Observations on historical, contemporary, and natural PCDD/Fs

Mechanisms of breast cancer progression induced by environment-polluting aryl hydrocarbon receptor agonists

Breast cancer is the most common invasive malignancy among women worldwide and constitutes a complex and heterogeneous disease. Interest has recently grown in the role of the aryl hydrocarbon receptor (AhR) in breast cancer and the contribution of environment-polluting AhR agonists. Here, we present a literature review addressing AhR ligands, including pesticides hexachlorobenzene and chlorpyrifos, polycyclic aromatic hydrocarbons, polychlorinated dibenzo-p-dioxins and dibenzofurans, polychlorinated biphenyls, parabens, and phthalates. The objectives of this review are a) to summarize recent original experimental, preclinical, and clinical studies on the biological mechanisms of AhR agonists which interfere with the regulation of breast endocrine functions, and b) to examine the biological effects of AhR ligands and their impact on breast cancer development and progression. We discuss biological mechanisms of action in cell viability, cell cycle, proliferation, epigenetic changes, epithelial to mesenchymal transition, and cell migration and invasion. In addition, we examine the effects of AhR ligands on angiogenic processes, metastasis, chemoresistance, and stem cell renewal. We conclude that exposure to AhR agonists stimulates pathways that promote breast cancer development and may contribute to tumor progression. Given the massive use of industrial and agricultural chemicals, ongoing evaluation of their effects in laboratory assays and preclinical studies in breast cancer at environmentally relevant doses is deemed essential. Likewise, awareness should be raised in the population regarding the most harmful toxicants to eradicate or minimize their use.

Occurrence and Source Identification of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans and Polychlorinated Biphenyls in Surface Sediments from Liangshui River in Beijing, China

Polychlorinated dibenzo-p-dioxins and dibenzofurans and polychlorinated biphenyls were measured in the surface sediments of Liangshui River, the second largest drainage river in Beijing, China. The sum concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans and polychlorinated biphenyls ranged from 3.5 to 3019 (mean value: 184) pg g^-1 dry weight and from 319 to 5949 (mean value: 1958) pg g^-1 dry weight, and the corresponding World Health Organization toxic equivalent quantity values were 0.0011-5.1 pg TEQ g^-1 dry weight and 0.0074-1.4 pg TEQ g^-1 dry weight, respectively. The spatial distributions of polychlorinated dibenzo-p-dioxins and dibenzofurans and polychlorinated biphenyls showed increasing trends from urban area and development area to suburb. Principal component analysis revealed that polychlorinated dibenzo-p-dioxins and dibenzofurans contamination in the sediments may originate from pentachlorophenol and sodium pentachlorophenate and municipal solid waste incineration. Regarding polychlorinated biphenyls, the steel industry, combustion processes and usage of some commercial polychlorinated biphenyl products were identified as the major sources. The emission from a former steel plant could be the main contributor to polychlorinated biphenyls in urban areas. The mean value of the total toxic equivalent quantities in the sediment samples exceeded the Canadian interim sediment quality guidelines. Long-term wastewater irrigation increases the load of sediment-bound pollutants in agricultural soil and may pose potential ecological risks to crops and human health.

Persistent Organic Pollutants (POPs) and Related Chemicals in the Global Environment: Some Personal Reflections

Persistent organic pollutants (POPs) and related chemicals are fascinating because of their combination of physical-chemical properties and complex effects. Most are man-made, but some also have natural origins. They are persistent in the environment, but they can be broken down variously by biodegradation, atmospheric reactions, and abiotic transformations. They can exist in the gas or particle phases, or both, in the atmosphere and in the dissolved or particulate phases, or both, in water. These combinations mean that they may undergo long-range transport in the atmosphere or oceans, or they may stay close to sources. Hence, emissions from one country are frequently a source of contamination to another country. They are also usually lipophilic, so-combined with persistence-this means they can accumulate in organisms and biomagnify through food chains. We all have a baseline of POPs residues in our tissues, even the unborn fetus via placental transfer and the newly born baby via mother's milk. POPs in biological systems occur in mixtures, so confirming effects caused by POPs on humans and other top predators is never straightforward. Depending on which papers you read, POPs may be relatively benign, or they could be responsible for key subchronic and chronic effects on reproductive potential, on immune response, as carcinogens, and on a range of behavioral and cognitive end points. They could be a factor behind diseases and conditions which have been increasingly reported and studied in modern societies. In short, they are endlessly fascinating to scientists and a nightmare to regulators and policy makers.

Spatial patterns of metals, PCDDs/Fs, PCBs, PBDEs and chemical status of sediments from a coastal lagoon (Pialassa Baiona, NW Adriatic, Italy)

The European Water Framework Directive (WFD) establishes a framework for the protection and improvement of all water bodies including transitional waters; its final objective is to achieve at least 'good status' by 2015. In the present work, a hierarchical sampling design was applied to analyze the influence of anthropogenic inputs on the spatial distribution of metals, polychlorinated dibenzo-p-dioxins (PCDDs) dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in sediment at four areas in Pialassa Baiona coastal lagoon. In order to assess the chemical status, levels of priority substances and other pollutants were compared with the recently developed national Environmental Quality Standards (EQS) and site specific background levels for metals. Levels of mercury and PCBs were particularly high and exceeded their national EQS values at all sampled areas, thus not contributing to the achievement of a good chemical status of this transitional water body according to the WFD classification.

Vertical and lateral redistribution of POPs in soils developed along a hydrological gradient

Study of the dispersion of persistent organic pollutants (POPs) throughout the environment is necessitated by their toxicological properties and propensity to accumulate in biota. In this study, we use data from the analysis of three (210)Pb dated soil profiles collected along a 30-m hydrological gradient to demonstrate postdepositional mobility of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) and polychlorinated biphenyls (PCBs). We found that (i) humus originating from litter exposed to surface fallout during the 1960-1970s contains the highest concentrations of PCDD/Fs and PCBs in the O-horizon of the soils; (ii) accumulation rates of PCDD/Fs and PCBs in the O-horizon (∼5.0 and ∼210 μg m(-2) yr(-1)) constituted only 9.1% and 3.5%, respectively, of the measured annual input, demonstrating that a minor fraction of the deposited material is retained within the O-horizon; (iii) POP inventories in the upper 0.5-0.9 m of the mineral soil constituted a considerable part (40-70%) of the total pool stored in the soil, implying significant vertical translocation of atmospheric derived POPs; and (iv) increasing downslope inventories of POPs suggest a lateral downward transport of POPs from uphill soils. The findings challenge the commonly accepted view that POPs fallout is effectively retained within O-horizons.

Comparison of the specificities and efficacies of primers for aromatic dioxygenase gene analysis of environmental samples

Aromatic dioxygenase genes have long been of interest for bioremediation and aromatic carbon cycling studies. To date, 115 primers and probes have been designed and used to analyze dioxygenase gene diversities in environmental samples. Here we analyze those primers' specificities, coverages, and PCR product lengths compared to known aromatic dioxygenase genes based on in silico analysis as well as summarize their differing advantages or effectiveness from over 50 reported experimental studies. We also provide some guidance for primer use in future studies.

Clay mediated route to natural formation of Polychlorodibenzo-p-dioxins

Recent studies have documented the ubiquitous occurrence of polychlorodibenzo-p-dioxins and dibenzofurans (PCDD/Fs) of unknown origin in soils and clay deposits. Interestingly, the PCDD/F congener profiles do not match any known natural or anthropogenic source, and global PCDD/F budgets fail to account for the observed levels in soils. To reconcile these observations, clay minerals had been hypothesized to play a central role in the natural in situ synthesis of PCDD/Fs. We recently demonstrated the clay-mediated formation of the most prevalent PCDD congener in soils, octachlorodibenzo-p-dioxin (OCDD), supporting this hypothesis. Here we report the formation of the direct precursors ("predioxins") of the most toxic PCDD congener, 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD), and of 1,2,4,7,8-pentachlorodizenzodioxin (1,2,4,7,8-PeCDD), and two additional dimers, from the reaction of 2,4,5-trichlorophenol (2,4,5-TCP) with Fe(III)-montmorillonite clay. We propose plausible reaction pathways, each initiated by single electron transfer from 2,4,5-TCP to Fe(III)-montmorillonite forming the 2,4,5-TCP radical cation. The operative reaction mechanisms, inferred from experimental results, are supported by quantum mechanical calculations. The key role of montmorillonite is apparently to stabilize the reactive radical cation intermediate. Fortuitously, PCDD formation reactions on clay surfaces are more facile for less toxic higher chlorinated congeners like OCDD, as predicted by the proposed reaction mechanism and consistent with the observed PCDD congener distributions in soils. Importantly, increasing the toxicity equivalency factor of OCDD would immediately cause many soils to exceed PCDD regulatory levels due to the predominance of this congener.

Historical trends of polychlorinated dibenzo-p-dioxins and dibenzofurans in three dated sediment cores from Mexico

This paper describes the first report of dioxins and furans (PCDDs/Fs) in sediment cores from Mexico. Sedimentation rates and vertical fluxes were estimated using (210)Pb dating. Two cores correspond to marine sediments and one to an endorheic lake. Concentrations of PCDDs/Fs found in the three sites are typical of non-impacted areas with low concentrations when compared to reference values. However the PCDDs/Fs sediment profiles show an increasing concentration trend in the upper core sections. This behavior is different from that found at many sites around the globe where diminishing concentrations have been reported. A strong predominance of OCDD was observed, and a comparison to typical composition profiles of industrial and other sources did not result in clear origin assignments for these measured compounds. We suggest that local sources may be responsible for the increase in concentration and, because these undetermined sources have not been curtailed, their importance is still growing.

TCDD adsorbed on silica as a model for TCDD contaminated soils: Evidence for suppression of humoral immunity in mice

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), the prototypical aryl hydrocarbon receptor (AhR) ligand, exhibits immune suppression in vivo and in vitro. Suppression of primary humoral immune responses in particular has been well characterized as one of the most sensitive functional immune endpoints in animals treated with TCDD. Previous studies have used purified TCDD to elucidate the mechanisms by which TCDD and dioxin-like compounds (DLC) impair IgM production by B cells, but did not represent the route by which animals and humans are likely to be exposed environmentally. In the studies reported here, mice were treated with TCDD adsorbed onto a well-defined synthetic silica phase of known purity and physical properties, followed by sensitization with sheep erythrocytes to initiate a humoral immune response. We found that surfactant-templated mesoporous forms of amorphous silica provided an ideal combination of purity, dispersibility and textural properties for immobilizing TCDD. TCDD-adsorbed silica distributed to the spleen and liver after oral administration as assessed by induction of cyp1a1 gene expression. Most notably, TCDD delivered in the adsorbed state on amorphous silica and as a solute in corn oil (CO) produced similar suppression of the anti-sheep red blood cell immunoglobulin M antibody forming cell (sRBC IgM AFC) response at equivalent doses of TCDD. These results suggest that TCDD immobilized on silicate particles found in soils distributes to the spleen and suppresses humoral immunity.

The analysis of dioxins and related compounds

The analysis of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, polychlorinated biphenyls, and other related compounds requires complex sample preparation and analytical procedures using highly sensitive and selective state-of-the-art instrumentation to meet very stringent data quality objectives. The analytical procedures (extraction, sample preparation), instrumentation (chromatographic separation and detection by mass spectrometry) and screening techniques for the determination of dioxins, furans, dioxin-like polychlorinated biphenyls and related compounds with a focus on new approaches and alternate techniques to standard regulatory methods are reviewed.

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in marine mussels from French coasts: levels, patterns and temporal trends from 1981 to 2005

The levels and temporal trends of toxic polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) were determined in archived marine mussels collected between 1981 and 2005 from selected sites along French coasts. The geographical distribution and levels of PCDD/Fs generally reflect regional inputs of these contaminants: the highest concentrations were determined in samples from the Seine river estuary (English Channel) and Toulon area (Mediterranean coast); the lowest levels were determined in Corsica (Mediterranean Sea). PCDD/F isomeric composition showed a fairly homogeneous distribution pattern throughout the various sampling sites. This pattern, dominated by 2,3,7,8-TCDF and OCDD, can be considered as typical for the study species. However, on a more local scale, some differences in isomeric composition in mussels were identified in relation to local source characteristics. The time trend study showed a pronounced decrease in PCDD/F concentrations over the 24-year period at most sites, except Toulon on the Mediterranean Sea, where the decrease was not significant. This overall decrease probably reflects the general drop in PCDD/F emissions in Europe since 1980. However, high concentrations were determined in mussels collected in recent years (1999, 2001 and 2005) from the mouth of the Seine river. These concentrations are related to particular hydrological conditions, and intensive sediment dredging due to a new port construction at the mouth of the estuary. The results presented in this paper provide reference data on the contamination of shellfish by persistent organic pollutants in the marine environment.

Octachlorodibenzodioxin formation on Fe(III)-montmorillonite clay

Polychlorinated dibenzo-p-dioxins (PCDDs) are ubiquitous and highly toxic environmental contaminants found in surface and subsurface soils and in clay deposits. Interestingly, the congener profiles of such PCDDs are inexplicably dissimilar to those of known anthropogenic (e.g., pesticide manufacture, waste incineration) or natural (e.g., forest fire) sources. Characteristic features of soil or clay-associated PCDDs are the dominance of octachlorodibenzo-p-dioxin (OCDD) as the most abundant congener and very low levels of polychlorinated dibenzofurans (PCDFs). These propensities led to the hypothesis of in situ PCDD formation in soils and geologic clay deposits. In this study, we demonstrate the formation of OCDD on the naturally occurring and widely distributed clay mineral montmorillonite under environmentally relevant conditions. When pentachlorophenol (PCP)was mixed with Fe(III)-montmorillonite, significant amounts of OCDD were rapidly (minutes to days) formed (approximately 5 mg OCDD/kg clay) at ambient temperature in the presence of water. This reaction is initiated by single electron transfer from PCP to Fe(III)-montmorillonite thereby forming the PCP radical cation. Subsequent dimerization, dechlorination, and ring closure reactions result in formation of OCDD. This study provides the first direct evidence for clay-catalyzed formation of OCDD supporting the plausibility of its in situ formation in soils.

The characterization of PCDDs, PCDFs and coplanar PCBs during the past 50 years in Gwangyang Bay, South Korea

The PCDD/DFs and coplanar PCBs (co-PCBs) in sediment samples from Gwangyang Bay in South Korea was investigated. The total concentration of dioxins and their toxic equivalent quantity (TEQ; calculated with the WHO 2005 Toxic Equivalency Factors) value in the surface sediment of the outer site (261 pg g(-1) TOC, 4.4 pg-TEQ g(-1)) were 3-fold higher than the inner site (90 pg g(-1) TOC, 1.1 pg-TEQ g(-1)) in the Bay. The dioxin in the sediment samples was found to come from a mixture of the impurities of pentachlorophenol (PCP), chloronitrofen (CNP) and combustion based on the result of hierarchical cluster analysis (HCA). These dioxin sources have been influenced by the characterization associated with this region which was both an agricultural-centered and industrial-centered area. According to principal component analysis (PCA) related to the Kow values for the congener-specific composition of co-PCBs in the sediment core, the Kanechlor (KC)-500 and the atmospheric deposition were identified as the possible sources. The maximum burden in the sediment core was 1.3 kg for 1967-1974 and the total burdens of PCDD/DFs and co-PCBs in the sediment core were estimated to be 6.6 kg during the past 50 years. The cumulative burdens of dioxin are still increasing in Gwangyang Bay.

Source identification of PCDD/Fs in agricultural soils near to a Chinese MSWI plant through isomer-specific data analysis

Isomer-specific data were investigated in order to identify the sources of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in agricultural soils, including Fluvo-aquic and paddy soils, in the vicinity of a Chinese municipal solid waste incineration (MSWI) plant. Homologue and isomer profiles of PCDD/Fs in soils were compared with those of potential sources, including combustion sources, i.e., MSWI flue gas and fly ash; and the impurities in agrochemicals, such as the pentachlorophenol (PCP), sodium pentachlorophenate (PCP-Na) and 1,3,5-trichloro-2-(4-nitrophenoxy) benzene (CNP). The results showed that the PCDD/F isomer profiles of combustion sources and agricultural soils were very similar, especially for PCDFs, although their homologue profiles varied, indicating that all the isomers within each homologue behave identically in the air and soil. Moreover, factor analysis of the isomer compositions among 33 soil samples revealed that the contamination of PCDD/Fs in agricultural soils near the MSWI plant were primarily influenced by the combustion sources, followed by the PCP/PCP-Na and CNP sources. This implication is consistent with our previous findings based on chemometric analysis of homologue profiles of soil and flue gas samples, and identifies PCP/PCP-Na as an additional important source of PCDD/Fs in the local area. This makes the similarities and differences of isomer profiles between Fluvo-aquic and paddy soils more explainable. It is, therefore, advisable to use isomer-specific data for PCDD/F source identifications where possible.

Microbial degradation of chlorinated dioxins

Polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) were introduced into the biosphere on a large scale as by-products from the manufacture of chlorinated phenols and the incineration of wastes. Due to their high toxicity they have been the subject of great public and scientific scrutiny. The evidence in the literature suggests that PCDD/F compounds are subject to biodegradation in the environment as part of the natural chlorine cycle. Lower chlorinated dioxins can be degraded by aerobic bacteria from the genera of Sphingomonas, Pseudomonas and Burkholderia. Most studies have evaluated the cometabolism of monochlorinated dioxins with unsubstituted dioxin as the primary substrate. The degradation is usually initiated by unique angular dioxygenases that attack the ring adjacent to the ether oxygen. Chlorinated dioxins can also be attacked cometabolically under aerobic conditions by white-rot fungi that utilize extracellular lignin degrading peroxidases. Recently, bacteria that can grow on monochlorinated dibenzo-p-dioxins as a sole source of carbon and energy have also been characterized (Pseudomonas veronii). Higher chlorinated dioxins are known to be reductively dechlorinated in anaerobic sediments. Similar to PCB and chlorinated benzenes, halorespiring bacteria from the genus Dehalococcoides are implicated in the dechlorination reactions. Anaerobic sediments have been shown to convert tetrachloro- to octachlorodibenzo-p-dioxins to lower chlorinated dioxins including monochlorinated congeners. Taken as a whole, these findings indicate that biodegradation is likely to contribute to the natural attenuation processes affecting PCDD/F compounds.

The status of soil contamination by semivolatile organic chemicals (SVOCs) in China: a review

This paper summarizes the published scientific data on the soil contamination by semivolatile organic chemicals (SVOCs) in China. Data has been found for more than 150 organic compounds which were grouped into six classes, namely, polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), polycyclic aromatic hydrocarbons (PAHs), polybrominated diphenyl ethers (PBDEs) and phthalic acid esters (PAEs). An overview of data collected from the literature is presented in this paper. The Chinese regulation and/or other maximum acceptable values for SVOCs were used for the characterization of soils. In general, the compounds that are mostly studied in Chinese soils are OCPs, PAHs and PCBs. According to the studies reviewed here, the most abundant compounds were PAEs and PAHs (up to 46 and 28 mg kg(-1) dry weight, respectively); PCBs and OCPs occurred generally at concentrations lower than 100 microg kg(-1) dry weight. Nevertheless, quite high concentrations of PCDD/Fs, PCBs and PBDEs were observed in contaminated sites (e.g., the sites affected by electronic waste activities). The average concentrations of PAHs and OCPs in soils of North China were higher than those in South China. The principal component analysis demonstrated different distribution patterns for PAH, PCB and PCDD/F congeners and for the various sites/regions examined. The isomer ratios of DDTs and hexachlorocyclohexanes (HCHs) indicated different sources and residue levels in soils. Finally, this review has highlighted several areas where further research is considered necessary.

Formation of trichlorinated dibenzo-p-dioxins from 2,4-dichlorophenol and 2,4,5-trichlorophenolate: a theoretical study

The reaction of the 2,4,5-trichlorophenolate anion with 2,4-dichlorophenol to afford trichlorinated dibenzo-p-dioxins (T3CDDs) is investigated at the B3LYP/6-31+G(d) and B3LYP/6-311+G(3df,2p)//B3LYP/6-31+G(d)+ZPVE(B3LYP/6-31+G(d)) levels of theory. The first stage of the process corresponds to the formation of a predioxin, which can evolve through four different routes. Two of them lead directly to the products 2,3,7-T3CDD and 1,3,8-T3CDD, and the other two afford different predioxin-type intermediates, which in turn can evolve through all or some of the four routes to give new predioxins or T3CDD. Consequently, the theoretical results obtained show plainly the complex chemistry implied in the formation of dioxins from chlorophenols via anionic mechanisms by disclosing all the critical structures through which the system evolves, thus allowing assessment of the viability of the different mechanistic routes and the accessible products. The statistical thermodynamics treatment at 1 atm and 298.15, 600, 900, and 1200 K indicates that at higher temperatures, the Gibbs energy barrier for the formation of the initial predioxin is clearly the rate-determining step for the whole process, but at lower temperatures the Gibbs energy barrier for this step is similar to those for its evolution into 2,3,7-T3CDD. This result is in contrast with previous proposals that the closure of the central ring is the rate-limiting step. Finally, according to our results the rate constant for the formation of polychlorinated dibenzo-p-dioxins increases with the temperature, in agreement with the experimental observation that the conversion of trichlorophenols increases when going from 600 to 900 K in the gas phase in the absence of catalysts, and with DFT molecular dynamics results.

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

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