A breast cancer case-control study of polybrominated diphenyl ether (PBDE) serum levels among California women

Association between brominated flame retardants and risk of endocrine-related cancer: A systematic review and meta-analysis

BACKGROUND

The incidence of endocrine-related cancer, which includes tumors in major endocrine glands such as the breast, thyroid, pituitary, and prostate, has been increasing year by year. Various studies have indicated that brominated flame retardants (BFRs) are neurotoxic, endocrine-toxic, reproductive-toxic, and even carcinogenic. However, the epidemiological relationship between BFR exposure and endocrine-related cancer risk remains unclear.

METHODS

We searched the PubMed, Google Scholar, and Web of Science databases for articles evaluating the association between BFR exposure and endocrine-related cancer risk. The odds ratio (OR) and its corresponding 95% confidence interval (95% CI) were used to assess the association. Statistical heterogeneity among studies was assessed with the Q-test and I2 statistics. Begg's test was performed to evaluate the publication bias.

RESULTS

We collected 15 studies, including 6 nested case-control and 9 case-control studies, with 3468 cases and 4187 controls. These studies assessed the risk of breast cancer, thyroid cancer, and endocrine-related cancers in relation to BFR levels. Our findings indicate a significant association between BFR exposure in adipose tissue and an increased risk of breast cancer. However, this association was not observed for thyroid cancer. Generally, BFR exposure appears to elevate the risk of endocrine-related cancers, with a notable increase in risk linked to higher levels of BDE-28, a specific polybrominated diphenyl ether congener.

CONCLUSIONS

In conclusion, although this meta-analysis has several limitations, our results suggest that BFR exposure is a significant risk factor for breast cancer, and low-brominated BDE-28 exposure could significantly increase the risk of endocrine-related cancers. Further research is essential to clarify the potential causal relationships between BFRs and endocrine-related cancers, and their carcinogenic mechanisms.

Exposure to Polybrominated Diphenyl Ethers and Risk of All-Cause and Cause-Specific Mortality

Importance

Polybrominated diphenyl ethers (PBDEs) are an important group of persistent organic pollutants with endocrine-disrupting properties. However, prospective cohort studies regarding the association of PBDE exposure with long-term health outcomes, particularly mortality, are lacking.

Objective

To examine the association of environmental exposure to PBDEs with risk of all-cause and cause-specific mortality.

Design, Setting, and Participants

This nationally representative cohort study used data from the National Health and Nutrition Examination Survey 2003 to 2004 and linked mortality information through December 31, 2019. Adults aged 20 years or older with available data on PBDE measurements and mortality were included. Statistical analysis was performed from February 2022 to April 2023.

Exposures

PBDE analytes in serum samples were measured using solid phase extraction and isotope dilution gas chromatography high-resolution mass spectrometry.

Main Outcomes and Measures

All-cause mortality, cancer mortality, and cardiovascular mortality.

Results

This study included 1100 participants (mean [SE] age, 42.9 [0.6] years; proportion [SE] female, 51.8% [1.6%]; proportion [SE] Hispanic, 12.9% [2.7%]; proportion [SE] non-Hispanic Black, 10.5% [1.6%]; proportion [SE] non-Hispanic White, 70.8% [3.7%]; proportion [SE] other race and ethnicity, 5.8% [1.1%]). During 16 162 person-years of follow-up (median [IQR] follow-up, 15.8 [15.2-16.3] years; maximum follow-up, 17 years), 199 deaths occurred. Participants with higher serum PBDE levels were at higher risk for death. After adjustment for age, sex, and race and ethnicity, lifestyle and socioeconomic factors, and body mass index, participants with the highest tertile of serum PBDE levels had an approximately 300% increased risk of cancer mortality (HR, 4.09 [95% CI, 1.71-9.79]) compared with those with the lowest tertile of serum PBDE levels. No significant association of PBDE exposure with all-cause mortality (HR, 1.43 [95% CI, 0.98-2.07]) or cardiovascular mortality (HR, 0.92 [95% CI, 0.41-2.08]) was observed.

Conclusions and Relevance

In this nationally representative cohort study, PBDE exposure was significantly associated with an increased risk of cancer mortality. Further studies are needed to replicate the findings and determine the underlying mechanisms.

The adverse role of endocrine disrupting chemicals in the reproductive system

Reproductive system diseases pose prominent threats to human physical and mental well-being. Besides being influenced by genetic material regulation and changes in lifestyle, the occurrence of these diseases is closely connected to exposure to harmful substances in the environment. Endocrine disrupting chemicals (EDCs), characterized by hormone-like effects, have a wide range of influences on the reproductive system. EDCs are ubiquitous in the natural environment and are present in a wide range of industrial and everyday products. Currently, thousands of chemicals have been reported to exhibit endocrine effects, and this number is likely to increase as the testing for potential EDCs has not been consistently required, and obtaining data has been limited, partly due to the long latency of many diseases. The ability to avoid exposure to EDCs, especially those of artificially synthesized origin, is increasingly challenging. While EDCs can be divided into persistent and non-persistent depending on their degree of degradation, due to the recent uptick in research studies in this area, we have chosen to focus on the research pertaining to the detrimental effects on reproductive health of exposure to several EDCs that are widely encountered in daily life over the past six years, specifically bisphenol A (BPA), phthalates (PAEs), polychlorinated biphenyls (PCBs), parabens, pesticides, heavy metals, and so on. By focusing on the impact of EDCs on the hypothalamic-pituitary-gonadal (HPG) axis, which leads to the occurrence and development of reproductive system diseases, this review aims to provide new insights into the molecular mechanisms of EDCs' damage to human health and to encourage further in-depth research to clarify the potentially harmful effects of EDC exposure through various other mechanisms. Ultimately, it offers a scientific basis to enhance EDCs risk management, an endeavor of significant scientific and societal importance for safeguarding reproductive health.

Update of the risk assessment of polybrominated diphenyl ethers (PBDEs) in food

The European Commission asked EFSA to update its 2011 risk assessment on polybrominated diphenyl ethers (PBDEs) in food, focusing on 10 congeners: BDE-28, -47, -49, -99, -100, -138, -153, -154, -183 and ‑209. The CONTAM Panel concluded that the neurodevelopmental effects on behaviour and reproductive/developmental effects are the critical effects in rodent studies. For four congeners (BDE-47, -99, -153, -209) the Panel derived Reference Points, i.e. benchmark doses and corresponding lower 95% confidence limits (BMDLs), for endpoint-specific benchmark responses. Since repeated exposure to PBDEs results in accumulation of these chemicals in the body, the Panel estimated the body burden at the BMDL in rodents, and the chronic intake that would lead to the same body burden in humans. For the remaining six congeners no studies were available to identify Reference Points. The Panel concluded that there is scientific basis for inclusion of all 10 congeners in a common assessment group and performed a combined risk assessment. The Panel concluded that the combined margin of exposure (MOET) approach was the most appropriate risk metric and applied a tiered approach to the risk characterisation. Over 84,000 analytical results for the 10 congeners in food were used to estimate the exposure across dietary surveys and age groups of the European population. The most important contributors to the chronic dietary Lower Bound exposure to PBDEs were meat and meat products and fish and seafood. Taking into account the uncertainties affecting the assessment, the Panel concluded that it is likely that current dietary exposure to PBDEs in the European population raises a health concern.

Novel Insights into Uptake, Translocation, and Transformation Mechanisms of 2,2',4,4'-Tetra Brominated Diphenyl Ether (BDE-47) in Wheat (Triticum aestivum L.): Implication by Compound-Specific Stable Isotope and Transcriptome Analysis

The uptake, translocation, and transformation of 2,2',4,4'-tetra brominated diphenyl ether (BDE-47) in wheat (Triticum aestivum L.) were comprehensively investigated by hydroponic experiments using compound-specific stable isotope analysis (CSIA) and transcriptome analysis. The results indicated that BDE-47 was quickly adsorbed on epidermis of wheat roots and then absorbed in roots via water and anion channels as well as an active process dependent on energy. A small fraction of BDE-47 in roots was subjected to translocation acropetally, and an increase of δ13C values in shoots than roots implied that BDE-47 in roots had to cross at least one lipid bilayer to enter the vascular bundle via transporters. In addition, accompanied by the decreasing concentrations, δ13C values of BDE-47 showed the increasing trend with time in shoots, indicating occurrence of BDE-47 transformation. OH-PBDEs were detected as transformation products, and the hydroxyl group preferentially substituted at the ortho-positions of BDE-47. Based on transcriptome analysis, genes encoding polybrominated diphenyl ether (PBDE)-metabolizing enzymes, including cytochrome P450 enzymes, nitrate reductases, and glutathione S-transferases, were significantly upregulated after exposure to BDE-47 in shoots, further evidencing BDE-47 transformation. This study first reported the stable carbon isotope fractionation of PBDEs during translocation and transformation in plants, and application of CSIA and transcriptome analysis allowed systematically characterize the environmental behaviors of pollutants in plants.

Polybrominated Diphenyl Ethers (PBDEs) and Human Health: Effects on Metabolism, Diabetes and Cancer

There is increasing evidence of the role of endocrine disruptors (EDs) derived from commonly employed compounds for manufacturing and processing in altering hormonal signaling and function. Due to their prolonged half-life and persistence, EDs can usually be found not only in industrial products but also in households and in the environment, creating the premises for long-lasting exposure. Polybrominated diphenyl ethers (PBDEs) are common EDs used in industrial products such as flame retardants, and recent studies are increasingly showing that they may interfere with both metabolic and oncogenic pathways. In this article, a multidisciplinary panel of experts of the Italian Association of Medical Diabetologists (AMD), the Italian Society of Diabetology (SID), the Italian Association of Medical Oncology (AIOM), the Italian Society of Endocrinology (SIE) and the Italian Society of Pharmacology (SIF) provides a review on the potential role of PBDEs in human health and disease, exploring both molecular and clinical aspects and focusing on metabolic and oncogenic pathways.

Adipose tissue levels of polybrominated diphenyl ethers in relation to prognostic biomarkers and progression-free survival time of breast cancer patients in eastern area of southern China: A hospital-based study

Evidence indicates that individual or groups of polybrominated diphenyl ethers (PBDEs) are associated with risk of breast cancer (BC). Epidemiological studies of PBDEs and BC progression are scarce. This study aimed to investigate the relationships between PBDE burdens in adipose tissues and prognostic biomarkers of BC as well as progression-free survival (PFS) of patients for the first time. The concentrations of 14 PBDE congeners in breast adipose tissues of 183 cases from the eastern area of southern China were analyzed by gas chromatography-mass spectrometry (GC-MS). Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated by logistic regression models for the associations between PBDE levels and prognostic biomarkers. Kaplan-Meier and Cox regression analyses were conducted to identify the correlations between PBDEs and PFS. The results showed that BDE-99 and 190 levels were positively associated with clinical stage and N stage respectively (OR = 2.61 [1.26-5.40], OR = 2.78 [1.04-7.46]). Concentrations of BDE-28 and BDE-183 were negatively associated with the expression of estrogen receptor (ER) (OR = 0.30 [0.11-0.81]; 0.39 [0.15-0.99]) and progesterone receptor (PR) (OR = 0.36 [0.14-0.92]; 0.37 [0.15-0.91]), and increased BDE-47 was associated with lower human epidermal growth factor receptor 2 (HER2) expression (OR = 0.44 [0.23-0.86]). Adipose levels of BDE-71, 99, 138, 153, 154 and total PBDEs were positively associated with p53 expression (all P < 0.05). Finally, BDE-47, 99 and 183 were considered as independent prognostic factors for shorter PFS in the Cox models (adjusted hazard ratios = 3.14 [1.26-7.82]; 2.25 [1.03-4.94]; 2.60 [1.08-6.25], respectively). The recurrence risk and prognosis of BC may be closely bound to the body burdens of certain PBDE congeners. Further epidemiological and experimental studies are needed for confirmation.

The role of polybrominated diphenyl ethers in the induction of cancer: a systematic review of insight into their mechanisms

Environmental pollution caused by persistent organic pollutants (POPs) has increased the challenge for the scientific communities. Polybrominated diphenyl ethers (PBDEs), classified as POPs, are widely applied in various materials as brominated flame retardants (BFRs). Because of the nature of these chemical compounds including toxicity, stability, and capability to bioaccumulate and biomagnify, PBDEs have posed a great challenge and risk to human health and wildlife. Therefore, the side effects of exposure to PBDEs as ubiquitous pollutants in the environment on cancer progression were investigated using a systematic review (SR) survey. To achieve this goal, forty studies were considered after defining the search terms and inclusion criteria, and/or exclusion criteria; the eligible records were collected from the international bibliographic databases. Based on the findings of the reviewed records, environmental exposure to the BFRs including PBDEs has a positive association with different mechanisms that induce cancer progression. However, the findings of the reviewed studies were not totally consistent with the mode of action and side effects are yet to be fully elucidated. Several articles have reported that BFRs can be carcinogenic and induce epithelial to mesenchymal transition via different mechanisms. The main mode of action involved in the environmental exposure to BFRs and the risk of cancer progression is endoplasmic reticulum and oxidative stress (OS). Generally, the imbalance of antioxidant mechanisms, reactive nitrogen species (RNSs) and reactive oxygen species (ROSs), during damage in cells, and stress caused OS, which increases tumorigenesis via multiple mechanisms, such as DNA damage, inflammation, and angiogenesis.

Positive association between dietary exposure to polybrominated diphenyl ethers and breast cancer risk in the French E3N cohort: The role of vegetable oil consumption

Exposure to endocrine-disrupting chemicals, like Polybrominated diphenyl ethers (PBDEs), is suspected of playing a role in the occurrence of breast cancer. Moreover, there is growing evidence that food chemical contaminants, especially lipophilic ones such as PBDEs, could interact with different components of the diet. The objective of the present study was to assess the association between dietary intake of PBDEs and breast cancer risk in the French E3N cohort study, and to investigate the potential modification of this association by vegetable oil consumption. The study included 67879 women. Intakes of eight PBDEs were estimated using food consumption data from a validated semi-quantitative food frequency questionnaire, and food contamination levels measured by the French Agency for Food, Environmental and Occupational Health and Safety (ANSES). Cox proportional hazards models were used to estimate Hazard Ratios (HR) and 95% Confidence Intervals (CI) for the association between total PBDEs dietary intake and breast cancer risk. Interaction measures for vegetable oil consumption were estimated on both additive and multiplicative scales. The women were followed for a maximum of 21.4 years, and 5 686 developed an incident breast cancer. A positive linear trend was highlighted between dietary intake of PBDEs in quintile groups and breast cancer risk, borderline with statistical significance (p-trend = 0.06, HR_Q5vsQ1 and 95% CI: 1.09 [0.99;1.20]). Interaction measures for vegetable oil consumption were significant in both additive and multiplicative scales. Higher effect sizes of the association were highlighted in high consumers of vegetable oil, i.e. ≥4.6 g/day (HR_Q5vsQ1 and 95% CI: 1.23 [1.08; 1.40]), and almost no effect were found in low consumers (HR_Q5vsQ1 and 95% CI: 0.97 [0.86; 1.10]). Highlighting such interactions between nutrients and chemicals is crucial to develop efficient dietary recommendations to limit the negative health effects associated with exposure to food chemical contaminants.

Associations between polybrominated diphenyl ethers (PBDEs) levels in adipose tissues and female menstrual cycle and menstrual bleeding duration in Shantou, China

The endocrine-disrupting effects of human exposure to polybrominated diphenyl ethers (PBDEs) have been studied, but their associations with menstrual status were not clearly clarified. This study was to evaluate the associations between PBDE levels in adipose tissues and the menstrual cycle and menstrual bleeding duration alteration. A total of 298 female cases undergoing surgery were recruited from two hospitals in Shantou, China. Demographic, clinical, and pathological information were collected, and adipose tissues were obtained during mammary or abdominal surgery. Gas chromatography with mass spectrometry was used to analyze 14 PBDE congeners in the adipose samples. The associations between PBDE levels and menstrual cycle (MC) and menstrual duration (MD) were analyzed by logistic regression models, estimating odds ratios (ORs) and 95% confidence intervals (CIs). BDE-153 had the highest level in the adipose samples, followed by BDE-209, BDE-183 and BDE-47. Compared with referents, median levels of BDE-47, -71, -153, -183 were higher in women with MC > 30 days (all P < 0.05); BDE-47, -153, -183, -209 were also higher in women with MD > 5.5 days (all P < 0.05). After adjusted for age and parity, BDE-47, -71, -153, -183 were associated with prolonged MC (OR = 1.20, 1.15, 1.12, 1.11, respectively, all P < 0.05) in the logistic regression models; and BDE-47, -153, -183, -209 were associated with the prolonged MD (OR = 1.13, 1.09, 1.10, 1.11, respectively, all P < 0.05). Several individual PBDE congeners in female adipose were found associated with prolonged menstrual cycle and menstrual duration. PBDEs may influence reproductive health of women by altering menstrual status.

Application of two statistical approaches (Bayesian Kernel Machine Regression and Principal Component Regression) to assess breast cancer risk in association to exposure to mixtures of brominated flame retardants and per- and polyfluorinated alkylated substances in the E3N cohort

BACKGROUND

Brominated flame retardants (BFR) and per- and polyfluorinated alkylated substances (PFAS) are two groups of substances suspected to act as endocrine disruptors. Such substances could therefore be implicated in the occurrence of breast cancer, nevertheless, previous studies have led to inconstant results. Due to the large correlation between these substances, and the possibly non-linear effects they exert, evaluating their joint impact as mixtures on health remains challenging. This exploratory study aimed to generate hypotheses on the relationship between circulating levels of 7 BFR (6 polybrominated diphenyl ethers and 1 polybrominated biphenyls) and 11 PFAS and the risk of breast cancer in a case-control study nested in the E3N French prospective cohort by performing two methods: Principal Component Regression (PCR) models, and Bayesian Kernel Machine Regression (BKMR) models.

METHODS

194 post-menopausal breast cancer cases and 194 controls were included in the present study. Circulating levels of BFR and PFAS were measured by gas chromatography coupled to high-resolution mass spectrometry and liquid chromatography coupled to tandem mass spectrometry, respectively. The first statistical approach was based on Principal Component Analysis (PCA) followed by logistic regression models that included the identified principal components as main exposure variables. The second approach used BKMR models with hierarchical variable selection, this latter being suitable for highly correlated exposures. Both approaches were also run separately for Estrogen Receptor positive (ER +) and Estrogen Receptor negative (ER-) breast cancer cases.

RESULTS

PCA identified four principal components accounting for 67% of the total variance. Component 3 showed a marginal association with ER + breast cancer risk. No clear association between BFR and PFAS mixtures and breast cancer was identified using BKMR models, and the credible intervals obtained were very wide. Finally, the BKMR models suggested a negative cumulative effect of BFR and PFAS on ER- breast cancer risk, and a positive cumulative effect on ER + breast cancer risk.

CONCLUSION

Although globally no clear association was identified, both approaches suggested a differential effect of BFR and PFAS mixtures on ER + and ER- breast cancer risk. However, the results for ER- breast cancer should be interpreted carefully due to the small number of ER- cases included in the study. Further studies evaluating mixtures of substances on larger study populations are needed.

Major contaminants of emerging concern in soils: a perspective on potential health risks

Soil pollution by the contaminants of emerging concern (CECs) or emerging contaminants deserves attention worldwide because of their toxic health effects and the need for developing regulatory guidelines. Though the global soil burden by certain CECs is in several metric tons, the source-tracking of these contaminants in soil environments is difficult due to heterogeneity of the medium and complexities associated with the interactive mechanisms. Most CECs have higher affinities towards solid matrices for adsorption. The CECs alter not only soil functionalities but also those of plants and animals. Their toxicities are at nmol to μmol levels in cell cultures and test animals. These contaminants have a higher propensity in accumulating mostly in root-based food crops, threatening human health. Poor understanding on the fate of certain CECs in anaerobic environments and their transfer pathways in the food web limits the development of effective bioremediation strategies and restoration of the contaminated soils and endorsement of global regulatory efforts. Despite their proven toxicities to the biotic components, there are no environmental laws or guidelines for certain CECs. Moreover, the information available on the impact of soil pollution with CECs on human health is fragmentary. Therefore, we provide here a comprehensive account on five significantly important CECs, viz., (i) PFAS, (ii) micro/nanoplastics, (iii) additives (biphenyls, phthalates), (iv) novel flame retardants, and (v) nanoparticles. The emphasis is on (a) degree of soil burden of CECs and the consequences, (b) endocrine disruption and immunotoxicity, (c) genotoxicity and carcinogenicity, and (d) soil health guidelines.

Contaminants of emerging concern: sources, soil burden, human exposure, and toxicities.

Thermal treatment of decabrominated diphenyl ether in its highly contaminated soil in Taiwan

Polybrominated diphenyl ethers (PBDEs) were commonly used flame retardants in the world, while some of PBDEs have been listed as persistent organic pollutants (POPs). Decabrominated diphenyl ether (BDE-209) was the most commercially used PBDEs. A farm near the factory located in Northern Taiwan was highly contaminated with BDE-209. Since PBDEs in the contaminated soils can be uptake by crops shown in our previous studies and could be potentially consumed by humans, it is very important to establish a feasible treatment method for PBDE remediation in this contaminated farm. Thermal treatment of PBDEs in soil was studied. The initial concentration of BDE-209 in contaminated soil was 1.472 mg/kg. A series of thermal experiments under different operating conditions including various temperature (105, 150, 200, 250, 300, 350, 400 and 450 °C), holding time (10, 20 and 30 min), heating rate (5, 10, 20 and 40 °C/min), and soil amount (10, 100, 1000 and 2000 g) were investigated. The optimal heating conditions for thermal treatment of contaminated soil were heating at 450 °C for 30 min with a heating rate of 10 °C/min. Under this condition, the removal of BDE-209 in the different weights of contaminated soil was tested. The soils in the contaminated farm were tested to further evaluate the feasibility of remediating the on-site PBDE contaminated soil through thermal treatment, suggesting that the holding time was extended to 2 h for the field-scale contaminated soil. The results showed that BDE-209 had been removed to below the detection limit in on-site soil. This investigation is the first study using thermal treatment to remediate soils really contaminated with PBDEs.

Application of dual carbon-bromine stable isotope analysis to characterize anaerobic micro-degradation mechanisms of PBDEs in wetland bottom-water

Polybrominated diphenyl ethers (PBDEs), one kind of persistent organic pollutants, were widely detected in coastal wetlands. Microbial reductive debromination is one of the most important attenuation processes for PBDEs in anaerobic environment, whereas the underlying reaction mechanisms remain elusive. Dual-element stable isotope analysis was recently recognized to distinguish different reaction mechanism for degradation of organic pollutants. In this study, the dual carbon-bromine isotope effects associated with the anaerobic microbial degradation were first investigated to characterize the reaction mechanisms for BDE-47 and BDE-153. Presence of lower brominated congeners indicated stepwise debromination as the main degradation pathway, with the preferential removal of bromine in para position > meta/ortho position. The pronounced isotope fractionation was observed for both carbon and bromine, with similar carbon (ε_C) and bromine isotope enrichment factor (ε_Br) between BDE-47 (ε_C = -5.98‰, ε_Br = -2.44‰) and BDE-153 (ε_C = -5.57‰, ε_Br = -2.06‰) during the microbial degradation. Compared to ε_C and ε_Br, the correlation of carbon and isotope effects (Λ_C/Br = Δδ⁸¹Br/Δδ¹³C) was almost the same between BDE-47 (0.436) and BDE-153 (0.435), indicating the similar reaction mechanism. The calculated carbon and bromine apparent kinetic isotope effects (AKIE_C and AKIE_Br) were 1.0773 and 1.0098 for BDE-47 and 1.0716 and 1.0125 for BDE-153, within range reported for degradation of halogenated compounds following nucleophilic substitution. Combination analysis of degradation products, Λ_C/Br and AKIE, all the results pointed to that the anaerobic reductive debromination of BDE-47 and BDE-153 followed the nucleophilic aromatic substitution, with the addition of cofactor to the benzene ring concomitant with dissociation of carbon-bromine bond via the inner-sphere electron transfer, and the cleavage of C-Br bond was the rate-determining step. This study contributed to the development of dual carbon-bromine isotope analysis as a robust approach to probe the fate of PBDEs in contaminated sites.

Methylation biomarkers of polybrominated diphenyl ethers (PBDEs) and association with breast cancer risk at the time of menopause

BACKGROUND

Exposure to polybrominated diphenyl ethers (PBDEs) may influence risk of developing post-menopausal breast cancer. Although mechanisms are poorly understood, epigenetic regulation of gene expression may play a role.

OBJECTIVES

To identify DNA methylation (DNAm) changes associated with PBDE serum levels and test the association of these biomarkers with breast cancer risk.

METHODS

We studied 397 healthy women (controls) and 133 women diagnosed with breast cancer (cases) between ages 40 and 58 years who participated in the California Teachers Study. PBDE levels were measured in blood. Infinium Human Methylation EPIC Bead Chips were used to measure DNAm. Using multivariable linear regression models, differentially methylated CpG sites (DMSs) and regions (DMRs) associated with serum PBDE levels were identified using controls. For top-ranked DMSs and DMRs, targeted next-generation bisulfite sequencing was used to measure DNAm for 133 invasive breast cancer cases and 301 age-matched controls. Conditional logistic regression was used to evaluate associations between DMSs and DMRs and breast cancer risk.

RESULTS

We identified 15 DMSs and 10 DMRs statistically significantly associated with PBDE levels (FDR < 0.05). Methylation changes in a DMS at BMP8B and DMRs at TP53 and A2M-AS1 were statistically significantly (FDR < 0.05) associated with breast cancer risk.

CONCLUSION

We show for the first time that serum PBDE levels are associated with differential methylation and that PBDE-associated DNAm changes in blood are associated with breast cancer risk.

Polybrominated Diphenyl Ether Quinone Exposure Induces Atherosclerosis Progression via CD36-Mediated Lipid Accumulation, NLRP3 Inflammasome Activation, and Pyroptosis

Polybrominated diphenyl ethers (PBDEs) are used worldwide in brominated flame retardants. Although due to the forbiddance of their application, PBDEs continuously exist in the environment due to their persistence. Therefore, it is important to expand the understanding of their potential toxicities and human risks. The underlying cardiovascular toxicological mechanisms of PBDEs are still largely unknown. Our previous studies indicated that PBDE quinone-type metabolite (PBDEQ) exposure causes reactive oxygen species (ROS)-driven cytotoxicity and various types of programmed cell death. Here, we first reported PBDEQ exposure induces atherosclerosis progression in bone marrow-derived macrophages (BMDMs) isolated from wild-type C57BL/6 or CD36-/- mice and J774A.1 macrophage models. First, we found that PBDEQ exposure induced lipid accumulation in oxidized low-density lipid (Ox-LDL)-treated J774A.1 macrophages. Consistently, in J774A.1 macrophages, PBDEQ exposure resulted in NLR family pyrin domain containing 3 (NLRP3) inflammasome activation and pyroptosis. CD36, a scavenger receptor responsible for the mediation of Ox-LDL uptake, was upregulated upon PBDEQ treatment. On the contrary, genetic knockout of CD36 or CD36 silencing by small interfering RNA efficiently attenuates PBDEQ-promoted lipid accumulation in BMDMs and J774A.1 macrophages. These findings highlight the effect of CD36 on the cardiovascular toxicity of PBDEs, which provides a better understanding of the pro-atherosclerosis effect of PBDEs.

Polybrominated diphenyl ethers (PBDEs) in raw milk from different animal species and in infant formula. Occurrence and risk assessment

Polybrominated diphenyl ethers (PBDEs) are widespread, persistent in the environment, and classified as global pollutants. Their presence has been confirmed in various types of food which adversely affect human health when consumed in sufficient amounts. Although milk has advantageous nutritional qualities and there are health benefits associated with its consumption, it could also contain toxic PBDEs. The aim of the study was the determination of the concentrations of ten congeners (BDE -28, -47, -49, -99, -100, -138, -153, -154, -183, and 209) in cow's, sheep's, and goat's milk obtained from Polish farms and their determination in infant formula. A total of 103 samples of raw milk and infant formula were tested using an accredited high-resolution gas chromatography-high-resolution mass spectrometry method. PBDEs were detected in all analyzed samples, the highest concentration being found in sheep's milk (11.9 ng g^-1 fat), and cow's milk containing the least contamination. BDE-209 makes the predominant contribution to the sum of the ten congeners, constituting at least 38%. The profiles of PBDEs were dependent on the milk type and the differences between its varieties are discussed. The highest median concentration of the sum of ten PBDEs (0.473 ng g^-1 fat) was determined in infant formula, which was identified as an important source of infants' exposure (5.48 ng kg^-1 b.w. day^-1 calculated based on P95 concentration). Milk is a source of PBDE in the diet; however, considered in isolation its consumption does not pose a risk to either adults' or children's health.

Exploring the Biological Activity and Mechanism of Xenoestrogens and Phytoestrogens in Cancers: Emerging Methods and Concepts

Xenoestrogens and phytoestrogens are referred to as "foreign estrogens" that are produced outside of the human body and have been shown to exert estrogen-like activity. Xenoestrogens are synthetic industrial chemicals, whereas phytoestrogens are chemicals present in the plant. Considering that these environmental estrogen mimics potentially promote hormone-related cancers, an understanding of how they interact with estrogenic pathways in human cells is crucial to resolve their possible impacts in cancer. Here, we conducted an extensive literature evaluation on the origins of these chemicals, emerging research techniques, updated molecular mechanisms, and ongoing clinical studies of estrogen mimics in human cancers. In this review, we describe new applications of patient-derived xenograft (PDX) models and single-cell RNA sequencing (scRNA-seq) techniques in shaping the current knowledge. At the molecular and cellular levels, we provide comprehensive and up-to-date insights into the mechanism of xenoestrogens and phytoestrogens in modulating the hallmarks of cancer. At the systemic level, we bring the emerging concept of window of susceptibility (WOS) into focus. WOS is the critical timing during the female lifespan that includes the prenatal, pubertal, pregnancy, and menopausal transition periods, during which the mammary glands are more sensitive to environmental exposures. Lastly, we reviewed 18 clinical trials on the application of phytoestrogens in the prevention or treatment of different cancers, conducted from 2002 to the present, and provide evidence-based perspectives on the clinical applications of phytoestrogens in cancers. Further research with carefully thought-through concepts and advanced methods on environmental estrogens will help to improve understanding for the identification of environmental influences, as well as provide novel mechanisms to guide the development of prevention and therapeutic approaches for human cancers.

Competitive microbial degradation among PBDE congeners in anaerobic wetland sediments: Implication by multiple-line evidences including compound-specific stable isotope analysis

Polybrominated diphenyl ethers (PBDEs) are widespread contaminants in the environment. Microbial reductive debromination is one of the important attenuation processes for PBDEs in the anaerobic sediments. This study first investigated the interaction between BDE-47 and BDE-153 during the microbial degradation in wetland sediments by the multiple-line approaches including biodegradation kinetics, microbial community structures and stable isotope composition. BDE-47 and BDE-153 biodegradation fitted pseudo-zero-order kinetics, with the higher degradation rates in single than combined exposure, indicating the mutual inhibition in co-exposure condition. BDE-47 and BDE-153 shared the common dehalogenators (genus Dehalococcoides and Acinetobacter) with enrichment in combined exposure, indicating the potential competition in dehalogenating bacteria during biodegradation. Microbial degradation could lead to the isotopic fractionation of BDE-47 and BDE-153, with the smaller changes in δ¹³C in combined than single exposure. The apparent kinetic isotope effect of carbon (AKIE_C) was different between BDE-47 and BDE-153 in single exposure, whilst identical in combined exposure, indicating the similar degradation mechanism for BDE-47 and BDE-153 in co-exposure condition. These results revealed that the competition on microbial degradation occurred among PBDEs in co-exposure condition, which was important for the comprehensive risk assessment of simultaneous exposure to multiple PBDE congeners in the environment.

Polybrominated diphenyl ethers in the environmental systems: a review

PBDEs are human-influenced chemicals utilized massively as flame retardants. They are environmentally persistent, not easily degraded, bioaccumulate in the biological tissue of organisms, and bio-magnify across the food web. They can travel over a long distance, with air and water being their possible transport media. They can be transferred to non-target organisms by inhalation, oral ingestion, breastfeeding, or dermal contact. These pollutants adsorb easily to solid matrices due to their lipophilicity and hydrophobicity; thus, sediments from rivers, lakes, estuaries, and ocean are becoming their major reservoirs aquatic environments. They have low acute toxicity, but the effects of interfering with the thyroid hormone metabolism in the endocrine system are long term. Many congeners of PBDEs are considered to pose a danger to humans and the aquatic environment. They have shown the possibility of causing many undesirable effects, together with neurologic, immunological, and reproductive disruptions and possible carcinogenicity in humans. PBDEs have been detected in small amounts in biological samples, including hair, human semen, blood, urine, and breastmilk, and environmental samples such as sediment, soil, sewage sludge, air, biota, fish, mussels, surface water, and wastewater. The congeners prevailing in environmental samples, with soil being the essential matrix, are BDE 47, 99, and 100. BDE 28, 47, 99, 100, 153, 154, and 183 are more frequently detected in human tissues, whereas in sediment and soil, BDE 100 and 183 predominate. Generally, BDE 153 and 154 appear very often across different matrices. However, BDE 209 seems not frequently determined, owing to its tendency to quickly breakdown into smaller congeners. This paper carried out an overview of PBDEs in the environmental, human, and biota niches with their characteristics, physicochemical properties, and fate in the environment, human exposure, and health effects.

Exposure to endocrine disruptors and risk of breast cancer: A systematic review

AIM

The aim of this study was to investigate the association between human exposure to endocrine disruptors (EDs) and the risk of breast cancer.

METHODS

This was a systematic review conducted by searching Cochrane Library, LILACS, Livivo, PubMed, and Science Direct. Observational studies addressing the association between exposure to EDs and breast cancer risk in adults were included. Risk of bias was assessed using the National Toxicology Program's Office of Health Assessment Translation tool.

RESULTS

a total of 37 studies were included. Most studies reported that exposure to organochlorine pesticides, phthalates, heavy metals, and polycyclic aromatic hydrocarbons was associated with increased breast cancer risk.

CONCLUSION

qualitative analysis of observational studies indicates that human exposure to EDs is associated with increased breast cancer risk. Additional studies are needed to determine whether this association is causal.

Endocrine disrupting chemicals and breast cancer: a systematic review of epidemiological studies

BACKGROUND

Endocrine-disrupting compounds (EDCs) are ubiquitous substances that are found in our everyday lives, including pesticides, plasticizers, pharmaceutical agents, personal care products, and also in food products and food packaging. Increasing epidemiological evidence suggest that EDCs may affect the development or progression of breast cancer and consequently lead to lifelong harmful health consequences, especially when exposure occurs during early life in humans. Yet so far no appraisal of the available evidence has been conducted on this topic.

OBJECTIVE

To systematically review all the available epidemiological studies about the association of the levels of environmental exposures of EDCs with breast cancer risk.

METHODS

The search was performed in accordance with the PRISMA guidelines. We retrieved articles from PubMed (MEDLINE) until 10 March 2021. The key words used in this research were: "Endocrine disruptor(s)" OR "Endocrine disrupting chemical(s)" OR any of the EDCs mentioned below AND "Breast cancer" to locate all relevant articles published. We included only cohort studies and case-control studies. All relevant articles were accessed in full text and were evaluated and summarized in tables.

RESULTS

We identified 131 studies that met the search criteria and were included in this systematic review. EDCs reviewed herein included pesticides (e.g. p,p'-dichlorodiphenyltrichloroethane (DDT), p,p'-dichlorodiphenyldichloroethylene (DDE), atrazine, 2,3,7,8-tetrachloridibenzo-p-dioxin (TCDD or dioxin)), synthetic chemicals (e.g. bisphenol A (BPA), phthalates, per- and polyfluoroalkyl substances (PFAS), parabens, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), contraceptive pills), phytoestrogens (e.g. genistein, resveratrol), and certain mycotoxins (e.g. zearalenone). Most studies assessed environmental EDCs exposure via biomarker measurements.

CONCLUSION

We identified certain EDC exposures could potentially elevate the risk of breast cancer. As majority of EDCs are highly persistent in the environment and bio-accumulative, it is essential to assess the long-term impacts of EDC exposures, especially multi-generational and transgenerational. Also, since food is often a major route of exposure to EDCs, well-designed exposure assessments of potential EDCs in food and food packing are necessary and their potential link to breast cancer development need to be carefully evaluated for subsequent EDC policy making and regulations.

Relationship between exposure to mixtures of persistent, bioaccumulative, and toxic chemicals and cancer risk: A systematic review

Environmental risks are responsible for one in five of all deaths worldwide. Persistent, bioaccumulative, and toxic substances are chemicals that can subsist for decades in human tissues and the environment. They include heavy metals, organochlorines, polychlorinated biphenyls, organobromines, organofluorines, and polycyclic aromatic hydrocarbons among others. Although humans are often exposed to multiple pollutants simultaneously, their negative effects on health have generally been studied for each one separately. Among the most severe of these harmful effects is cancer. Here, to compile and analyze the available evidence on the relationship between exposure to mixtures of persistent, bioaccumulative, and toxic chemicals and the risk of developing cancer in the general population, we provide a systematic review based on the main databases (Cochrane, PubMed and Embase), together with complementary sources, using the general methodology of the PRISMA Statement. The articles analyzed were selected by two researchers working independently and their quality was evaluated by reference to the Newcastle-Ottawa scale. The initial search yielded 2379 results from the main sources of information and 22 from the complementary ones. After the article selection process, 22 were included in the final review (21 case-control studies and one cohort study). Analysis of the selected studies revealed that most of the mixtures analyzed were positively associated with risk of cancer, especially that of the breast, colon-rectum or testis, and more strongly so than each contaminant alone. In view of the possible stronger association observed with the development of cancer for some mixtures of pollutants than when each one is present separately, exposure to mixtures should also be monitored and measured, preferably in cohort designs, to complement the traditional approach to persistent, bioaccumulative, and toxic chemicals. The results presented should be taken into account in public health policies in order to strengthen the regulatory framework for cancer prevention and control.

Environmental exposures and breast cancer risk in the context of underlying susceptibility: A systematic review of the epidemiological literature

BACKGROUND

The evidence evaluating environmental chemical exposures (ECE) and breast cancer (BC) risk is heterogeneous which may stem in part as few studies measure ECE during key BC windows of susceptibility (WOS). Another possibility may be that most BC studies are skewed towards individuals at average risk, which may limit the ability to detect signals from ECE.

OBJECTIVES

We reviewed the literature on ECE and BC focusing on three types of studies or subgroup analyses based on higher absolute BC risk: BC family history (Type 1); early onset BC (Type 2); and/or genetic susceptibility (Type 3).

METHODS

We systematically searched the PubMed database to identify epidemiologic studies examining ECE and BC risk published through June 1, 2019.

RESULTS

We identified 100 publications in 56 unique epidemiologic studies. Of these 56 studies, only 2 (3.6%) were enriched with BC family history and only 11% of studies (6/56) were specifically enriched with early onset cases. 80% of the publications from these 8 enriched studies (Type 1: 8/10 publications; Type 2: 8/10 publications) supported a statistically significant association between ECE and BC risk including studies of PAH, indoor cooking, NO₂, DDT; PCBs, PFOSA; metals; personal care products; and occupational exposure to industrial dyes. 74% of Type 3 publications (20/27) supported statistically significant associations for PAHs, traffic-related air pollution, PCBs, phthalates, and PFOSAs in subgroups of women with greater genetic susceptibility due to variants in carcinogen metabolism, DNA repair, oxidative stress, cellular apoptosis and tumor suppressor genes.

DISCUSSION

Studies enriched for women at higher BC risk through family history, younger age of onset and/or genetic susceptibility consistently support an association between an ECE and BC risk. In addition to measuring exposures during WOS, designing studies that are enriched with women at higher absolute risk are necessary to robustly measure the role of ECE on BC risk.

Exposure pathways, levels and toxicity of polybrominated diphenyl ethers in humans: A review

Polybrominated diphenyl ethers (PBDEs) are extensively used as brominated flame retardants (BFRs) in different types of materials, which have been listed as Persistent Organic Pollutants (POPs) by the Stockholm Convention in 2009 and 2017. Due to their ubiquities in the environment and toxicities, PBDEs have posed great threat to both human health and ecosystems. The aim of this review is to offer a comprehensive understanding of the exposure pathways, levels and trends and associated health risks of PBDEs in human body in a global scale. We systematically reviewed and described the scientific data of PBDE researches worldwide from 2010 to March 2020, focusing on the following three areas: (1) sources and human external exposure pathways of PBDEs; (2) PBDE levels and trends in humans; (3) human data of PBDEs toxicity. Dietary intake and dust ingestion are dominant human exposure pathways. PBDEs were widely detected in human samples, especially in human serum and human milk. Data showed that PBDEs are generally declining in human samples worldwide as a result of their phasing out. Due to the common use of PBDEs, their levels in humans from the USA were generally higher than that in other countries. High concentrations of PBDEs have been detected in humans from PBDE production regions and e-waste recycling sites. BDE-47, -153 and -99 were proved to be the primary congeners in humans. Human toxicity data demonstrated that PBDEs have extensively endocrine disruption effects, developmental effects, and carcinogenic effects among different populations.

Plasma concentration of brominated flame retardants and postmenopausal breast cancer risk: a nested case-control study in the French E3N cohort

BACKGROUND

Brominated flame retardants (BFRs) are lipophilic substances with endocrine-disrupting properties. To date, only few investigations, mainly retrospective case-control studies, have explored the link between internal levels of BFRs and the risk of breast cancer, leading to conflicting results. We investigated the associations between plasma concentrations of two main groups of BFRs, PBDEs (pentabromodiphenyl ethers) and PBBs (polybrominated biphenyls), and the risk of breast cancer in a nested case-control study.

METHODS

A total of 197 incident breast cancer cases and 197 controls with a blood sample collected in 1994-1999 were included. Plasma levels of PBDE congeners (BDE-28, BDE-47, BDE-99, BDE-100, BDE153, BDE-154) and of PBB-153 were measured by gas chromatography coupled to high-resolution mass spectrometry. Conditional logistic regression models, adjusted for potential confounders, were used to estimate odds ratios (ORs) and 95% confidence intervals (CIs).

RESULTS

Women were aged 56 years on average at blood draw. All cases, except for one, were diagnosed after menopause, with an average age at diagnosis of 68 years. Overall, we found no evidence of an association between plasma levels of PBDEs and PBB-153 and postmenopausal breast cancer risk (log-concentrations of BFRs yielding non-statistically significant ORs of 0.87 to 1.07). The analysis showed a non-linear inverse association for BDE-100 and BDE-153 and postmenopausal breast cancer risk; nevertheless, these findings were statistically significant only when the exposure was modeled as ng/L plasma (third vs. first quintile: OR = 0.42, 95%CI = 0.19-0.93 and OR = 0.42, 95%CI = 0.18-0.98, respectively) and not when modeled as ng/gr of lipids (OR = 0.58, 95%CI = 0.27-1.25 and OR = 0.53, 95%CI = 0.25-1.17). These results were unchanged in stratified analyses by tumor hormone receptor expression or body mass index.

CONCLUSIONS

Our results suggest no clear association between internal levels of PBDEs and PBB-153 and the risk of breast cancer in postmenopausal women. However, these findings need to be carefully interpreted, taking into account limitations due to the limited number of women included in the study, the lack of information concerning genetic susceptibility of cases, and the unavailability of exposure assessment during critical windows of susceptibility for breast cancer. More studies are warranted to further investigate the relationships between PBDE and PBB exposure and breast cancer risk.

Assessing microbial degradation degree and bioavailability of BDE-153 in natural wetland soils: Implication by compound-specific stable isotope analysis

Microbial degradation is an important pathway for the attenuation of polybrominated diphenyl ethers (PBDEs) in natural soils. In this study, the compound-specific stable isotope analysis (CSIA) was applied to characterize microbial degradation of BDE-153, one of the prevailing and toxic PBDE congeners, in natural wetland soils. During the 45-day incubation, the residual percentages of BDE-153 decreased to 67.9% and 73.6% in non-sterilized soils spiked with 1.0 and 5.0 μg/g, respectively, which were both much lower than those in sterilized soils (96.0% and 97.2%). This result indicated that microbial degradation could accelerate BDE-153 elimination in wetland soils. Meanwhile, the significant carbon isotope fractionation was observed in non-sterilized soils, with δ¹³C of BDE-153 shifting from -29.4‰ to -26.7‰ for 1.0 μg/g and to -27.2‰ for 5.0 μg/g, respectively, whilst not in sterilized soils. This phenomenon indicated microbial degradation could induce stable carbon isotope fractionation of BDE-153. The carbon isotope enrichment factor (ε_c) for BDE-153 microbial degradation was first determined as -7.58‰, which could be used to assess the microbial degradation and bioavailability of BDE-153 in wetland soils. Based on δ¹³C and ε_c, the new methods were developed to dynamically and quantitatively estimate degradation degree and bioavailability of BDE-153 during degradation process, respectively, which could exclude interference of physical processes. This work revealed that CSIA was a promising method to investigate in situ microbial degradation of PBDEs in field studies.

Serum Levels of Commonly Detected Persistent Organic Pollutants and Per- and Polyfluoroalkyl Substances (PFASs) and Mammographic Density in Postmenopausal Women

There are little epidemiological data on the impact of persistent organic pollutants (POPs) and endocrine disruptors on mammographic density (MD), a strong predictor of breast cancer. We assessed MD in 116 non-Hispanic white post-menopausal women for whom serum concentrations of 23 commonly detected chemicals including 3 polybrominated diphenyl ethers (PBDEs), 8 per- and polyfluoroalkyl substances (PFASs), and 12 polychlorinated biphenyls (PCBs) had been measured. Linear regression analyses adjusting for potential confounders were used to examine the associations between the levels of the chemical compounds, modeled as continuous and dichotomized (above/below median) variables, and square-root-transformed MD. None of the associations were statistically significant after correcting for multiple testing. Prior to correction for multiple testing, all chemicals with un-corrected p-values < 0.05 had regression coefficients less than zero, suggesting inverse associations between increased levels and MD, if any. The smallest p-value was observed for PCB-153 (regression coefficient for above-median vs. below-median levels: −0.87, un-corrected p = 0.008). Neither parity nor body mass index modified the associations. Our results do not support an association between higher MD and serum levels of PBDEs, PCBs, or PFASs commonly detected in postmenopausal women.