, respectively). The results based on lipid-standardized PCBs were slightly attenuated. No association was found between PCB serum levels and occurrence of diabetes and endocrine disorders. Stratified analysis by body mass index showed an increased risk of hypertension in subjects at 2nd and 3rd tertile of serum PCB distribution in overweight/obese subjects only.

CONCLUSIONS

These results suggest that PCBs might play a role in the development of hypertension and possibly cardiovascular disease, though alternative explanations are to be considered too.

Temporal trends of contaminants in Arctic human populations

The first Arctic Monitoring and Assessment Programme (AMAP) report was published in 1998 and followed by three assessment reports of human health (AMAP 2003, 2009 and 2015). The focus area of the AMAP reports was to monitor levels of environmental contaminants in the Arctic and to assess the health effects connected with detected levels in Arctic countries. This review gives an overview of temporal trends of contaminants and their health effects in humans of the Arctic based on data published by AMAP, as well as Russian scientific literature. Several time series of 31 contaminants in humans of the Arctic from different cohorts are reported. The lengths of time series and periods covered differ from each other. International restrictions have decreased the levels of most persistent organic pollutants in humans and food webs. Percentage changes for contaminants in human biological matrices (blood samples from children, mothers and males and breast milk samples) for the period of sampling showed declining trends in most of the monitored Arctic locations, with the exception of oxychlordane, hexachlorobenzene (HCB), 2,2',4,4',5,5'-hexabromodiphenyl ether (PBDE153) and perfluorinated compounds (PFCs).

Urinary metabolites of phosphate flame retardants in workers occupied with e-waste recycling and incineration

Urinary metabolites of phosphate flame retardants (PFRs) were determined in workers from an electronic waste (e-waste) recycling site and an incineration plant, in order to assess the PFR exposure risks of workers occupied with e-waste recycling and incineration. Bis(2-chloroethyl) phosphate (BCEP), bis(1,3-dichloro-2-propyl) phosphate (BDCIPP), and diphenyl phosphate (DPHP) were the most frequently detected chemicals (82-93%). The median concentrations of BCEP, BDCIPP, and DPHP were 1.77, 0.23, and 0.70 ng/mL, and 1.44, 0.22, and 0.11 ng/mL in samples from the e-waste site and the incineration plant, respectively. Dibutyl phosphate (DBP) was detected in all samples from the incineration plant, with a median level of 0.30 ng/mL. The concentrations of BDCIPP (r = -0.31, p < 0.05) were significantly correlated with the occupational exposure time rather than age in workers from the e-waste site. Negative and significant correlations were also observed between the concentrations of BCEP (r = -0.42, p < 0.05), BDCIPP (r = -0.37, p < 0.05), and DPHP (r = -0.37, p < 0.05) and occupational exposure time rather than age in workers from the incineration plant. No gender differences were observed in levels of PFR metabolites in urine samples (p > 0.05). Concentrations of BDCIPP in female were significantly correlated with occupational exposure time (r = -0.507, p < 0.01). Concentrations of PFR metabolites in male were not significantly correlated with age or occupational exposure time (p > 0.05). Overall, the workers with occupational exposure to PFRs had different profiles of urinary PFR metabolites. The age, occupational exposure time, and gender seemed not to be main factors mediating the exposure to PFRs for workers occupied with e-waste recycling and incineration.

Polychlorinated biphenyls, indicators of thyroid function and thyroid autoantibodies in the Anniston Community Health Survey I (ACHS-I)

In this study, we examined associations between serum concentrations of 35 polychlorinated biphenyl (PCB) congeners, pesticides, and indicators of thyroid function in participants of the Anniston Community Health Survey (ACHS). Study subjects lived in the vicinity of a former PCB production facility and had PCB concentrations 2 to 3 times higher than similar age and race groups from the general population. We investigated associations among serum levels of thyroid hormones (thyroxin [T4], free thyroxin [fT4], triiodothyronine [T3], thyroid stimulation hormone [TSH]) and auto-antibodies (thyroglobulin antibody [TgAb] or thyroperoxidase antibody [TPOAb]) and combined indicators of thyroid function with the sum of PCBs, varying PCB groups, individual PCB congeners, and 8 pesticides. Logistic and linear regression models were adjusted for log10 transformed total lipids, age, sex, ethnicity, BMI, smoking, and family history of thyroid disease. We also performed analyses stratified by ethnicity and sex. Linear regression showed inverse associations between TT3 and thyroid-like PCBs (sum of PCBs 28, 52, 74, 101, 105, and 118; p = .0004), two pesticides (hexachlorobenzene, and pp'-DDE), and individual congeners (PCBs 74, 105). Null associations were observed between PCBs, pesticides, TSH, TT4, and fT4. Logistic regression analyses did not provide support for TT3 findings and found no association with other thyroid hormones, antibodies, or combined indicator of thyroid function. These results suggest there is little evidence that these chemicals have any major clinical effect on thyroid function in this highly PCB exposed population.

Association of prenatal exposure to PCDD/Fs and PCBs with maternal and infant thyroid hormones: The Hokkaido Study on Environment and Children's Health

Polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and biphenyls (PCBs) are persistent organic pollutants that are universally detected. Some congeners of PCDDs, PCDFs or PCBs have dioxin-like toxicity, whereas non-dioxin-like PCBs are considered to have different toxicity. Reports of the relationships between prenatal exposure to PCDDs, PCDFs or PCBs and thyroid homeostasis in pregnant women and infants have been inconsistent. The aim of this study was to investigate the effect of maternal serum PCDD/F or PCB levels on maternal and neonatal thyroid hormone (TH) levels in a prospective cohort. Of the 514 subjects in the prospective cohort, 386 mothers and 410 infants were included for analysis. Fifteen dioxins and seventy PCBs in maternal blood collected between 23 and 41weeks of gestation were measured using high-resolution gas chromatography and high-resolution mass spectrometry. Blood samples to measure thyroid stimulating hormone (TSH) and free thyroxine (FT4) levels were obtained from mothers at an early gestational stage (median ten weeks), and from infants between four and seven days of age, respectively. Multiple linear regression analysis was conducted. Median concentration of total PCBs, PCB 153 were 104,700, and 20,500pg/g lipid, respectively. Median total dioxin-TEQ was 13.8pg/g lipid. Total dioxin-TEQ, coplanar PCBs were positively associated with neonatal FT4 (beta=0.224, 0.206, respectively). The association was stronger in boys (beta=0.299, 0.282, respectively). Several PCDD/F and PCB isomers were also positively associated with neonatal FT4. Total PCBs or non-dioxin-like PCBs were not associated with any maternal or neonatal THs. No DLC grouping or congeners were associated with neonatal TSH. Non-ortho PCBs were positively associated with maternal FT4. Three PCB congeners had significant positive association(s) with maternal THs. In conclusion, the results of our study suggest that perinatal exposure to background-level DLCs increases neonatal FT4, especially in boys.

Uptake of radiolabeled 3,3',4,4'-tetrachlorobiphenyl into Japanese quail egg compartments and embryo following air cell and albumen injection

The avian embryo is an excellent model for testing adverse developmental effects of environmental chemicals as well as uptake and movement of xenobiotics within the egg compartments. Before incubation at embryonic day 0, ¹⁴ C 3,3',4,4'-tetrachlorobiphenyl (¹⁴ C PCB 77) was injected into Japanese quail eggs either onto the air cell or into the albumen. All egg components were collected on embryonic day 1, 5, or 10, and concentrations of ¹⁴ C PCB 77 were measured in various egg components (shell, membrane, yolk, albumen, and embryo). The results showed measurable ¹⁴ C PCB 77 in all egg components, with changing concentrations in each egg component over the course of embryonic development. Specifically, concentrations in the shell content decreased between embryonic days 1 and 10, increased in albumen from embryonic days 1 to 5 and then decreased at embryonic day 10, and increased in both yolk and embryo from embryonic days 1 to 10. Vehicle and injection site both influenced ¹⁴ C PCB 77 allantoic fluid concentrations, with little effect on other egg components except for the inner shell membrane. The fatty acid vehicle injected into the albumen yielded the highest ¹⁴ C PCB 77 recovery. These findings demonstrate dynamic movement of toxicants throughout the egg components during avian embryonic development and a steady increase of relatively low levels of ¹⁴ C PCB 77 in the embryo compared with the yolk, albumen, and shell, suggesting that embryonic uptake (i.e., exposure) mirrors utilization of egg components for nutrition and growth during development. Environ Toxicol Chem 2018;37:126-135. © 2017 SETAC.

Serum Polybrominated Biphenyls (PBBs) and Polychlorinated Biphenyls (PCBs) and Thyroid Function among Michigan Adults Several Decades after the 1973-1974 PBB Contamination of Livestock Feed

BACKGROUND

In 1973-1974, Michigan residents were exposed to polybrominated biphenyls (PBBs) through an accidental contamination of the food supply. Residents were enrolled in a registry assembled after the incident, and they and their children participated in follow-up studies to assess subsequent health outcomes.

OBJECTIVES

We evaluated associations between serum PBBs and polychlorinated biphenyls (PCBs) and markers of thyroid function among Michigan adults.

METHODS

Serum concentrations of four PBB and four PCB congeners were measured at least once in 753 adults, including 79 women who participated in a 2004-2006 study and 683 women and men with follow-up during 2012-2015. Participants completed questionnaires on health conditions (including physician-diagnosed thyroid disease), behaviors, and demographics. Thyroid hormones were measured in a subset without thyroid disease (n=551). In multivariable linear regression models, PBB and PCB congener concentrations, on both the volume (nanogram/milliliter) and lipid (nanogram/gram lipid) basis, were assessed in relation to thyroid hormones. Logistic regression models were used to estimate associations between serum PBBs and PCBs and thyroid disease.

RESULTS

Thyroid disease was common (18% overall; 25% among women). Among women, all odds ratios (ORs) for PBB-153 and thyroid disease were positive for quintiles above the reference level, but estimates were imprecise and were without a monotonic increase. For an interquartile range (IQR) increase in PBB-153 (0.43 ng/mL), the OR (any thyroid disease)=1.12; (95% CI: 0.83, 1.52) (n=105 cases); for hypothyroidism, OR=1.35 (95% CI: 0.86, 2.13) (n=49 cases). There were 21 cases of thyroid disease in men [OR=0.69 (95% CI: 0.33); 1.44 for an IQR increase (0.75 ng/mL) in serum PBB-153]. PCB congeners were statistically significantly associated with greater total and free thyroxine and total triiodothyronine among women and with total and free triiodothyronine among men in lipid-standardized models.

CONCLUSIONS

We found some evidence to support associations of PBBs and PCBs with thyroid disease and thyroid hormone levels. https://doi.org/10.1289/EHP1302.

Association of Polybrominated Diphenyl Ethers (PBDEs) and Polychlorinated Biphenyls (PCBs) with Hyperthyroidism in Domestic Felines, Sentinels for Thyroid Hormone Disruption

BACKGROUND

Hyperthyroidism is the most common endocrine disorder observed in domestic felines; however, its etiology is largely unknown. Two classes of persistent organic pollutants, polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) are known to interfere with thyroid hormone (TH) signaling and regulation; thus, it is postulated that they contribute to the etiopathogenesis of feline hyperthyroidism and pose a risk to humans and other species. In this case-control study, the concentrations of 13 PBDE and 11 PCB congeners were measured by gas chromatography mass spectrometry in serum or plasma samples from 20 hyperthyroid and 31 control cats in order to investigate the association between concentration of PBDE and PCB congeners and feline hyperthyroidism. Logistic regression analysis was used to determine whether elevated concentrations of individual congeners were associated with a higher risk of feline hyperthyroidism.

RESULTS

Hyperthyroid cats had higher concentrations of four PBDE congeners (BDE17, BDE100, BDE47, and BDE49) and five PCB congeners (PCB131, PCB153, PCB174, PCB180, and PCB196), compared to control cats. In addition, the sum of both PBDE and PCB congener concentrations were elevated in the hyperthyroid group compared to control cats; however, only the increased PCB concentrations were statistically significant. The sum total PBDE concentrations in our feline samples were approximately 50 times greater than concentrations previously reported in human populations from a geographically similar area, whereas sum total PCB concentrations were comparable to those previously reported in humans.

CONCLUSIONS

These observational findings support the hypothesis that PBDEs and PCBs may contribute to the etiopathogenesis of hyperthyroidism in felines. As domestic house cats are often exposed to higher concentrations of PBDEs than humans, they may serve as sentinels for the risk of TH disruption that these pollutants pose to humans and other species.

Disruption of thyroid hormone (TH) levels and TH-regulated gene expression by polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs), and hydroxylated PCBs in e-waste recycling workers

Polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) are the primary toxicants released by electronic waste (e-waste) recycling, but their adverse effects on people working in e-waste recycling or living near e-waste sites have not been studied well. In the present study, the serum concentrations of PBDEs, PCBs, and hydroxylated PCBs, the circulating levels of thyroid hormones (THs), and the mRNA levels of seven TH-regulated genes in peripheral blood leukocytes of e-waste recycling workers were analyzed. The associations of the hormone levels and gene expression with the exposure to these contaminants were examined using multiple linear regression models. There were nearly no associations of the TH levels with PCBs and hydroxylated PCBs, whereas elevated hormone (T₄ and T₃) levels were associated with certain lower-brominated BDEs. While not statistically significant, we did observe a negative association between highly brominated PBDE congeners and thyroid-stimulating hormone (TSH) levels in the e-waste workers. The TH-regulated gene expression was more significantly associated with the organohalogen compounds (OHCs) than the TH levels in these workers. The TH-regulated gene expression was significantly associated with certain PCB and hydroxylated PCB congeners. However, the expression of most target genes was suppressed by PBDEs (mostly highly brominated congeners). This is the first evidence of alterations in TH-regulated gene expression in humans exposed to OHCs. Our findings indicated that OHCs may interfere with TH signaling and/or exert TH-like effects, leading to alterations in related gene expression in humans. Further research is needed to investigate the mechanisms of action and associated biological consequences of the gene expression disruption by OHCs.

Health effects associated with measured levels of contaminants in the Arctic

The Human Health Assessment Group has over the past decade recommended that effect studies be conducted in the circumpolar area. Such studies examine the association between contaminant exposure in the Arctic populations and health effects. Because foetuses and young children are the most vulnerable, effect studies are often prospective child cohort studies. The emphasis in this article is on a description of the effects associated with contaminant exposure in the Arctic. The main topics addressed are neurobehavioural, immunological, reproductive, cardiovascular, endocrine and carcinogenic effect. For each topic, the association between exposure and effects is described, and some results are reported for similar studies outside the Arctic.

Using systematic reviews for hazard and risk assessment of endocrine disrupting chemicals

The possibility that endocrine disrupting chemicals (EDCs) in our environment contribute to hormonally related effects and diseases observed in human and wildlife populations has caused concern among decision makers and researchers alike. EDCs challenge principles traditionally applied in chemical risk assessment and the identification and assessment of these compounds has been a much debated topic during the last decade. State of the science reports and risk assessments of potential EDCs have been criticized for not using systematic and transparent approaches in the evaluation of evidence. In the fields of medicine and health care, systematic review methodologies have been developed and used to enable objectivity and transparency in the evaluation of scientific evidence for decision making. Lately, such approaches have also been promoted for use in the environmental health sciences and risk assessment of chemicals. Systematic review approaches could provide a tool for improving the evaluation of evidence for decision making regarding EDCs, e.g. by enabling systematic and transparent use of academic research data in this process. In this review we discuss the advantages and challenges of applying systematic review methodology in the identification and assessment of EDCs.

Human urinary/seminal phthalates or their metabolite levels and semen quality: A meta-analysis

Health concerns surrounding human exposure to phthalates include diminished semen quality. Epidemiological findings remain inconsistent. We have performed a quality appraisal and meta-analysis to quantitatively summarize evidence for associations between phthalate exposures and human semen quality. Pubmed and Web of Science were searched for pertinent studies through October 2014. Cited references were reviewed to identify secondary studies. Studies that reported quantitative estimates of the association between phthalates or their metabolite levels in humans and semen quality were eligible. Random effects models were used to calculate pooled effects estimates. Overall, 20 studies met our inclusion criteria. Subsequently, 14 studies were included in the meta-analysis. Urinary monobutyl phthalate (MBP) and monobenzyl phthalate (MBzP) were associated with reduced sperm concentration (MBP [7.4-25.3 µg/L], pooled odds ratio [OR]=2.60, 95% confidence interval [CI]=1.32-5.15; MBzP [14.0-540.2 µg/L], pooled OR=2.23, 95% CI=1.16-4.30). Both MBP (24.6-14,459.0 µg/L) and MEHP (3.1-208.1 µg/L) were inversely associated with straight line velocity (VSL; MBP, pooled β=-2.51, 95% CI=-4.44, -0.59; MEHP, pooled β=-1.06, 95% CI=-1.99, -0.12). An IQR increase in MBzP and MEP levels (MBzP, IQR=11.35 µg/L; MEP, IQR=449.4 µg/L) was associated with an increase in comet extent (CE; MBzP, pooled β=3.57, 95% CI=0.89-6.25; MEP, pooled β=4.22, 95% CI=1.66-6.77). No associations were observed between monomethyl phthalate and any semen parameters. Our meta-analysis strengthens the evidence that specific phthalates or their metabolite levels may affect semen quality.

Impact of endocrine-disrupting chemicals on thyroid function and brain development

Endocrine disrupting chemicals (EDCs) are synthetic or natural substances in the environment. EDCs have been shown to disrupt reproductive, developmental and other homeostatic systems by interfering with the synthesis, secretion, transport, metabolism and action of endogenous hormones including the thyroid hormone (TH) system. Since TH plays a critical role in brain development, the exposure to TH-system disrupting EDCs during development may have serious consequences. In this article, representative previous studies showing the effect of representative EDCs on the TH system are summarized. Then, the molecular mechanisms of action of polychlorinated biphenyls and polybrominated diphenyl ethers on the TH system are discussed further. Particularly, the effect of polychlorinated biphenyls and polybrominated diphenyl ethers on TH-mediated brain development is discussed. Our recent studies may provide a novel idea regarding the effect of EDCs on the TH system.

Polybrominated diphenyl ether (DE-71) interferes with thyroid hormone action independent of effects on circulating levels of thyroid hormone in male rats

Polybrominated diphenyl ethers (PBDEs) are routinely found in human tissues including cord blood and breast milk. PBDEs may interfere with thyroid hormone (TH) during development, which could produce neurobehavioral deficits. An assumption in experimental and epidemiological studies is that PBDE effects on serum TH levels will reflect PBDE effects on TH action in tissues. To test whether this assumption is correct, we performed the following experiments. First, five concentrations of diphenyl ether (0-30 mg/kg) were fed daily to pregnant rats to postnatal day 21. PBDEs were measured in dam liver and heart to estimate internal dose. The results were compared with a separate study in which four concentrations of propylthiouracil (PTU; 0, 1, 2, and 3 ppm) was provided to pregnant rats in drinking water for the same duration as for diphenyl ether. PBDE exposure reduced serum T4 similar in magnitude to PTU, but serum TSH was not elevated by PBDE. PBDE treatment did not affect the expression of TH response genes in the liver or heart as did PTU treatment. PTU treatment reduced T4 in liver and heart, but PBDE treatment reduced T4 only in the heart. Tissue PBDEs were in the micrograms per gram lipid range, only slightly higher than observed in human fetal tissues. Thus, PBDE exposure reduces serum T4 but does not produce effects on tissues typical of low TH produced by PTU, demonstrating that the effects of chemical exposure on serum T4 levels may not always be a faithful proxy measure of chemical effects on the ability of thyroid hormone to regulate development and adult physiology.

Thyroid hormones are associated with exposure to persistent organic pollutants in aging residents of upper Hudson River communities

The aim of this study was to evaluate the association between persistent organic pollutants (POPs) and thyroid hormones in an aging population. Forty-eight women and 66 men, aged 55-74 years and living in upper Hudson River communities completed a questionnaire and provided blood specimens. Serum was analyzed for thyrotropin (thyroid stimulating hormone, TSH), free (fT4) and total thyroxine (T4), total triiodothyronine (T3), and for POPs. POPs included 39 polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT) and dichlorodiphenyldichloroethylene (DDE) determined by gas chromatography with electron capture detection (GC-ECD), and nine polybrominated diphenyl ethers (PBDEs) determined by high-resolution gas chromatography with high-resolution mass spectrometry detection (HRGC-HRMS). Multivariable linear regression analysis was used to evaluate associations between thyroid hormones and sums of POPs, adjusted for covariates and stratified by sex. Effects were expressed as differences in thyroid hormone levels associated with a doubling in the level of exposure. Among women, DDT+DDE increased T4 by 0.34μg/dL (P=0.04) and T3 by 2.78ng/dL (P=0.05). Also in women, sums of PCBs in conjunction with PBDEs elicited increases of 24.39-80.85ng/dL T3 (P<0.05), and sums of PCBs in conjunction with DDT+DDE elicited increases of 0.18-0.31μg/dL T4 (P<0.05). For men estrogenic PCBs were associated with a 19.82ng/dL T3 decrease (P=0.003), and the sum of estrogenic PCBs in conjunction with DDT+DDE elicited an 18.02ng/dL T3 decrease (P=0.04). Given age-related declines in physiologic reserve, the influence of POPs on thyroid hormones in aging populations may have clinical implications and merits further investigation.

Endocrine disruption of the epigenome: a breast cancer link

The heritable component of breast cancer accounts for only a small proportion of total incidences. Environmental and lifestyle factors are therefore considered to among the major influencing components increasing breast cancer risk. Endocrine-disrupting chemicals (EDCs) are ubiquitous in the environment. The estrogenic property of EDCs has thus shown many associations between ongoing exposures and the development of endocrine-related diseases, including breast cancer. The environment consists of a heterogenous population of EDCs and despite many identified modes of action, including that of altering the epigenome, drawing definitive correlations regarding breast cancer has been a point of much discussion. In this review, we describe in detail well-characterized EDCs and their actions in the environment, their ability to disrupt mammary gland formation in animal and human experimental models and their associations with exposure and breast cancer risk. We also highlight the susceptibility of early-life exposure to each EDC to mediate epigenetic alterations, and where possible describe how these epigenome changes influence breast cancer risk.

Serum concentrations of polychlorinated biphenyls (PCBs) in participants of the Anniston Community Health Survey

Serum concentrations of 35 ortho-substituted polychlorinated biphenyl congeners (PCBs) were measured in 765 adults from Anniston, Alabama, where PCBs were manufactured between 1929 and 1971. As part of the Anniston Community Health Survey (ACHS), demographic data, questionnaire information, and blood samples were collected from participants in 2005-2007. Forty-six percent of study participants were African-American, 70% were female, and the median age was 56 years. The median concentration of the sum of 35 PCB congeners (ΣPCBs) was 528 ng/g lipid, with a 90th percentile of 2,600 ng/g lipid, minimum of 17.0 ng/g lipid, and maximum of 27,337 ng/g lipid. The least square geometric mean ΣPCBs was more than 2.5 times higher for African-American participants than for White participants (866 ng/g lipid vs. 331 ng/g lipid); this difference did not change materially after adjustment for age, sex, body mass index (BMI) and current smoking. In spite of large differences in absolute PCB levels, relative contributions of individual congeners to ΣPCBs were quite similar between race groups. Nevertheless, while percent contributions to ΣPCBs for most of the most abundant penta- to heptachlorobiphenyls were higher among African-Americans, the percentages were higher in Whites for the lower-chlorinated PCBs 28 and 74 and for octa- to decachlorinated PCBs. No major differences were observed in geometric mean ΣPCBs between women and men when adjusted for age, race, BMI and current smoking (516 ng/g lipid vs. 526 ng/g lipid). Principal component analysis revealed groups of co-varying congeners that appear to be determined by chlorine substitution patterns. These congener groupings were similar between ACHS participants and the National Health and Nutrition Examination Survey (NHANES) 2003-04 sample of the general United States population, despite ACHS participants having serum concentrations of ΣPCBs two to three times higher than those in comparable age and race groups from NHANES.

Systematic analysis of the relationship between standardized biological levels of polychlorinated biphenyls and thyroid function in pregnant women and newborns

The impact polychlorinated biphenyl (PCB) exposure on thyroid status in pregnant women and newborns was investigated in various epidemiological studies, but findings show inconsistencies, and differences in biological indicators of exposure between studies limits comparison of results. The aim of this research was to use a procedure previously developed to standardize PCB biological concentration data between published studies to perform a systematic analysis of associations between PCB exposure and thyroid hormones (THs) (total and free T3 and T4) or thyroid stimulating hormone (TSH) in pregnant women and newborns. Biological concentrations from nineteen studies were expressed in total PCB equivalent per kg of lipids in maternal plasma (μg PCBMPEQ kg(-1) lipids). Systematic analysis of the "standardized biological concentration-thyroid parameters" relationship was conducted through the application of methodological criteria in both pregnant women and newborns. Standardization of PCB levels and application of methodological criteria led to assign higher confidence to ten of the reviewed studies. Among the retained studies in pregnant women, only one reported a significant association between PCBs and total T3 levels, but no association were observed when circulating TSH and free T4 levels were used to assess thyroid function. Regarding the association between prenatal PCB exposure and thyroid status in newborns, a lack of significant association was consistently obtained in the retained studies assigned an overall high confidence. The weight of evidence of a significant impact of PCB exposure on TSH and TH levels at the described biological levels in pregnant women and newborns (mean<1000 μg PCBMPEQ kg(-1) lipids) appears low according to this systematical analysis.

Maternal and cord-blood thyroid hormone levels and exposure to polybrominated diphenyl ethers and polychlorinated biphenyls during early pregnancy

Thyroid hormones play a critical role in the growth of many organs, especially the brain. Polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) interact with the thyroid pathway and may disturb neurodevelopment. This prospective study was designed to examine associations between maternal blood PBDEs and PCBs in early pregnancy and levels of thyroid hormones in maternal and umbilical-cord blood. Levels of low-brominated PBDEs, 3 PCB congeners, total and free thyroid hormones (triiodothyronine (T3) and thyroxine (T4)), thyroid-stimulating hormone, thyroid peroxidase antibodies, iodine, selenium, and mercury were measured in 380 pregnant women in the first trimester who were recruited at the University Hospital Center of Sherbrooke (Quebec, Canada) between September 2007 and December 2008. Thyroid hormone levels were also assessed at delivery and in cord blood (n = 260). Data were analyzed on both a volume basis and a lipid basis. At less than 20 weeks of pregnancy, no relationship was statistically significant in volume-based analysis. In lipid-based models, an inverse association between maternal PBDEs and total T3 and total T4 and a direct association with free T3 and free T4 were observed. At delivery, in both analyses, we observed negative associations between maternal total T4, free T3, cord-blood free T4, and PBDEs and between maternal free T3 and PCBs. Our results suggest that exposure to PBDEs and PCBs in pregnancy may interfere with thyroid hormone levels.

Polychlorinated biphenyls and cancer: an epidemiological assessment

Polychlorinated biphenyls (PCBs) are toxic and persistent chemicals produced between 1930s and 1980s primarily for insulating fluids in heavy-duty electrical equipment in power plants, industries, and large buildings. They persist in the environment and accumulate in plants and animals, and have been classified as probable carcinogens to humans. We performed a systematic review and meta-analysis of scientific literature on the relationship between PCB exposure and human cancer. Two cohorts of people highly exposed to PCBs through ingestion of contaminated rice oil and some cohorts of occupationally exposed workers failed to show a definite increase in total cancer mortality and provided inconsistent results regarding single cancers. Several cohort and case-control studies investigated the association between PCBs and specific cancers, showing an association between PCB serum levels and non-Hodgkin lymphomas (NHL), with a summary odds ratio of 1.5 (95% confidence interval: 1.1-1.7), but no consistent results for the other cancer sites and types. In conclusion, this review provides some evidence for the role of PCBs in the development of NHL, although the inconsistent results of studies performed on highly polluted people and occupationally exposed workers do not allow a firm conclusion to be drawn.

Serum levels of hydroxylated PCBs, PCBs and thyroid hormone measures of Japanese pregnant women

OBJECTIVES

The purpose of this study was to investigate the associations between serum concentrations of hydroxylated PCBs (OH-PCBs) and PCBs and measures of thyroid hormone status of Japanese pregnant women.

METHODS

The concentrations of free thyroxine (fT4), thyroid stimulating hormone (TSH), and thyroxine binding globulin (TBG) as well as 16 OH-PCB isomers and 29 PCB isomers were analyzed in the serum of 129 women sampled in the first trimester of gestation. Dietary and lifestyle information of the subjects was obtained by self-administered questionnaire. Multiple regression analysis was performed using measures of thyroid hormones as the dependent variable and serum levels of OH-PCBs/PCBs, urinary iodine concentration, and other potential covariates (age, BMI, smoking, etc.) as independent variables.

RESULTS

Geometric mean (GM) concentration of the sum of 16 isomers of OH-PCBs was 120 pg/g wet wt. and that of 29 isomers of PCBs was 68 ng/g lipid wt., respectively, in the serum of the subjects. Iodine nutrition was considered adequate to high from urinary iodine level (GM, 370 μg/g creatinine). The mean concentration of TSH, fT4 and TBG was 1.34 ± 1.37 μIU/mL, 1.22 ± 0.16 ng/dL and 33.0 ± 6.4 μg/mL, respectively, with a small number of subjects who were outside the reference range. Multiple regression analysis revealed that serum concentrations of OH-PCBs/PCBs were not significantly associated with any of the measures of thyroid hormone status.

CONCLUSIONS

Exposure/body burden of OH-PCBs and PCBs at environmental levels does not have a measurable effect on thyroid hormones.

Upstream adverse effects in risk assessment: a model of polychlorinated biphenyls, thyroid hormone disruption and neurological outcomes in humans

BACKGROUND

Increasing data on early biological changes from chemical exposures requires new interpretation tools to support decision-making.

OBJECTIVES

To test the possibility of applying a quantitative approach using human data linking chemical exposures and upstream biological perturbations to overt downstream outcomes.

METHODS

Using polychlorinated biphenyl (PCB) exposures and maternal thyroid hormone (TH) perturbations as a case study, we model three relationships: (1) prenatal PCB exposures and TH changes, using free T(4) (FT(4)); (2) prenatal TH and childhood neurodevelopmental outcomes; and (3) prenatal PCB exposures and childhood neurodevelopmental outcomes (IQ). We surveyed the epidemiological literature; extracted relevant quantitative data; and developed models for each relationship, applying meta-analysis where appropriate.

RESULTS

For relationship 1, a meta-analysis of 3 studies gives a coefficient of -0.27 pg/mL FT(4) per ln(sum of PCBs) (95% confidence interval [CI] -0.82 to 0.27). For relationship 2, regression coefficients from three studies of maternal FT(4) levels and cognitive scores ranged between 0.99 IQ points/(pg/mL FT(4)) (95% CI -0.31 to 2.2) and 7.6 points/(pg/mL FT(4)) (95% CI 1.2 to 16.3). For relationship 3, a meta-analysis of five studies produces a coefficient of -1.98 IQ points (95% CI -4.46 to 0.50) per unit increase in ln(sum of PCBs). Combining relationships 1 and 2 yields an estimate of -2.0 to -0.27 points of IQ per unit increase in ln(sum of PCBs).

CONCLUSIONS

Combining analysis of chemical exposures and early biological perturbations (PCBs and FT(4)) with analysis of early biological perturbations and downstream overt effects (FT(4) and IQ) yields estimates within the range of studies of exposures and overt effects (PCBs and IQ). This is an example approach using upstream biological perturbations for effect prediction.

Serum concentrations of p, p'-DDE, HCB, PCBs and reproductive hormones among men of reproductive age

Exposure to polychlorinated biphenyls (PCBs) has been associated with changes in reproductive hormone levels, however most groups studied have been highly exposed. We investigated the association of PCBs, hexachlorobenzene (HCB) and p, p'-DDE with serum sex hormones in 341 adult men from a US infertility clinic with exposure levels consistent with those observed in the general population. In crude regression models we observed several negative associations of PCBs and HCB with steroid hormone-binding globulin (SHBG) and total and free testosterone. After adjustment for lipids, age and BMI, nearly all significant associations were attenuated. A negative relationship remained between PCB 118 and SHBG (p<0.01), and relationships of dioxin-like PCBs with SHBG and total testosterone, and between PCB 118 and total testosterone, were suggestive. These results suggest a minimal relationship between PCB exposures at low background levels similar to those observed in the general population of the US and circulating reproductive hormones.

Polybrominated diphenyl ethers and polychlorinated biphenyls in freshwater fish from Taihu Lake, China: their levels and the factors that influence biomagnification

Polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs), two types of persistent organic pollutants that have been used widely, can be released into the environment and accumulate in organisms. To obtain a better understanding of the biomagnification of PBDEs and PCBs in fish, as well as the influences on biomagnification by fish size and physical properties of PBDEs and PCBs, a total of 200 samples of 24 fish species were collected and analyzed from Taihu Lake, the second largest freshwater lake in China. The concentrations of PBDEs and PCBs ranged from 8.59 to 74.28 ng/g lipid weight (lw) and from 10.30 to 165.20 ng/g lw, respectively. Trophic magnification factors (TMFs) were used to estimate the PBDE and PCB biomagnification potentials. The TMF values of PBDEs and PCBs ranged from 0.78 to 2.95 and from 0.92 to 2.60, respectively. Most of the TMFs were greater than 1, indicating that these contaminants were biomagnified in food chains. Fish size might influence the biomagnification evaluation, because different sized fish had different lipid content, leading to different lipid-based concentrations of PBDEs and PCBs. Parabolic relationships were observed between the TMFs and logK(OW) , as well as between the TMFs and the molecular volumes of PBDE and PCB congeners. The congeners with logK(OW) values of approximately 7 or molecular volumes of approximately 8 × 10⁻⁵  nm³ had the greatest biomagnification potentials. Compared to molecular weight, molecular volume seems to be the better standard for analyzing the influence of molecular size on biomagnification.

Individual polychlorinated biphenyl (PCB) congeners produce tissue- and gene-specific effects on thyroid hormone signaling during development

Polychlorinated biphenyls (PCB) are industrial chemicals linked to developmental deficits that may be caused in part by disrupting thyroid hormone (TH) action by either reducing serum TH or interacting directly with the TH receptor (TR). Individual PCB congeners can activate the TR in vitro when the metabolic enzyme cytochrome P4501A1 (CYP1A1) is induced, suggesting that specific PCB metabolites act as TR agonists. To test this hypothesis in vivo, we compared two combinations of PCB congeners that either activate the TR (PCB 105 and 118) or not (PCB 138 and 153) in the presence or absence of a PCB congener (PCB 126) that induces CYP1A1 in vitro. Aroclor 1254 was used as a positive control, and a group treated with propylthiouracil was included to characterize the effects of low serum TH. We monitored the effects on TH signaling in several peripheral tissues by measuring the mRNA expression of well-known TH-response genes in these tissues. Aroclor 1254 and its component PCB 105/118/126 reduced total T(4) to the same extent as that of propylthiouracil but increased the expression of some TH target genes in liver. This effect was strongly correlated with CYP1A1 expression supporting the hypothesis that metabolism is necessary. Effects were gene and tissue specific, indicating that tissue-specific metabolism is an important component of PCB disruption of TH action and that PCB metabolites interact in complex ways with the TR. These are essential mechanisms to consider when evaluating the health risks of contaminant exposures, for both PCB and other polycyclic compounds known to interact with nuclear hormone receptors.

Maternal exposure to polychlorinated biphenyls and the secondary sex ratio: an occupational cohort study

BACKGROUND

Though commercial production of polychlorinated biphenyls was banned in the United States in 1977, exposure continues due to their environmental persistence. Several studies have examined the association between environmental polychlorinated biphenyl exposure and modulations of the secondary sex ratio, with conflicting results.

OBJECTIVE

Our objective was to evaluate the association between maternal preconceptional occupational polychlorinated biphenyl exposure and the secondary sex ratio.

METHODS

We examined primipara singleton births of 2595 women, who worked in three capacitor plants at least one year during the period polychlorinated biphenyls were used. Cumulative estimated maternal occupational polychlorinated biphenyl exposure at the time of the infant's conception was calculated from plant-specific job-exposure matrices. A logistic regression analysis was used to evaluate the association between maternal polychlorinated biphenyl exposure and male sex at birth (yes/no).

RESULTS

Maternal body mass index at age 20, smoking status, and race did not vary between those occupationally exposed and those unexposed before the child's conception. Polychlorinated biphenyl-exposed mothers were, however, more likely to have used oral contraceptives and to have been older at the birth of their first child than non-occupationally exposed women. Among 1506 infants liveborn to polychlorinated biphenyl-exposed primiparous women, 49.8% were male; compared to 49.9% among those not exposed (n = 1089). Multivariate analyses controlling for mother's age and year of birth found no significant association between the odds of a male birth and mother's cumulative estimated polychlorinated biphenyl exposure to time of conception.

CONCLUSIONS

Based on these data, we find no evidence of altered sex ratio among children born to primiparous polychlorinated biphenyl-exposed female workers.

Epigenetics meets endocrinology

Although genetics determines endocrine phenotypes, it cannot fully explain the great variability and reversibility of the system in response to environmental changes. Evidence now suggests that epigenetics, i.e. heritable but reversible changes in gene function without changes in nucleotide sequence, links genetics and environment in shaping endocrine function. Epigenetic mechanisms, including DNA methylation, histone modification, and microRNA, partition the genome into active and inactive domains based on endogenous and exogenous environmental changes and developmental stages, creating phenotype plasticity that can explain interindividual and population endocrine variability. We will review the current understanding of epigenetics in endocrinology, specifically, the regulation by epigenetics of the three levels of hormone action (synthesis and release, circulating and target tissue levels, and target-organ responsiveness) and the epigenetic action of endocrine disruptors. We will also discuss the impacts of hormones on epigenetics. We propose a three-dimensional model (genetics, environment, and developmental stage) to explain the phenomena related to progressive changes in endocrine functions with age, the early origin of endocrine disorders, phenotype discordance between monozygotic twins, rapid shifts in disease patterns among populations experiencing major lifestyle changes such as immigration, and the many endocrine disruptions in contemporary life. We emphasize that the key for understanding epigenetics in endocrinology is the identification, through advanced high-throughput screening technologies, of plasticity genes or loci that respond directly to a specific environmental stimulus. Investigations to determine whether epigenetic changes induced by today's lifestyles or environmental 'exposures' can be inherited and are reversible should open doors for applying epigenetics to the prevention and treatment of endocrine disorders.

The impacts of organochlorines and other persistent pollutants on thyroid and metabolic health

High prevalence of thyroid and metabolic disorders has been repeatedly observed in the population living in the area of eastern Slovakia highly polluted by a mixture of PCBs, DDE and HCB since about 50 years ago. Among thyroid disorders, increase of thyroid volume as measured by ultrasound volumetry may be suggested as one of notable findings which appeared possibly related to increased OCs levels and to autoimmunity signs (e.g. positive thyroperoxidase antibodies in blood and/or hypoechogenicity image obtained by ultrasound), while some participation of individual susceptibility and also of immunogenic effect of OCs and iodine in this iodine replete country cannot be excluded. Another notable finding has been the increase of blood FT4 and TT3 positively related to high PCBs level. Such increased FT4 level has been found associated with TSH level in hyperthyroid range in about 2% of examined population from polluted area. High prevalence of thyroid autoimmune disorders strongly supported the assumption on impaired immune system and thus also on presumably increased prevalence of other autoimmune disorders in highly exposed population. In addition, markedly increased prevalence of prediabetes and diabetes significantly related to major OCs (PCBs, DDE and HCB) levels and accompanied by increasing level of cholesterol and triglycerides has been observed. The observations also suggested a role of prenatal exposure to OCs in the development of several adverse health signs (e.g. increased prevalence of thyroid antibodies, impaired fasting glucose level, increased thyroid volume, decreased thymus volume, decreased neurobehavioral performance, increased hearing and dental disorders) in young generation born to highly exposed mothers in polluted area.

Subacute toxicity of p,p'-DDT on rat thyroid: Hormonal and histopathological changes

The purpose of this study is to assess the effect of p,p'-DDT on thyroid activity of male Wistar rats. Pesticide was administered intraperitoneally (i.p.) for 10 consecutive days at doses of 50 and 100mg/kg/day. At the end of the treatment, the endpoints examined included serum total levels of triiodothyronine (T(3)), total thyroxine (T(4)), and thyroid stimulating hormone (TSH). Thyroid gland histopathology and tissue metabolism of thyroid hormone (T(4) UDP-glucuronyltransferase UDP-GT and 5'-deiodinases) were determined. DDT treatment altered thyroid function namely by increasing hepatic excretion of T(4) glucuronide. At the dose of 50mg/kg it decreased T(4) circulating levels and increased thyroid 5'-deiodinase type I (5'-D-I) and brown adipose tissue (BAT) 5'-deiodinase type II (5'-D-II) activities but it did not affect liver 5'-D-I activity which might contribute to the maintenance of the serum T(3) level. Treatment with 100mgDDT/kg decreased serum thyroid hormone concentration and tissue 5'-D-I activity without affecting BAT 5'-D-II activity. Gland histomorphological analysis showed hyperplasia and squamous metaplasia with abundant colloid. These observations associated to the elevated serum TSH levels and gland hypertrophy suggest that DDT exposure induced an hypothyroidism state with a colloid goiter in rats.

Development of TEFs for PCB congeners by using an alternative biomarker--thyroid hormone levels

Polychlorinated biphenyls (PCBs) are ubiquitous toxic contaminants. Health risk assessment for this class of chemicals is complex: the current toxic equivalency factor (TEF) method covers dioxin-like (DL-) PCBs, dibenzofurans, and dioxins, but excludes non-DL-PCBs. To address this deficiency, we evaluated published data for several PCB congeners to determine common biomarkers of effect. We found that the most sensitive biomarkers for DL-non-ortho-PCB 77 and PCB 126 are liver enzyme (e.g., ethoxyresorufin-O-deethylase, EROD) induction, circulating thyroxine (T4) decrease, and brain dopamine (DA) elevation. For DL-ortho-PCB 118 and non-DL-ortho-PCB 28 and PCB 153, the most sensitive biomarkers are brain DA decrease and circulating T4 decrease. The only consistent biomarker for both DL- and non-DL-PCBs is circulating T4 decrease. The calculated TEF-(TH), based on the effective dose to decrease T4 by 30% (ED(30)) with reference to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), is identical to both TEF-(WHO98) and TEF-(WHO05) for TCDD and DL-PCBs (correlation coefficients are r=1.00, P<0.001; and r=0.99, P<0.001, respectively). We conclude that T4 decrease is a prospective biomarker for generating a new TEF scheme which includes some non-DL-congeners. The new TEF-(TH) parallels the TEF-(WHO) for DL-PCBs and, most importantly, is useful for non-DL-PCBs in risk assessment to address thyroid endocrine disruption and potentially the neurotoxic effects of PCBs.

Endocrine disruptors and thyroid hormone physiology

Endocrine disruptors are man-made chemicals that can disrupt the synthesis, circulating levels, and peripheral action of hormones. The disruption of sex hormones was subject of intensive research, but thyroid hormone synthesis and signaling are now also recognized as important targets of endocrine disruptors. The neurological development of mammals is largely dependent on normal thyroid hormone homeostasis, and it is likely to be particularly sensitive to disruption of the thyroid axis. Here, we survey the main thyroid-disrupting chemicals, such as polychlorinated biphenyls, perchlorates, and brominated flame-retardants, that are characteristic disruptors of thyroid hormone homeostasis, and look at their suspected relationships to impaired development of the human central nervous system. The review then focuses on disrupting mechanisms known to be directly or indirectly related to the transcriptional activity of the thyroid hormone receptors.

Relationships of putative endocrine disruptors to human sexual maturation and thyroid activity in youth

Endocrine disruption has become a significant human health concern, but is difficult to study outside of the laboratory for several reasons including the multiplicity of exposures, the difficulty in assessing each exposure, and the variety of possible outcomes among human populations. This review summarizes our studies of the relationships of measured persistent organic pollutants (PCBs, p,p'-DDE, HCB and mirex), and heavy metals (lead and mercury), to outcomes directly related to thyroid function and sexual maturation. These studies were conducted in a sample of Native American youth from the Akwesasne Mohawk community. The participants were first studied during puberty (10-16.9 years of age) and then at approximately 18 years of age. Results from these studies show that PCB levels are positively related to TSH and negatively to free T4. Further, these effects are conditioned by breastfeeding history. Anti-thyroid peroxidase antibody levels also are related to PCB levels suggesting elevated risk of autoimmune disease among the exposed. Earlier age at menarche is associated with higher PCB levels while risk of delay is associated with higher lead levels. Some evidence that the timing of exposure produces different effects is presented, and the level of exposure in the participants suggests that effects observed may be relevant to a considerable proportion of the US population. Further investigations are warranted to determine effect thresholds and mechanisms.