Interactions of persistent environmental organohalogens with the thyroid hormone system: mechanisms and possible consequences for animal and human health

Effects of complex organohalogen contaminant mixtures on thyroid homeostasis in hooded seal (Cystophora cristata) mother-pup pairs

Many lipid-soluble and phenolic compounds present in the complex mixture of orgaohalogen contaminants (OHCs) that arctic wildlife is exposed to have the ability to interfere with the thyroid hormone (TH) system. The aim of this study was to identify compounds that might interfere with thyroid homeostasis in 14 nursing hooded seal (Cystophora cristata) mothers and their pups (1-4d old) sampled in the West Ice in March 2008. Multivariate modelling was used to assess the potential effects of measured plasma levels of OHCs on circulating TH levels of the measured free (F) and total (T) levels of triidothyrine (T3) and thyroxine (T4). Biological factors were important in all models (e.g. age and sex). In both mothers and pups, TT3:FT3 ratios were associated with α- and β-hexachlorocyclohexane (HCH), ortho-PCBs, chlordanes and DDTs. The similarities between the modelled TT3:FT3 responses to OHC levels in hooded seal mothers and pups most probably reflects similar exposure patterns, but could also indicate interconnected TH responses. There were some differences in the modelled TH responses of mothers and pups. Most importantly, the negative relationships between many OH-PCBs (particularly 3'-OH-CB138) and TT3:FT3 ratio and the positive relationships between TT4:FT4 ratios and polybrominated diphenyl ether [PBDE]-99, -100 and 4-OH-CB107 in pups, which was not found in mothers. Although statistical associations are not evidence per se of biological cause-effect relationships, the results suggest that thyroid homeostasis is affected in hooded seals, and that the inclusion of the fullest possible OHC mixture is important when assessing TH related effects in wildlife.

Persistent toxic burdens of halogenated phenolic compounds in humans and wildlife

Halogenated phenolic compounds (HPCs) including hydroxylated polychlorobiphenyls (OH-PCBs) and hydroxylated polybromodiphenyl-ethers (OH-PBDEs) can be persistent organic pollutant (POP) metabolites or natural marine compounds. Structurally similar to thyroid hormones (THs), they are retained in blood, transported through selective barriers, and the cause of endocrine and neuronal POP effects. This study presents a meta-analysis of HPC burdens in human and wildlife tissues, including OH-PCBs, OH-PBDEs, Pentachlorophenol, and polybromophenols. HPC blood plasma levels were also compared to known in vitro and in vivo toxicological effect concentrations. Blood, highly perfused, and fetal tissues contained the highest levels of HPCs. Plasma concentrations of analyzed OH-PCBs/PBDEs ranged from 0.1 to 100 nM in humans and up to 240, 454, 800, and 7650 nM for birds, fish, cetaceans, and other mammals, respectively. These concentrations fully fall within the in vitro effect concentrations reported in literature for HPCs of 0.05-10000 nM. We strongly advise further study of HPC blood levels in the general population, children, and fetal tissue to establish background levels and the risk at sensitive development stages. As not all HPCs are, or can be, chemically analyzed, the application of additional bioanalysis might reveal an even greater toxicological relevance of HPCs. In addition, metabolic activation should always be included within in vitro hazard assessment of POPs.

Sulfated metabolites of polychlorinated biphenyls are high-affinity ligands for the thyroid hormone transport protein transthyretin

BACKGROUND

The displacement of l-thyroxine (T4) from binding sites on transthyretin (TTR) is considered a significant contributing mechanism in polychlorinated biphenyl (PCB)-induced thyroid disruption. Previous research has discovered hydroxylated PCB metabolites (OH-PCBs) as high-affinity ligands for TTR, but the binding potential of conjugated PCB metabolites such as PCB sulfates has not been explored.

OBJECTIVES

We evaluated the binding of five lower-chlorinated PCB sulfates to human TTR and compared their binding characteristics to those determined for their OH-PCB precursors and for T4.

METHODS

We used fluorescence probe displacement studies and molecular docking simulations to characterize the binding of PCB sulfates to TTR. The stability of PCB sulfates and the reversibility of these interactions were characterized by HPLC analysis of PCB sulfates after their binding to TTR. The ability of OH-PCBs to serve as substrates for human cytosolic sulfotransferase 1A1 (hSULT1A1) was assessed by OH-PCB-dependent formation of adenosine-3',5'-diphosphate, an end product of the sulfation reaction.

RESULTS

All five PCB sulfates were able to bind to the high-affinity binding site of TTR with equilibrium dissociation constants (Kd values) in the low nanomolar range (4.8-16.8 nM), similar to that observed for T4 (4.7 nM). Docking simulations provided corroborating evidence for these binding interactions and indicated multiple high-affinity modes of binding. All OH-PCB precursors for these sulfates were found to be substrates for hSULT1A1.

CONCLUSIONS

Our findings show that PCB sulfates are high-affinity ligands for human TTR and therefore indicate, for the first time, a potential relevance for these metabolites in PCB-induced thyroid disruption.

Transthyretin-binding activity of contaminants in blood from polar bear (Ursus maritimus) cubs

We determined the transthyretin (TTR)-binding activity of blood-accumulating contaminants in blood plasma samples of approximately 4-months-old polar bear (Ursus maritimus) cubs from Svalbard sampled in 1998 and 2008. The TTR-binding activity was measured as thyroxine (T4)-like equivalents (T4-EQMeas). Our findings show that the TTR-binding activity related to contaminant levels was significantly lower (45%) in 2008 than in 1998 (mean ± standard error of mean: 1998, 2265 ± 231 nM; 2008, 1258 ± 170 nM). Although we cannot exclude a potential influence of between-year differences in capture location and cub body mass, our findings most likely reflect reductions of TTR-binding contaminants or their precursors in the arctic environment (e.g., polychlorinated biphenyls [PCBs]). The measured TTR-binding activity correlated positively with the cubs' plasma levels of hydroxylated PCBs (OH-PCBs). No such association was found between TTR-binding activity and the plasma levels of perfluoroalkyl substances (PFASs). The OH-PCBs explained 60 ± 7% and 54 ± 4% of the TTR-binding activity in 1998 and 2008, respectively, and PFASs explained ≤1.2% both years. Still, almost half the TTR-binding activity could not be explained by the contaminants we examined. The considerable levels of TTR-binding contaminants warrant further effect directed analysis (EDA) to identify the contaminants responsible for the unexplained part of the observed TTR-binding activity.

Systematic analysis of the relationship between standardized prenatal exposure to polychlorinated biphenyls and mental and motor development during follow-up of nine children cohorts

Impact of prenatal exposure to polychlorinated biphenyls (PCBs) on mental and motor development has been investigated in various children cohorts, but findings show temporal inconsistencies. Because a direct comparison of results obtained from different cohorts remains difficult, temporal relationship between biological PCB concentrations and long-term developmental effects is still not clearly established. The objective of this research was to use a procedure previously developed to standardize PCB biological concentration data across cohorts in order to perform a systematic analysis of temporal associations between prenatal PCB exposure and mental and motor development from neonatal period (or a young age) until school age. Prenatal exposure data from nine cohorts were standardized in terms of total PCBs per kg of lipids in maternal plasma. Systematic analysis of the "standardized biological concentration-development" relationship during follow-up of each cohort was then conducted through the application of Hill criteria. This led to retain six of the studied cohorts in the final analysis. A biological level of prenatal PCB exposure below which risk of mental or motor development should be negligible was established in the order of 1000μg/kg of lipids in maternal plasma.

Peri-conceptional changes in maternal exposure to sewage sludge chemicals disturbs fetal thyroid gland development in sheep

Ewes were exposed to sewage sludge-fertilized pastures in a study designed investigate pre-conceptual and/or gestational exposure to environmental chemicals. The in utero impact on fetal thyroid morphology and function at day 110 (of 145) of pregnancy was then determined. Pre-conceptual exposure increased the relative thyroid organ weights in male fetuses. The number of thyroid follicles in thyroids of fetuses after pre-conceptual or gestational exposure was reduced. This correlated with an increase in Ki67 positive cells. Pre-conceptual exposure to sewage sludge reduced small blood vessels in fetal thyroids. Thyroid tissues of exposed fetuses contained regions where mature angio-follicular units were reduced exhibiting decreased immunostaining for sodium-iodide symporter (NIS). Fetal plasma levels of fT3 and fT4 in exposed animals, however, were not different from controls suggesting compensatory changes in the thyroid gland to maintain homeostasis in exposed fetuses. The regional aberrations in thyroid morphology may impact on the post-natal life of the exposed offspring.

Mechanism-based testing strategy using in vitro approaches for identification of thyroid hormone disrupting chemicals

The thyroid hormone (TH) system is involved in several important physiological processes, including regulation of energy metabolism, growth and differentiation, development and maintenance of brain function, thermo-regulation, osmo-regulation, and axis of regulation of other endocrine systems, sexual behaviour and fertility and cardiovascular function. Therefore, concern about TH disruption (THD) has resulted in strategies being developed to identify THD chemicals (THDCs). Information on potential of chemicals causing THD is typically derived from animal studies. For the majority of chemicals, however, this information is either limited or unavailable. It is also unlikely that animal experiments will be performed for all THD relevant chemicals in the near future for ethical, financial and practical reasons. In addition, typical animal experiments often do not provide information on the mechanism of action of THDC, making it harder to extrapolate results across species. Relevant effects may not be identified in animal studies when the effects are delayed, life stage specific, not assessed by the experimental paradigm (e.g., behaviour) or only occur when an organism has to adapt to environmental factors by modulating TH levels. Therefore, in vitro and in silico alternatives to identify THDC and quantify their potency are needed. THDC have many potential mechanisms of action, including altered hormone production, transport, metabolism, receptor activation and disruption of several feed-back mechanisms. In vitro assays are available for many of these endpoints, and the application of modern '-omics' technologies, applicable for in vivo studies can help to reveal relevant and possibly new endpoints for inclusion in a targeted THDC in vitro test battery. Within the framework of the ASAT initiative (Assuring Safety without Animal Testing), an international group consisting of experts in the areas of thyroid endocrinology, toxicology of endocrine disruption, neurotoxicology, high-throughput screening, computational biology, and regulatory affairs has reviewed the state of science for (1) known mechanisms for THD plus examples of THDC; (2) in vitro THD tests currently available or under development related to these mechanisms; and (3) in silico methods for estimating the blood levels of THDC. Based on this scientific review, the panel has recommended a battery of test methods to be able to classify chemicals as of less or high concern for further hazard and risk assessment for THD. In addition, research gaps and needs are identified to be able to optimize and validate the targeted THD in vitro test battery for a mechanism-based strategy for a decision to opt out or to proceed with further testing for THD.

Contrasting retinoid and thyroid hormone status in differentially-contaminated northern fulmar colonies from the Canadian Arctic, Svalbard and the Faroe Islands

The northern fulmar (Fulmarus glacialis) has previously been shown to accumulate a wide range, and occasionally high concentrations of organochlorines (OCs) (e.g., PCBs, chlorobenzenes, DDT- and chlordane-related compounds, dioxins and furans). The present study aimed to investigate, using a meta-analysis approach, the variations in cytochrome P450 (CYP) 1A-like enzyme induction based on ethoxyresorufin O-deethylase activity (EROD) and selected physiological variables (retinoids and thyroid hormones) in northern fulmar breeding in three differentially OC-exposed populations: Nunavut (Canadian Arctic), Svalbard (Norwegian Arctic) and the Faroe Islands. Substantially higher (roughly two-fold) OC levels were uncovered in the liver of this long-lived fulmarine petrel breeding in the Faroe Islands relative to Svalbard and Nunavut. Liver levels of PCDDs, PCDFs and non-ortho PCBs in Faroe Islands fulmars were amongst the highest reported thus far in any seabirds from the northern regions. Positive correlations were depicted in combined fulmars (all three populations) between hepatic EROD activity and concentrations of OCs, in which strongest associations were found for dioxin-like compound (PCDFs and PCDDs) and TEQ concentrations. Moreover, moderate to strong positive correlations were found between liver OC concentrations and plasma total thyroxin (TT(4)) levels and TT(4)/total triiodothyronine (TT(3)) level ratios, as well as strong negative correlations between the same suite of OCs and plasma TT(3) levels. Hepatic OC concentrations (PCBs, PCDDs, PCDFs, HCB, p,p'-DDE and oxychlordane) also were positively correlated with hepatic retinyl palmitate levels which, in turn, were associated with a significant decrease in plasma retinol levels and somewhat unchanged liver retinol levels. The present meta-analysis investigation on northern fulmar breeding in three geographically-distant sites illustrated that OC exposure (mainly PCBs and dioxins/furans) may be associated with modulation of the thyroid and retinoid homeostasis. However, the impact of confounding environmental factors (e.g., temperature and nutritional status) on current physiological variable variations could not be ruled out, and thus any cause-effect linkages between thyroid and retinoid system perturbation and OC exposure cannot be ascertained.

Interactions between chemical and climate stressors: a role for mechanistic toxicology in assessing climate change risks

Incorporation of global climate change (GCC) effects into assessments of chemical risk and injury requires integrated examinations of chemical and nonchemical stressors. Environmental variables altered by GCC (temperature, precipitation, salinity, pH) can influence the toxicokinetics of chemical absorption, distribution, metabolism, and excretion as well as toxicodynamic interactions between chemicals and target molecules. In addition, GCC challenges processes critical for coping with the external environment (water balance, thermoregulation, nutrition, and the immune, endocrine, and neurological systems), leaving organisms sensitive to even slight perturbations by chemicals when pushed to the limits of their physiological tolerance range. In simplest terms, GCC can make organisms more sensitive to chemical stressors, while alternatively, exposure to chemicals can make organisms more sensitive to GCC stressors. One challenge is to identify potential interactions between nonchemical and chemical stressors affecting key physiological processes in an organism. We employed adverse outcome pathways, constructs depicting linkages between mechanism-based molecular initiating events and impacts on individuals or populations, to assess how chemical- and climate-specific variables interact to lead to adverse outcomes. Case examples are presented for prospective scenarios, hypothesizing potential chemical-GCC interactions, and retrospective scenarios, proposing mechanisms for demonstrated chemical-climate interactions in natural populations. Understanding GCC interactions along adverse outcome pathways facilitates extrapolation between species or other levels of organization, development of hypotheses and focal areas for further research, and improved inputs for risk and resource injury assessments.

Effects of polychlorobiphenyls, polybromodiphenylethers, organochlorine pesticides and their metabolites on vitamin A status in lactating grey seals

Polychlorobiphenyls (PCBs), polybromodiphenylethers (PBDEs) and organochlorine pesticides (OCPs), such as dichlorodiphenyltrichloroethane (DDT) and hexachlorobenzene (HCB), are considered as endocrine disruptors in laboratory and wild animals. This study investigated whether these compounds and their hydroxylated metabolites (HO-PCBs and HO-PBDEs) may affect the homoeostasis of vitamin A, a dietary hormone, in the blubber and serum of twenty lactating grey seals sampled at early and late lactation on the Isle of May, Scotland. The effect of naturally produced compounds such as the methoxylated (MeO)-PBDEs was also examined. Vitamin A levels in inner blubber (37±9 μg/g wet weight (ww) and 92±32 μg/g ww at early and late lactation, respectively) and serum (408±143 and 390±98 ng/ml at early and late lactation, respectively) appeared to be positively related to ΣPCBs, ΣPBDEs and several individual PCB and PBDE congeners in inner blubber and serum. These findings may suggest enhanced mobilisation of hepatic retinoid stores and redistribution in the blubber, a storage site for vitamin A in marine mammals. We have also reported that serum concentrations of ΣHO-PCBs and 4-OH-CB107 tended to increase with circulating vitamin A levels. Although the direction of the relationships may sometimes differ from those reported in the literature, our results are in agreement with previous findings highlighting a disruption of vitamin A homoeostasis in the blubber and bloodstream following exposure to environmental pollutants. The fact that vitamin A and PCBs appeared to share common mechanisms of mobilisation and transfer during lactation in grey seals (Debier et al., 2004; Vanden Berghe et al., 2010) may also play a role in the different relationships observed between vitamin A and lipophilic pollutants.

Polychlorinated biphenyls and their hydroxylated metabolites in wild fish from Wheatley Harbour Area of Concern, Ontario, Canada

Whole-body polychlorinated biphenyls (ΣPCBs) and plasma hydroxylated PCBs (OH-PCBs) concentrations were determined in brown bullhead (Ameiurus nebulosus) from Wheatley Harbour, Ontario, Canada. Elevated ΣPCBs in Wheatley Harbour are suspected to have originated from industrial waste disposal and/or discharges from nearby fish processing through discarding of fish remains. Mean ΣPCB concentrations in brown bullhead from Wheatley Harbour were approximately 250 ng/g wet weight compared with approximately 40 ng/g wet weight for brown bullhead from the reference sites, Hillman Marsh and Turkey Creek (both in Ontario, Canada). A significant relationship was found between the concentrations of non-ortho and mono-ortho PCB concentrations (toxic equivalents) and liver mixed-function oxygenase in brown bullhead (r = 0.74, p < 0.001). Plasma OH-PCB concentrations were greater in Wheatley Harbour brown bullhead than in those from Hillman Marsh (3.6 vs 1.5 ng/g wet wt, p < 0.01), and were detected infrequently in those from Turkey Creek (0.1 ng/g wet wt, n = 2). The OH-PCB congeners most frequently detected were 4'-OH-CB172, 3'-OH-CB180, 4-OH-CB187, 4-OH-CB146, 3-OH-CB138, and 4-OH-CB130, which are structurally similar to the thyroid hormones. To test the hypothesis of fish waste as the cause of the observed PCB contamination of Wheatley Harbour brown bullhead, a principal component analysis (PCA) was used to compare the brown bullhead PCB congener data with equivalent data for Lake Erie walleye, Lake Erie sediment, and industrial Aroclor mixtures. The relative proportions of each Aroclor mixture were estimated using the conjugated gradient method. The high similarity between the congener signatures for Lake Erie walleye and Wheatley Harbour brown bullhead supports the hypothesis of contamination from the fish processing industry.

Assessment of the health status of wild fish from the Wheatley Harbour Area of Concern, Ontario, Canada

The overall health and endocrine function of wild brown bullhead (Ameiurus nebulosus) and goldfish (Carassius auratus) from the Wheatley Harbour Area of Concern (Lake Erie, Ontario, Canada) was assessed using a suite of physiological and biochemical endpoints. Smaller gonads were detected in female brown bullhead and goldfish from Wheatley Harbour compared with Hillman Marsh (Ontario, Canada) reference fish. Female brown bullhead exhibited decreased in vitro synthesis of 17β-estradiol. Female goldfish had decreased plasma vitellogenin concentrations. Plasma testosterone and 11-ketotestosterone were significantly depressed in males of both species. Perturbations in the thyroid status were detected, but varied between sexes and species. Observed differences included lower plasma concentrations of thyroid hormones and/or elevated liver deiodinase activity. Histological evaluation of the thyroid tissue indicated that in the case of female goldfish, those perturbations stimulated the thyroid (as indicated by increased thyroid epithelial cell height) and partially depleted the thyroxine reserves, as indicated by decreased colloid and elevated thyroid activation index. Increased mixed-function oxygenase activity in brown bullhead from Wheatley Harbour was consistent with exposure to planar aromatic contaminants. A principal component analysis of selected variables showed the separation of fish by collection site. The endpoints most strongly associated with the separation were generally those exhibiting significant differences between sites. The results of the present study indicate that the health of fish populations within Wheatley Harbour warrants continued attention.

Polychlorinated biphenyls impair blood–brain barrier integrity via disruption of tight junction proteins in cerebrum, cerebellum and hippocampus of female Wistar rats

Polychlorinated biphenyls (PCBs) comprise a ubiquitous class of toxic substances associated with carcinogenic and tumor-promoting effects as well as neurotoxic properties. Reactive oxygen species, which is produced from PCBs, alters blood–brain barrier (BBB) integrity, which is paralleled by cytoskeletal rearrangements and redistribution and disappearance of tight junction proteins (TJPs) like claudin-5 and occludin. Quercetin, a potent antioxidant present in onion and other vegetables, appears to protect brain cells against oxidative stress, a tissue-damaging process associated with Alzheimer’s and other neurodegenerative disorders. The aim of this study is to analyze the role of quercetin on oxidative stress markers and transcription of transmembrane and cytoplasmic accessory TJPs on cerebrum, cerebellum and hippocampus of female rats exposed to PCBs. Rats were divided into the following four groups. Group I: received only vehicle (corn oil) intraperitoneally (i.p.); group II: received Aroclor 1254 at a dose of 2 mg/kg body weight (bwt)/day (i.p); group III: received Aroclor 1254 (i.p.) and simultaneously quercetin 50 mg/kg bwt/day through gavage and group IV: received quercetin alone gavage. From the experiment, the levels of hydrogen peroxide, lipid peroxidation and thiobarbituric acid reactive substances were observed to increase significantly in cerebrum, cerebellum and hippocampus as 50%, 25% and 20%, respectively, after exposure to PCB, and the messenger RNA expression of TJP in rats exposed to PCBs is decreased and is retrieved to the normal level simultaneously in quercetin-treated rats. Hence, quercetin can be used as a preventive medicine to PCBs exposure and prevents neurodegenerative disorders.

Dichlorodiphenyltrichloroethane (DDT), DDT metabolites and pregnancy outcomes

Organochlorine pesticides (OCPs) are persistent endocrine disruptors. OCPs cross the placenta; this prenatal exposure has been associated with adverse pregnancy outcomes. We investigated associations between prenatal exposure to OCPs and gestational age and birth weight in 600 infants born between 1960 and 1963. The primary OCP was 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (p,p'-DDT), its primary metabolite, 1,1'-dichloro-2,2'-bis(p-chlorophenyl)ethylene (p,p'-DDE) and the contaminant, 1,1,1-trichloro-2-(p-chlorophenyl)-2-(o-chlorophenyl)-ethane (o,p'-DDT). Regression analysis indicated that for each natural log unit increase in p,p'-DDT, birth weight increased by 274 g (95% CI: 122, 425) when controlling for p,p'-DDE and o,p'-DDT. At a given level of p,p'-DDT exposure, o,p'-DDT and p,p'-DDE were associated with decreased birth weight. p,p'-DDE was negatively associated with length of gestation, controlling for p,p'-DDT and o,p'-DDT. These findings suggest opposing associations between exposure to p,p'-DDT and p,p'-DDE and birth weight. We did not find evidence to support mediation by maternal thyroid hormone status nor that the association differed by sex.

Prenatal polychlorinated biphenyl exposure is associated with decreased gestational length but not birth weight: archived samples from the Child Health and Development Studies pregnancy cohort

BACKGROUND

Polychlorinated biphenyls (PCBs), known endocrine disruptors, were banned in 1979 but persist in the environment. Previous studies are inconsistent regarding prenatal exposure to PCBs and pregnancy outcomes. We investigated associations between prenatal exposure to PCBs and gestational length and birth weight.

METHODS

In a sample of 600 infants (born between 1960 and 1963) randomly selected from Child Health and Development Studies participants followed through adolescence we measured 11 PCB congeners in maternal post partum sera (within three days of delivery). Length of gestation was computed from the reported first day of the last menstrual period (LMP) and delivery date. Linear regression was used to estimate associations between PCB exposure and gestational age and birth weight, adjusting for potential confounders. PCBs were grouped according to hypothesized biological action (1b (sum of weak phenobarbital inducers), 2b (sum of limited dioxin activity), and 3 (sum of CYP1A and CYP2b inducers)) or degree of ortho- substitution (mono, di, tri). Secondary analyses examined associations between total PCB exposure and exposure to individual congeners.

RESULTS

Each unit increase in mono-ortho substituted PCBs was associated with a 0.30 week decrease (95% confidence interval (CI) -0.59, -0.016), corresponding to a 2.1 (95% CI -4.13, -0.11) day decrease in length of gestation. Similar associations were estimated for di-ortho substituted PCBs, (1.4 day decrease; (95% CI -2.9, 0.1)) and group 3 PCBs (0.84 day decrease; (95% CI -1.8, 0.11). We found similar associations in congener specific analyses and for the sum of congeners.

CONCLUSIONS

Our study provides new evidence that PCB exposure shortens length of gestation in humans. This may have public health implications for population exposures.

Cosmetics as a potential source of environmental contamination in the UK

Chemicals of emerging concern (CECs) are frequently used in cosmetic formulations and can potentially reach the environment at concentrations that may cause harm. A methodology was developed to assess over 120 chemicals assembled from product ingredient listings to identify and validate potential CECs in cosmetics, based on Annex XIII of REACH legislation. Ten potential CECs were identified: polydimethylsiloxane, butylated hydroxylanisole (BHA), butylated hydroxytoluene, triclosan, nano titanium dioxide, nano zinc oxide, butylparaben, diethyl phthalate, octinoxate methoxycinnamate and benzophenone. These chemicals were quantified based on their consumption and concentrations in cosmetics and percentage market penetration. The initial predicted environmental concentrations (PEC initial) were estimated to determine their exposure to the environment. With the exception of BHA, the PEC initial highlighted levels of exposure to the environment that triggered the need for further investigation of the chemicals. These chemicals were linked to cosmetics to highlight products with the potential to cause environmental harm. Skin care products had the highest quantities of CECs, with titanium dioxide and zinc oxide nanomaterials being dominant potential contaminants. Further research is required to assess the exposure pathways and fate of these chemicals to determine environmental risks associated with their use and disposal.

Adverse effects in risk assessment: modeling polychlorinated biphenyls and thyroid hormone disruption outcomes in animals and humans

There is a growing need for quantitative approaches to extrapolate relationships between chemical exposures and early biological perturbations from animals to humans given increasing use of biological assays to evaluate toxicity pathways. We have developed such an approach using polychlorinated biphenyls (PCBs) and thyroid hormone (TH) disruption as a case study. We reviewed and identified experimental animal literature from which we developed a low-dose, linear model of PCB body burdens and decrements in free thyroxine (FT(4)) and total thyroxine (TT(4)), accounting for 33 PCB congeners; extrapolated the dose-response from animals to humans; and compared the animal dose-response to the dose-response of PCB body burdens and TH changes from eleven human epidemiological studies. We estimated a range of potencies for PCB congeners (over 4 orders of magnitude), with the strongest for PCB 126. Our approach to developing toxic equivalency models produced relative potencies similar to the toxicity equivalency factors (TEFs) from the World Health Organization (WHO). We generally found that the dose-response extrapolated from the animal studies tends to under-predict the dose-response estimated from human epidemiological studies. A quantitative approach to evaluating the relationship between chemical exposures and TH perturbations, based on animal data can be used to assess human health consequences of thyroid toxicity and inform decision-making.

Thyroid hormone metabolism and environmental chemical exposure

BACKGROUND

Polychlorinated dioxins and -furans (PCDD/Fs) and polychlorinated-biphenyls (PCBs) are environmental toxicants that have been proven to influence thyroid metabolism both in animal studies and in human beings. In recent years polybrominated diphenyl ethers (PBDEs) also have been found to have a negative influence on thyroid hormone metabolism. The lower brominated flame retardants are now banned in the EU, however higher brominated decabromo-diphenyl ether (DBDE) and the brominated flame retardant hexabromocyclododecane (HBCD) are not yet banned. They too can negatively influence thyroid hormone metabolism. An additional brominated flame retardant that is still in use is tetrabromobisphenol-A (TBBPA), which has also been shown to influence thyroid hormone metabolism.Influences of brominated flame retardants, PCDD/F's and dioxin like-PCBs (dl-PCB's) on thyroid hormone metabolism in adolescence in the Netherlands will be presented in this study and determined if there are reasons for concern to human health for these toxins. In the period 1987-1991, a cohort of mother-baby pairs was formed in order to detect abnormalities in relation to dioxin levels in the perinatal period. The study demonstrated that PCDD/Fs were found around the time of birth, suggesting a modulation of the setpoint of thyroid hormone metabolism with a higher 3,3', 5,5'tetrathyroxine (T4) levels and an increased thyroid stimulating hormone (TSH). While the same serum thyroid hormone tests (- TSH and T4) were again normal by 2 years of age and were still normal at 8-12 years, adolescence is a period with extra stress on thyroid hormone metabolism. Therefore we measured serum levels of TSH, T4, 3,3',5- triiodothyronine (T3), free T4 (FT4), antibodies and thyroxine-binding globulin (TBG) in our adolescent cohort.

METHODS

Vena puncture was performed to obtain samples for the measurement of thyroid hormone metabolism related parameters and the current serum dioxin (PCDD/Fs), PCB and PBDE levels.

RESULTS

The current levels of T3 were positively correlated to BDE-99. A positive trend with FT4 and BDE-99 was also seen, while a positive correlation with T3 and dl-PCB was also seen. No correlation with TBG was seen for any of the contaminants. Neither the prenatal nor the current PCDD/F levels showed a relationship with the thyroid parameters in this relatively small group.

CONCLUSION

Once again the thyroid hormone metabolism (an increase in T3) seems to have been influenced by current background levels of common environmental contaminants: dl-PCBs and BDE-99. T3 is a product of target organs and abnormalities might indicate effects on hormone transporters and could cause pathology. While the influence on T3 levels may have been compensated, because the adolescents functioned normal at the time of the study period, it is questionable if this compensation is enough for all organs depending on thyroid hormones.

Differential changes of fat-soluble vitamins and pollutants during lactation in northern elephant seal mother-pup pairs

We investigated the changes of vitamins A and E as well as PCBs and DDTs during lactation in northern elephant seal (Mirounga angustirostris) mother-pup pairs. On average, milk vitamin A concentrations were 6 times higher during late lactation than during early lactation, a pattern that differs dramatically from terrestrial mammals. Vitamin A concentrations also significantly increased in the inner blubber throughout lactation, whereas they remained constant in the outer blubber. Similar dynamics were observed for PCBs and DDTs in maternal blubber and milk. Blubber appears to be an important storage site for vitamin A and organochlorines in seals and a direct transfer of those molecules to the mammary gland may occur. The dynamics of vitamin A, PCBs and DDTs differed from those of vitamin E. There was a significant drop in milk vitamin E concentrations between early and late lactation, which is the usual pattern observed in terrestrial mammals. The dynamics of vitamin E in the blubber layers also differed from those of vitamin A, suggesting different mechanisms of mobilization and transfer into the milk.

Triiodothyronine-induced changes in the zebrafish transcriptome during the eleutheroembryonic stage: implications for bisphenol A developmental toxicity

Thyroid disruption during early development is a current matter of concern due to its significant human health implications. We present here a transcriptome analysis of thyroid hormone-regulated genes in zebrafish during the eleutheroembryonic stage (days 2-5 post fertilization) to detect potential markers of thyroid disruption. Exposure to 3,5,3'-triiodo-l-thyroxine (T3, 50 nM) induced changes in a minor portion (less than 2%) of the zebrafish transcriptome, with a significant fraction of genes involved in the haematopoietic system, eye formation, and ossification/skeletal system, including the thyroid receptor thra gene. Some of the transcriptomic changes were reflected macroscopically, as an allometric decrease of eye size and an increase on thra hybridization signal in the skeletal tissue. Using this information, changes on transcription of three genes (adult alpha globin gene si:ch211-5 k11.6, embryonic globin gene hbae3, and long wavelength cone opsin gene opn1/w1) were analyzed to monitor the effect of the suspected thyroid disrupter bisphenol A (BPA) on the thyroid system during this period of development of zebrafish. BPA acted as a weak T3 agonist when tested alone, but it strongly enhanced the effect of subsaturating concentrations of T3. In thyroxine immunofluorescence quantitative disruption tests (TIQDT), BPA did not prevent the ability of thyroid follicles to synthesize thyroxine, a landmark for direct goitrogens. Our results suggest that BPA potentiates the effect of endogenous T3 in early development and demonstrate the requirement for the use of in vivo, multi-endpoint methods to evaluate thyroid disruption hazards on early developmental processes in vertebrates.

Levels of selected persistent organic pollutants in blood from delivering women in seven selected areas of São Paulo State, Brazil

Persistent organic pollutants (POPs) present in the living environment are thought to have detrimental health effects on the population, with pregnant women and the developing foetus being at highest risk. We report on the levels of selected POPs in maternal blood of 155 delivering women residing in seven regions within the São Paulo State, Brazil. The following selected POPs were measured in the maternal whole blood: 12 polychlorinated biphenyls (PCBs) congeners (IUPAC Nos. 99, 101, 118, 138, 153, 156, 163, 170, 180, 183, 187, 194); dichlordiphenyltrichloroethane p,p'-DDT, diphenyldichloroethylene p,p'-DDE and other pesticides such as hexachlorocyclohexanes (α-HCH, β-HCH, γ-HCH), hexachlorobenzene (HCB), chlordane derivatives cis-chlordane, trans-chlordane, oxy-chlordane, cis-nonachlor and trans-nonachlor. Statistical comparisons between regions were performed only on compounds having concentrations above LOD in 70% of the samples. PCB118 congener was found to be highest in the industrial site (mean 4.97 ng/g lipids); PCB138 congener concentration was highest in the Urban 3 site (mean 4.27 ng/g lipids) and congener PCB153 was highest in the industrial and Urban 3 sites with mean concentration of 7.2 ng/g lipids and 5.89ng/g lipids respectively. Large differences in levels of p,p'-DDE between regions were observed with the Urban 3 and industrial sites having the highest concentrations of 645 ng/g lipids and 417 ng/g lipids, respectively; β-HCH was found to be highest in the Rural 1 site; the γ-HCH in Rural 1 and industrial; the HCB in the Rural 1 and industrial sites and oxy-chlordane and t-NC in the Rural 2 sites. An association between levels of some contaminants and maternal age and parity was also found.

Developmental coexposure to polychlorinated biphenyls and polybrominated diphenyl ethers has additive effects on circulating thyroxine levels in rats

Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) are widespread environmental contaminants found in seafood and dairy products. PCBs and PBDEs are structurally similar chemicals and affect thyroid hormone function and behavior in children and laboratory rodents. Although coexposure frequently exists, the in vivo developmental effects of combined exposure to PCBs and PBDEs on thyroxine (T4) levels are unknown. We examined the effects of PCB and PBDE coexposure from gestational day 6 through postnatal day (p) 21, alone and in combination, on T4 levels in rat offspring. In males, exposure to PCBs and PBDEs at 1.7, 5, 10, 20, 40, and 60 μmol/kg/day induced equivalent and dose-dependent reductions in T4 from p 7 to p 21. Exposure to equimolar mixtures of PCBs and PBDEs at 3.4, 10, 20, 40, and 80 μmol/kg/day additively reduced T4 from p 7 to p 21 in males. In a second series of experiments, we determined sex effects on the mixture exposures and found that coexposure to PCBs and PBDEs had similar additive effects on T4 levels in male and female offspring. This study demonstrates that equimolar exposure to PCBs and PBDEs induces similar reductions in T4 levels and that coexposure to a mixture of PCBs and PBDEs has additive effects on T4 levels. These thyroid hormone effects of coexposure to PCBs and PBDEs are important when considering the cumulative effects of coexposure to multiple environmental thyroid hormone-disrupting agents in risk assessment for developmental disorders.

PCBs and OH-PCBs in polar bear mother-cub pairs: a comparative study based on plasma levels in 1998 and 2008

The aim of this study was to examine the plasma concentrations and prevalence of polychlorinated biphenyls (PCBs) and hydroxylated PCB-metabolites (OH-PCBs) in polar bear (Ursus maritimus) mothers (n=26) and their 4 months old cubs-of-the-year (n=38) from Svalbard to gain insight into the mother-cub transfer, biotransformation and to evaluate the health risk associated with the exposure to these contaminants. As samplings were performed in 1997/1998 and 2008, we further investigated the differences in levels and pattern of PCBs between the two sampling years. The plasma concentrations of Σ(21)PCBs (1997/1998: 5710 ± 3090 ng/g lipid weight [lw], 2008: 2560 ± 1500 ng/g lw) and Σ(6)OH-PCBs (1997/1998: 228 ± 60 ng/g wet weight [ww], 2008: 80 ± 38 ng/g ww) in mothers were significantly lower in 2008 compared to in 1997/1998. In cubs, the plasma concentrations of Σ(21)PCBs (1997/1998: 14680 ± 5350 ng/g lw, 2008: 6070 ± 2590 ng/g lw) and Σ(6)OH-PCBs (1997/1998: 98 ± 23 ng/g ww, 2008: 49 ± 21 ng/g ww) were also significantly lower in 2008 than in 1997/1998. Σ(21)PCBs in cubs was 2.7 ± 0.7 times higher than in their mothers. This is due to a significant maternal transfer of these contaminants. In contrast, Σ(6)OH-PCBs in cubs were approximately 0.53 ± 0.16 times the concentration in their mothers. This indicates a lower maternal transfer of OH-PCBs compared to PCBs. The majority of the metabolite/precursor-ratios were lower in cubs compared to mothers. This may indicate that cubs have a lower endogenous capacity to biotransform PCBs to OH-PCBs than polar bear mothers. Exposure to PCBs and OH-PCBs is a potential health risk for polar bears, and the levels of PCBs and OH-PCBs in cubs from 2008 were still above levels associated with health effects in humans and wildlife.

Birth weight and prenatal exposure to polychlorinated biphenyls (PCBs) and dichlorodiphenyldichloroethylene (DDE): a meta-analysis within 12 European Birth Cohorts

OBJECTIVES

Exposure to high concentrations of persistent organochlorines may cause fetal toxicity, but the evidence at low exposure levels is limited. Large studies with substantial exposure contrasts and appropriate exposure assessment are warranted. Within the framework of the EU (European Union) ENRIECO (ENvironmental Health RIsks in European Birth Cohorts) and EU OBELIX (OBesogenic Endocrine disrupting chemicals: LInking prenatal eXposure to the development of obesity later in life) projects, we examined the hypothesis that the combination of polychlorinated biphenyls (PCBs) and dichlorodiphenyldichloroethylene (DDE) adversely affects birth weight.

METHODS

We used maternal and cord blood and breast milk samples of 7,990 women enrolled in 15 study populations from 12 European birth cohorts from 1990 through 2008. Using identical variable definitions, we performed for each cohort linear regression of birth weight on estimates of cord serum concentration of PCB-153 and p,p´-DDE adjusted for gestational age and a priori selected covariates. We obtained summary estimates by meta-analysis and performed analyses of interactions.

RESULTS

The median concentration of cord serum PCB-153 was 140 ng/L (range of cohort medians 20-484 ng/L) and that of p,p´-DDE was 528 ng/L (range of cohort medians 50-1,208 ng/L). Birth weight decreased with increasing cord serum concentration of PCB-153 after adjustment for potential confounders in 12 of 15 study populations. The meta-analysis including all cohorts indicated a birth weight decline of 150 g [95% confidence interval (CI): -250, -50 g] per 1-µg/L increase in PCB-153, an exposure contrast that is close to the range of exposures across the cohorts. A 1-µg/L increase in p,p´-DDE was associated with a 7-g decrease in birth weight (95% CI: -18, 4 g).

CONCLUSIONS

The findings suggest that low-level exposure to PCB (or correlated exposures) impairs fetal growth, but that exposure to p,p´-DDE does not. The study adds to mounting evidence that low-level exposure to PCBs is inversely associated with fetal growth.

Molecular profiling of marine fauna: integration of omics with environmental assessment of the world's oceans

Many species that contribute to the commercial and ecological richness of our marine ecosystems are harbingers of environmental change. The ability of organisms to rapidly detect and respond to changes in the surrounding environment represents the foundation for application of molecular profiling technologies towards marine sentinel species in an attempt to identify signature profiles that may reside within the transcriptome, proteome, or metabolome and that are indicative of a particular environmental exposure event. The current review highlights recent examples of the biological information obtained for marine sentinel teleosts, mammals, and invertebrates. While in its infancy, such basal information can provide a systems biology framework in the detection and evaluation of environmental chemical contaminant effects on marine fauna. Repeated evaluation across different seasons and local marine environs will lead to discrimination between signature profiles representing normal variation within the complex milieu of environmental factors that trigger biological response in a given sentinel species and permit a greater understanding of normal versus anthropogenic-associated modulation of biological pathways, which prove detrimental to marine fauna. It is anticipated that incorporation of contaminant-specific molecular signatures into current risk assessment paradigms will lead to enhanced wildlife management strategies that minimize the impacts of our industrialized society on marine ecosystems.

Dietary contaminant exposure affects plasma testosterone, but not thyroid hormones, vitamin A, and vitamin E, in male juvenile arctic foxes (Vulpes lagopus)

Levels of persistent organic pollutants (POP), such as polychlorinated biphenyls (PCB), are high in many Arctic top predators, including the Arctic fox (Vulpes lagopus). The aim of this study was to examine possible endocrine-disruptive effects of dietary POP exposure in male juvenile Arctic foxes in a controlled exposure experiment. The study was conducted using domesticated farmed blue foxes (Vulpes lagopus) as a model species. Two groups of newly weaned male foxes received a diet supplemented with either minke whale (Baleneoptera acutorostrata) blubber that was naturally contaminated with POP (exposed group, n = 5 or 21), or pork (Sus scrofa) fat (control group, n = 5 or 21). When the foxes were 6 mo old and had received the 2 diets for approximately 4 mo (147 d), effects of the dietary exposure to POP on plasma concentrations of testosterone (T), thyroid hormones (TH), thyroid-stimulating hormone (TSH), retinol (vitamin A), and tocopherol (viramin E) were examined. At sampling, the total body concentrations of 104 PCB congeners were 0.1 ± 0.03 μg/g lipid weight (l.w.; n = 5 [mean ± standard deviation]) and 1.5 ± 0.17 μg/g l.w. (n = 5) in the control and exposed groups, respectively. Plasma testosterone concentrations in the exposed male foxes were significantly lower than in the control males, being approximately 25% of that in the exposed foxes. There were no between-treatment differences for TH, TSH, retinol, or tocopherol. The results suggest that the high POP levels experienced by costal populations of Arctic foxes, such as in Svalbard and Iceland, may result in delayed masculine maturation during adolescence. Sex hormone disruption during puberty may thus have lifetime consequences on all aspects of reproductive function in adult male foxes.

Histologic, immunologic and endocrine biomarkers indicate contaminant effects in fishes of the Ashtabula River

The use of fish as sentinels of aquatic ecosystem health is a biologically relevant approach to environmental monitoring and assessment. We examined the health of the Ashtabula River using histologic, immunologic, and endocrine biomarkers in brown bullhead (BB; Ameiurus nebulosus) and largemouth bass (Micropterus salmoides) and compared fish collected from a reference site (Conneaut Creek). Seasonal analysis was necessary to distinguish differences in fish between the two rivers. Overall BB from the Ashtabula River had a lower condition factor and significantly more macrophage aggregates than those from the reference site. Reduced bactericidal and cytotoxic-cell activity was observed in anterior kidney leukocytes from both BB and largemouth bass from the Ashtabula River. Lower plasma thyroxine and triiodo-L-thyronine in both species in the Ashtabula River indicated disruption of the thyroid axis. Differences in physiological biomarker responses were supported by body burden chemical concentrations when data were analyzed on a seasonal basis. The use of two fish species added a level of rigor that demonstrated biological effects were not exclusive to a single species. The results provide strong evidence that contaminants have affected fish in the Ashtabula River, a Great Lakes Area of Concern, and provide a baseline by which to evaluate remediation activities.

Halogenated organic contaminants and their correlations with circulating thyroid hormones in developing Arctic seabirds

Thyroid hormones are essential for normal growth and development and disruption of thyroid homeostasis can be critical to young developing individuals. The aim of the present study was to assess plasma concentrations of halogenated organic contaminants (HOCs) in chicks of two seabird species and to investigate possible correlations of HOCs with circulating thyroid hormone (TH) concentrations. Plasma from black-legged kittiwake (Rissa tridactyla) and northern fulmar (Fulmarus glacialis) chicks were sampled in Kongsfjorden, Svalbard in 2006. The samples were analyzed for thyroid hormones and a wide range of HOCs (polychlorinated biphenyls (PCBs), hydroxylated (OH-) and methylsulphoned (MeSO-) PCB metabolites, organochlorine pesticides (OCPs), brominated flame retardants (BFRs), and perfluorinated compounds (PFCs)). Concentrations of HOCs were generally low in kittiwake and fulmar chicks compared to previous reports. HOC concentrations were five times higher in fulmar chicks compared to in kittiwake chicks. PFCs dominated the summed HOCs concentrations in both species (77% in kittiwakes and 69% in fulmars). Positive associations between total thyroxin (TT4) and PFCs (PFHpS, PFOS, PFNA) were found in both species. Although correlations do not implicate causal relationships per se, the correlations are of concern as disruption of TH homeostasis may cause developmental effects in young birds.

PCB-associated changes in mRNA expression in killer whales (Orcinus orca) from the NE Pacific Ocean

Killer whales in the NE Pacific Ocean are among the world's most PCB-contaminated marine mammals, raising concerns about implications for their health. Sixteen health-related killer whale mRNA transcripts were analyzed in blubber biopsies collected from 35 free-ranging killer whales in British Columbia using real-time quantitative polymerase chain reaction. We observed PCB-related increases in the expression of five gene targets, including the aryl hydrocarbon receptor (AhR; r(2) = 0.83; p < 0.001), thyroid hormone α receptor (TRα; r(2) = 0.64; p < 0.001), estrogen α receptor (ERα; r(2) = 0.70; p < 0.001), interleukin 10 (IL-10; r(2) = 0.74 and 0.68, males and females, respectively; p < 0.001), and metallothionein 1 (MT1; r(2) = 0.58; p < 0.001). Best-fit models indicated that population (dietary preference), age, and sex were not confounding factors, except for IL-10, where males differed from females. While the population-level consequences are unclear, the PCB-associated alterations in mRNA abundance of such pivotal end points provide compelling evidence of adverse physiological effects of persistent environmental contaminants in these endangered killer whales.

The OBELIX project: early life exposure to endocrine disruptors and obesity

The hypothesis of whether early life exposure (both pre- and early postnatal) to endocrine-disrupting chemicals (EDCs) may be a risk factor for obesity and related metabolic diseases later in life will be tested in the European research project OBELIX (OBesogenic Endocrine disrupting chemicals: LInking prenatal eXposure to the development of obesity later in life). OBELIX is a 4-y project that started in May 2009 and which has the following 5 main objectives: 1) to assess early life exposure in humans to major classes of EDCs identified as potential inducers of obesity (ie, dioxin-like compounds, non-dioxin-like polychlorinated biphenyls, organochlorine pesticides, brominated flame retardants, phthalates, and perfluorinated compounds) by using mother-child cohorts from 4 European regions with different food-contaminant exposure patterns; 2) to relate early life exposure to EDCs with clinical markers, novel biomarkers, and health-effect data related to obesity; 3) to perform hazard characterization of early life exposure to EDCs for the development of obesity later in life by using a mouse model; 4) to determine mechanisms of action of obesogenic EDCs on developmental programming with in vivo and in vitro genomics and epigenetic analyses; and 5) to perform risk assessments of prenatal exposure to obesogenic EDCs in food by integrating maternal exposure through food-contaminant exposure and health-effect data in children and hazard data in animal studies.

Parallel biotransformation of tetrabromobisphenol A in Xenopus laevis and mammals: Xenopus as a model for endocrine perturbation studies

The flame retardant tetrabromobisphenol A (TBBPA) is a high production flame retardant that interferes with thyroid hormone (TH) signaling. Despite its rapid metabolism in mammals, TBBPA is found in significant amounts in different tissues. Such findings highlight first a need to better understand the effects of TBBPA and its metabolites and second the need to develop models to address these questions experimentally. We used Xenopus laevis tadpoles to follow radiolabeled (14)C-TBBPA uptake and metabolism. Extensive and rapid uptake of radioactivity was observed, tadpoles metabolizing > 94% of (14)C-TBBPA within 8 h. Four metabolites were identified in water and tadpole extracts: TBBPA-glucuronide, TBBPA-glucuronide-sulfate, TBBPA-sulfate, and TBBPA-disulfate. These metabolites are identical to the TBBPA conjugates characterized in mammals, including humans. Most radioactivity (> 75%) was associated with sulfated conjugates. The antithyroid effects of TBBPA and the metabolites were compared using two in vivo measures: tadpole morphology and an in vivo tadpole TH reporter gene assay. Only TBBPA, and not the sulfated metabolites, disrupted thyroid signaling. Moreover, TBBPA treatment did not affect expression of phase II enzymes involved in TH metabolism, suggesting that the antithyroid effects of TBBPA are not due to indirect effects on TH metabolism. Finally, we show that only the parent TBBPA inhibits T3-induced transactivation in cells expressing human, zebrafish, or X. laevis TH receptor, TRα. We conclude, first, that perturbation of thyroid signaling by TBBPA is likely due to rapid direct action of the parent compound, and second, that Xenopus is an excellent vertebrate model for biotransformation studies, displaying homologous pathways to mammals.

Blood-based biomarkers of selenium and thyroid status indicate possible adverse biological effects of mercury and polychlorinated biphenyls in Southern Beaufort Sea polar bears

We examined biomarkers of selenium status (whole blood Se; serum Se; glutathione peroxidase activity) and thyroid status (concentrations and ratios of thyroxine, T4; tri-iodothyronine, T3; albumin) in polar bears to assess variations among cohorts, and relationships to circulating concentrations of contaminants. Concentrations of total mercury (Hg) in whole blood were similar among cohorts (prime aged males and females, older animals, ages≥16 years, and young animals, ages 1-5 years; 48.44±35. 81; p=0.253). Concentrations of sum of seven polychlorinated biphenyls (∑PCB7) in whole blood were greater in females (with and without cubs, 26.44±25.82 ng/g ww) and young (26.81±10.67 ng/g ww) compared to males (8.88±5.76 ng/g ww, p<0.001), and significantly related to reduced body condition scores (p<0.001). Concentrations of Se and albumin were significantly greater in males than females (whole blood Se, males, 42.34 pmol/g ww, females, 36.25±6.27 pmol/g ww, p=0.019; albumin, males, 4.34±0.34 g/dl, females, 4.10±0.29 g/dL, p=0.018). Glutathione peroxidase activity ranged from 109.1 to 207.8 mU/mg hemoglobin, but did not differ significantly by sex or age (p>0.08). Thyroid hormones were greater in females (solitary females and females with cubs) compared to males (p<0.001). Biomarkers of Se status and concentrations of T3 were significantly positively related to Hg in all prime aged polar bears (p<0.03). Albumin concentrations were significantly positively related to total TT4, and significantly negatively related to concentrations of ∑PCB7 (p<0.003). Total thyroxine (TT4) was significantly negatively associated with blood concentrations of ∑PCB7 in solitary females (p=0.045). These data suggest that female polar bears were more susceptible to changes in blood-based biomarkers of selenium and thyroid status than males. Further classifications of the physiologic states of polar bears and repeated measures of individuals over time are needed to accurately assess the biological impact of combined toxicant exposures.

Associations between polybrominated diphenyl ether (PBDE) flame retardants, phenolic metabolites, and thyroid hormones during pregnancy

BACKGROUND

Polybrominated diphenyl ethers (PBDEs) are chemical additives used as flame retardants in commercial products. PBDEs are bioaccumulative and persistent and have been linked to several adverse health outcomes.

OBJECTIVES

This study leverages an ongoing pregnancy cohort to measure PBDEs and PBDE metabolites in serum collected from an understudied population of pregnant women late in their third trimester. A secondary objective was to determine whether the PBDEs or their metabolites were associated with maternal thyroid hormones.

METHODS

One hundred forty pregnant women > 34 weeks into their pregnancy were recruited into this study between 2008 and 2010. Blood samples were collected during a routine prenatal clinic visit. Serum was analyzed for a suite of PBDEs, three phenolic metabolites (i.e., containing an -OH moiety), and five thyroid hormones.

RESULTS

PBDEs were detected in all samples and ranged from 3.6 to 694 ng/g lipid. Two hydroxylated BDE congeners (4´-OH-BDE 49 and 6-OH-BDE 47) were detected in > 67% of the samples. BDEs 47, 99, and 100 were significantly and positively associated with free and total thyroxine (T4) levels and with total triiodothyronine levels above the normal range. Associations between T4 and PBDEs remained after controlling for smoking status, maternal age, race, gestational age, and parity.

CONCLUSIONS

PBDEs and OH-BDEs are prevalent in this cohort, and levels are similar to those in the general population. Given their long half-lives, PBDEs may be affecting thyroid regulation throughout pregnancy. Further research is warranted to determine mechanisms through which PBDEs affect thyroid hormone levels in developing fetuses and newborn babies.

Biomarker responses associated with halogenated organic contaminants in northern fulmars (Fulmarus glacialis) breeding in the Canadian Arctic

We examined relationships between hepatic concentrations of halogenated organic contaminants and ethoxyresorufin O-deethylase (EROD) activity and retinoid (vitamin A) concentrations in livers, as well as retinol and thyroid hormone (TT(3), TT(4)) levels in blood plasma, of northern fulmars at two breeding colonies in the Canadian High Arctic. Biomarker levels or responses did not differ significantly between males and females at either colony, nor was there any significant difference between colonies. No significant relationships were found between thyroid hormone or hepatic retinoid concentrations and any of the dioxin-like compounds or their Toxic Equivalents (TEQs) although significant positive correlations were found with plasma retinol (p < 0.03). EROD activity was significantly correlated with hepatic dioxin-like compounds and their TEQs (p < 0.001) as well as total PCBs (p < 0.01), which suggests that EROD induction occurs in northern fulmars at environmentally-relevant concentrations.

Levels and patterns of hydroxylated polychlorinated biphenyls (OH-PCBs) and their associations with thyroid hormones in hooded seal (Cystophora cristata) mother-pup pairs

Blood (plasma/serum) samples from 14 adult female and their pups (1-4 days old) captured in the West Ice, east of Greenland were analysed for concentrations of total and free thyroxine and triiodothyronine (TT4, FT4, TT3, FT3), and hydroxylated polychlorinated biphenyls (OH-PCBs). The levels of all thyroid hormones (THs) were significantly higher in pups than in mothers. Sum OH-PCB levels (ΣOH-PCBs: 4-OH-CB107, 3'-OH-CB138, 4-OH-CB146, 4'-OH-CB172, 4-OH-CB187) were significantly higher in mothers (3.98 ± 1.55 pmol/g; 1.40 ± 0.54 ng/g wet weight) as compared to pups (1.95 ± 0.78 pmol/g; 0.68 ± 0.28 ng/g wet weight). Plasma levels of TT4 and FT4 in mothers increased as a function of pup age, as did levels of individual OH-PCBs in both mothers and pups. The pattern of OH-PCBs in the pups was similar to their mothers. We suggest that OH-PCBs found in pups are transferred from their mothers during gestation and that the transfer also continues after parturition via milk. Principal component analysis (PCA) showed that in pups, 4-OH-CB107 and 3'-OH-CB138 were negatively associated with FT4:FT3 and TT3:FT3 ratios, respectively. These relationships were confirmed by partial correlation analysis correcting for pup age. PCA suggested that 4'-OH-CB172 and 4-OH-CB187 were negatively associated with TT3 in mothers. However, this was not confirmed by correlation tests. Although statistical relationships should be interpreted with caution, the study indicates that young developing seals are more sensitive compared to adults with respect to TH-related effects of OH-PCBs.

Thyroid dysfunction in sea bass (Dicentrarchus labrax): underlying mechanisms and effects of polychlorinated biphenyls on thyroid hormone physiology and metabolism

The current study examines the effect of subchronic exposure to a mixture of Aroclor standards on thyroid hormone physiology and metabolism in juvenile sea bass. The contaminant mixture was formulated to reflect the persistent organic pollution to which the European sea bass population could conceivably be exposed (0.3, 0.6 and 1.0 μg Σ7PCBs per g food pellets) and higher (10 μg Σ7PCBs per g food pellets). After 120 days of exposure, histomorphometry of thyroid tissue, muscular thyroid hormone concentration and activity of enzymes involved in metabolism of thyroid hormones were assessed. Mean concentrations of 8, 86, 142, 214 and 2279 ng g(-1)ww (Σ7 ICES PCB congeners) were determined after 120 days exposure. The results show that the effects of PCB exposures on the thyroid system are dose-dependent. Exposure to environmentally relevant doses of PCB (0.3-1.0 μg Σ7PCBs per g food pellets) induced a larger variability of the follicle diameter and stimulated hepatic T(4) outer ring deiodinase. Muscular thyroid hormone levels were preserved thanks to the PCB induced changes in T(4) dynamics. At 10 times higher concentrations (10 μg Σ7PCBs per g food pellets) an important depression of T(3) and T(4) levels could be observed which are apparently caused by degenerative histological changes in the thyroid tissue.

Blood plasma sample preparation method for the assessment of thyroid hormone-disrupting potency in effect-directed analysis

A sample preparation method combining solid-phase extraction (SPE) and liquid-liquid extraction (LLE) was developed to be used in Effect-Directed Analysis (EDA) of blood plasma. Until now such a method was not available. It can be used for extraction of a broad range of thyroid hormone (TH)-disruptors from plasma with high recoveries. Validation of the method using spiked cow plasma showed good recoveries for hydroxylated polybrominated diphenyl ethers (OH-PBDEs; 93.8 ± 19.5%), hydroxylated polychlorinated biphenyls (OH-PCBs; 93.8 ± 15.5%), other halogenated phenols (OHPs; 107 ± 8.1%), and for short-chain (<8 C-atoms) perfluoroalkyl substances (PFASs; 85.2 ± 24.6%). In the same extracts, the potency of the compound classes spiked to the cow plasma to competitively bind to transthyretin (TTR) was recovered by 84.9 ± 8.8%. Furthermore, the SPE-LLE method efficiently removed endogenous THs from the extracts, thereby eliminating their possible contribution to the binding assay response. The SPE-LLE method was applied to polar bear plasma samples to investigate its applicability in future EDA studies focusing on TH-disrupting compounds in this top predator species that is exposed to relatively high levels of bioaccumulating pollutants. A first screening revealed TTR-binding potency in the polar bear plasma extracts, which could be explained for 60-85% by the presence of OH-PCBs.

Environmental contaminants and children's health: Cause for concern, time for action

The present paper provides an outline of the developmental and behavioural characteristics that make children, especially the fetus and young child, more vulnerable to contaminants than adults. The major categories of contaminants are briefly described. The evidence for their possible effects on neurobehavioural development; immune, endocrine and respiratory systems; childhood cancer based on research studies with animals; children exposed to catastrophic 'accidents' involving overdose exposures; and pregnant women and children from communities with high 'background' levels of contamination who participated in studies is reviewed. While the data are worrisome, especially for children living in northern and certain urban communities, much remains to be learned about possible subtle effects and the potential for long term effects of the current background contamination experienced by the majority of Canadian children before its significance to their health can be fully evaluated. The present regulatory processes, which are based on risk assessment, are so cumbersome and costly that the great majority of chemicals in use have not been fully evaluated, and the ingenuity of new chemical production continually exceeds the capacity to test the new chemicals. Moreover, despite past insistence on scientific proof of adverse effects and safety, unanticipated effects have occurred that will threaten the sustainability of human life unless more effective control measures are taken to limit the release of toxic substances and persistent chemicals into the environment. Therefore, the shortcomings of risk assessment are discussed, and the precautionary principle, which is used in some countries and is proposed for use internationally as an alternative measure that may offer improved control for the future, is outlined. Finally, opportunities for physician action are suggested.

Effects of pre- and postnatal polychlorinated biphenyl exposure on emotional reactivity observed in lambs before weaning

Humans and animals are exposed to PCBs and influences on developmental and endocrine processes are among the most pronounced effects. In the present study it was hypothesised that exposure to PCBs may interfere with sexually dimorphic behaviour. To test this hypothesis, behavioural studies in developmentally exposed sheep were conducted. Ewes were orally administered PCB 153 (98 μg/kg bw day), PCB 118 (49 μg/kg bw day) or corn oil from conception until delivery. However, because of accidental cross-contamination occurring twice causing a mixed exposure scenario in all three groups, the focus of this paper is to compare three distinct groups of lambs with different PCB levels (PCB 153 high-PCB 153 h, PCB 118 high-PCB 118 h, and low combined group-LC) rather than comparing animals exposed to single PCB congeners to those of a control group. Lambs were tested between 2 and 6 weeks of age. When LC males started the light/dark choice test in a dark box, they spent significantly more time in the dark part of the pen than LC females. This gender-related difference was not found in groups exposed to PCBs. A significant inhibitory effect on the activity level of males exposed to stress of confinement was found in the PCB 118 h group. In a high stress situation females from PCB 118 h and males from PCB 153 h were less active than their gender counterparts. The results support the hypothesis that intrauterine exposure to PCBs can alter sexually dimorphic behaviour of offspring.

Disruptive effects of persistent organohalogen contaminants on thyroid function in white whales (Delphinapterus leucas) from Svalbard

We analysed levels of 56 organohalogen contaminants (OHCs) including brominated flame retardants, polychlorinated biphenyls (PCBs), and organochlorine pesticides in the blubber of white (beluga) whales (Delphinapterus leucas) from Svalbard, Norway (N=12; 6 adults [5 males and 1 female] and 6 subadults [4 males and 2 females]) collected in 1996-2001. We also measured circulating levels of thyroid hormones (THs) and thyroid stimulating hormone (TSH) in the whales. The results confirm that OHC levels in these white whales are among the highest levels recorded in wildlife from Svalbard, and at the high end of the range when compared to white whales from the North American Arctic. A projection to latent structure (PLS) model (subadults and adult males grouped together) revealed that known or suspected thyroid disruptive contaminants (polybrominated diphenylether [PBDE]-28, -47, -99, -100, and -154, hexachlorobenzene [HCB], and PCB-105) were negatively correlated with circulating levels of total thyroxin (TT4), free T4 (FT4) and free triiodothyronine (FT3). Most of these negative relationships were also confirmed using partial correlations controlling for length (and thus age) of the whales. The positive correlations of TT4, FT4 and FT3 with hexabromocyclododecane (HBCD), α-hexachlorocyclohexane (α-HCH), chlorinated bornanes CHB-40 and CHB-62 revealed by the PLS model were not confirmed by partial correlations. TH levels in the present study appeared to be somewhat lower than levels measured in beluga whales from the Canadian Arctic. However, we were not able to determine if this was caused by different levels of OHCs, or differences in biological factors (e.g. age, sex, moulting status, and season) and analytical methods between the studies. Although the sample sizes were low and statistical models cannot depict the biological cause-effect relationships, this study suggests negative influences of specific OHCs, particularly PBDEs, on thyroid hormone levels in white whales. The impact this might have on individual and population health is unknown.

Anaemia, hypothyroidism and immune suppression associated with polychlorinated biphenyl exposure in bottlenose dolphins (Tursiops truncatus)

Polychlorinated biphenyls (PCBs), persistent chemicals widely used for industrial purposes, have been banned in most parts of the world for decades. Owing to their bioaccumulative nature, PCBs are still found in high concentrations in marine mammals, particularly those that occupy upper trophic positions. While PCB-related health effects have been well-documented in some mammals, studies among dolphins and whales are limited. We conducted health evaluations of bottlenose dolphins (Tursiops truncatus) near a site on the Georgia, United States coast heavily contaminated by Aroclor 1268, an uncommon PCB mixture primarily comprised of octa- through deca-chlorobiphenyl congeners. A high proportion (26%) of sampled dolphins suffered anaemia, a finding previously reported from primate laboratory studies using high doses of a more common PCB mixture, Aroclor 1254. In addition, the dolphins showed reduced thyroid hormone levels and total thyroxine, free thyroxine and triiodothyronine negatively correlated with PCB concentration measured in blubber (p = 0.039, < 0.001, 0.009, respectively). Similarly, T-lymphocyte proliferation and indices of innate immunity decreased with blubber PCB concentration, suggesting an increased susceptibility to infectious disease. Other persistent contaminants such as DDT which could potentially confound results were similar in the Georgia dolphins when compared with previously sampled reference sites, and therefore probably did not contribute to the observed correlations. Our results clearly demonstrate that dolphins are vulnerable to PCB-related toxic effects, at least partially mediated through the endocrine system. The severity of the effects suggests that the PCB mixture to which the Georgia dolphins were exposed has substantial toxic potential and further studies are warranted to elucidate mechanisms and potential impacts on other top-level predators, including humans, who regularly consume fish from the same marine waters.

Ameliorative effect of vitamin C on alterations in thyroid hormones concentrations induced by subchronic coadministration of chlorpyrifos and lead in wistar rats

The present study evaluated the ameliorative effect of vitamin C on alteration in thyroid hormones induced by low-dose subchronic coadministration of chlorpyrifos (CPF) and lead (Pb). Forty Wistar rats were divided into 4 groups of 10 animals each. Groups I and II were administered soya oil (2 mL/kg) and vitamin C (100 mg/kg), respectively. Group III was coadministered CPF (4.25 mg/kg ~1/20th LD₅₀) and Pb (250 mg/kg ~1/20th LD₅₀), respectively. Group IV was pretreated with vitamin C (100 mg/kg) and then coadministered with CPF (4.25 mg/kg) and Pb (250 mg/kg), 30 min later. The regimens were administered by gavage for a period of 9 weeks. The marginal decrease in serum triiodothyronine and thyroxine and the significant increase in the concentrations of thyroid stimulating hormone and malonaldehyde in the group coadministered with CPF and Pb were ameliorated by vitamin C partly due to its antioxidant properties.

A possible mechanism for 2,2',4,4',5,5'-hexachlorobiphenyl-mediated decrease in serum thyroxine level in mice

Serum total thyroxine (T₄) level was markedly decreased, without significant increases in the levels of hepatic T₄-UDP-glucuronosyltransferase (T₄-UGT) and serum thyroid-stimulating hormone, 3 days after treatment with 2,2',4,4',5,5'-hexachlorobiphenyl (CB153) (100mg/kg, ip) in both 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-sensitive C57BL/6 and TCDD-resistant DBA/2 mice. Likewise, in either strain of mice, no CB153-mediated changes in the binding levels of [(125)I]T₄ to serum proteins, such as transthyretin, albumin, and thyroxine binding globulin, were observed, while in CB153-pretreated C57BL/6 mice, but not in CB153-pretreated DBA/2 mice, the levels of biliary [(125)I]₄T and [(125)I]T₄-glucuronide at 90-120 min after injection of [(125)I]T₄ slightly increased, as compared with those in the corresponding control mice. Concerning tissue distribution of [(125)I]T₄, liver-selective increases in the [(125)I]T₄ accumulation by CB153-pretreatment were observed in both C57BL/6 and DBA/2 mice, and the hepatic levels of [(125)I]T₄ in the C57BL/6 and DBA/2 mice became more than 44% and 34% of the [(125)I]T₄ dosed, respectively. The present findings indicated that the CB153-mediated decreases in the level of serum total T₄in C57BL/6 and DBA/2 mice occur mainly through an increase in the accumulation of T₄ in the liver.

Changes in retinol-binding protein concentrations and thyroid homeostasis with nonoccupational exposure to DDT

BACKGROUND

The insecticide dichlorodiphenyltrichloroethane (DDT) has been used for malaria vector control in the northern and eastern parts of the Vhembe District of Limpopo Province, South Africa, since 1945. Bioaccumulation of DDT raises concern because it reportedly affects thyroid function.

OBJECTIVE

Our objective was to investigate the association between DDT uptake (as reflected in plasma concentrations) and thyroid homeostasis while considering related factors.

METHODS

We compared dietary intake, serum retinol-binding protein (RBP), transthyretin (TTR) and albumin concentrations, and liver and thyroid function between cases with evidence of a body burden of DDT in the circulation (concentration of any DDT isomer ≥ 0.02 µg/g lipid; n = 278) and controls (concentration of all DDT isomers < 0.02 µg/g lipid; n = 40) in a cross-sectional study. Further analyses were performed to assess the relevance of changes in RBP status associated with DDT uptake.

RESULTS

RBP concentrations below the reference range were more prevalent in cases (54% vs. 10% in controls; χ² = 27.4; p < 0.001), which could not be explained by nutrient intake. We observed significantly lower thyroid hormone concentrations among cases (p ≤ 0.01). We also observed a significant linear trend for serum concentrations of free thyroxine and free triiodothyronine (p < 0.001) and a significant quadratic trend for serum thyroid-stimulating hormone (p = 0.025) and TTR (p < 0.001) across the control group and case groups with normal and relatively low RBP concentrations. Relatively low RBP concentrations were associated with significantly higher DDT and 1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene (DDE) isomer concentrations and with a higher DDE/DDT ratio (p ≤ 0.01), which signifies long-term exposure. Inadequate intake of vitamin A and zinc were observed in 84% and 58%, respectively, of the total study population.

CONCLUSION

RBP concentrations appear to decrease in the presence of long-term DDT uptake, which may have deleterious effects on thyroid function and vitamin A nutritional status. This is of major concern in a population with poor vitamin A and zinc intake.