Polychlorinated Dibenzo-p-dioxins Congeners Research Articles

Comprehensive model for predicting toxic equivalents (TEQ) reduction due to dechlorination of polychlorinated dibenzo-p-dioxin and dibenzofurans (PCDD/F congeners)

Remediation-focused predictive tools for polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) rely on transformation models to evaluate the reduction in total contaminant load and toxic equivalency (TEQ). In this study, a comprehensive model predicting the profiles of PCDD/F congeners and the associated TEQs was developed. The model employs first-order kinetics to describe the transformation of 256 reactions for 75 PCDD congeners and 421 reactions for 135 PCDF congeners. It integrates the growth of anaerobic microbial guilds using Monod kinetics on hydrogen release compounds and stoichiometric growth for Dehalococcoides sp. The effects of temperature, salinity, pH, and availability of vitamin B12 (a cofactor) were also integrated. The PCDD/F congeners model was used to extract the first-order dechlorination rate constants from a number of pure culture and mixed microbial microcosm studies. Simulations for the transformation of PCDD/F congeners at concentrations representative of the Tittabawassee or Saginaw Rivers and watershed in MI, USA were carried out. For a starting TEQ of 5000 ng per kg dry sediment (ppt), the model predicted a decrease in the overall TEQ to below 2000 ppt after 2.6 years and below 250 ppt after ∼21 years. The developed model may be used for extracting rates from microcosm studies and to evaluate the effect of engineering interventions on TEQ reduction.

Analysis of PCDD/Fs in environmental samples by using gas chromatography in combination with high resolution mass spectrometry: optimization of sample preparation

ABSTRACT This study developed a simple, economical and time-saving clean-up procedure based on an in-house packed column system for the determination of the most toxic-relevant 17 PCDD (polychlorinated dibenzo-p-dioxin) and PCDF (polychlorinated dibenzofuran) congeners in environmental samples following accelerated solvent extraction. The extract solution was cleaned up using a manually packed column system consisting of a multi-layer silica gel column and an activated carbon column. After clean-up, dioxins and furans were analysed by using gas chromatography in combination with high-resolution mass spectrometry. Isotopic labelled spiking experiments investigated the recovery of all dioxin and furan congeners. Then, the clean-up procedure for environmental samples was validated by applying the analysis of both clean soil reference material (CRM EDF-5183) and heavily contaminated sediment reference material (CRM EDF-5184) samples, as well as participating in the proficiency test (PT) for sediment samples. The recovery efficiency of isotope-labelled standard compounds in certified reference material (CRM) samples and PT samples ranged from 35% to 101% and between 46.1% and 105%, respectively. The mass concentrations of 17 PCDD/Fs in CRM samples were in the acceptable range. The absolute z-score value for each PCDD/F congener in the PT samples was below 1, confirming the analytical procedure’s high accuracy. The applied clean-up procedure in this study has demonstrated accuracy, repeatability and a significant increase in sample extraction/preparation productivity by reducing the time for sample preparation.

Associations of PCBS, dioxins and furans with follicle-stimulating hormone and luteinizing hormone in postmenopausal women: National Health and Nutrition Examination Survey 1999–2002

BackgroundThe general population is exposed to the group of endocrine disrupting chemicals persistent organic pollutants (POPs), that includes polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). ObjectivesThe aim of this research was to evaluate the associations of serum levels of PCB, PCDD, and PCDF congeners with follicle stimulating hormone (FSH) and luteinizing hormone (LH) in postmenopausal women not taking exogenous hormones. We hypothesized that associations of POPs with these gonadotropins could be modified by factors affecting endogenous hormones. MethodsCross-sectional analyses were conducted on data from 89 postmenopausal women using data from the National Health and Nutrition Examination Survey (NHANES). POPs were summarized based on classification schemes thought to reflect toxicological properties. Associations of POPs and gonadotropin hormones were modeled with multivariable regression models. When evidence of interaction was found, conditional effects were estimated. ResultsWe found inverse associations of LH, but not FSH, with exposure to anti-estrogenic and/or dioxin-like POPs, but not with non dioxin-like PCBs. A doubling of dioxin-like toxic equivalents (TEQs) was associated with a decrease in LH of 11.9% (95% CI = −21.3%, −1.4%, p = 0.03). Inverse associations were enhanced by potential effect modifiers related to both direct and indirect estrogenicity, including obesity and the obesity-related condition inflammation. ConclusionsThese investigations support a pattern of endocrine-disrupting effects by dioxin-like POPs among postmenopausal women, especially those with conditions related to peripheral estrogenicity.

Exploring the associations of serum concentrations of PCBs, PCDDs, and PCDFs with walking speed in the U.S. general population: Beyond standard linear models

Studies have shown that persistent organic pollutants (POPs) can have various health effects. However, little is known about the effects of multiple chemicals with possible common sources of exposure on walking speed, a proxy index reflecting lower limb neuromuscular function and physical function. We simultaneously applied multiple linear and nonlinear statistical models to explore the complex exposure-response relationship between a mixture of 22 selected POPs and walking speed. A total of 14 polychlorinated biphenyls (PCBs), 3 polychlorinated dibenzo-p-dioxins (PCDDs), and 5 polychlorinated dibenzofurans (PCDFs) were measured in the serum of participants in the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2002. Walking speed was measured during a physical examination. Linear regression (LR), least absolute shrinkage and selection operator (LASSO), and group LASSO were used to evaluate the linearity of mixtures, while restricted cubic spline (RCS) regression, random forest (RF), and Bayesian kernel machine regression (BKMR) models were used to evaluate the nonlinearity of mixtures. Potential confounders were adjusted in the above models. A total of 436 subjects were included in our final analysis. The results of the LR model did not identify any POP exposure that was significantly associated with walking speed. The LASSO results revealed an inverse association of one PCDD congener and two PCDF congeners with walking speed, while the group LASSO analysis identified PCDFs at the exposure level and at the group level. In the RCS analysis, two PCB congeners presented significant overall associations with walking speed. The PCB congener PCB194 showed statistically significant effects on the outcome (P = 0.01) when a permutation-based RF was used. The BKMR analysis suggested that PCBs and PCDFs (probabilities = 0.887 and 0.909, respectively) are potentially associated with walking speed. Complex statistical models, such as RCS regression, RF and BKMR models, can detect the nonlinear and nonadditive relationships between PCBs and walking speed, while LASSO and group LASSO can identify only the linear relationships between PCDFs and walking speed. Fully considering the influence of collinearity in each method during modelling can increase the comprehensiveness and reliability of conclusions in studies of multiple chemicals.

Association of dioxin exposure and reproductive hormone levels in men living near the Bien Hoa airbase, Vietnam

Dioxins are endocrine-disrupting chemicals, and their effects on reproductive functions are well-documented. The aim of the present study was to measure the levels of reproductive hormones in 42 men residing near a dioxin-contaminated area in Vietnam. We measured levels of 17 2,3,7,8-substituted congeners of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) and four non-ortho polychlorinated biphenyls (PCBs) in blood. Levels of follicle-stimulating hormone, luteinizing hormone, progesterone, prolactin, estradiol, and total testosterone were measured in serum. Blood dioxin levels were elevated; the levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin was 7.3pg/g fat. Seven of the men had testosterone levels below 250ng/dL, and nine men had prolactin levels above 9.7ng/mL. Four PCDD congeners, two PCDF congeners, one PCB congener, and the sum TEQ of PCDDs, PCDDs/Fs, and PCDDs/Fs/PCBs were positively and significantly correlated with prolactin levels. Two PCDD congeners, six PCDF congeners, two PCB congeners, and the TEQs of PCDFs and PCBs were negatively and significantly correlated with testosterone levels. There were no significant correlations between dioxin congeners and follicle-stimulating hormone, luteinizing hormone, or progesterone levels.

Chemical-looping combustion of plastic wastes for in situ inhibition of dioxins

Polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) as toxic by-products are inevitably emitted during conventional air incineration processes of chlorine containing wastes (typically, plastic wastes). The presence of O2 in the conventional waste incineration not only participates in carbon gasification and rearrangement as an oxygen source during the de novo synthesis process of PCDD/Fs, but also promotes chlorination through generating more active Cl2 via Deacon reaction. Chemical looping combustion (CLC), which creates an O2-free atmosphere in the fuel reactor, was proposed to dispose plastic wastes. Comparative experiments [conventional PW incineration vs. in situ gasification-chemical looping combustion (iG-CLC) using CaO-decorated Fe2O3/Al2O3 as oxygen carrier] were conducted to measure the distribution properties of 17 toxic PCDD/Fs congeners. The total amount and toxic equivalency quantity of PCDD/Fs have been reduced by 94 % and 89 %, respectively, in iG-CLC. The absence of O2 in fuel reactor and lower Cl2 yield (due to the restriction of Deacon reaction and effective dechlorination by CaO) lead to the significant inhibition of the PCDD/Fs formation. Chlorine substitution modelling also demonstrated that the chlorine substitution probabilities for the formation of 7 toxic congeners of PCDDs and 10 toxic congeners of PCDFs are significantly reduced in iG-CLC.

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

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

The exposure of the Croatian population to toxic environmental contaminants – “Dioxin-like” PCBs

We measured the concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), dioxin-like polychlorinated biphenyls (PCBs), and non-dioxin-like PCBs in paired samples of blood and breast milk collected from 67 secundiparas in Sapporo City, Japan, and combined this data with those of the 30 secundiparas previously measured. The arithmetic mean total toxic equivalents (TEQ-WHO) concentrations of PCDDs, PCDFs, non-ortho PCBs, and mono-ortho PCBs in blood and breast milk of the 97 secundiparous subjects were 3.0–23 (mean: 13, median: 14) and 2.7–20 (mean: 8.6, median: 8.5) pg TEQ g−1 lipid, respectively. The sums of the concentrations of 56 non-dioxin-like PCB congeners that were measured in the subjects’ blood and breast milk were 16–326 (mean: 107, median: 100) and 12–252 (mean: 73, median: 67) ng g−1 lipid, respectively. The partitioning ratios of individual congeners of PCDDs, PCDFs, dioxin-like PCBs, and non-dioxin-like PCBs from blood to breast milk in secundiparas were almost the same as those of primiparas that have been recently reported, suggesting that the partitioning ratios of these compounds from maternal blood to breast milk in women is little affected by delivery. Furthermore, the partition of PCB congeners with chlorine at the 2-, 3-, 4′-, and 5-positions or the 2-, 4-, 4′-, and 5-positions of the biphenyl ring from the blood to the breast milk tended to occur at a higher level than that of other congeners. In particular, the levels of tetraCB-74 and hexaCB-146 in the breast milk for both primiparous and secundiparous mothers were slightly higher than those in the blood.

Chlorinated dibenzo-p-dioxin and dibenzofuran congener and homologue distributions in tree bark from Sauget, Illinois, U.S.

Polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF) are ubiquitous urban/industrial contaminants found in tree bark, which acts as a long-term passive atmospheric sampler. Twenty seven bark samples (tree age 8–92 years) were collected from residential and industrial areas near Sauget, IL to identify the trends of 2,3,7,8-Cl PCDD & PCDF congener distributions, toxic equivalents (TEQ), and PCDD & PCDF homologue distributions. The Sauget area is heavily industrialized, with a long history of chlorine production, and is the largest single contributor to air pollution exposure risk in St. Louis. Analysis of seven 2,3,7,8 Cl-substituted PCDD and 10 PCDF congeners showed ∑PCDD7 ranging from 2214 to 71821 pg g(–1) lipid and ∑PCDF10 from 355 to 13707 pg g(–1) lipid, the highest in trees <20 years old in both cases. OctaCCD and octaCDF respectively dominated ∑PCDD7 (89% average) and ∑PCDF10 (57% average). The 2,3,7,8-Cl congener profiles showed slight differences among samples showing that all were affected by similar sources but at different magnitudes. ∑TEQ ranged from 35 to 624 pg g(–1) lipid, dominated by 1,2,3,7,8-PeCDD (average = 41.3% of total TEQ). Tetra-Cl through hepta-Cl homologues were dominated by non-2,3,7,8-Cl compounds for both CDD and CDF. Homologue profiles for 26 samples had a “sink” profile dominated by octaCDD, whereas one sample showed effects of a local source.

Serum concentrations of polychlorinated dibenzo-p-dioxins among ceramicists

Polychlorinated dibenzo-p-dioxins (PCDDs) occur naturally in ball clay at elevated concentrations. Thus, persons who habitually work with clay may be at risk for exposure to PCDDs. An earlier case report provided some evidence of elevated PCDD levels in serum for long-term hobby ceramicists; however, no previous study has measured serum dioxin concentrations among ceramicists. This study measured PCDD serum levels for 27 individuals involved in ceramics making. The average residual, defined as the average of the [log measured serum lipid concentration – log background serum lipid concentration], was calculated and then tested to determine whether it was significantly different from zero. The p-values for the average residuals indicated that the serum lipid concentrations for several PCDD congeners were elevated relative to background. The number of significant residuals increased dramatically if the background concentrations were adjusted to account for the fact that they were not contemporaneous with the measurements for the ceramicists. The ratio of the 1,2,3,6,7,8-HxCDD concentration to the 1,2,3,7,8,9-HxCDD concentration was greater than 1.0, unlike in ball clay, suggesting that although long-term working with ball clay elevates the PCDD levels in serum somewhat, it is not the predominant source of the PCDD body burden for ceramicists.

EPA's National Dioxin Air Monitoring Network (NDAMN): Design, implementation, and final results

The U.S. Environmental Protection Agency (U.S. EPA) established the National Dioxin Air Monitoring Network (NDAMN) in June of 1998, and operated it until November of 2004. The objective of NDAMN was to determine background air concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and dioxin-like polychlorinated biphenyls (dl-PCBs). NDAMN started with 10 sampling sites, adding more over time until the final count of 34 sites was reached by the beginning of 2003. Samples were taken quarterly, and the final sample count was 685. All samples were measured for 17 PCDD/PCDF congeners, 8 PCDD/PCDF homologue groups, and 7 dl-PCBs (note: 5 additional dl-PCBs were added for samples starting in the summer of 2002; 317 samples had measurements of 12 dl-PCBs). The overall average total toxic equivalent (TEQ) concentration in the United States was 11.2 fg TEQ m−3 with dl-PCBs contributing 0.8 fg TEQ m−3 (7%) to this total. The archetype dioxin and furan background air congener profile was seen in the survey averages and in most individual samples. This archetype profile is characterized by low and similar concentrations for tetra – through hexa PCDD/PCDF congeners, with elevations in four congeners – a hepta dioxin and furan congener, and both octa congeners. Sites were generally categorized as urban (4 sites), rural (23 sites), or remote (7 sites). The average TEQ concentrations over all sites and samples within these categories were: urban = 15.9 fg TEQ m−3, rural = 13.9 fg TEQ m−3, and remote = 1.2 fg TEQ m−3. Rural sites showed elevations during the fall or winter months when compared to the spring or summer months, and the same might be said for urban sites, but the remote sites appear to show little variation over time. The four highest individual moment measurements were 847, 292, 241, and 132 fg TEQ m−3. For the 847 and 292 fg TEQ m−3 samples, the concentrations of all congeners were elevated over their site averages, but for the 241 and 132 fg TEQ m−3 measurements, only the PCDD congeners were elevated while PCDF and dl-PCB concentrations were similar to the site averages.

Reduction of PCDD, PCDF and PCB during co-combustion of biomass with waste products from pulp and paper industry

The use of waste wood as an energy carrier has increased during the last decade. However, elevated levels of alkali metals and chlorine in waste wood compared to virgin biomass can cause increased deposit formation and higher concentrations of organic pollutants. In this study, we investigated the effect of the ChlorOut technique on concentrations of organic pollutants. Ammonium sulfate was injected into the combustion system to inhibit formation of KCl (which causes deposits) and persistent organic pollutants, namely polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and biphenyls (PCBs). The results showed that concentrations of the toxic congeners of PCDD, PCDF and PCB decreased in the presence of ammonium sulfate.

Individual breast milk consumption and exposure to PCBs and PCDD/Fs in Hungarian infants: A time-course analysis of the first three months of lactation

Polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are persistent, bioaccumulative and toxic chemicals. These compounds are transferred to breast milk, therefore breastfed infants are at risk of being exposed to considerable amounts of PCBs and PCDD/Fs during this sensitive age.In the present study individual breast milk samples were collected at three time points (days 5, 12 and 84 postpartum) from 22 mothers who delivered their infants during 2007 in Baranya County, Hungary. Breast milk samples were analyzed for 17 PCDD/Fs, 12 dioxin-like (DL) PCBs and 7 non-dioxin-like (NDL) PCBs using high-resolution gas chromatography/high-resolution mass spectrometry. Each infant's daily breast milk consumptions have been measured biweekly over three months.The concentration of several PCB and PCDD congeners in breast milk decreased significantly during lactation, with a main decline between days 5 and 12. The total toxic equivalent (TEQ) concentrations, derived from PCDD/Fs and DL-PCBs, were 3.17±1.72, 2.70±1.57 and 2.41±1.47pg TEQ/g fat at the three time points, respectively. The corresponding NDL-PCB concentrations were 33.5±29.2, 27.4±20.6 and 26.9±24.8ng/g fat, respectively. The results highlight the importance of timing of breast milk sampling for consistent exposure assessment estimation. Levels of pollutants in Hungarian breast milk samples were at the lower concentration range when data from Europe are considered. This is the first study in Hungary where each infant's daily intakes of PCBs and PCDD/Fs via breast milk have been measured. The daily intakes of PCDD/Fs and DL-PCBs via breastfeeding per kg body weight were 11.79±6.42, 16.54±13.02 and 11.59±7.70pg TEQ/kg bw on days 5, 12 and 84, respectively. The exposure was the highest on day 12 but at all three time points each infants' daily exposure to PCDD/Fs and DL-PCBs via breastfeeding exceeded the tolerable daily intake (TDI) of 2pg TEQ/kg bw per day. These levels are still lower than corresponding levels recently measured in many European countries. Whether the milk-derived POP exposure levels of infants reported here constitute any health risk that may manifest later in life awaits further scrutiny.

Hydrothermal Degradation of Polychlorinated Dibenzo-p-dioxins and Polychlorinated Dibenzofurans in Fly Ash from Municipal Solid Waste Incineration under Non-oxidative and Oxidative Conditions

Hydrothermal technology was investigated as a degradation method for polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in municipal solid waste incineration (MSWI) fly ash at 150, 200, and 250 °C under both non-oxidative and oxidative conditions. The results show that the removal efficiency of PCDDs/PCDFs in fly ash was accelerated by oxidative degradation and increased with an increasing temperature. The distributions of PCDD/PCDF homologues and isomers in fly ash were also analyzed after this hydrothermal process. There were no new isomers generated, and PCDD/PCDF degradation was not significantly dependent upon the position of the chlorine atoms. To further identify the PCDD/PCDF degradation pathways and avoid organic interfering substances in fly ash, octa-chlorinated dibenzo-p-dioxin (OCDD)-added aqueous solution degradation trials were conducted. All tetra- to octa-chlorinated PCDD and PCDF congeners were detected under both non-oxidative and oxidative atmospheres after OCDD-added decomposition. The formation of lower chlorinated PCDDs was attributed to a hydrodechlorination reaction, and those PCDF isomers arose as intermediates of OCDD degradation.

Concentrations of polychlorinated dibenzo- p-dioxins, polychlorinated dibenzofurans, and polychlorinated biphenyls in blood and breast milk collected from pregnant women in Sapporo City, Japan

We measured the concentrations of polychlorinated dibenzo- p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), dioxin-like polychlorinated biphenyls (PCBs), and non-dioxin-like PCBs in paired samples of blood and breast milk collected from 67 secundiparas in Sapporo City, Japan, and combined this data with those of the 30 secundiparas previously measured. The arithmetic mean total toxic equivalents (TEQ-WHO) concentrations of PCDDs, PCDFs, non- ortho PCBs, and mono- ortho PCBs in blood and breast milk of the 97 secundiparous subjects were 3.0–23 (mean: 13, median: 14) and 2.7–20 (mean: 8.6, median: 8.5) pg TEQ g −1 lipid, respectively. The sums of the concentrations of 56 non-dioxin-like PCB congeners that were measured in the subjects’ blood and breast milk were 16–326 (mean: 107, median: 100) and 12–252 (mean: 73, median: 67) ng g −1 lipid, respectively. The partitioning ratios of individual congeners of PCDDs, PCDFs, dioxin-like PCBs, and non-dioxin-like PCBs from blood to breast milk in secundiparas were almost the same as those of primiparas that have been recently reported, suggesting that the partitioning ratios of these compounds from maternal blood to breast milk in women is little affected by delivery. Furthermore, the partition of PCB congeners with chlorine at the 2-, 3-, 4′-, and 5-positions or the 2-, 4-, 4′-, and 5-positions of the biphenyl ring from the blood to the breast milk tended to occur at a higher level than that of other congeners. In particular, the levels of tetraCB-74 and hexaCB-146 in the breast milk for both primiparous and secundiparous mothers were slightly higher than those in the blood.

Correlations of fish intake and plasma docosahexaenoic acid levels with each congener of PCDDs/PCDFs/dioxin-like PCBs in blood from the Japanese population

The purpose of the present study was to investigate the factors associated with blood levels of each congener of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and dioxin-like polychlorinated biphenyls (DL-PCBs) in the Japanese population. A cross-sectional study was performed on 1,656 subjects (755 men and 901 women) aged 15-73years, who were living in 90 different areas of 30 prefectures in Japan. Blood levels of 29 PCDD, PCDF, and DL-PCB congeners were determined by high-resolution gas chromatography/mass spectrometry. In addition, a questionnaire survey on life style, including dietary habit, was carried out. The median total toxicity equivalent (TEQ) was 17 pgTEQ/g lipid. After adjustment for age, sex, body mass index, smoking habit, and consumption of other food groups, six PCDDs/PCDFs with 4-6 substituted chlorine atoms and 10 DL-PCBs, but not HeptaCDD/F or OctaCDD, showed significant positive correlations with the frequency of intake of fish and shellfish. Furthermore, significant positive relationships were also found between plasma levels of docosahexaenoic acid (DHA), a biomarker of fish intake, and 10 PCDDs/PCDFs with 4-6 chlorine atoms and 10 DL-PCBs. The partial correlation coefficients with plasma DHA were significantly higher for DL-PCBs than for PCDDs/PCDFs, and partial correlation coefficients for PCDDs/PCDFs significantly decreased with increasing number of chlorine atoms (Spearman r=-0.80, P=0.001). Blood levels of PCDDs/PCDFs with 4-6 chlorine atoms and DL-PCBs were positively associated with fish intake in the Japanese population. These results may be explained by the higher degree of bioaccumulation of these congeners in fish and shellfish in the ecosystem, and the high consumption of fish among the Japanese population.

Rules of thumb for assessing reductive dechlorination pathways of PCDDs in specific systems

This paper reports a theoretical validation and proposition of the reductive dechlorination pathways for polychlorinated dibenzo- p-dioxin (PCDD) congeners. Density functional theory (DFT) calculations were carried out at the B3LYP/6-31G(d) level for all PCDDs and Mulliken atomic charges on chlorine atoms were adopted as the probe of the dechlorination reaction activity. The experimentally substantiated dechlorination pathways of 1,2,3,4-tetrachlorodibenzo- p-dioxin (1,2,3,4-TCDD) and its daughter products in the presence of zero-valent zinc were validated and the complete pathway of dechlorination of octachlorodibenzo- p-dioxin (OCDD) was proposed. The proposed pathways were found to be consistent with anaerobic biotransformation of several PCDD congeners. Four rules of thumb arrived from this study include (1) the chlorine atoms in the longitudinal (1,4,6,9) positions are removed in preference to the chlorine atoms on lateral (2,3,7,8) positions; (2) the chlorine atom that has more neighboring chlorine atoms at ortho-, meta- and para-positions is to be eliminated; (3) reductive dechlorination prefers to take place on the benzene ring having more chlorine substitutions; and (4) a chlorine atom on the side of the longitudinal symmetry axis containing more chlorine atoms is preferentially eliminated. These rules of thumb can be conveniently used for rapidly predicting the major dechlorination pathway for a given PCDD in specific systems.

Modeling the Reductive Dechlorination of Polychlorinated Dibenzo-p-Dioxins: Kinetics, Pathway, and Equivalent Toxicity

Reductive dechlorination of polychlorinated dibenzo-p-dioxins (PCDDs) involves 256 reactions linking 76 congeners with highly variable toxicities, so it is challenging to assess the overall effect of this process on the environmental impact of PCDD contamination. This study describes a quantitative solution to this problem that allows calculation of the toxic equivalent quantity (TEQ) of the mixture of PCDD congeners predicted by a linear free-energy relationship (LFER) that relates rate constants of dechlorination to calculated reduction potentials. The reduction potentials were derived from Gibbs free energies, calculated using density functional theory (DFT) and vapor pressures and solubilities for individual congeners. The LFER was calibrated with rate constants that we recently reported for PCDD dechlorination by nano-zerovalent iron (nZVI). Simulation done with this model predicts that more than 100 years would be required for complete dechlorination of octachlorinated dibenzo-p-dioxin (OCDD) to dibenzo-p-dioxin (DD) under conditions representative of treatment with nZVI and that the TEQ of the mixture of intermediates during this process increases 10-fold, peaking at around 3-6 years, mainly because of the higher toxicity of 2,3,7,8-substituted congeners.

Post-combustion formation of PCDD, PCDF, PCBz, and PCPh in a laboratory-scale reactor: Influence of dibenzo- p-dioxin injection

Formation of polychlorinated dibenzo- p-dioxins (PCDD), dibenzofurans (PCDF), benzenes (PCBz), and phenols (PCPh) was studied during combustion of an artificial municipal solid waste (MSW) in a laboratory-scale fluidized-bed reactor with simultaneous collection of flue gas samples at three different temperatures in the post-combustion zone (450 °C, 300 °C, and 200 °C). PCDF, PCBz, and PCPh were predominantly formed at or above the first sampling point (450 °C) with a dominance of the lower chlorinated homologues. PCDDs, on the other hand, were dominated by the intermediately chlorinated homologues with concentrations peaking at 300 °C. The dominating PCPh congeners clearly displayed the ortho–para directionality, which is indicative of electrophilic aromatic substitution, as did the PCBz isomer distribution patterns to some extent. Comparison of the observed PCBz isomer distribution patterns to prior work may indicate coupling of aliphatic species in chlorobenzene formation. The PCDDs seemed to be largely influenced by chlorophenol condensation reactions and to some extent chlorination reactions, while the PCDFs displayed a chlorination-oriented pattern for the mono- to tri-chlorinated homologues and a PCPh condensation pattern for the higher chlorinated homologues. Injection of non-chlorinated dibenzo- p-dioxin at 650 °C resulted in increased formation of Tri-HxCDD and a decrease in the dibenzofuran levels. The affected PCDD and PCDF congeners were not products expected to form from chlorine substitution, but instead are well known chlorophenol condensation products.

Theoretical study of the quantitative structure–activity relationships for the toxicity of dibenzo- p-dioxins

Density functional theory calculations of polychlorinated dibenzo- p-dioxins (PCDDs) were carried out to obtain the electronic descriptors, polarizabilities, and traceless quadrupole moments of 76 PCDD congeners. No simple relationships were found for the electronic descriptors with the relevant aryl hydrocarbon receptor (AhR) binding affinities of PCDDs, which suggests that they alone may not be sufficient to explain the variation in toxicity. However, quantitative structure–activity relationships (QSARs) were developed with the polarizabilities and traceless quadrupole moments, explaining about 74% and 59% of variation in AhR binding affinities of PCDDs, respectively. To explain the nature of toxic interaction, a mathematical model based on the ligand–receptor binding and solute–solvent interaction was presented, and then a multiple regression analysis of all the above parameters was performed to evaluate the contributions of the parameters to the bonding affinities. Other data for PCDFs found in the literature were also included in the regression analysis to minimize data over-fitting. The results suggest that dispersion and electrostatic interactions are equally important for the interaction of PCDD/Fs with the AhR.