2,3,7,8-Tetrachlorodibenzo-p-dioxin plasma levels in Seveso 20 years after the accident

Impact of dioxins on reproductive health in female mammals

Extensive research has been conducted to investigate the toxicological impact of dioxins on mammals, revealing profound effects on the female reproductive system in both humans and animals. Dioxin exposure significantly disrupts the intricate functions of the ovary, a pivotal organ responsible for reproductive and endocrine processes. This disruption manifests as infertility, premature ovarian failure, and disturbances in sex steroid hormone levels. Comprehensive studies, encompassing accidental human exposure and experimental animal data, have raised a wealth of information with consistent yet varied conclusion influenced by experimental factors. This review begins by providing an overarching background on the ovary, emphasizing its fundamental role in reproductive health, particularly in ovarian steroidogenesis and hormone receptor regulation. Subsequently, a detailed examination of the Aryl hydrocarbon Receptor (AhR) and its role in governing ovarian function is presented. The review then outlines the sources and toxicity of dioxins, with a specific focus on AhR involvement in mediating reproductive toxicity in mammals. Within this context, the impact of dioxins, notably 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), on Folliculogenesis and Preimplantation embryos is discussed. Furthermore, the review delves into the disruptions of the female hormonal system caused by TCDD and their ramifications in endometriosis. Notably, variations in the effects of TCDD on the female reproductive and hormonal system are highlighted in relation to TCDD dose, animal species, and age. As a forward-looking perspective, questions arise regarding the potential involvement of molecular mechanisms beyond AhR in mediating the female reproductive toxicity of dioxins.

Association of endocrine active environmental compounds with body mass index and weight loss following bariatric surgery

INTRODUCTION

The objective of this study was to study associations of a wide range of halogenated biphenyls, dibenzo-p-dioxins, dibenzofurans and diphenylethers with body mass index (BMI) and evaluate changes in their concentration following bariatric surgery.

METHODS

Subcutaneous fat, visceral fat and liver tissue samples were collected from 106 patients undergoing Roux-en-Y gastric bypass surgery for weight loss or patients who were undergoing abdominal surgery for nonbariatric reasons. We measured concentrations of an extensive panel of chlorinated and brominated biphenyls, dioxins, and furans, and brominated diphenylethers in the samples. We conducted linear regression to examine associations with BMI, adjusting for age and gender. Changes in concentration for indicator chemicals were evaluated in samples collected following bariatric surgery in a small subpopulation.

RESULTS

After adjustments for age and gender and correction for multiple testing, seven ortho-chlorinated biphenyls, one nonortho-chlorinated biphenyl, four PCDD/Fs and one ortho-brominated biphenyl were associated with BMI. The strongest associations between BMI and lipid-adjusted concentrations were seen with PCB-105 in subcutaneous fat (beta = 16.838 P-val = 1.45E-06) PCB-126 in visceral fat (beta = 15.067 P-val = 7.72E-06) and PCB-118 (beta = 14.101 P-val = 2.66E-05) in liver. The concentrations of sum PCBs, chlorinated toxic equivalent quantity (TEQ's) and brominated compounds increased significantly with weight loss in subcutaneous fat in a group of ten individuals resampled up to five years after bariatric surgery and substantial weight loss.

CONCLUSION

We show that selected polychlorinated biphenyls PCBs and structurally related polychlorinated dibenzo-p-dioxins dibenzofurans (PCDD/Fs) were associated with BMI. Concentrations of these lipophilic compounds in subcutaneous fat increased following bariatric surgery.

The Seveso accident: A look at 40 years of health research and beyond

A 1976 chemical factory explosion near Seveso, Italy exposed residents to high levels of 2,3,7,8-tetracholorodibenzo-p-dioxin (TCDD or dioxin). Dioxin is a known human carcinogen and potent endocrine disruptor. It is highly lipophilic and has a long half-life in humans. Much of what we know and can learn about the risks of dioxin exposure on human health arose from the tragic circumstances of Seveso. This review aims to describe the Seveso accident, summarize the results of 40 years of research on the health of the Seveso population since the accident, and discuss next-stage research on the health of Seveso residents, their children, and grandchildren.

Risk for animal and human health related to the presence of dioxins and dioxin-like PCBs in feed and food

The European Commission asked EFSA for a scientific opinion on the risks for animal and human health related to the presence of dioxins (PCDD/Fs) and DL-PCBs in feed and food. The data from experimental animal and epidemiological studies were reviewed and it was decided to base the human risk assessment on effects observed in humans and to use animal data as supportive evidence. The critical effect was on semen quality, following pre- and postnatal exposure. The critical study showed a NOAEL of 7.0 pg WHO2005-TEQ/g fat in blood sampled at age 9 years based on PCDD/F-TEQs. No association was observed when including DL-PCB-TEQs. Using toxicokinetic modelling and taking into account the exposure from breastfeeding and a twofold higher intake during childhood, it was estimated that daily exposure in adolescents and adults should be below 0.25 pg TEQ/kg bw/day. The CONTAM Panel established a TWI of 2 pg TEQ/kg bw/week. With occurrence and consumption data from European countries, the mean and P95 intake of total TEQ by Adolescents, Adults, Elderly and Very Elderly varied between, respectively, 2.1 to 10.5, and 5.3 to 30.4 pg TEQ/kg bw/week, implying a considerable exceedance of the TWI. Toddlers and Other Children showed a higher exposure than older age groups, but this was accounted for when deriving the TWI. Exposure to PCDD/F-TEQ only was on average 2.4- and 2.7-fold lower for mean and P95 exposure than for total TEQ. PCDD/Fs and DL-PCBs are transferred to milk and eggs, and accumulate in fatty tissues and liver. Transfer rates and bioconcentration factors were identified for various species. The CONTAM Panel was not able to identify reference values in most farm and companion animals with the exception of NOAELs for mink, chicken and some fish species. The estimated exposure from feed for these species does not imply a risk.

Genistein Prevents BRCA1 CpG Methylation and Proliferation in Human Breast Cancer Cells with Activated Aromatic Hydrocarbon Receptor

Background: Previous studies have suggested a causative role for agonists of the aromatic hydrocarbon receptor (AhR) in the etiology of breast cancer 1, early-onset (BRCA-1)-silenced breast tumors, for which prospects for treatment remain poor. Objectives: We investigated the regulation of BRCA1 by the soy isoflavone genistein (GEN) in human estrogen receptor α (ERα)-positive Michigan Cancer Foundation-7 (MCF-7) and ERα-negative sporadic University of Arizona Cell Culture-3199 (UACC-3199) breast cancer cells, respectively, with inducible and constitutively active AhR. Methods: In MCF-7 cells, we analyzed the dose- and time-dependent effects of GEN and (-)-epigallocatechin-3-gallate (EGCG) control, selected as prototype dietary DNA methyltransferase (DNMT) inhibitors, on BRCA-1 expression after AhR activation with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and in TCDD-washout experiments. We compared the effects of GEN and EGCG on BRCA1 cytosine-phosphate-guanine (CpG) methylation and cell proliferation. Controls for DNA methylation and proliferation were changes in expression of DNMT-1, cyclin D1, and p53, respectively. In UACC-3199 cells, we compared the effects of GEN and α-naphthoflavone (αNF; 7,8-benzoflavone), a synthetic flavone and AhR antagonist, on BRCA1 expression and CpG methylation, cyclin D1, and cell growth. Finally, we examined the effects of GEN and αNF on BRCA1, AhR-inducible cytochrome P450 (CYP)-1A1 (CYP1A1) and CYP1B1, and AhR mRNA expression. Results: In MCF-7 cells, GEN exerted dose- and time-dependent preventative effects against TCDD-dependent downregulation of BRCA-1. After TCDD washout, GEN rescued BRCA-1 protein expression while reducing DNMT-1 and cyclin D1. GEN and EGCG reduced BRCA1 CpG methylation and cell proliferation associated with increased p53. In UACC-3199 cells, GEN reduced BRCA1 and estrogen receptor-1 (ESR1) CpG methylation, cyclin D1, and cell growth while inducing BRCA-1 and CYP1A1. Conclusions: Results suggest preventative effects for GEN and EGCG against BRCA1 CpG methylation and downregulation in ERα-positive breast cancer cells with activated AhR. GEN and flavone antagonists of AhR may be useful for reactivation of BRCA1 and ERα via CpG demethylation in ERα-negative breast cancer cells harboring constitutively active AhR.

A PBPK model to estimate PCDD/F levels in adipose tissue: comparison with experimental values of residents near a hazardous waste incinerator

This study was aimed at determining the concentrations of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) in 15 samples of adipose tissue from subjects who had been living in the vicinity of a hazardous waste incinerator (HWI). The results were compared with levels obtained in previous surveys carried out in 1998 (baseline study), 2002 and 2007. The current (2013) concentrations of PCDD/Fs in adipose tissue ranged from 2.8 to 46.3 pg WHO-TEQ/g fat (mean and median concentrations: 11.5 and 7.4 pg WHO-TEQ/g fat, respectively), being significantly lower (64%) than those observed in 1998. In contrast, no significant differences in the mean PCDD/F concentrations were noted in the period 2002-2013. The significant decrease of the PCDD/F content in fat, also noted in other biological monitors such as plasma and breast milk, is in agreement with the reduction in the dietary intake of PCDD/Fs found in the same area of study. Similarly to other investigations across Europe, an increase of PCDD/F levels in adipose tissue in relation to age was observed, while no significant differences were noted according to gender. A multicompartmental physiologically-based pharmacokinetic (PBPK) model was also applied to estimate the levels of PCDD/Fs in adipose tissue. When comparing the modeled and experimental concentrations of PCDD/Fs in that tissue, very similar values were obtained for the four surveys, which indicates this can be a reliable tool to predict the internal dose of PCDD/Fs.

Serum TCDD and TEQ concentrations among Seveso women, 20 years after the explosion

The Seveso Women's Health Study (SWHS) is a historical cohort study of the female population residing near Seveso, Italy, on 10 July 1976, when a chemical explosion resulted in the highest known residential exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Individual TCDD concentration was measured in serum collected near the time of the explosion, and in 1996, we collected adequate blood for TCDD and total dioxin toxic equivalent (TEQ) measurement. Polychlorinated dibenzo-p-dioxins, dibenzofurans, and biphenyls were measured in 1996 serum for a sample (n=225, 23%) of the SWHS cohort and WHO 2005 TEQs were calculated. We examined characteristics that predict 1996 TCDD concentrations and estimated TCDD elimination half-life over the 20-year period since the explosion. Median lipid-adjusted TCDD and total TEQ concentrations in 1996 serum were 7.3 and 26.2 p.p.t., respectively. Initial 1976 TCDD and age at explosion were the strongest predictors of 1996 TCDD. The TCDD elimination half-life was 7.1 years for women older than 10 years in 1976, but was shorter in those who were younger. Twenty years after the explosion, TCDD concentrations in this SWHS sample, the majority of who were children in 1976, remain elevated relative to background. These data add to the limited data available on TCDD elimination half-life in children.

The effect of misunderstanding the chemical properties of environmental contaminants on exposure beliefs: a case involving dioxins

Chemical properties of contaminants lead them to behave in particular ways in the environment and hence have specific pathways to human exposure. If residents of affected communities lack awareness of these properties, however, they could make incorrect assumptions about where and how exposure occurs. We conducted a mailed survey of 904 residents of Midland and Saginaw counties in Michigan, USA to assess to what degree residents of a community with known dioxin contamination appear to understand the hydrophobic nature of dioxins and the implications of that fact on different potential exposure pathways. Participants assessed whether various statements about dioxins were true, including multiple statements assessing beliefs about dioxins in different types of water. Participants also stated whether they believed different exposure pathways were currently significant sources of dioxin exposure in this community. A majority of residents believed that dioxins can be found in river water that has been filtered to completely remove all particulates, well water, and even city tap water, beliefs which are incongruous with the hydrophobic nature of dioxins. Mistrust of government and personal concern about dioxins predicted greater beliefs about dioxins in water. In turn, holding more beliefs about dioxins in water predicted beliefs that drinking and touching water are currently significant exposure pathways for dioxins. Ensuring that community residents' mental models accurately reflect the chemical properties of different contaminants can be important to helping them to adjust their risk perceptions and potentially their risk mitigation behaviors accordingly.

Development and validation of prediction models for blood concentrations of dioxins and PCBs using dietary intakes

BACKGROUND

Dioxins and PCBs accumulate in the food chain and might exert toxic effects in animals and humans. In large epidemiologic studies, exposure estimates of these compounds based on analyses of biological material might not be available or affordable.

OBJECTIVES

To develop and then validate models for predicting concentrations of dioxins and PCBs in blood using a comprehensive food frequency questionnaire and blood concentrations.

METHODS

Prediction models were built on data from one study (n=195), and validated in an independent study group (n=66). We used linear regression to develop predictive models for dioxins and PCBs, both sums of congeners and 33 single congeners (7 and 10 polychlorinated dibenzo-p-dioxins and furans (PCDDs/PCDFs), 12 dioxin-like polychlorinated biphenyls (PCBs: 4 non-ortho and 8 mono-ortho), sum of all the 29 dioxin-like compounds (total TEQ) and sum of 4 non dioxin-like PCBs (∑ CB-101, 138, 153, 183=PCB(4)). We used the blood concentration and dietary intake of each of the above as dependent and independent variables, while sex, parity, age, place of living, smoking status, energy intake and education were covariates. We validated the models in a new study population comparing the predicted blood concentrations with the measured blood concentrations using correlation coefficients and Weighted Kappa (К(W)) as measures of agreement, considering К(W)>0.40 as successful prediction.

RESULTS

The models explained 78% (sum dioxin-like compounds), 76% (PCDDs), 76% (PCDFs), 74% (no-PCBs), 69% (mo-PCBs), 68% (PCB(4)) and 63% (CB-153) of the variance. In addition to dietary intake, age and sex were the most important covariates. The predicted blood concentrations were highly correlated with the measured values, with r=0.75 for dl-compounds 0.70 for PCB(4), (p<0.001) and 0.66 (p<0.001) for CB-153. К(W) was 0.68 for sum dl-compounds 0.65 for both PCB(4) and CB-153. Out of 33 congeners 16 (13dl-compounds and 3 ndl PCBs) had К(W)>0.40.

CONCLUSIONS

The models developed had high power to predict blood levels of dioxins and PCBs and to correctly rank subjects according to high or low exposure based on dietary intake and demographic information. These models underline the value of dietary intake data for use in investigations of associations between dioxin and PCB exposure and health outcomes in large epidemiological studies with limited biomaterial for chemical analysis.

Blood levels of dioxins, furans, dioxin-like PCBs, and TEQs in general populations: a review, 1989-2010

A comprehensive worldwide literature review of blood levels of dioxins and dioxin-like compounds in non-exposed adult general populations was performed. The studies published in 1989-2010 reporting information on polychlorinated dibenzo-para-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), non-ortho-PCBs (nPCBs), mono-ortho-PCBs (mPCBs) levels and Toxic Equivalencies (TEQs, a summary weighted measure of their combined toxicity) were reviewed. TEQs were calculated using as standard the most recent WHO 2005 reevaluation of Toxic Equivalency Factors (TEFs). Weighted multiple regression analyses adjusted for year, subject's age, type of sample analyzed, method used for values below detection limit, and central tendency measure used were performed for each congener and standardized TEQs (log-transformed). We identified 187 studies regarding 29,687 subjects of 26 countries. Year of blood collection ranged from 1985 to 2008. The studies reporting congener levels 161. In adjusted analyses, European countries showed higher levels of most dioxin-like congeners and TEQs. A strong positive association of subjects' age with most congeners and with TEQ values was found, confirming previous findings. Significant decreases over time (1985-2008) were documented for PCCDs, PCDFs, and TEQs including their contributions. No significant decrease was found for non-ortho-PCBs, notably PCB 126. Only some mono-ortho-PCBs showed clear significant declines. Accordingly, TEQs including only PCB contribution did not decrease over time. In interpreting these findings, it should be considered that for dioxin-like PCBs the analysis period was shorter (17 years), since these compounds were first measured in 1992.

Plasma levels of dioxins, furans, non-ortho-PCBs, and TEQs in the Seveso population 17 years after the accident

BACKGROUND

The Seveso accident (Italy) in 1976 caused the contamination of a large population by 2,3,7,8-tetrachlorodibenzo-para-dioxin (2,3, 7,8-TCDD). The contaminated territory was divided into three zones: A (very high contamination), B (high contamination), and R (low contamination). We report here the plasma concentrations of seven polychlorinated dibenzo-para-dioxins (PCDDs), 10 polychlorinated dibenzofurans (PCDFs), four non-ortho-polychlorinated biphenyls PCBs (nPCBs), and Toxic Equivalencies (TEQs) in a sample of residents in the most polluted zones A and B and in a reference non-contaminated zone.

METHODS

From December 1992 to March 1994, 62 individuals were randomly selected from the population living in zone A (No. =7) and B (No. =55). A sample of 59 subjects living in a surrounding non-contaminated area (non-ABR), frequency-matched by gender, age, and smoking history, was used as reference. All subjects were administered a questionnaire surveying demographic, lifestyle, medical history, and accident-related factors. We assayed plasma PCDD, PCDF, and nPCB concentrations by high-resolution gas chromatography/high resolution mass spectrometric (HRGC/HRMS) analysis, with results reported as pg/g of lipid, or parts per trillion (ppt). We calculated TEQs using the WHO 2005 Toxic Equivalency Factors (TEFs).

RESULTS

We found elevated median levels of 2,3, 7,8-TCDD in plasma samples of subjects living in zone A (73.3 ppt) and zone B (12.4 ppt), compared with residents in the reference zone (5.5 ppt). In analyses adjusted for gender, age, smoking, and body mass index (BMI), none of the other congeners showed levels higher than reference in the contaminated zones. Compared with men, women showed higher levels (113%) of 2,3, 7,8-TCDD and a slight elevation (17%) of TEQ for the other congeners. Age was strongly positively associated with most congener levels; TEQs for PCDDs, PCDFs, and nPCBs showed respectively 12%, 24%, and 41% increases for every 10 years of age. Current smokers had lower (from -37% to -67%) TEQ levels than subjects who had never smoked. BMI was negatively associated with levels of a few congeners, but with no impact on TEQ values.

CONCLUSIONS

The Seveso accident caused a severe exposure of the population to 2,3,7,8-TCDD only. None of the other congeners analyzed showed variation across zones. Age showed a strong positive association with TEQs for all classes of compounds (PCDDs, PCDFs, and nPCBs).

Predictors of serum dioxins and PCBs among peripubertal Russian boys

BACKGROUND

Although sources and routes of exposure to dioxins and polychlorinated biphenyls (PCBs) have been studied, information regarding exposure among children is limited. Breast-feeding and diet are two important contributors to early life exposure. To further understand other significant contributors to childhood exposure, we studied a cohort of children from a city with high environmental dioxin levels.

OBJECTIVES

We investigated predictors of serum concentrations of polychlorinated dibenzo-p-dioxins (PCDDs)/polychlorinated dibenzofurans (PCDFs)/co-planar PCBs (C-PCBs), toxic equivalents (TEQs), and PCBs among 8- to 9-year-old boys in Chapaevsk, Russia.

METHODS

We used general linear regression models to explore associations of log(10)-transformed serum concentrations of PCDDs/PCDFs/C-PCBs, TEQs, and PCBs at study entry with anthropometric, demographic, geographic, and dietary factors in 482 boys in Chapaevsk, Russia.

RESULTS

The median (25th, 75th percentile) concentration for total 2005 TEQs was 21.1 pg/g lipid (14.4, 33.2). Boys who were older, consumed local foods, were breast-fed longer, and whose mothers were employed at the Khimprom chemical plant (where chlorinated chemicals were produced) or gardened locally had significantly higher serum dioxins and PCBs, whereas boys with higher body mass index or more educated parents had significantly lower serum dioxins and PCBs. Boys who lived < 2 km from Khimprom had higher total TEQs (picograms per gram lipid) [adjusted mean = 30.6; 95% confidence interval (CI), 26.8-35.0] than boys who lived > 5 km away (adjusted mean = 18.8; 95% CI, 17.2-20.6).

CONCLUSIONS

Our findings suggest that there are specific local sources of dioxin and PCB exposure among children in Chapaevsk including maternal gardening, consumption of locally grown food, and residential proximity to the Khimprom plant.

Cancer incidence in the population exposed to dioxin after the "Seveso accident": twenty years of follow-up

BACKGROUND

The Seveso, Italy accident in 1976 caused the contamination of a large population by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Possible long-term effects have been examined through mortality and cancer incidence studies. We have updated the cancer incidence study which now covers the period 1977-96.

METHODS

The study population includes subjects resident at the time of the accident in three contaminated zones with decreasing TCDD soil levels (zone A, very high; zone B, high; zone R, low) and in a surrounding non-contaminated reference territory. Gender-, age-, and period-adjusted rate ratios (RR) and 95% confidence intervals (95% CI) were calculated by using Poisson regression for subjects aged 0-74 years.

RESULTS

All cancer incidence did not differ from expectations in any of the contaminated zones. An excess of lymphatic and hematopoietic tissue neoplasms was observed in zones A (four cases; RR, 1.39; 95% CI, 0.52-3.71) and B (29 cases; RR, 1.56; 95% CI, 1.07-2.27) consistent with the findings of the concurrent mortality study. An increased risk of breast cancer was detected in zone A females after 15 years since the accident (five cases, RR, 2.57; 95% CI, 1.07-6.20). No cases of soft tissue sarcomas occurred in the most exposed zones (A and B, 1.17 expected). No cancer cases were observed among subjects diagnosed with chloracne early after the accident.

CONCLUSION

The extension of the Seveso cancer incidence study confirmed an excess risk of lymphatic and hematopoietic tissue neoplasms in the most exposed zones. No clear pattern by time since the accident and zones was evident partly because of the low number of cases. The elevated risk of breast cancer in zone A females after 15 years since the accident deserves further and thorough investigation. The follow-up is continuing in order to cover the long time period (even decades) usually elapsing from exposure to carcinogenic chemicals and disease occurrence.

The University of Michigan Dioxin Exposure Study: predictors of human serum dioxin concentrations in Midland and Saginaw, Michigan

BACKGROUND

We conducted a population-based human exposure study in response to concerns among the population of Midland and Saginaw counties, Michigan, that discharges by the Dow Chemical Company of dioxin-like compounds into the nearby river and air had led to an increase in residents' body burdens of polychlorinated dibenzofurans (PCDDs), polychlorinated dibenzofurans (PCDFs), and dioxin-like polychlorinated biphenyls (PCBs), here collectively referred to as "dioxins."

OBJECTIVES

We sought to identify factors that explained variation in serum dioxin concentrations among the residents of Midland and Saginaw counties. Exposures to dioxins in soil, river sediments, household dust, historic emissions, and contaminated fish and game were of primary interest.

METHODS

We studied 946 people in four populations in the contaminated area and in a referent population, by interview and by collection of serum, household dust, and residential soil. Linear regression was used to identify factors associated with serum dioxins.

RESULTS

Demographic factors explained a large proportion of variation in serum dioxin concentrations. Historic exposures before 1980, including living in the Midland/Saginaw area, hunting and fishing in the contaminated areas, and working at Dow, contributed to serum dioxin levels. Exposures since 1980 in Midland and Saginaw counties contributed little to serum dioxins.

CONCLUSIONS

This study provides valuable insights into the relationships between serum dioxins and environmental factors, age, sex, body mass index, smoking, and breast-feeding. These factors together explain a substantial proportion of the variation in serum dioxin concentrations in the general population. Historic exposures to environmental contamination appeared to be of greater importance than recent exposures for dioxins.

The University of Michigan Dioxin Exposure Study: methods for an environmental exposure study of polychlorinated dioxins, furans, and biphenyls

BACKGROUND

The University of Michigan Dioxin Exposure Study (UMDES) was undertaken in response to concerns that the discharge of dioxin-like compounds from the Dow Chemical Company facilities in Midland, Michigan, resulted in contamination of soils in the Tittabawassee River floodplain and areas of the city of Midland, leading to an increase in residents' body burdens of polychlorinated dibenzodioxins and polychlorinated dibenzofurans.

OBJECTIVES

The UMDES is a hypothesis-driven study designed to answer important questions about human exposure to dioxins in the environment of Midland, where the Dow Chemical Company has operated for > 100 years, and in neighboring Saginaw, Michigan. In addition, the UMDES includes a referent population from an area of Michigan in which there are no unusual sources of dioxin exposure and from which inferences regarding the general Michigan population can be derived. A central goal of the study is to determine which factors explain variation in serum dioxin levels and to quantify how much variation each factor explains.

CONCLUSIONS

In this article we describe the study design and methods for a large population-based study of dioxin contamination and its relationship to blood dioxin levels. The study collected questionnaire, blood, dust, and soil samples on 731 people. This study provides a foundation for understanding the exposure pathways by which dioxins in soils, sediments, fish and game, and homegrown produce lead to increased body burdens of these compounds.

Bone mineral density changes in relation to environmental PCB exposure

BACKGROUND

Bone toxicity has been linked to organochlorine exposure following a few notable poisoning incidents, but epidemiologic studies in populations with environmental organochlorine exposure have yielded inconsistent results.

OBJECTIVES

The aim of this study was to investigate whether organochlorine exposure was associated with bone mineral density (BMD) in a population 60-81 years of age (154 males, 167 females) living near the Baltic coast, close to a river contaminated by polychlorinated biphenyls (PCBs).

METHODS

We measured forearm BMD in participants using dual energy X-ray absorptiometry; and we assessed low BMD using age- and sex-standardized Z-scores. We analyzed blood samples for five dioxin-like PCBs, the three most abundant non-dioxin-like PCBs, and p,p'-dichloro-phenyldichloroethylene (p,p'-DDE).

RESULTS

In males, dioxin-like chlorobiphenyl (CB)-118 was negatively associated with BMD; the odds ratio for low BMD (Z-score less than -1) was 1.06 (95% confidence interval, 1.01-1.12) per 10 pg/mL CB-118. The sum of the three most abundant non-dioxin-like PCBs was positively associated with BMD, but not with a decreased risk of low BMD. In females, CB-118 was positively associated with BMD, but this congener did not influence the risk of low BMD in women.

CONCLUSIONS

Environmental organochlorine exposures experienced by this population sample since the 1930s in Sweden may have been sufficient to result in sex-specific changes in BMD.

Total TEQ reference range (PCDDs, PCDFs, cPCBs, mono-PCBs) for the US population 2001-2002

We report reference ranges for the total toxic equivalency (TEQ) and TEQ sub-fractions of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), coplanar biphenyls (cPCBs), and mono-ortho-substituted biphenyls (mPCBs) in a statistically designed sampling of the US population in 2001-2002. The TEQ and TEQ sub-fractions have been stratified by age, sex, and race/ethnicity. The TEQ levels are lower using the 2005 toxic equivalency factors (TEFs) compared to using the 1998 TEF values, principally due to the much lower 2005 TEF values assigned to the mPCBs. Mexican Americans (MA) have significantly lower TEQ levels than both non-Hispanic whites (NHW) and non-Hispanic blacks (NHB). Using the 1998 or 2005 TEF values, males and females have nearly the same distribution of TEQ sub-fractions. We found a significant increase in TEQ levels with age for males, females, and NHW. About 80-90% of the total TEQ can be estimated by using seven congeners, namely 2,3,7,8-TCDD, 1,2,3,7,8-PeCDD, 1,2,3,6,7,8-HxCDD, 2,3,4,7,8-PeCDF, PCB-126, PCB-118, and PCB-156. We also measured geometric mean TEQ levels in pooled samples from the US population. The geometric mean TEQ levels also increase with age. In the youngest age group (12-19 years), the TEQ levels were higher in males than in females while females had higher TEQ levels than males in all older age groups. In the pools, as age increases the percent contribution of the PCDD TEQ levels increases while the percent contribution of the PCDF TEQ levels decreases for all race/ethnicity and sex strata.

Neonatal thyroid function in Seveso 25 years after maternal exposure to dioxin

BACKGROUND

Neonatal hypothyroidism has been associated in animal models with maternal exposure to several environmental contaminants; however, evidence for such an association in humans is inconsistent. We evaluated whether maternal exposure to 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), a persistent and widespread toxic environmental contaminant, is associated with modified neonatal thyroid function in a large, highly exposed population in Seveso, Italy.

METHODS AND FINDINGS

Between 1994 and 2005, in individuals exposed to TCDD after the 1976 Seveso accident we conducted: (i) a residence-based population study on 1,014 children born to the 1,772 women of reproductive age in the most contaminated zones (A, very high contamination; B, high contamination), and 1,772 age-matched women from the surrounding noncontaminated area (reference); (ii) a biomarker study on 51 mother-child pairs for whom recent maternal plasma dioxin measurements were available. Neonatal blood thyroid-stimulating hormone (b-TSH) was measured on all children. We performed crude and multivariate analyses adjusting for gender, birth weight, birth order, maternal age, hospital, and type of delivery. Mean neonatal b-TSH was 0.98 microU/ml (95% confidence interval [CI] 0.90-1.08) in the reference area (n = 533), 1.35 microU/ml (95% CI 1.22-1.49) in zone B (n = 425), and 1.66 microU/ml (95% CI 1.19-2.31) in zone A (n = 56) (p < 0.001). The proportion of children with b-TSH > 5 microU/ml was 2.8% in the reference area, 4.9% in zone B, and 16.1% in zone A (p < 0.001). Neonatal b-TSH was correlated with current maternal plasma TCDD (n = 51, beta = 0.47, p < 0.001) and plasma toxic equivalents of coplanar dioxin-like compounds (n = 51, beta = 0.45, p = 0.005).

CONCLUSIONS

Our data indicate that environmental contaminants such as dioxins have a long-lasting capability to modify neonatal thyroid function after the initial exposure.

Challenges of exposure assessment for health studies in the aftermath of chemical incidents and disasters

Exposure assessment during and after acute chemical incidents and disasters is essential for health studies that may follow. During chemical incidents, the focus usually lies on risk assessment and afterward attention shifts toward possible (long-term) health effects. This may lead to insufficient available data on exposure to study the association between exposure and health outcome, and collection of additional exposure data is often required. Literature on health studies conducted after several chemical incidents was reviewed to obtain better insight on the needs of health studies. Four different types of scenarios were distinguished based on when exposure data were collected and the exposure data used for health studies. These four scenarios gave insight on exposure data needed for conclusive health studies and when different methods of exposure data collection should be used. Literature indicated that adequate and rapid exposure assessment during chemical incidents is vital for health studies, because data that are not collected during or directly after an incident may be irretrievably lost. Poor exposure assessment is not always the only problem in health studies. Problems in health studies including poor exposure assessment may be prevented when the general design and needs of health studies are taken into account when designing contingency plans. Together with measures that will help facilitate funding, design, and coordination of health studies, disaster management programs should, among others, prepare for methods that lead to a swift identification of released substances, determination of concentrations and dispersion of released substances, designing basic questionnaire outlines, and rapid evaluation of the usefulness and necessity of employing biological sampling.

Assessing and managing risks arising from exposure to endocrine-active chemicals

Managing risks to human health and the environment produced by endocrine-active chemicals (EAC) is dependent on sound principles of risk assessment and risk management, which need to be adapted to address the uncertainties in the state of the science of EAC. Quantifying EAC hazard identification, mechanisms of action, and dose-response curves is complicated by a range of chemical structure/toxicology classes, receptors and receptor subtypes, and nonlinear dose-response curves with low-dose effects. Advances in risk science including toxicogenomics and quantitative structure-activity relationships (QSAR) along with a return to the biological process of hormesis are proposed to complement existing risk assessment strategies, including that of the Endocrine Disruptor Screening and Testing Advisory Committee (EDSTAC 1998). EAC represents a policy issue that has captured the public's fears and concerns about environmental health. This overview describes the process of EAC risk assessment and risk management in the context of traditional risk management frameworks, with emphasis on the National Research Council Framework (1983), taking into consideration the strategies for EAC management in Canada, the United States, and the European Union.

Factors related to dioxin and furan body levels among Michigan workers

We evaluated serum concentrations of five selected dioxin, furan, and polychlorinated biphenyls (PCB) congeners among 412 workers at a Midland, Michigan plant that manufactured trichlorophenol and pentachlorophenol (PCP) and formulated chlorophenol-based products. We examined occupational indicators of exposure to these chlorophenols taking into account intrinsic factors such as age and body fat and potential environmental sources of exposure from consumption of local game and fish and other occupations. All five congeners were significantly associated with age and body fat. 2378-TCDD serum concentrations were associated with trichlorophenol operations, total years employed at the plant, as well as working as a hazardous waste worker. 123678-H(6)CDD serum concentrations were related to occupational PCP exposure, chloracne, recent weight loss, eating local game, and working as a hazardous waste worker. Serum concentrations of PCB126 were related to smoking (inversely), and eating local fish or local game. Other factors such as diet and jobs outside of the chlorophenol plant exposures had only a very minor impact on dioxin and furan concentrations in these workers.

Cancer incidence and mortality in a New Zealand community potentially exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin from 2,4,5-trichlorophenoxyacetic acid manufacture

OBJECTIVE

To investigate whether the rates of all cancers and four cancers (soft tissue sarcoma, non-Hodgkin's lymphoma, Hodgkin's disease and chronic lymphocytic leukaemia) associated with dioxin exposure are higher in New Plymouth, the site of a former 2,4,5-T manufacturing plant, than for the rest of New Zealand.

METHODS

Analysis of 1970-2001 cancer data from the New Zealand Cancer Registry was undertaken for New Plymouth and the rest of New Zealand.

RESULTS

There is no evidence of an increased cancer risk apart from one period (1970-74), which falls partly outside the 1962-1987 manufacturing period if 10-year latency is assumed. For 1970-74, there was an elevated risk for all cancer incidence (SIR = 111, 95% CI 104-119), and for two of the four specific cancers that are associated with dioxin exposure (non-Hodgkin's lymphoma SIR = 175, 95% CI 121-246 and chronic lymphocytic leukaemia SIR = 251, 95% CI 144-408).

CONCLUSIONS AND IMPLICATIONS

The results do not suggest an increased cancer risk among the New Plymouth population related to the period of 2,4,5-T manufacture, although the study's limitations mean the possibility of an undetectable small elevation in cancer risk cannot be excluded. Although TCDD exposure in the first few years of 2,4,5-T manufacture may have contributed to cancer incidence in 1970-74, unknown exposure(s) before the start of 2,4,5-T manufacture and chance are also possible explanations.

Body mass index and serum chlorinated dibenzo-p-dioxin and dibenzofuran levels

Several studies have found that current levels of 2,3,7,8 tetrachlorodibenzo-p-dioxin in serum lipids are related to age with older persons generally having higher levels. To account for this age pattern, reference ranges based on national samples have been established in order to allow determination of background levels for regional studies. In several studies, body mass index (BMI), has also been associated with current 2,3,7,8 tetrachlorodibenzo-p-dioxin levels with increasing body mass index related to increasing levels. We measured lipid-adjusted serum levels for all 2,3,7,8-substituted dioxins and furans in 62 chemical manufacturing workers with chlorophenol exposures and 36 workers without chlorophenol exposures employed at the same location. We then assessed the impact of age and BMI on the serum levels of all these compounds in the presence of other potential confounders. We found that both factors are important independent determinants of serum levels of 2,3,7,8-substituted dioxins and furans. Specifically, age and BMI are both important factors for assessing background levels of 2,3,7,8 tetrachlorodibenzo-p-dioxin, 1,2,3,7,8 pentachlorodibenzo-p-dioxin and the calculated total toxic equivalency. BMI, but not age, is important for assessing background levels of higher chlorinated dioxins and some hexachlorofurans. We conclude that age and BMI are both important considerations when comparing a potentially exposed group to a referent group, or to national norms. Further, age and BMI may also be important in epidemiology studies where back-extrapolation from current dioxin levels is used to assess historical chlorophenol exposure.

Microarray analysis of gene expression in peripheral blood mononuclear cells from dioxin-exposed human subjects

Tetrachlorodibenzo-p-dioxin (TCDD) is classified as a human carcinogen and exerts toxic effects on the skin (chloracne). Effects on reproductive, immunological, and endocrine systems have also been observed in animal models. TCDD acts through the aryl hydrocarbon receptor (AhR) pathway influencing largely unknown gene networks. An industrial accident in Seveso, Italy in 1976 exposed thousands of people to substantial quantities of TCDD. Twenty years after the exposure, this study examines global gene expression in the mononuclear cells of 26 Seveso female never smokers, with similar age, alcohol consumption, use of medications, and background plasma levels of 22 dioxin congeners unrelated to the Seveso accident. Plasma dioxin levels were still elevated in the exposed subjects. We performed analyses in two different comparison groups. The first included high-exposed study subjects compared with individuals with background TCDD levels (average plasma levels 99.4 and 6.7ppt, respectively); the second compared subjects who developed chloracne after the accident, and those who did not develop this disease. Overall, we observed a modest alteration of gene expression based on dioxin levels or on chloracne status. In the comparison between high levels and background levels of TCDD, four histone genes were up-regulated and modified expression of HIST1H3H was confirmed by real-time PCR. In the comparison between chloracne case-control subjects, five hemoglobin genes were up-regulated. Pathway analysis revealed two major networks for each comparison, involving cell proliferation, apoptosis, immunological and hematological disease, and other pathways. Further examination of the role of these genes in dioxin induced-toxicity is warranted.

Dioxins: an overview

This review article summarizes what is known about human health following exposure to dioxins. It is meant primarily for health professionals but was also written with the general public in mind. The need for such an article became apparent to the authors following media inquiries at the time the then Ukraine presidential candidate Victor Yushchenko was deliberately poisoned with the most toxic dioxin, tetrachlorodibenzodioxin or TCDD.

Adverse health effects in humans exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

The environmental contaminant 2,3,7,8-tetrachlordibenzo-p-dioxin (TCDD) belongs to the category of highly toxic, persistent organic pollutants that accumulate in animal fat and plant tissues. Today, background TCDD levels in human fat are showing a decreasing trend. The food chain is the main source of exposure in the human population. TCDD regulates the expression of a wide range of drug-metabolizing enzymes and has an impact on a large number of biological systems. The most pronounced effects have occurred in occupational settings following the uncontrolled formation of TCDD after industrial accidents, as well as in rare intentional intoxications. Although the acute effects of TCDD exposure are well described in the literature, the long-term consequences have been underevaluated. The most well-known symptoms of severe acute intoxication are chloracne, porphyria, transient hepatotoxicity, and peripheral and central neurotoxicity. Because of the long-term persistence of TCDD in the human body, atherosclerosis, hypertension, diabetes, vascular ocular changes, and signs of neural system damage, including neuropsychological impairment, can be present several decades after massive exposure. Such chronic effects are nonspecific, multifactorial, and may be causally linked to TCDD only in heavily intoxicated subjects. This opinion is supported by the dose-dependent effect of TCDD found in exposed workers and by experimental animal studies.

Dioxin effects on neonatal and infant thyroid function: routes of perinatal exposure, mechanisms of action and evidence from epidemiology studies

OBJECTIVES

Animal experiments suggest that thyroid function alterations in newborns and infants may represent one of the most sensitive markers of toxicity from 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Dioxin can be transferred from the mother to the offspring either in utero or through lactation. It has been suggested that thyroid-hormone alterations produced by dioxin in utero or shortly after birth may underlie long-term effects, such as cognitive-ability and neurodevelopment impairment. In the present review article, we appraise available evidence on the effects of perinatal exposure to dioxin on fetal and infant thyroid function.

METHODS

We summarized the routes of perinatal dioxin exposure and research results on possible mechanisms of dioxin toxic effects on thyroid function. We performed a systematic review of epidemiology studies conducted on mother-child pairs exposed to background environmental levels to investigate dioxin effects on neonatal and infant thyroid function.

RESULTS

Toxicological and mechanistic data indicate that dioxin may impair thyroid function in exposed newborns and infants. Investigations on background-exposed children have not consistently demonstrated an association between perinatal TCDD exposure and thyroid function, although some of the studies suggest that sub-clinical hypothyroidism may be induced by perinatal dioxin exposure within 3 months from birth. Between studies inconsistencies may be related to lab method differences, mixed exposures, and small sample size of the populations evaluated.

CONCLUSION

Epidemiology studies have as yet failed to demonstrate an association between perinatal TCDD exposure and thyroid function alterations in human subjects, although suggestive evidence from animal and in-vitro experimental data is available.

Health status and plasma dioxin levels in chloracne cases 20 years after the Seveso, Italy accident

BACKGROUND

The Seveso, Italy accident of 1976 exposed a large population to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD or simply dioxin). The accident resulted, mostly among children, in one of the largest ever-reported outbreaks of chloracne, the typical skin disorder due to halogenated-hydrocarbon compounds.

OBJECTIVES

Approximately 20 years after the accident, we conducted an epidemiological study in Seveso to investigate (a) the health status of chloracne cases; (b) TCDD-chloracne exposure-response relationship; and (c) factors modifying TCDD toxicity.

METHODS

From 1993 to 1998, we recruited 101 chloracne cases and 211 controls. Trained interviewers administered a structured questionnaire assessing, among other epidemiological variables, information on an extensive list of diseases. During the interview, individual pigmentary characteristics were determined. We measured plasma TCDD levels using high-resolution gas chromatography/mass spectrometry.

RESULTS

Plasma TCDD was still elevated (> 10 ppt) in 78 (26.6%) of the 293 subjects with adequate plasma samples, particularly in females, in subjects who had eaten home-grown animals, and in individuals with older age, higher body mass index and residence near the accident site. After 20 years, health conditions of chloracne cases were similar to those of controls from the Seveso area. Elevated plasma TCDD was associated with chloracne [odds ratio (OR) = 3.7, 95% confidence interval (CI) 1.6-8.8, adjusted for age, sex and residence]. Chloracne risk was higher in subjects younger than 8 years at the accident (OR = 7.4, 95% CI 1.8-30.3) and, contrary to previous hypotheses, did not increase at puberty onset or in teenage years. Subjects with elevated TCDD levels and light hair colour had higher relative odds of chloracne (OR = 9.2, 95% CI 2.6-32.5).

CONCLUSIONS

Dioxin toxicity in chloracne cases was confined to the acute dermatotoxic effects. Chloracne occurrence appeared related to younger age and light hair colour. Age-related dioxin elimination or dilution must be taken into account in interpreting these results.

Dioxin-Like TEQ of women from the Seveso, Italy area by ID-HRGC/HRMS and CALUX

Polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs) are widespread environmental contaminants that exist as complex mixtures and are frequently detected at part-per-trillion (ppt) levels in humans. Using isotope dilution high-resolution gas chromatography/ high-resolution mass spectrometry (HRGC/HRMS), we measure the PCDDs, PCDFs, and PCBs in serum of a population of 78 women residing in an area near Seveso, Italy where a TCDD explosion occurred in 1976 and where furniture is manufactured. The average total dioxin-like toxic equivalents (TEQ) of these women was 25.3 ppt, lipid-adjusted, comparable to other parts of Europe. TCDD levels, however, were higher among the few women who resided in the exposed area in 1976. We examined the possibility of using the CALUX (chemical-activated luciferase gene expression) bioassay to estimate total TEQ in a small volume of plasma from this population. A total of 32 archived plasma specimens were selected for CALUX bioassay, based on the distribution of Total TEQ by HRGC/HRMS. The CALUX bioassay was performed blind to HRGC/HRMS results with 2 ml plasma per replicate analysis. Of 32 samples, 10 were below detection limits in the CALUX bioassay. For the 32 samples, the CALUX-TEQ averaged 25.4 ppt, lipid-adjusted (range: 0-127.6) and was not significantly different from the HRGC/HRMS Total TEQ average of 31.2 ppt, lipid-adjusted (range: 12.7-88.3) (t = 0.88, P = 0.38), however, the two measures were not significantly correlated (R(s) = 0.04, P=0.82). More validation of the CALUX bioassay with larger sample volume is needed before application as an exposure measure in large-scale epidemiologic studies of health effects of dioxin-like compounds.

CYP1A1 and CYP1B1 genotypes, haplotypes, and TCDD-induced gene expression in subjects from Seveso, Italy

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is highly toxic in experimental animals, and is known to induce cytochrome P450 (CYP) gene expression. We investigated the effect of CYP1A1 and CYP1B1 variant genotypes and haplotypes on CYP1A1 and CYP1B1 mRNA expression and ethoxyresorufin-O-deethylase (EROD) activity in lymphocytes from 121 subjects from the Seveso population, Italy, accidentally exposed to TCDD in 1976. The 3'UTR 3801T>C and I462V variants of CYP1A1 were present in 16% and 6% of the subjects, respectively. The frequency of CYP1B1 variants was 85.2% for L432V, 49.6% for R48G and A119S, and 28.7% for N453S. There was complete linkage disequilibrium (LD) among the CYP1B1 variant loci (D'=-1) and high LD among the CYP1A1 loci (D'=0.86). Gene expression measured by RT-PCR did not vary by CYP1B1 genotype in uncultured lymphocytes. However, when lymphocytes were treated in vitro with 10 nM TCDD, CYP1B1 and CYP1A1 mRNA expression was strongly induced and modified by CYP variant alleles. Specifically, the CYP1B1*3 haplotype (L432V) was associated with increased CYP1B1 mRNA expression (P=0.03), following an additive model; the CYP1A1 I462V polymorphism was positively, although not significantly, associated with CYP1A1 expression. The CYP1B1*3 variant may have affected CYP1B1 expression in subjects highly and acutely exposed to dioxin at the time of the accident. Although based on small number of subjects, a slight increase in eczema (P=0.05, n=8) and urticaria (P=0.02, n=2) was observed 20 years after the accident in subjects carrying the CYP1B1*3 allele. Genetic variation in cytochrome P450 induction may identify subjects with variable responsiveness to TCDD and potentially increased risk of disease.

Concentrations of environmental chemicals associated with neurodevelopmental effects in U.S. population

Humans are exposed to many environmental chemicals, some of which can potentially affect neurodevelopment. Fetuses, infants, and young children are the most susceptible to the effects of these chemicals. As part of the National Health and Examination Survey, 1999-2000, the Centers for Disease Control and Prevention analyzed biological samples for many of these chemicals in a representative sampling of the U.S. population. Concentration data of selected metals, persistent organic pollutants, organophosphorus and carbamate insecticides, and cotinine are presented. For example, the 95th percentile estimates for serum total PCBs (whole weight) in the population aged 20 years and older is about 2.7 ng/g. The 95th percentile estimates for serum dioxin total toxic equivalence in the U.S. population aged 20 years and older is between 40 and 50 pg/g lipid basis. In general, human levels of these chemicals are decreasing over time in the U.S. population. This reflects the effects of legislation, industry efforts, and changes in lifestyle/activity patterns in the U.S. population. These data will continue to be collected in 2-year cycles and thus allow changes in human levels to be followed.

Concentration-dependent TCDD elimination kinetics in humans: toxicokinetic modeling for moderately to highly exposed adults from Seveso, Italy, and Vienna, Austria, and impact on dose estimates for the NIOSH cohort

Serial measurements of serum lipid 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) concentrations in 36 adults from Seveso, Italy, and three patients from Vienna, Austria, with initial serum lipid TCDD concentrations ranging from 130 to 144,000 ppt, were modeled using a modified version of a previously published toxicokinetic model for the distribution and elimination of dioxins. The original model structure accounted for a concentration-dependent increase in overall elimination rate for TCDD due to nonlinear distribution of TCDD to the liver (secondary to induction of the binding protein CYP1A2), from which elimination takes place via a first-order process. The original model structure was modified to include elimination due to lipid partitioning of TCDD from circulation into the large intestine, based on published human data. We optimized the fit of the modified model to the data by varying the hepatic elimination rate parameter for each of the 39 people. The model fits indicate that there is significant interindividual variability of TCDD elimination efficiency in humans and also demonstrate faster elimination in men compared to women, and in younger vs. older persons. The data and model results indicate that, for males, the mean apparent half-life for TCDD (as reflected in changes in predicted serum lipid TCDD level) ranges from less than 3 years at serum lipid levels above 10,000 ppt to over 10 years at serum lipid levels below 50 ppt. Application of the model to serum sampling data from the cohort of US herbicide-manufacturing workers assembled by the National Institute of Occupational Safety and Health (NIOSH) indicates that previous estimates of peak serum lipid TCDD concentrations in dioxin-exposed manufacturing workers, based on first-order back-extrapolations with half-lives of 7-9 years, may have underestimated the maximum concentrations in these workers and other occupational cohorts by several-fold to an order of magnitude or more. Such dose estimates, based on a single sampling point decades after last exposure, are highly variable and dependent on a variety of assumptions and factors that cannot be fully determined, including interindividual variations in elimination efficiency. Dose estimates for these cohorts should be re-evaluated in light of the demonstration of concentration-dependent elimination kinetics for TCDD, and the large degree of uncertainty in back-calculated dose estimates should be explicitly incorporated in quantitative estimates of TCDD's carcinogenic potency based on such data.

Modulation of the hepatic CYP1A1 system in the marine fish Gobius niger, exposed to xenobiotic compounds

Anthropogenic chemicals in the aquatic environment are known to cause reproductive disturbances in vertebrate and invertebrate organisms by interfering with the endocrine systems. Large efforts have recently been devoted to dissect the mechanisms of action of xenobiotics in aquatic species, with the ultimate aim of detecting and controlling the effects of chemical exposure on the aquatic ecosystem and humans. In the present paper, males of a marine species, the black goby (Gobius niger), were treated with estrogenic and dioxin-like compounds commonly discharged into the environment from industry, agriculture, and urban waste such as nonylphenol (NP) and beta-naphthoflavone (beta-NF). Their effects were compared with those induced by estradiol (E2), analyzing the expression of biomarkers commonly used in ecotoxicological studies such as vitellogenin (VTG) and cytochrome P4501A1. The treatment with NP induced the synthesis of the female specific protein VTG in males, showing its estrogenic activity. NP and E2 lowered cytochrome P4501A1 basal levels while beta-NF determined a significant rise of its expression. The detoxification pathway was investigated, and the most relevant finding of this paper was the evidence that cytochrome P4501A1 inhibition by estrogen and estrogen-like compounds is mediated through the activation of the aryl hydrocarbon receptor repressor.

Relationship of serum TCDD concentrations and age at exposure of female residents of Seveso, Italy

In 1976, a chemical plant explosion near Seveso, Italy, resulted in the highest known exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in residential populations. In 1996, we initiated the Seveso Women's Health Study (SWHS), a historical cohort study of females who were 40 years old at the time of explosion and residents of the most heavily contaminated areas, zones A and B. Serum samples collected near the time of the explosion were analyzed for TCDD. We also analyzed pooled serum samples collected in 1976 from females who resided in zone non-ABR, the "unexposed" zone, to assess concurrent background exposures to other dioxins, furans, and coplanar polychlorinated biphenyls (PCBs). The median lipid-adjusted TCDD level for residents of zones A and B combined was 56 ppt (range = 2.5-56,000 ppt). Zone A residents had 5-fold higher TCDD levels (n = 67, median = 272 ppt) than did zone B residents (n = 814, median = 47 ppt). The youngest children had the highest TCDD levels, which decreased with age at explosion until approximately 13 years of age and were constant thereafter. Therefore, children living in zones A and B received a disproportionately higher exposure to TCDD as a result of the explosion. Zone of residence and age were the strongest predictors of TCDD level. Chloracne, nearby animal mortality, location (outdoors vs. indoors) at the time of explosion, and consumption of homegrown food were also related to serum TCDD levels. The serum pools from zone non-ABR residents had an average TCDD concentration of 20.2 ppt, and average total toxic equivalent (TEQ) concentration of 100.4 ppt. Therefore, background exposure to dioxins, furans, and PCBs unrelated to the explosion may have been substantial. As a consequence, previous SWHS studies that considered only TCDD exposure may have underestimated health effects due to total TEQ concentrations.

Possible range of dioxin concentration in human tissues: simulation with a physiologically based model

In risk evaluation of dioxins, monitoring chemical concentrations in human tissues is an important step, and these concentration data can be utilized along with animal toxicity data for extrapolation of human manifestation. However large differences in dioxin concentrations usually exist even among individuals who have never been accidentally exposed to high quantities of dioxin, and this may cause problems in risk analysis. Body size, age, and history of food consumption are factors responsible for these interindividual differences in addition to exposure levels. Using a physiologically based pharmacokinetic (PBPK) model, the influence of differences in body weight, gastrointestinal absorption, and half-life and intake of dioxin were examined on tissue chemical concentration. Dioxin concentrations over a 40-yr time course in human liver, kidneys, fat, blood, muscle and richly perfused tissue were simulated for polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and coplanar polychlorinated biphenyls (CoPCBs). Model parameters such as tissue-blood partition coefficients for CoPCBs were prepared, and sensitivity analysis was also performed on these parameters. The range of tissue concentrations was approximately 0.17 to 4.1 times the standard concentration, which was calculated using standard model parameters. The simulated ranges included more than 80% of the individual anatomical data for 2,3,7,8-tetrachlorodibenzo-p-dioxin, 1,2,3,7,-pentachlorodibenzo-p-dioxin, and 3,3',4,4',5-pentachlorobiphenyl in liver, fat, and blood. These results suggest that differences in body weight, gastrointestinal absorption, and food intake behavior may partially explain variation in tissue concentrations among individuals, and the possible interindividual uncertainty, which is approximately 24 for the general Japanese population.

Immunologic effects of dioxin: new results from Seveso and comparison with other studies

Animal studies indicate that the immune system is one of the most sensitive targets of the toxic effects of 2,3,7,8-tetrachloro-p-dibenzodioxin (TCDD). TCDD inhibits immunoglobulin secretion and decreases resistance to bacterial, viral, and parasitic infections in exposed animals. Nearly 20 years after the Seveso, Italy, accident, we measured immunoglobulin and complement plasma levels in a random sample of the population in the most highly exposed zones (n = 62) and in the surrounding noncontaminated area (n = 58). Plasma IgG levels decreased with increasing TCDD plasma concentration (r = -0.35, p = 0.0002). Median IgG concentration decreased from 1,526 mg/dL in the group with the lowest (< 3.5 ppt) TCDD levels to 1,163 mg/dL in the group with the highest (20.1-89.9 ppt) TCDD levels (p = 0.002). The association was significant (p = 0.0004) after adjusting for age, sex, smoking, and consumption of domestic livestock and poultry in multiple regression analysis and persisted after exclusion of subjects with inflammatory diseases and those using antibiotics or nonsteroidal anti-inflammatory drugs. IgM, IgA, C3, and C4 plasma concentrations did not exhibit any consistent association with TCDD levels. We performed a systematic review of all the articles published between 1966 and 2001 on human subjects exposed to TCDD reporting information on circulating levels of immunoglobulins and/or complement components. The literature indicates that the evidence for effects of TCDD on humoral immunity is sparse. Methodologic issues, results, and possible sources of variation between studies are discussed. The possible long-term immunologic effects of TCDD exhibited by the participants of the present study, coupled with the increased incidence of lymphatic tumors in the area of the accident, warrant further investigation.

Half-lives of tetra-, penta-, hexa-, hepta-, and octachlorodibenzo-p-dioxin in rats, monkeys, and humans--a critical review

The elimination half-lives (t1/2) in Sprague-Dawley rats for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 1,2, 3,7,8-pentachlorodibenzo-p-dioxin (PeCDD), 1,2,3,4,7,8-hexachlorodibenzo-p-dioxin (HxCDD), 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin (HpCDD) and 1,2,3,4,6,7,8,9-octachlorodibenzo-p-dioxin (OCDD) were estimated in long-term studies by Schlatter, Poiger and others. Furthermore, there are some published half-lives of TCDD in adult humans. The average half-life of TCDD in adult humans is approximately 2840 days, while in Sprague-Dawley rats the average t1/2 of TCDD is 19 days. The t1/2 of TCDD in humans is about 150 times that of rats. This factor was used to calculate the t1/2 values of the other polychlorinated dibenzo-p-dioxins (PCDDs) in humans from the rat data. Furthermore, the terminal t1/2 values of PCDDs in adult humans were calculated from the regression equation: logt1/2H = 1.34 logt1/2R + 1.25 which was recently established for 50 xenobiotics (t1/2H = terminal half-lives in days for humans, t1/2R = terminal half-lives in days for rats). The following terminal half-lives in adult humans were obtained: 12.6 years for 1,2,3,7,8-PeCDD, 26-45 years for 1,2,3,4,7,8-HxCDD, 80-102 years for 1,2,3,4,6,7,8-HpCDD and ca. 112-132 years for OCDD. These half-lives of PCDDs are critically compared with measured t1/2 values of PCDDs and other persistent organic pollutants in rats, monkeys and humans.

Is hepatic cytochrome P4501A1 expression predictive of hepatic burdens of dioxins, furans, and PCBs in Atlantic tomcod from the Hudson River estuary?

Hepatic cytochrome P4501A1 (CYP1A1) expression in fishes is frequently used to evaluate bioavailable aromatic hydrocarbon contamination of aquatic ecosystems. In controlled laboratory experiments, CYP1A1 expression in naïve fishes is usually dose-responsive to aromatic hydrocarbons and in field studies levels of gene expression in natural populations often correspond with known levels of sediment-borne contaminants. We quantified CYP1A1 mRNA levels in juvenile Atlantic tomcod Microgadus tomcod from 42 sites in the Hudson River estuary to evaluate the correspondence between hepatic CYP1A1 expression and hepatic concentrations of persistent halogenated aromatic hydrocarbons and to determine the utility of CYP1A1 expression as a biomarker in evaluating the microgeographic distribution of bioavailable contaminants within a large aquatic ecosystem. We found significant spatial heterogeneity in CYP1A1 mRNA levels among collection sites with levels of gene expression differing in some cases by 23-34 folds. CYP1A1 mRNA expression was highest in tomcod from the Newark Bay complex and lowest in tomcod from the most upriver collection sites in the main stem of the Hudson River. Although levels of PCDDs, PCDFs, and PCBs expressed as TCDD TEQs and CYP1A1 mRNA were highest in tomcod from the Newark Bay complex, there was no relationship between hepatic halogenated aromatic hydrocarbon levels and hepatic CYP1A1 mRNA in tomcod from sites in the main stem of the Hudson River. These results suggest that levels of CYP1A1 expression in fish from sites highly polluted with mixtures of halogenated aromatic hydrocarbons and other xenobiotics may not always be reflective of levels of bioavailable aromatic hydrocarbon contaminants. Based on these results and earlier controlled laboratory experiments, we hypothesize that elevated levels of CYP1A1 expression in tomcod from the Hudson River may be due primarily to PAHs or other contaminants not measured in this study.

Toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin and related compounds

Dioxin-type chemicals produce a variety of toxic and biochemical changes, some of which occur at very low doses and last for long periods of time. The most consistent toxin effect is body weight loss. In animals, the histopathologic changes, which are hyperplastic and hypertrophic, affect the gastrointestinal mucosa and the urinary track epithelium. In contrast, atrophic responses are seen in the thymus. Both hyperplasia and necrosis are observed in the liver. The administration of 2,3,7,8-tetrachlorodibenzo-p-dioxin also produces endocrine effects and changes in carbohydrate and lipid metabolism. The most serious toxic effects and the biochemical background of the lesions are reviewed.

Persistence of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) in Ya-Er Lake area, China

The concentrations of polychlorinaxed dibenzo-p-dioxins and dibenzofurans (PCDD/F) in surface sediment, soil, human hair, and fish muscle from Ya-Er Lake area, China, were analyzed. The results showed that there were very high concentrations of PCDD/F existing in these samples. The results also indicated that Ya-Er Lake, which received a large amount of waste water from a nearby chloroalkali plant, was heavily polluted by PCDD/F. The present study demonstrated that those congeners, which possess at least three chlorine atoms in the lateral position with a fourth chlorine atom in the neighborhood bond of the third single chlorine atom, such as 1,2,7,8-TCDF and 2,3,6,7-TCDF, were very resistant to biodegradation due to the "neighbor effect" of every two chlorine atoms. The present study suggested that human hair may be a suitable alternative bioindicator for detecting PCDD/F exposure.

Accumulation and partition of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) in the muscle and liver of fish

The present study monitored fish from sites contaminated for many years, and the data reflected the results of actual, long-term environmental exposure. The sum concentrations and TEQs of PCDD/F in the muscle of common carp (Cyprinus carpio (linnaeus)) and big head (Aristichthys nobilis) from the different site of a heavily polluted lake in China are decreased with decrease of PCDD/F concentration in sediment and water. Concentration in fish can be highly variable, but the concentration is comparable in muscle between different species of fish if the concentrations are normalized by lipid content. PCDD/F accumulate in certain tissues with the highest proportions found in the liver of fish. The concentrations and TEQs in livers were also decreased with concentrations of sediments and water. The concentrations of PCDD/F in muscle are significantly correlated with those in liver. BCFs of 2,3,7,8-substituted PCDD/F calculated directly from water were consistent with that calculated indirectly from sediment. PCDD/F concentrations in sediment are much higher than that in water, therefore the measurement is much easier and the results are more accurate. Estimated BCFs for superhydrophobic chemicals derived from sediment may also serve as acceptable surrogates for "true" bioaccumulation potential.

Environmental exposure to dioxin: the Seveso experience

The toxicity in humans of 2,3,7,8-tetrachlorodibenzo-p-dioxin, a man-made compound and environmental pollutant, is still debated. The industrial accident at Seveso, Italy, in 1976 exposed a large population of both sexes and of all ages to a massive concentration of 2,3,7,8-tetrachlorodibenzo-p-dioxin. Monitoring of soil and measurement of blood samples allowed classification of the exposed population into three categories: A, B and R (high, medium and low exposure, respectively). This article presents data from longitudinal health monitoring of the population, including liver function, immune function, neurological impairment, dermatological effects, reproductive pathology, and mortality.

Distribution, transformation, and long-term accumulation of polychlorinated dibenzo-p-dioxins and dibenzofurans in different tissues of fish and piscivorous birds

The present study monitored 10-year-old fish and piscivorous birds from sites contaminated for many years. The data reflected the results of actual, long-term environmental exposures. The results demonstrate that different tissues of fish have quite different concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F). The concentration order of PCDD/F within fish is liver congruent with egg congruent with intestine>kidney congruent with heart>gill congruent with bladder>muscle>brain. The concentration order of PCDD/F within piscivorous birds was liver>egg congruent with heart>muscle congruent with stomach>brain. The results obtained also demonstrate that the accumulation patterns of piscivorous birds and fish are quite different. The tissues of fish and piscivorous birds have different capacities for bioaccumulation and biotransformation of PCDD/F; variable proportions of TEQs were also found throughout their bodies. In fish, toxic equivalency quotient (TEQ): PCDD/F ratios in various tissues ranged from 0.01 to 0.07, whereas in birds the ratios ranged from 0.07 to 0.43. If the concentrations are normalized with lipid content, the results vary less. The effect of different lipid properties is obvious in the case of brain tissue, which is richer in phospholipids.

Paternal concentrations of dioxin and sex ratio of offspring

BACKGROUND

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD or dioxin), is commonly considered the most toxic man-made substance. We have previously shown that high serum concentrations of TCDD in parents from Seveso, Italy, were linked to their having a relative increase in the number of female births after the parents exposure to a release of dioxin in 1976. We have continued the study to determine whether the parents' sex and/or age at exposure affected the sex ratio of their children.

METHODS

We measured the TCDD concentrations in serum samples from potentially exposed parents collected in 1976 and 1977, and investigated the sex ratio of their offspring.

FINDINGS

Serum samples were collected from 239 men and 296 women. 346 girls and 328 boys were born to potentially exposed parents between 1977 and 1996, showing an increased probability of female births (lower sex ratio) with increasing TCDD concentrations in the serum samples from the fathers (p=0.008). This effect starts at concentrations less than 20 ng per kg bodyweight. Fathers exposed when they were younger than 19 years of age sired significantly more girls than boys (sex ratio 0.38 [95% CI 0.30-0.47]).

INTERPRETATION

Exposure of men to TCDD is linked to a lowered male/female sex ratio in their offspring, which may persist for years after exposure. The median concentration of dioxin in fathers in this study is similar to doses that induce epididymal impairments in rats and is about 20 times the estimated average concentration of TCDD currently found in human beings in industrialised countries. These observations could have important public-health implications.

Centers needed to study women's environmental health

The view of women as primarily fecund beings goes back to prehistory, where it is expressed in the well-known series of Venuses--stone figures of women with enlarged breasts, who are often represented as pregnant. Although the Venus figures date from the late Paleolithic era, this view of women did not change much in the next 20,000 years. With the approaching millennium, however, the field of health research has begun to consider women apart from their children or prospective progeny. Reflecting this shift in viewpoint, funds for research on the environmental health of women have now become available. However, no coordinated program has been launched on the scale of the newly established Centers for Children's Environmental Health and Disease Prevention Research (1). Should women, like children, be the focus of a concerted research effort?

Breast Milk Monitoring Programs (BMMPs): world-wide early warning system for polyhalogenated POPs and for targeting studies in children's environmental health

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Analysis of breast milk to assess exposure to chlorinated contaminants in Kazakhstan: sources of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposures in an agricultural region of southern Kazakhstan

High levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; up to 208 pg/g fat) were measured in samples of breast milk collected in 1997 from 64 donors [41 first-time mothers (primiparae)] living on state farms in southern Kazakhstan. TCDD was the major contributor (70%) to the toxic equivalents, matching the congener patterns found in breast milk and serum samples collected in 1994 and 1996 from donors in nearby villages. The highest TCDD levels were found in state farms adjacent to a reservoir (zone A), which receives agricultural runoff from cotton fields. TCDD levels in zone A were significantly higher than levels in a region more distant (zone B; > 10 miles) from the reservoir (zone A: mean 53 pg/g, n = 17; zone B: mean 21 pg/g, n = 24; p = 0.0017). Levels of TCDD in breast milk and animal-derived foodstuffs were 10 times U.S. levels. Body burden and dietary data suggest that exposures to TCDD are chronic, environmental, and long term and may be related to the use of chemicals in cotton agriculture. The data suggest that the most likely source is the use of cotton defoliants contaminated with TCDD, and the most likely pathway for human exposure is via the consumption of contaminated foodstuffs.