Dioxin-like compound exposures and DNA methylation in the Anniston Community Health Survey Phase II

The Anniston Community Health Survey (ACHS-I) was initially conducted from 2005 to 2007 to assess polychlorinated biphenyl (PCB) exposures in Anniston, Alabama residents. In 2014, a follow-up study (ACHS-II) was conducted to measure the same PCBs as in ACHS-I and additional compounds e.g., polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and dioxin-like non-ortho (cPCBs) substituted PCBs. In this epigenome-wide association study (EWAS), we examined the associations between PCDD, PCDF, and PCB exposures and DNA methylation. Whole blood DNA methylation was measured using Illumina EPIC arrays (n=292). We modeled lipid-adjusted toxic equivalencies (TEQs) for: ΣDioxins (sum of 28 PCDDs, PCDFs, cPCBs, and mPCBs), PCDDs, PCDFs, cPCBs, and mPCBs using robust multivariable linear regression adjusting for age, race, sex, smoking, bisulfite conversion batch, and estimated percentages of six blood cell types. Among all exposures we identified 10 genome-wide (Bonferroni p≤6.74E-08) and 116 FDR (p≤5.00E-02) significant associations representing 10 and 113 unique CpGs, respectively. Of the 10 genome-wide associations, seven (70%) occurred in the PCDDs and four (40%) of these associations had an absolute differential methylation ≥1.00%, based on the methylation difference between the highest and lowest exposure quartiles. Most of the associations (six, 60%) represented hypomethylation changes. Of the 10 unique CpGs, eight (80%) were in genes shown to be associated with dioxins and/or PCBs based on data from the 2019 Comparative Toxicogenomics Database. In this study, we have identified a set of CpGs in blood DNA that may be particularly susceptible to dioxin, furan, and dioxin-like PCB exposures.

Polychlorinated biphenyl exposure and DNA methylation in the Anniston Community Health Survey

Anniston, Alabama was home to a major polychlorinated biphenyl (PCB) production facility from 1929 until 1971. The Anniston Community Health Survey I and II (ACHS-I 2005-2007, ACHS-II 2013-2014) were conducted to explore the effects of PCB exposures. In this report we examined associations between PCB exposure and DNA methylation in whole blood using EPIC arrays (ACHS-I, n = 518; ACHS-II, n = 299). For both cohorts, 35 PCBs were measured in serum. We modelled methylation versus PCB wet-weight concentrations for: the sum of 35 PCBs, mono-ortho substituted PCBs, di-ortho substituted PCBs, tri/tetra-ortho substituted PCBs, oestrogenic PCBs, and antiestrogenic PCBs. Using robust multivariable linear regression, we adjusted for age, race, sex, smoking, total lipids, and six blood cell-type percentages. We carried out a two-stage analysis; discovery in ACHS-I followed by replication in ACHS-II. In ACHS-I, we identified 28 associations (17 unique CpGs) at p ≤ 6.70E-08 and 369 associations (286 unique CpGs) at FDR p ≤ 5.00E-02. A large proportion of the genes have been observed to interact with PCBs or dioxins in model studies. Among the 28 genome-wide significant CpG/PCB associations, 14 displayed replicated directional effects in ACHS-II; however, only one in ACHS-II was statistically significant at p ≤ 1.70E-04. While we identified many novel CpGs significantly associated with PCB exposures in ACHS-I, the differential methylation was modest and the effect was attenuated seven years later in ACHS-II, suggesting a lack of persistence of the associations between PCB exposures and altered DNA methylation in blood cells.

Facile synthesis of bromo- and mixed bromo/chloro dibenzo-p-dioxins and [14C]-labeled 1,3,7,8-tetrabromodibenzo-p-dioxin

Polybrominated dibenzo-p-dioxins (PBDDs) and mixed bromo/chloro dibenzo-p-dioxins (PXDDs) are persistent organic pollutants that can possess the same toxicity as their fully chlorinated analogs (PCDDs) and have been identified in the same matrices. Herein a general synthetic methodology is described to produce multiple congeners of PBDDs and PXDDs with varying degrees of halogenation and substitution patterns for use as analytical and/or internal standards, and for absorption, disposition, metabolism, and excretion (ADME) studies. The syntheses of PBDDs and PXDDs were accomplished by condensing a common precursor, 4,5-dibromo catechol, with variable precursors, i.e., polychlorinated 1-chloro-2-nitrobenzenes or polybrominated 1-fluoro-2-nitrobenzenes, to introduce a desired number of halogens and specific substitution patterns. Initial attempts to synthesize PBDDs and PXDDs were performed in potassium carbonate with DMSO at 145-150 °C. PXDDs syntheses resulted in formation of the desired products at >90% purity but attempts at higher brominated PBDDs syntheses resulted in dehalogenated by-products. To preclude by-product formation, additional syntheses for some PBDDs were conducted by refluxing the precursors in acetonitrile, which resulted in pure products at higher yield. Six PXDDs ranging from four to six halogens were synthesized (20-84% yield), of which three contained the halogen substitution pattern of 2,3,7,8. Five PBDDs ranging from four to six bromines were produced in 23-83% yield, three of which were toxic. Using the initial DMSO method, [¹⁴C]-1,3,7,8-tetrabromodibenzo-p-dioxin (0.26 μCi/μmol; 11% overall yield) was synthesized from commercially available [¹⁴C]-phenol to allow an ADME study to be conducted.

Effect of reducing agent on catalytic hydrodechlorination of aqueous-phase OCDD/F

Removal/destruction of aqueous-phase octachlorodibenzo-p-dioxin (OCDD) and octachlorodibenzofuran (OCDF) via hydrodechlorination process (HDC) is experimentally evaluated over palladium/activated carbon (Pd/AC) catalyst. Pd catalyst is mainly used as active component for effectiveness in removing dioxin from wastewater. Studies on the removal of PCDD/Fs accomplished with HDC reaction in aqueous phase are limited and the influencing factors have not been clarified. In this study, high-concentration OCDD/F are selected as targets, and the effects of solvent and operating temperature on dechlorination efficiency are investigated via experimental tests. The results indicate that the highest hydrodechlorination efficiency is achieved with isopropanol as solvent. The OCDD/F removal efficiency achieved with the solution of 80% isopropanol is higher than that of 50% isopropanol, whereas the destruction efficiency of OCDD/F reveals the opposite trend. Generally, the removal and destruction efficiencies of PCDFs are higher than those of PCDDs. In addition, the activation energies of OCDD and OCDF are calculated with the Arrhenius equation as 24.8 and 23.1 kJ/mol, respectively. Stability tests are conducted with three cycles. Overall, the results indicate that a high performance (≥99%) can be achieved by combining hydrodechlorination with Pd/AC at a temperature range of 303-353 K, demonstrating that Pd/AC has good potential for removing PCDD/Fs from wastewater.

Dioxins and furans legacy of lindane manufacture in Sabiñánigo (Spain). The Bailín landfill site case study

Lindane (γ-hexachlorocyclohexane) manufacture in Spain generated nearly 200,000tonnes of HCH wastes; near 160,000tonnes were originated by the Inquinosa factory located in Sabiñánigo (northern Spain) and were deposited in unlined landfill sites. This study reports for the first time the content of polychlorinated dibenzo-p-dioxin/dibenzofuran (PCDD/Fs) in non-recycled HCH wastes that had been disposed in the Bailín landfill site in Sabiñánigo. Samples from solid HCH powder residues (white HCH and δ-paste wastes) and the dense non-aqueous phase liquids (DNAPLs), as well as landfill leachates, soil and sediments have been characterized. White HCH wastes exhibited a toxicity of 1488ngWHO-TEQ₂₀₀₅·kg^-1 (Σ₁₇ PCDD/Fs), while δ-paste wastes presented a noticeable higher toxicity (12,094ngWHO-TEQ₂₀₀₅·kg^-1). Nevertheless, the maximum toxicity value was found for DNAPLs (37,353ngWHO-TEQ₂₀₀₅·L^-1). Dioxins were predominant in the DNAPL waste whereas furans predominated in the landfill leachates, soil and sediments. However, in solid HCH wastes, PCDD and PCDFs contributed in a similar proportion. The PCDD/Fs congener profiles in landfill leachates, soil and sediments do not resemble the PCDD/Fs profiles found for the HCH wastes. These preliminary results will be of paramount importance in order to estimate the total quantities of PCDD/Fs disposed to the landfill site and to assess the potential mobility of PCDD/Fs, especially to groundwater and landfill leachates. Besides, this information is of great value to design periodical monitoring plans to evaluate the presence of PCDD/Fs in the impacted groundwater and leachates and finally, to evaluate the risk of PCDD/Fs for the environment and human health.

Relative effect potency estimates of dioxin-like activity for dioxins, furans, and dioxin-like PCBs in adults based on cytochrome P450 1A1 and 1B1 gene expression in blood

BACKGROUND

In the risk assessment of PCDDs, PCDFs, and dioxin-like (DL) PCBs, regulatory authorities support the use of the toxic equivalency factor (TEF)-scheme derived from a heterogeneous data set of the relative effect potency (REPs) estimates.

OBJECTIVES

We sought to determine REPs for dioxin-like compounds (DLCs) using expression of cytochrome P450 (CYP) 1A1 and 1B1 mRNA in human peripheral blood mononuclear cells representing two different pathways.

METHODS

We used a sex and age adjusted regression-based approach comparing the strength of association between each DLC and the cytochrome P450 (CYP) 1A1 and 1B1 mRNA expression in 320 adults residing in an organochlorine-polluted area of eastern Slovakia.

RESULTS

We calculated REPs based on CYP1A1 expression for 4 PCDDs, 8 PCDFs, and 1 PCB congener, and based on CYP1B1 expression for 5 PCDFs and 11 PCB congeners. REPs from CYP1A1 correlated with REPs previously derived from thyroid volume (ρ=0.85; p<0.001) and serum FT4 (ρ=0.77; p=0.009). The 13 log REPs from CYP1A1 correlated with log WHO-TEFs (r=0.63; p=0.015) and 11 log PCB REPs with PCB consensus toxicity factors (CTFs) for compounds with WHO-TEFs (r=0.80; p=0.003). The complete set of derived 56 log REPs correlated with the log CTFs (r=0.77; p=0.001) and log WHO-TEFs (r=0.81; p<0.001).

CONCLUSIONS

REPs calculated from thyroid and cytochrome P450 endpoints realistically reflect human exposure scenarios because they are based on human chronic and low-dose exposures. While the CYP 1A1 seems more suitable for toxicity evaluation of PCDD/Fs, the CYP 1B1 is more apt for PCDFs and PCBs and reflects different pathways.

Meeting the European Commission performance criteria for the use of triple quadrupole GC-MS/MS as a confirmatory method for PCDD/Fs and dl-PCBs in food and feed samples

Until recently, European Union (EU) legislation required the use of high-resolution gas chromatography coupled to high-resolution mass spectrometry (HRGC-HRMS) based on magnetic sector analyzers as a standard approach for confirmatory analysis of dioxins (PCDDs) and furans (PCDFs) in feed and food. However, recent technological advances in MS instruments enabled other alternative analytical techniques to meet the same analytical criteria as those requested for HRGC-HRMS. In this sense, triple quadrupoles (GC-MS/MS) can be a realistic alternative for the analysis of dioxins. In this work, the performance of GC-MS/MS technology was evaluated against the criteria demanded by the EU for confirmatory analysis of dioxins and PCBs in food and feed. Thus, the study comprises a number of parameters including chromatographic separation, limit of quantification, linearity, repeatability, and ion ratio precision. Analyses of solvent standards as well as sample extracts (inter-calibration extracts and certified reference materials) were also considered within the scope of this study. Additionally, direct comparisons of the results obtained by GC-MS/MS with those from GC-HRMS were made. The results of this work suggested that GC-MS/MS was highly sensitive and selective for confirmatory analysis of PCDD/Fs and related compounds in food and feed samples and meets all the criteria requested by the European Commission.

Estimating the physicochemical properties of polyhalogenated aromatic and aliphatic compounds using UPPER: part 1. Boiling point and melting point

The UPPER (Unified Physicochemical Property Estimation Relationships) model uses enthalpic and entropic parameters to estimate 20 biologically relevant properties of organic compounds. The model has been validated by Lian and Yalkowsky on a data set of 700 hydrocarbons. The aim of this work is to expand the UPPER model to estimate the boiling and melting points of polyhalogenated compounds. In this work, 19 new group descriptors are defined and used to predict the transition temperatures of an additional 1288 compounds. The boiling points of 808 and the melting points of 742 polyhalogenated compounds are predicted with average absolute errors of 13.56 K and 25.85 K, respectively.