The association of cancer risks with pentachlorophenol exposure: Focusing on community population in the areas along certain section of Yangtze River in China

Occurrence of pentachlorophenol in surface water from the upper to lower reaches of the Yangtze River and treated water in Wuhan, China

Pentachlorophenol (PCP), a persistent organic pollutant, has been banned in many countries, but it is still used in China as a wood preservative, molluscicide, or reagent for fish-pond cleaning, which may pose risks to the ecosystem and humans. However, data on the occurrence of PCP in the environment are scarce in the recent decade. The Yangtze River was regarded as a priority area of PCP pollution according to previous documents. This study aimed to examine the spatial distribution of PCP in the Yangtze River water, the differences in dry and wet seasons, the ecological risk for aquatic organisms, and its removal efficiency in tap water treatment plants. The river water samples (n = 144) were collected from the upper, middle, and lower reaches across ten provinces (or municipalities) in December 2020 and June 2021, respectively. PCP was detected in 88.9% of all the samples, ranging from  Collapse

Key Words

• Pentachlorophenol
• Removal
• Seasonal difference
• Spatial variations
• Surface water
• Yangtze River

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MESH Headings

• Humans
• Animals
• Pentachlorophenol/analysis
• Ecosystem
• Water Pollutants, Chemical/analysis
• Environmental Monitoring
• Rivers
• Cities
• China
• Risk Assessment
• Aquatic Organisms

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Grants

• WJ2019H307 Health Commission of Hubei Province
• WJ2019H303 Health Commission of Hubei Province
• 42277428 National Natural Science Foundation of China
• 21407117 National Natural Science Foundation of China

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Affiliation(s)

Fengting Yang Key Laboratory of Environment and Health, Ministry of Education & Ministry of Environmental Protection, and State Key Laboratory of Environmental Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, 13 Hangkong Road, Wuhan, 430030, Hubei, China
Yanjian Wan Center for Public Health Laboratory Service, Institute of Environmental Health, Wuhan Centers for Disease Prevention & Control, Wuhan, Hubei, 430024, People's Republic of China
Yan Wang Key Laboratory of Environment and Health, Ministry of Education & Ministry of Environmental Protection, and State Key Laboratory of Environmental Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, 13 Hangkong Road, Wuhan, 430030, Hubei, China
Shulan Li Key Laboratory of Environment and Health, Ministry of Education & Ministry of Environmental Protection, and State Key Laboratory of Environmental Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, 13 Hangkong Road, Wuhan, 430030, Hubei, China
Shunqing Xu Key Laboratory of Environment and Health, Ministry of Education & Ministry of Environmental Protection, and State Key Laboratory of Environmental Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, 13 Hangkong Road, Wuhan, 430030, Hubei, China
Wei Xia Key Laboratory of Environment and Health, Ministry of Education & Ministry of Environmental Protection, and State Key Laboratory of Environmental Health, School of Public Health, Tongji Medical College, Huazhong University of Science and Technology, 13 Hangkong Road, Wuhan, 430030, Hubei, China.

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An insights of organochlorine pesticides categories, properties, eco-toxicity and new developments in bioremediation process

Organochlorine pesticides (OCPs) have been used in agriculture, increasing crop yields and representing a serious and persistent global contaminant that is harmful to the environment and human health. OCPs are typically bioaccumulative and persistent chemicals that can spread over long distances. The challenge is to reduce the impacts caused by OCPs, which can be achieved by treating OCPs in an appropriate soil and water environment. Therefore, this report summarizes the process of bioremediation with commercially available OCPs, considering their types, impacts, and characteristics in soil and water sources. The methods explained in this report were considered to be an effective and environmentally friendly technique because they result in the complete transformation of OCPs into a non-toxic end product. This report suggests that the bioremediation process can overcome the challenges and limitations of physical and chemical treatment for OCP removal. Advanced methods such as biosurfactants and genetically modified strains can be used to promote bioremediation of OCPs.

Organochlorine pesticides and polycyclic aromatic hydrocarbons in serum of Beijing population: Exposure and health risk assessment

Organochlorine pesticides (OCPs) and polycyclic aromatic hydrocarbons (PAHs) are widespread environmental contaminants, but large-scale human biomonitoring and health risk assessment data on these contaminants remain limited. In this study, concentrations of 6 OCPs and 5 PAHs were determined by GC-MS/MS in 1268 human serum samples which were collected from the participants in 2017 Beijing Chronic Disease and Risk Factor Surveillance. The detection frequencies of OCPs and PAHs ranged from 64.7 % to 96.5 % and 89.4 % to 99.6 %, respectively. The most abundant contaminants in OCPs and PAHs were pentachlorophenol (PCP) and pyrene (Pyr) with median concentrations reaching up to 3.13 and 8.48 μg/L, respectively. Nonparametric tests were employed to assess the correlations among contaminants levels, demographic characteristics (age, gender, body mass index, residence) and serum biochemical indexes. Significantly higher serum levels of all PAHs were observed in suburb residents than that in urban residents (P < 0.001). Binary logistic regression analysis demonstrated that exposure to benzo(a)pyrene (OR 2.17 [1.29, 3.63]), phenanthrene (OR 1.06 [1.02, 1.11]), fluoranthene (OR 1.04 [1.02, 1.07]) and Pyr (OR 1.02 [1.01, 1.03]) might increase the occurrence of hyperglycemia, and exposure to hexachlorobenzene (HCB) (OR 1.53 [1.05, 2.22]) and pentachlorobenzene (OR 1.14 [1.02, 1.27]) were positively associated with hyperlipidemia. Furthermore, the hazard quotients (HQs) for serum HCB, PCP and p,p'-dichlorodiphenyldichloroethylene were calculated based on health-based guidance values to predict health risks. 0.2 % and 4.3 % of serum samples showed HQ values exceeding 1 for HCB and PCP, respectively, in case of the non-carcinogenic risk, while 23.1 % of HQs for HCB were above 1 in case of the carcinogenic risk for a risk level 10^-5. Our study reveals that the body burden of the Beijing general population relative to OCPs and PAHs was nonnegligible. The past exposure of HCB and PCP might adversely affect the health status of the Beijing population.

Probabilistic risk assessment of dietary exposure to pentachlorophenol in Guangzhou, China

Pentachlorophenol (PCP) is a ubiquitous environmental contaminant commonly existing as its sodium salt (NaPCP), which enters the human body primarily through long term but low-level dietary exposure. PCP contributes to chemical carcinogenesis and teratogenesis. In this study, the probabilistic risk of dietary exposure to PCP in Guangzhou citizens was investigated. In total, 923 food samples in the categories of pork, livestock (beef and lamb), poultry, offal, eggs, and freshwater fish (considered to be relatively susceptible to PCP contamination) were collected from various markets in Guangzhou and tested for PCP. Probabilistic risk assessment model calculations for PCP dietary exposure and margin of exposure (MOE) values were performed using @RISK software, based on a Monte Carlo simulation with 10,000 iterations. The overall detection rate of PCP (above 1 μg kg^-1, the detection limit) was 19.9% (184/923), with an average of 7.9 μg kg^-1. The highest rate of PCP detection, 28.2%, was in livestock (beef and lamb). The MOE value for dietary PCP exposure in general Guangzhou residents averaged 400, which was far below 5,000 (the borderline for judging a health risk). The lowest MOE value, 190, was observed in the 3- to-6-year old population and indicates a significant risk. In conclusion, this study suggests that PCP exposure in Guangzhou residents is of considerable health risk, especially for the pre-school young children.

Mild pentachlorophenol-mediated uncoupling of mitochondria depletes ATP but does not cause an oxidized redox state or dopaminergic neurodegeneration in Caenorhabditis elegans

Aims

Mitochondrial dysfunction is implicated in several diseases, including neurological disorders such as Parkinson's disease. However, there is uncertainty about which of the many mechanisms by which mitochondrial function can be disrupted may lead to neurodegeneration. Pentachlorophenol (PCP) is an organic pollutant reported to cause mitochondrial dysfunction including oxidative stress and mitochondrial uncoupling. We investigated the effects of PCP exposure in Caenorhabditis elegans, including effects on mitochondria and dopaminergic neurons. We hypothesized that mild mitochondrial uncoupling by PCP would impair bioenergetics while decreasing oxidative stress, and therefore would not cause dopaminergic neurodegeneration.

Results

A 48-hour developmental exposure to PCP causing mild growth delay (∼10 % decrease in growth during 48 h, covering all larval stages) reduced whole-organism ATP content > 50 %, and spare respiratory capacity ∼ 30 %. Proton leak was also markedly increased. These findings suggest a main toxic mechanism of mitochondrial uncoupling rather than oxidative stress, which was further supported by a concomitant shift toward a more reduced cellular redox state measured at the whole organism level. However, exposure to PCP did not cause dopaminergic neurodegeneration, nor did it sensitize animals to a neurotoxic challenge with 6-hydroxydopamine. Whole-organism uptake and PCP metabolism measurements revealed low overall uptake of PCP in our experimental conditions (50 μM PCP in the liquid exposure medium resulted in organismal concentrations of < 0.25 μM), and no measurable production of the oxidative metabolites tetra-1,4-benzoquinone and tetrachloro-p-hydroquinone.

Innovation

This study provides new insights into the mechanistic interplay between mitochondrial uncoupling, oxidative stress, and neurodegeneration in C. elegans. These findings support the premise of mild uncoupling-mediated neuroprotection, but are inconsistent with proposed broad "mitochondrial dysfunction"-mediated neurodegeneration models, and highlight the utility of the C. elegans model for studying mitochondrial and neurotoxicity.

Conclusions

Developmental exposure to pentachlorophenol causes gross toxicological effects (growth delay and arrest) at high levels. At a lower level of exposure, still causing mild growth delay, we observed mitochondrial dysfunction including uncoupling and decreased ATP levels. However, this was associated with a more-reduced cellular redox tone and did not exacerbate dopaminergic neurotoxicity of 6-hydroxydopamine, instead trending toward protection. These findings may be informative of efforts to define nuanced mitochondrial dysfunction-related adverse outcome pathways that will differ depending on the form of initial mitochondrial toxicity.

Pentachlorophenol exposure in early pregnancy and gestational diabetes mellitus: A nested case-control study

Pentachlorophenol (PCP) is an endocrine-disrupting chemical that is ubiquitously found in the environment. Few studies have reported PCP exposure in pregnant women and its association with gestational diabetes mellitus (GDM). This nested case-control study aimed to determine the concentration of urinary PCP in early pregnancy and explore the association between PCP exposure and GDM risk. This study included 293 GDM cases and 586 non-GDM controls matched by fetal sex and maternal age from a birth cohort in Wuhan, China. PCP concentrations in spot urine samples collected between 8 and 16 weeks of gestation were measured by ultra-performance liquid chromatography-tandem mass spectrometry. Conditional logistic regression was used to assess the association between PCP exposure and the odds ratio of GDM. The median concentrations of specific gravity-adjusted PCP in controls and cases were 0.70 and 0.80 ng/mL, respectively, with no significant differences (P > 0.05). The multivariate-adjusted odds ratios (ORs) (95% confidence intervals) for GDM across quartiles of urinary PCP were 1 (reference), 1.63 (1.06-2.50), 1.70 (1.11-2.61), and 1.35 (0.87-2.08), respectively, showing a potential "inverted-U" shaped association. In addition, PCP levels and maternal age or fetal sex had significant interactions with GDM risk (both P for interaction < 0.05). Among older women and those carrying female fetuses, the ORs of GDM risk were higher. This study suggests that pregnant women in central China are widely exposed to PCP, and this is the first time to report that PCP exposure may increase the risk of GDM (with potential effect modifications by maternal age and fetal sex). The association observed is in agreement with PCP's "inverted-U" anti-estrogenic effect in vivo; thus, such an effect in humans at environmentally relevant doses should be studied further.

Exposure to 2,4-dichlorophenol, 2,4,6-trichlorophenol, pentachlorophenol and risk of thyroid cancer: a case-control study in China

Thyroid cancer (TC) has inflicted huge threats to the health of mankind. Chlorophenols (CPs) were persistent organic pollutant and can lead to adverse effects in human health, especially in thyroid. However, epidemiological studies have revealed a rare and inconsistent relationship between internal exposure to CPs and TC risk. The purpose of this study was to investigate the correlation between urinary CPs and TC risk in Chinese population. From June 2017 to September 2019, a total of 297 histologically confirmed TC cases were recruited. Age- and gender-matched controls were enrolled at the same time. Gas chromatography-mass spectrometry (GC-MS) was used to determine the levels of three CPs in urine. Conditional logistic regression models were adopted to assess the potential association. Restricted cubic spline function was used to explore the non-liner association. After adjusting for confounding factors, multivariate analysis showed that, compared with the first quartile, the fourth quartile concentrations of 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TCP), and pentachlorophenol (PCP) were associated with TC risk (odds ratio (OR)_2,4-DCP =2.28, 95% confidence interval (CI): 1.24-4.18; OR_2,4,6-TCP =3.09, 95% CI: 1.66-5.77; OR_PCP =3.30, 95% CI: 1.71-6.36, respectively), when CPs were included in the multivariate model and restricted cubic spline function as continuous variables, presenting significant dose-response relationships. Meanwhile, whether in the TC group with tumor diameter > 1 cm or metastatic TC, the changes of 2,4,6 TCP and PCP concentrations were positively correlated with the risk of TC. Our study suggests that higher concentrations of urinary CPs are associated with increased TC risks. Moreover, 2,4,6-TCP and PCP have certain effects on the invasiveness of thyroid cancer. Targeted public health policies should be formulated to reduce the CP pollution. These findings need further in-depth studies to confirm and relevant mechanism also needed to be clarified.

Multiple metal exposure and obesity: A prospective cohort study of adults living along the Yangtze River, China

Association between long-term exposure to multiple metals and obesity remains inconclusive, and prospective evidence on the region along the Yangtze River was limited. Thus, our study aimed to examine the association of multiple metal exposure and obesity. We measured baseline urine levels of 22 metals of 982 adults living along the Yangtze River, incidence of obesity was calculated from body mass index (BMI) and waist circumference (WC) measured at follow-up survey. Cox proportional hazards models were used to examine the hazard ratios (HR) and 95% confidence interval (CI) for the association between urinary metals and obesity, and the mixing effect of metals on obesity was estimated by using quantile g-computation. In multiple-metal models, arsenic was significantly associated with BMI/obesity, with the HR in the highest quartiles of 0.33 (95% CI: 0.16, 0.69; p-trend = 0.004). The HRs for WC/obesity of arsenic and molybdenum were 0.49 (95% CI: 0.32, 0.75 for the fourth vs. first quartile; p-trend = 0.002) and 1.83 (95% CI: 1.25, 2.70; p-trend = 0.001), respectively. Quantile g-computation mixtures approach showed a significantly negative joint effect of multiple metals on WC/obesity, with the HR of 0.26 (95% CI: 0.14, 0.47; p < 0.001) when increasing all seventeen metals by one quartile. Our study suggests that all seventeen metal mixed exposure may be negatively associated with obesity. Further cohort studies are needed to confirm these findings and clarify the underlying biological mechanisms.

Probabilistic Risk Assessment of Dietary Exposure to Chloramphenicol in Guangzhou, China

Chloramphenicol has been used in veterinary medicine, where its residues can remain in food of animal origin, thus potentially causing adverse health effects. This facilitated the ban for its use in food-producing animals globally, but its residues have remained ubiquitous. In this study, food commodities possibly contaminated with chloramphenicol, including livestock meat, poultry, edible viscera, fish, shrimp and crab, molluscs, milk, and eggs, were collected from domestic retail shops in all the 11 districts of Guangzhou and tested for its residue. Probabilistic risk assessment model calculations for its dietary exposure, and the margin of exposure (displayed as mean values and 5th percentile to 95th percentile ranges) were performed by using @RISK software based on a Monte Carlo simulation with 10,000 iterations. The results indicated the detection of chloramphenicol in 248 out of 1454 samples (17.1%), which averaged to a level of 29.1 μg/kg. The highest average value was observed in molluscs (148.2 μg/kg, with the top value as 8196 μg/kg); meanwhile, based on the dietary structure of a typical Cantonese, pond fish, pork, and poultry meat contributed most (about 80%) to the residents’ dietary exposure to chloramphenicol. The margin of exposure for dietary chloramphenicol exposure in Guangzhou residents was 2489, which was apparently below 5000 (the borderline for judging a health risk), particularly low in preschool children (2094, suggesting an increased risk). In conclusion, the study suggests that chloramphenicol exposure in Guangzhou residents is considerable, and its relevant health hazard, especially for preschool children, is worthy of further investigation.

Mechanistic Study on Oxidative DNA Damage and Modifications by Haloquinoid Carcinogenic Intermediates and Disinfection Byproducts

Haloquinones (XQs) are a group of carcinogenic intermediates of the haloaromatic environmental pollutants and newly identified chlorination disinfection byproducts (DBPs) in drinking water. The highly reactive hydroxyl radicals/alkoxyl radicals and quinone enoxy/ketoxy radicals were found to arise in XQs and H₂O₂ or organic hydroperoxides system, independent of transition-metal ions. However, it was not clear whether these haloquinoid carcinogens and hydroperoxides can cause oxidative DNA damage and modifications, and if so, what are the underlying molecular mechanisms. We found that 8-oxodeoxyguanosine (8-oxodG), DNA strand breaks, and three methyl oxidation products could arise when DNA was treated with tetrachloro-1,4-benzoquinone and H₂O₂ via a metal-independent and intercalation-enhanced oxidation mechanism. Similar effects were observed with other XQs, which are generally more efficient than the typical Fenton system. We further extended our studies from isolated DNA to genomic DNA in living cells. We also found that potent oxidation of DNA to the more mutagenic imidazolone dIz could be induced by XQs and organic hydroperoxides such as t-butylhydroperoxide or the physiologically relevant hydroperoxide 13S-hydroperoxy-9Z,11E-octadecadienoic acid via an unprecedented quinone-enoxy radical-mediated mechanism. These findings should provide new perspectives to explain the potential genotoxicity, mutagenesis, and carcinogenicity for the ubiquitous haloquinoid carcinogenic intermediates and DBPs.

Electrocatalytic oxidation of PCP-Na by a novel nano-PbO2 anode: degradation mechanism and toxicity assessment

This study aims at investigating the electrocatalytic oxidation of sodium pentachlorophenate (PCP-Na) using a novel nano-PbO₂ powder anode. The nano-PbO₂ powder (marked as HL-PbO₂) was prepared by a simple hydrolysis process, and hydrothermal treatment was followed to improve the activity of HL-PbO₂. The HL-PbO₂ treated for 24 h by hydrothermal process (HL/HT-PbO₂-24) was confirmed to possess higher crystallinity, higher oxygen evolution potential, and more active sites, resulting in stronger OH radical generation capacity and higher electrochemical activity. Compared with conventional electrodeposited PbO₂ (ED-PbO₂) anode, the HL/HT-PbO₂-24 anode showed higher PCP-Na degradation rate. Under the same operating conditions, the mineralization current efficiency at HL/HT-PbO₂-24 was 2.7 times than that at ED-PbO₂. Five intermediates were detected in PCP-Na degradation solution and possible degradation mechanism of PCP-Na was discussed. In addition, the acute toxicity of PCP-Na degradation solution to zebrafish embryos and the oxidative stress induced in zebrafish embryos/larvae were studied to evaluate the ecological security of electrocatalytic oxidation of PCP-Na.

Mineralization of pentachlorophenol by ferrioxalate-assisted solar photo-Fenton process at mild pH

This work reports the use of ferrioxalate complexes to assist solar photo-Fenton treatment of pentachlorophenol (PCP) in aqueous medium at mild pH, which inhibits the precipitation of iron hydroxides and allows working at a low iron dosage. The experimental parameters were optimized by assessing the effect of initial concentrations of H₂O₂ (0-2.5 mM) and Fe(II) (2-10 mg/L), pH (3.0-9.0) and iron/oxalic acid molar ratios (1:0-1:13.5) on total organic carbon (TOC) removal. Ferrioxalate-assisted solar photo-Fenton achieved 97.5% mineralization in 120 min, clearly outperforming conventional Fenton and solar photo-Fenton. The presence of photosensitive ferrioxalate complexes accounted for the enhancement, as a result of Fe(II) regeneration that accelerated the hydroxyl radical (OH) production. The time course of H₂O₂ and Fe(II) concentrations was evaluated under different iron/oxalic acid ratios. The five carboxylic acids determined by ion-exclusion HPLC and the eight aromatic by-products identified by GC-MS allowed the proposal of a degradation pathway that included hydroxylation, dechlorination and dimerization steps. Complete chloride ion release was achieved after 90 min of treatment.

Genome-Wide Analysis of Transcriptional Changes and Genes That Contribute to Fitness during Degradation of the Anthropogenic Pollutant Pentachlorophenol by Sphingobium chlorophenolicum

Pentachlorophenol (PCP) is a highly toxic pesticide that was first introduced in the 1930s. The alphaproteobacterium Sphingobium chlorophenolicum, which was isolated from PCP-contaminated sediment, has assembled a metabolic pathway capable of completely degrading PCP. This pathway produces four toxic intermediates, including a chlorinated benzoquinone that is a potent alkylating agent and three chlorinated hydroquinones that react with O2 to produce reactive oxygen species (ROS). RNA-seq analysis revealed that PCP causes a global stress response that resembles responses to proton motive force uncoupling and membrane disruption, while surprisingly, little of the response resembles the responses expected to be produced by the PCP degradation intermediates. Tn-seq was used to identify genes important for fitness in the presence of PCP. By comparing the genes that are important for fitness in wild-type S. chlorophenolicum and a non-PCP-degrading mutant, we identified genes that are important only when the PCP degradation intermediates are produced. These include genes encoding two enzymes that are likely to be involved in protection against ROS. In addition to these enzymes, the endogenous levels of other enzymes that protect cells from oxidative stress appear to mitigate the toxic effects of the chlorinated benzoquinone and hydroquinone metabolites of PCP. The combination of RNA-seq and Tn-seq results identify important mechanisms for defense against the toxicity of PCP. IMPORTANCE Phenolic compounds such as pentachlorophenol (PCP), triclosan, and 2,4-dichlorophenoxyacetic acid (2,4-D) represent a common class of anthropogenic biocides. Despite the novelty of these compounds, many can be degraded by microbes isolated from contaminated sites. However, degradation of this class of chemicals often generates toxic intermediates, which may contribute to their recalcitrance to biodegradation. We have addressed the stresses associated with degradation of PCP by Sphingobium chlorophenolicum by examining the transcriptional response after PCP exposure and identifying genes necessary for growth during both exposure to and degradation of PCP. This work identifies some of the mechanisms that protect cells from this toxic compound and facilitate its degradation. This information could be used to engineer strains capable of improved biodegradation of PCP or similar phenolic pollutants.

Occurrence and profiles of halogenated phenols, polybrominated diphenyl ethers and hydroxylated polybrominated diphenyl ethers in the effluents of waste water treatment plants around Huang-Bo Sea, North China

Halogenated organic pollutants (HOPs), as ubiquitous environment contaminants, have attracted increasing concerns due to the potential adverse health impacts on organisms and even humans. Waste water treatment plants (WWTPs) are one source of HOPs to the environment through their discharge of treated effluent. In this study, the presence and profiles of 6 halogenated phenols (HP), 17 polybrominated diphenyl ethers (PBDE) and 11 hydroxylated polybrominated diphenyl ethers (OH-PBDE) were investigated in 12 WWTP effluent samples collected near Huang-Bo Sea in Dalian, China. These targeted organohalogen pollutants were found in all the effluent samples with the total concentrations of ΣHPs, ΣPBDEs and ΣOH-PBDEs ranging from 77.2 to 168.5ng/L, from not-detected to 5.3ng/L and from 0.08 to 0.88ng/L, respectively. The most abundant congeners of HPs and PBDEs in the effluents were pentachlorophenol (PCP), BDE-47 and BDE-99, while for OH-PBDEs, 6-OH-BDE-47 and 5-OH-BDE-47 were the most abundant. In addition, the statistical analysis showed that a significant (p<0.05) positive correlation was observed between BDE-47 and its metabolite 6-OH-BDE-47, indicating that PBDEs may be a source of OH-PBDEs detected in the effluents.

Typical Soil Redox Processes in Pentachlorophenol Polluted Soil Following Biochar Addition

Reductive dechlorination is the primary pathway for environmental removal of pentachlorophenol (PCP) in soil under anaerobic condition. This process has been verified to be coupled with other soil redox processes of typical biogenic elements such as carbon, iron and sulfur. Meanwhile, biochar has received increasing interest in its potential for remediation of contaminated soil, with the effect seldom investigated under anaerobic environment. In this study, a 120-day anaerobic incubation experiment was conducted to investigate the effects of biochar on soil redox processes and thereby the reductive dechlorination of PCP under anaerobic condition. Biochar addition (1%, w/w) enhanced the dissimilatory iron reduction and sulfate reduction while simultaneously decreased the PCP reduction significantly. Instead, the production of methane was not affected by biochar. Interestingly, however, PCP reduction was promoted by biochar when microbial sulfate reduction was suppressed by addition of typical inhibitor molybdate. Together with Illumina sequencing data regarding analysis of soil bacteria and archaea responses, our results suggest that under anaerobic condition, the main competition mechanisms of these typical soil redox processes on the reductive dechlorination of PCP may be different in the presence of biochar. In particularly, the effect of biochar on sulfate reduction process is mainly through promoting the growth of sulfate reducer (Desulfobulbaceae and Desulfobacteraceae) but not as an electron shuttle. With the supplementary addition of molybdate, biochar application is suggested as an improved strategy for a better remediation results by coordinating the interaction between dechlorination and its coupled soil redox processes, with minimum production of toxic sulfur reducing substances and relatively small emission of greenhouse gas (CH4) while maximum removal of PCP.