Degree Of Chlorination Research Articles

Theoretical and experimental formation of low chlorinated dibenzo-p-dioxins and dibenzofurans in the Fenton oxidation of chlorophenol solutions

The formation of chlorinated and non-chlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) has been experimentally investigated after the Fenton oxidation of 2-chlorophenol (2-CP, 15.56 mM) aqueous solutions by assessing the influence of iron concentration (0.09–2.88 mM), hydrogen peroxide dose (40.44–202.20 mM), temperature (20–70 °C) and chloride concentration (0–56.35 mM). The presence of chloride in the medium together with room temperature and substoichiometric Fenton conditions (40.44 mM H2O2) led to an increase in total PCDD/Fs concentration from less than 1 ng L−1 to 2 μg L−1. Results showed a dominance of the dichlorinated species (DCDD/Fs) in the homologue profile of total PCDD/Fs reaching values up to 1.5 μg L−1. Furthermore, the products distribution exhibited a gradual decrease in the homologue concentration as the chlorination degree increased from di-to octachloro-substituted positions. Considering the characteristics of the reaction medium, the experimental results, and the information gathered in bibliography with regard to the generation of active radicals from 2-chlorophenol, a mechanism describing the formation of low chlorinated PCDD/Fs in a Fenton oxidizing aqueous system has been proposed.

Toxicity of hydroxylated polychlorinated biphenyls (HO-PCBs) using the bioluminescent assay Microtox(®).

Hydroxylated polychlorinated biphenyls (HO-PCBs) are toxic contaminants which are produced in the environment by biological or abiotic oxidation of PCBs. The toxicity of a suite of 23 mono-hydroxylated derivatives of PCBs and 12 parent PCBs was determined using the bacterial bioluminescent assay Microtox(®). All HO-PCBs tested exhibited higher toxicity than the corresponding parent PCB, with effect concentration 50% (EC50) ranging from 0.07 to 133mg L(-1). The highest toxicities were recorded with 4-hydroxylated derivatives of di-chlorinated biphenyls (EC50=0.07-0.36mg L(-1)) and 2-hydroxylated derivatives of tri-chlorinated biphenyls carrying a chlorine substituent on the phenolic ring (EC50=0.34-0.48mg L(-1)). The toxicity of HO-PCBs generally decreased when the degree of chlorination increased. Consistently with this observation, a significant positive correlation was measured between toxicity (measured by EC50) and octanol-water partition coefficient (pK ow) for the HO-PCBs under study (Pearson's correlation coefficient, r=0.74), which may be explained by the lower solubility and bioavailability generally associated with higher hydrophobicity. This study is the first one which assessed the toxicity of a suite of PCBs and HO-PCBs using the bioluminescent assay Microtox(®), showing an inverse correlation between toxicity and hydrophobicity.

Formation of persistent organic pollutants from 2,4,5-trichlorothiophenol combustion: a density functional theory investigation.

Polychlorinated dibenzothiophene (PCDT) and polychlorinated thianthrene (PCTA) are sulfur analogues of dioxins, such as polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F). In this work, we present a detailed mechanistic and kinetic analysis of PCDT and PCTA formation from the combustion of 2,4,5-trichlorothiophenol. It is shown that the formation of these persistent organic pollutants is more favourable, both kinetically and thermodynamically, than their analogous dioxin counterparts. This is rationalised in terms of the different influences of the S-H and O-H moieties in the 2,4,5-trichlorothiophenol and 2,4,5-trichlorophenol precursors. Kinetic parameters also indicate that the yield of PCDT should exceed that of PCDD. Finally, we demonstrate here that the degree and pattern of chlorination on the 2,4,5-trichlorothiophenol precursor leads to subtle thermodynamic and kinetic changes to the PCDT/PCTA formation mechanisms. Graphical abstract Formation mechanisms of persistant organic pollutants, PCDT and PCTA, from 2,4,5-trichlorothiophenol combustion, has been investigated using density functional theory.

Design and testing of a new sampler for simplified vacuum-assisted headspace solid-phase microextraction

The design and testing of a new and low-cost experimental setup used for vacuum-assisted headspace solid-phase microextraction (Vac-HSSPME) is reported here. The device consists of a specially designed O-ring seal screw cap offering gas-tight seal to commercially available headspace vials. The new polytetrafluoroethylene (PTFE) cap was molded by a local manufacturer and had a hole that could tightly accommodate a septum. All operations were performed through the septum: air evacuation of the sampler, sample introduction and HSSPME sampling. The analytical performance of the new sampler was evaluated using 22 mL headspace vials with 9 mL water samples spiked with polychlorinated biphenyls (PCBs). Several experimental parameters were controlled and the optimized conditions were: 1000 rpm agitation speed; 30 min extraction time; 40 °C sampling temperature; polydimethylsiloxane-divinylbenzene (PDMS-DVB) fiber. The lack of accurate Henry's law constant (KH) values and information regarding how they change with temperature was a major limitation in predicting the phase location of evaporation resistance during Vac-HSSPME. Nevertheless, the combined effects of system conditions indicated the increasing importance of gas phase resistance with increasing degree of PCBs chlorination. Stirring enhancements were not recorded for the higher chlorinated PCBs suggesting that the hyperhydrophobic gas/water interface was the preferred location for these compounds. Analytically, the developed method was found to yield linear calibration curves with limits of detection in the sub ng L−1 level and relative standard deviations ranging between 5.8 and 14%. To compensate for the low recoveries of the higher chlorinated PCB congeners in spiked river water the standard addition methodology was applied. Overall, the compact design of the new and reusable sample container allows efficient HSSPME sampling of organic analytes in water within short extraction times and at low sampling temperatures compared to other published HSSPME methods.

Catalytic decomposition of dioxins and other unintentional POPs in flue gas from a municipal waste incinerator (MWI) in China: a pilot testing.

Unintentionally produced persistent organic pollutants (UPOPs) include polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), dioxin-like polychlorinated biphenyls (dl-PCBs), pentachlorobenzene (PeCBz), and hexachlorobenzene (HxCBz). With the booming of municipal waste incinerators (MWIs) in China, the emission of UPOPs has generated great concern. As an alternative technology of dioxin control, catalytic decomposition has not been used in China, mainly due to the absence of national demonstration projects. Also, the simultaneous removal of various UPOPs has not been well investigated.In this study, a pilot-scale selective catalytic oxidative (SCO) system using a self-developed honeycomb catalyst was built and tested in a typical municipal waste incinerator (MWI) of China. The original concentration of PCDD/Fs in flue gas after the treatment of activated carbon injection (ACI) still exceeded the national emission standard (0.1ng I-TEQ/Nm3), while the concentrations of PeCBz and HxCBz were one order of magnitude higher than that of PCDD/Fs. For the testing temperature varying from 300 to 200°C, the removal efficiency of PCDD/Fs range from 39 to 95%, followed by dl-PCBs with the range of 56-89%. PeCBz and HxCBz were also removed, though their removal efficiencies were lower than those of PCDD/Fs and dl-PCBs. Both temperature and degree of chlorination influence the removal efficiencies.

The halogen effects of disinfectant by-products on nutrient concentration, oxidative stress, fatty acids and α-tocopherol concentrations in membrane lipids of two Solanum lycopersicum cultivars

A 30-day exposure time experiment was designed to investigate whether the extent of physiological impacts of trihalomethane exposure on two Solanum lycopersicum cultivars correlated with either the number of bromine or chlorine atoms in the trihalomethane molecules, focusing on biomass gain, nutrient concentration, oxidative stress, fatty acids and α-tocopherol contents in membrane lipids. The gain of biomass in tomato seedlings decreased with an increase in the degree of bromination. Concentrations of essential nutrients required for plant growth such as nitrogen, phosphorus, potassium, sulphur and boron decreased in plant dry matter that correlated with the increasing number of chlorine atoms in the trihalomethane molecules. Trihalomethane exposure resulted in an increase in oxidative stress response in both tomato cultivars with parameters such as total phenolic content, ferric reducing antioxidant power, oxygen radical absorbance capacity and the activities of antioxidant peroxidase enzymes, all correlating with an increasing number of chlorine atoms in the trihalomethane molecule; hence, oxidative damage increased with a higher degree of chlorination. However, no such correlations were observed in superoxide dismutase activity, general lipid peroxidation, α-tocopherol content and total soluble proteins. In plant membrane lipids, an increase in the saturated fat hexadecanoic acid was observed in both tomato cultivars that correlated with the degree of chlorination in the trihalomethane molecule. The increase in α-linolenic acid stress signaling correlated with an increase in the degree of chlorination in only one tomato cultivar suggesting variable tolerance between cultivars to chemical action.

Immunotoxicity Monitoring in a Population Exposed to Polychlorinated Biphenyls.

The relationship between polychlorinated biphenyl (PCB) burden and several indicators of immune function was investigated as part of the HELPcB (Health Effects in High-Level Exposure to PCB) program, offering bio-monitoring to workers, relatives, and neighbors exposed to PCBs by a German transformers and capacitors recycling company. The present retrospective observational study evaluates the correlation of plasma levels of total PCBs, five indicator congeners (28, 101, 138, 153, 180), and seven dioxin-like congeners (105, 114, 118, 156, 157, 167, 189) with several parameters of immune function. The cross-sectional study was performed immediately after the end of exposure (258 subjects), and one (218 subjects), and two (177 subjects) years later. At the first time point, measurements showed significant positive correlation between congeners with low to medium chlorination and the relative proportion of CD19 positive B-cells among lymphocytes, as well as a negative correlation of PCB114 with serum IgM, and of PCB 28 with suppressor T-cell and NK-cell numbers. Congeners with a high degree of chlorination, in particular PCB157 and 189, were positively associated with expression of the activation marker CD25 on T-cells in the cohort of the second time point. No associations between PCB levels and IFN-y production by T-cells and killing by NK-cells were found. In conclusion, there were several effects on the cellular composition of adaptive immunity, affecting both T- and B-cells. However, the values were not generally outside the reference ranges for healthy adult individuals and did not indicate overt functional immunodeficiency, even in subjects with the uppermost PCB burden.

The effect of long-range atmospheric transport of organochlorine compounds by soil studies from Mongolia to the Arctic

The results of studies on the distribution regularities are presented for polychlorinated biphenyls (PCBs) of different degrees of chlorination and for organochlorine pesticides (OCPs): hexachlorobenzene (HCB), hexachlorocyclohexane (HCCH), and DDT with its metabolites in the soils along the Lena River valley and in background areas of Eastern Siberia and Mongolia. A statistically reliable correlation is found between the PCB–OCP and Corg concentrations. The highest levels of HCB are registered in the soils between 50 and 60° N. The concentrations of αand γ-HCCH increase reliably, while those of pp′-DDT and pp′-DDE decrease from south to north. A trend of the decrease in concentrations from Mongolia to the Laptev Sea is revealed for tri-, tetra-, and penta-chlorine-substituted PCB congeners. However, the soils sampled northwards from 60° N show a reliable increase in the concentrations of tetra-, penta-, and hexachlorine-substituted congeners.

Mass spectrometric study of the bromination of technical mixtures of polychlorinated biphenyls

The products of bromination of polychlorinated biphenyls (PCBs) that constitute Trichlorobiphenyl and Sovol PCB technical mixtures were studied by gas chromatography–mass spectrometry. On the basis of mass spectrometric data, the reaction was shown to result in formation of a mixture of poly(bromochloro)biphenyls containing from one to five bromine atoms and from two to six chlorine atoms in different combinations. It was found that the content of monobromo derivatives increases while the content of di-, tri-, and tetrabromo PCB derivatives decreases when the chlorination degree of the initial PCBs increases.

Determination of short-chain chlorinated paraffins in ambient air using high-volume sampling combined with high resolutimi gas chromatography-electron capture negative ion-low resolution mass spectrometry

An analytical method for quantifying short-chain chlorinated paraffins (SCCPs) in ambient air using high-volume sampling combined with high resolution gas chromatography-electron capture negative ion-low resolution mass spectrometry ( HRGC-ECNI-LRMS) was developed. An acidified silica gel column and a basic alumina column were used to optimize the cleanup procedures. The results showed a good linearity (R2>0. 99) between the total response factors and the degree of chlorination of SCCPs in the content range of 58. 1%-63. 3%. The limits of detection (S/N ≥3) and the limits of quantification (S/N ≥ 10) were 4. 2 and 12 µg, respectively. The method detection limit (MDL) for SCCPs was 0. 34 ng/m3 (n = 7). The recoveries of SCCPs in air samples were in the range of 81. 9% to 94. 2%. It is demonstrated that the method is suitable for the quantitative analysis of SCCPs in air samples.

Chlorination pattern effect on thermodynamic parameters and environmental degradability for C10-SCCPs: Quantum chemical calculation based on virtual combinational library

Short-chain chlorinated paraffins (SCCPs) are still controversial candidates for inclusion in the Stockholm Convention. The inherent mixture nature of SCCPs makes it rather difficult to explore their environmental behaviors. A virtual molecule library of 42,720 C10-SCCP congeners covering the full structure spectrum was constructed. We explored the structural effects on the thermodynamic parameters and environmental degradability of C10-SCCPs through semi-empirical quantum chemical calculations. The thermodynamic properties were acquired using the AM1 method, and frontier molecular orbital analysis was carried out to obtain the EHOMO, ELUMO and ELUMO–EHOMO for degradability exploration at the same level. The influence of the chlorination degree (NCl) on the relative stability and environmental degradation was elucidated. A novel structural descriptor, μ, was proposed to measure the dispersion of the chlorine atoms within a molecule. There were significant correlations between thermodynamic values and NCl, while the reported NCl-dependent pollution profile of C10-SCCPs in environmental samples was basically consistent with the predicted order of formation stability of C10-SCCP congeners. In addition, isomers with large μ showed higher relative stability than those with small μ. This could be further verified by the relationship between μ and the reactivity of nucleophilic substitution and OH attack respectively. The C10-SCCP congeners with less Cl substitution and lower dispersion degree are susceptible to environmental degradation via nucleophilic substitution and hydroxyl radical attack, while direct photolysis of C10-SCCP congeners cannot readily occur due to the large ELUMO–EHOMO values. The chlorination effect and the conclusions were further checked with appropriate density functional theory (DFT) calculations.

Congener profiles of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) in sediment, water, and fish at a soil contamination site in Taiwan

ABSTRACTThe relationship of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) in sediment, water, and fish was studied for 55 fish farms near a contaminated site in Tainan, Taiwan. Samples were collected from the farms and analyzed for seventeen 2,3,7,8-substituted PCDD/Fs congeners. High correlations were found between PCDD/Fs in water and sediment in regard to both concentration and toxicity (R2 = 0.933 for concentration and R2 = 0.832 for toxicity). The congener profiles of the 17 PCDD/Fs in water were similar to those in the sediment. However, the PCDD/Fs congener composition in the fish and fish belly samples were different from those in the sediment and water samples obtained from the same fish farm and were also different among the fish samples. It is thus suggested that the biotic PCDD/Fs distribution is more complex than the abiotic PCDD/Fs distribution. Among the seven factors analyzed, only the lipid percentage presented a relationship with the PCDD/Fs congener composition in the fish and fish bellies. A multiple linear regression of the concentration of each congener in the fish was conducted using the concentration of each congener in the site-matched sediment and the lipid content of the fish as independent variables. The results showed that only seven PCDD/Fs congeners with a lower degree of chlorination, which were 4-6 chlorine substitutes, in the fish presented a significant correlation with the lipid content in the fish and their concentration in sediment (r > 0.65, P < 0.005 for both independent variables). In addition, the octanol-water partition coefficients were not significantly related to this distribution behavior.

High Temperature Chemistry of Chlorinated Acenaphthylene. 3C Bay Acetylene Additions and Annealing by Five-Membered Ring Shifts.

Experimental and theoretical results concerning the growth and isomerization of chlorinated acenaphthylene, C12H8, during the pyrolysis of chlorohydrocarbons are presented here. A fullerene subunit, C12H8, is a useful system to investigate regarding C60 formation. However, direct experimental observation of isomerization and annealing processes in particular are difficult to confirm due to the high symmetry of the parent molecule. Chlorination lowers the symmetry, essentially labeling carbon atoms, allowing growth and isomerization to be followed directly. Pyrolysis of dichloro- and trichloroethylene, and their copyrolyses with trichlorobenzenes, provides an efficient and general source of chlorinated acenaphthylenes in a range of degrees of chlorination and over a number of unique congeners. Analysis of congener yields as a function of reagents employed, guided by DFT/B3LYP/6-311G(d,p) level calculations, strongly suggests that C2 addition across three-carbon bays in naphthalene is a major driver of growth. Additionally, extremely facile five-membered ring shifts are operative, with chlorine promoting isomerization. Theoretical study of C16H10- and C18H10-based congeners indicate that this is a general phenomenon, and with chlorine also favoring internal cyclopentafused rings in addition to increased isomerization rates, this suggests halogen moieties may be an important feature for efficient fullerene growth.

PCDDs, PCDFs and PCNs in products of microwave-assisted pyrolysis of woody biomass--Distribution among solid, liquid and gaseous phases and effects of material composition.

Microwave-assisted pyrolysis (MAP) of lignocellulosic biomass is a technique that could potentially be used to produce and upgrade renewable energy carriers. However, there is no available information about the formation of dioxins and other organic pollutants in MAP treatment of woody biomass. In this study, MAP experiments were conducted in lab-scale using virgin softwood, bark, and impregnated wood as feedstocks. The non-condensable gas, liquid (fractionated into aqueous and oil phases), and char fractions generated during pyrolysis were collected and analysed for polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and naphthalenes (PCNs). The concentrations of PCDDs, PCDFs and PCNs in the pyrolysis products ranged from 0.52 to 43.7 ng kg(-1). All investigated compound groups were most abundant in the oil fraction, accounting for up to 68% (w/w) of the total concentrations. The highest PCDD, PCDF and PCN concentrations were found from the pyrolysis of bark, which has relatively high contents of chlorine and mineral matter, followed by impregnated wood, which contains organic and metal-based preservatives. The homologue profiles of all three compound groups were dominated by the less chlorinated homologues. The homologue abundance decreased as the degree of chlorination increased. This trend was observed for all three feedstocks.

PAMAM dendrimers as nano carriers to investigate inflammatory responses induced by pulmonary exposure of PCB metabolites in Sprague-Dawley rats

Polychlorinated biphenyls (PCBs) persist and accumulate in the ecosystem depending upon the degree of chlorination of the biphenyl rings. Airborne PCBs are especially susceptible to oxidative metabolism, yielding mono- and di-hydroxy metabolites. We have previously demonstrated that 4-chlorobiphenyl hydroquinones (4-CB-HQs) acted as cosubstrates for arachidonic acid metabolism by prostaglandin H synthase (PGHS) and resulted in an increase of prostaglandin production in vitro. In the present study, we tested the capability of 4-CB-HQ to act as a co-substrate for PGHS catalysis in vivo. BQ and 4-CB-2',5'-HQ were administered intratracheally to male Sprague-Dawley rats (2.5 μmol/kg body weight) using nanosized polyamidoamine (PAMAM) dendrimers as carriers. We found that 24 h post application, PGE2 metabolites in kidney of rats treated with 4-CB-2',5'-HQ were significantly increased compared to the controls. The increase of PGE2 metabolites was correlated with increased alveolar macrophages in lung lavage fluid. The elevation of PGE2 synthesis is of great interest since it plays a crucial role in balancing homeostasis and inflammation where a chronic disturbance may increase risk of cancer. PAMAM dentrimers proved to be an effective transport medium and did not stimulate an inflammatory response themselves.

Formation Pathways of Mono- to Octa-Chlorinated Dibenzo-p-dioxins and Dibenzofurans in Main Organochemical Industries.

The concentrations and formation pathways of mono- to octa-chlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) were investigated in main organochemical industries. High levels of PCDDs and PCDFs were detected. The total concentrations of 27 PCDD/F congeners in chloranil, 2,4-D, and 1,4-dichlorobenzene were 5302397 ± 8944449, 20963 ± 15908, and 242 ± 67 pg g(-1), respectively, and the less-chlorinated PCDD/F levels were 12006 ± 20155, 9536 ± 5594, and 195 ± 94 pg g(-1), respectively. The distribution trends of less and more chlorinated PCDD/Fs were similar in different chemical plants because of their similar formation pathways, which may also be related to the degree of chlorination of chemical products and purification processes. 1,2,3,4-TeCDF and 2,4,8-TrCDF were selected as model molecules to calculate the bond dissociation energy, showing that 2-MCDF, 3-MCDF, and 2,8-DCDF are more easily formatted as shown by the analytical results. The formation pathways of less to more chlorinated PCDFs are proposed to explain why 2-MoCDF, 2,8-DiCDF, 2,4,8-TrCDF, and 2,3,4,7,8-PeCDF are the dominant congeners and to explain why 2,3,4,7,8-PeCDF is the largest contributor of I-TEQs in most studies.

Prenatal Polychlorinated Biphenyls Exposure And Reproductive Hormones In Adult Male Offspring: Results From The Child Health And Development Studies

Introduction: Polychlorinated biphenyls (PCBs) are ubiquitous persistent organic pollutants which act as endocrine disruptors. The effect of in utero exposure to PCBs on hormonal concentrations in md-life remains unclear. Except for three studies, previous research investigating the relationship between PCB exposure and male sex hormones has been cross-sectional. Here, we examine whether in utero PCB exposure is associated with concentrations of testosterone and follicular stimulating hormone (FSH) in adult males. Methods: We used data from the Study of the Environment and Reproduction (SER), a follow up of adult male offspring from the Child Health and Development Study. Of those men who participated, 204 (mean age 43.7 years) gave a blood sample for the measurement of total testosterone and FSH. Prenatal PCB exposure to 15 congeners was measured in maternal blood samples in the immediate postpartum period. Multivariable regression was used to determine the association between prenatal PCB exposure and concentrations of testosterone and FSH, controlling for age, race, total lipids and BMI. PCBs were grouped according to their proposed mechanism of action and according to the degree of chlorination; individual congeners were also assessed as separate exposure measures. Hormone and PCB concentrations were positively skewed and transformed using the natural log function. Results: Mean (standard deviation) concentrations of total testosterone and FSH were 386 (183) ng/dL and 5.83 (3.99) mIU/mL, respectively. We did not find any associations between exposure and FSH. In both unadjusted and adjusted analyses, maternal PCB183 was associated with increased total testosterone. For each log unit increase in maternal PCB183, log total testosterone increased by 0.15 ng/dL (95% confidence interval (-0.01, 0.31). Conclusions: These results suggest that prenatal exposure to specific PCB congeners is associated with testosterone levels in adulthood.

Comparison of PCDD/F levels and profiles in fly ash samples from multiple industrial thermal sources

A comprehensive comparison of the levels and profiles of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) in fly ash samples from multiple industrial sources may help to prioritize sources and to understand discrepancies in profiles. In this study, PCDD/F data from 113 fly ash samples from 14 sources reported in previous studies were summarized and compared. The highest PCDD/F levels occurred in samples from secondary copper smelting (SCu). Although PCDD/F levels from secondary zinc smelting (SZn) were slightly lower than those of SCu, the PCDD/F profiles varied widely between the two sources. For SCu, more chlorinated homologs were dominant, with highest degrees of chlorination being 6.6 for PCDF and 7.2 for PCDD. For SZn, less chlorinated homologs were dominant, with lowest degrees of chlorination being 4.4 for PCDF and 4.8 for PCDD. We speculate that copper and zinc might promote PCDD/F formation by catalyzing different pathways of thermal reactions. Diagnostic ratios of specific PCDD/F congeners for different sources were suggested to identify potential sources of PCDD/Fs in the environment. Equations describing correlations between congeners and PCDD/F toxic equivalents were established, which may be useful for rapid and inexpensive screening of the toxic levels of PCDD/Fs in fly ash samples.

Theoretical study on the oxidative damage to cholesterol induced by peroxyl radicals

The density functional and the transition state theories were used to estimate detailed thermochemical and kinetic data for the oxidative damage to cholesterol induced by peroxyl radicals (ROO•) in lipid media. Two mechanisms of reactions were considered, the hydrogen transfer and the radical adduct formation, and it was found that hydrogen transfer is the only important route in this case, particularly at allylic sites. 7α products are predicted to represent more than 90% of the total initial damage, albeit 7β products are expected to be found in small but not negligible proportion. The chlorination degree was found to play an important role in the extent of the oxidative damage to cholesterol inflicted by the ROO• family. The estimated rate constants are 2.74 × 105, 1.32 × 105, 3.09 × 102, 6.07 × 101, and 8.75 × 10−1 M−1 s−1 for the reactions with •OOCHCl2, •OOCCl3, •OOCH2Cl, •OOH, and •OOCH3, respectively. These values indicate that only chlorinated peroxyl radicals represent a significant hazard to the chemical integrity of cholesterol. Copyright © 2015 John Wiley & Sons, Ltd.

Effects of occupational exposure to polychlorinated biphenyls on urinary metabolites of neurotransmitters: A cross-sectional and longitudinal perspective.

Polychlorinated biphenyls (PCBs) are chemicals which were used for industrial purposes and are known to induce various adverse health effects. They are also known to be neurotoxic and numerous targets within the central nervous system have been identified in previous studies. Specifically, the neurotransmitters dopamine (DA) and norepinephrine (NE) are influenced by PCBs as indicated in studies involving animals. However, limited evidence has been published documenting PCB induced changes in the neurotransmitter system in humans. In the present study, we examined the association between a higher PCB body burden following occupational exposure and possible changes in human neurotransmitter metabolites. Within a medical surveillance programme called HELPcB (Health Effects in High-Level Exposure to PCB) that monitors adverse health effects of occupational PCB exposure, urine samples were obtained (n(T1) = 166; n(T2) = 177 and n(T3) = 141). The urinary concentrations of the metabolites homovanillic acid (HVA; for DA) and vanillylmandelic acid (VMA; for NE) were analyzed. Blood samples were obtained by vena puncture in order to determine the internal exposure to PCBs with human biomonitoring. A cross-sectional analysis indicated a significant negative effect of PCB exposure on HVA and VMA. Longitudinally, an initially higher exposure to higher chlorinated PCBs was followed by constant reduced HVA level over three consecutive years. Exploratory analyses show different long-term effects for different PCBs according to their chlorination degree. A higher exposure with lower chlorinated PCBs leads to an increase of VMA and HVA. Conversely, a higher exposure to all PCBs results in a reduction of HVA. This study, to our knowledge, is the first to document changes in neurotransmitter metabolites after occupational PCB exposure in humans. This finding advances evidence obtained from past research, and identifies one potential pathomechanism in the central dopaminergic system of humans.