Biodegradation of chlordane and hexachlorobenzenes in river sediment

Meta-Analysis and Machine Learning Models for Anaerobic Biodegradation Rates of Organic Contaminants in Sediments and Sludge

Anaerobic biodegradation rates (half-lives) of organic chemicals are pivotal for environmental risk assessment and remediation. Traditional experimental evaluation, constrained by prolonged, oxygen-free conditions, struggles to keep pace with emerging contaminants. Data-driven machine learning (ML) models serve as promising complements. However, reported quantitative structure-biodegradation relationships or ML models on anaerobic biodegradation are mostly based on small data sets (<100 records) and neglect experimental conditions, usually achieving compromised predictions. This work aimed to develop ML models for predicting the biodegradation half-lives of organic pollutants in anaerobic environments (i.e., sediment/soil and sludge). Focusing on important features of both chemicals and experimental conditions, we first curated two data sets, one for sediment/soil (SED) and the other for sludge (SLD), covering 978 records for 206 chemicals from the literature, and then conducted a meta-analysis. Next, we built a binary classification (half-life of 30 days as the cutoff) model with an accuracy of 81% and a regression model with R2 of 0.56 for SED based on LightGBM (80% and 0.31 for SLD based on Extra tree, respectively). The model interpretations underscored the significance of experimental conditions (e.g., temperature and inoculum dosage), as evidenced by their high feature importance, and the models were found to correctly capture the effects of chemical substructures, for example, branched structures and aromatic rings prolonged half-lives while methyl group and ortho-substitution on rings shortened half-lives. The applicability domains of the models were also defined, resulting in reasonable prediction for the half-lives of 41% (SED) or 67% (SLD) of over 4000 persistent, bioaccumulative, and toxic chemicals. Overall, this study pioneers ML models for predicting the anaerobic degradation half-lives, offering valuable support for future evaluation and implementation of chemical anaerobic biodegradation.

The emerging and legacy persistent organic contaminants in corals of the South China Sea

Seawater warming, ocean acidification and chemical pollution are the main threats to coral growth and even survival. The legacy persistent organic contaminants (POCs), such as polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs), and the emerging contaminants, including polybrominated diphenyl ethers (PBDEs), dechlorane plus (DPs) and novel brominated flame retardants (NBFRs) were studied in corals from Luhuitou fringing reef in Sanya Bay and Yongle atoll in Xisha Islands, the South China Sea (SCS). Total average concentrations of ∑16PAHs, ∑23OCPs, ∑34PCBs, ∑8PBDEs, ∑2DPs and ∑5NBFRs in 20 coral species (43 samples) from the SCS were 40.7 ± 34.6, 5.20 ± 5.10, 0.197 ± 0.159, 3.30 ± 3.70, 0.041 ± 0.042 and 36.4 ± 112 ng g-1 dw, respectively. PAHs and NBFRs were the most abundant compounds and they are likely to be dangerous pollutants for future coral growth. Compared to those found in other coral reef regions, these pollutants concentrations in corals were at low to median levels. Except for PBDEs, POCs in massive Porites were significantly higher than those in branch Acropora and Pocillopora (p < 0.01), as large, closely packed corals may be beneficial for retaining more pollutant. The current study contributes valuable data on POCs, particularly for halogenated flame retardants (HFRs, including PBDEs, DPs and NBFRs), in corals from the SCS, and will improve our knowledge of the occurrence and fate of these pollutants in coral reef ecosystems.

Levels and species-specific organochlorine accumulation in three shark species from the western Gulf of California with different life history traits

Organochlorine compounds (OCs), such as organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs), remain ubiquitous in marine ecosystems despite their prohibition or restriction, posing a risk to marine wildlife and humans. Their accumulation in liver tissue and potential toxicity in three exploited shark species (the scalloped hammerhead, Sphyrna lewini; the Pacific sharpnose shark, Rhizoprionodon longurio; and the Pacific angel shark, Squatina californica) with different physiological and ecological features from the western Gulf of California (GC) were investigated. Forty of the 47 OCs analyzed were identified, evidencing a greater agricultural than industrial influence considering the high DDTs/PCBs ratios. The DDT group was the main contributor to ∑OCs in the three species, while hexa- and hepta-CBs dominated the PCB profiles. S. lewini (juveniles) and R. longurio (juveniles and adults) had similar and significantly (p < 0.05) higher ∑OCP concentrations than S. californica (juveniles and adults), which is attributed to their migration to other polluted regions of the gulf. The three species' ∑PCB levels (lipid weight) were comparable and considered low in comparison to those documented in prior studies conducted worldwide. No intraspecific differences were observed when comparing by sex, but OC concentrations were higher in larger individuals. S. lewini and R. longurio showed different OC bioaccumulation trends against size, while no relationship between size and ∑OC concentrations was observed in S. californica. All shark species' toxic equivalents (TEQs) were calculated from dioxin-like PCB concentrations and were far below the established TEQ fish thresholds. However, future research is needed regarding the possible PCB and OCP effects in elasmobranchs. This study provides the basis for monitoring organic contaminants in predatory sharks from the western GC. It also highlights the importance of further research on unintentionally produced organochlorine environmental levels and sources.

Possible Processes and Mechanisms of Hexachlorobenzene Decomposition by the Selected Comamonas testosteroni Bacterial Strains

Background: The bacterial destructing activity toward pesticides has been the focus of research in the last few decades. Hexachlorobenzene is included in the organochlorine pesticides group that are prohibited for use. However, large hexachlorobenzene amounts are still concentrated in the soil, stressing the relevance of research on hexachlorobenzene-destroying bacteria. Methods: The ability to destroy hexachlorobenzene by Comamonas testosteroni UCM B-400, B-401, B-213 strains was investigated and established. Bacteria were cultivated (7 days at 28 °C) in mineral Luria-Bertrani (LB) medium with three hexachlorobenzene doses: 10, 20, 50 mg/L. The hexachlorobenzene concentrations were recorded by a gas chromatography method. Results: The results showed that C. testosteroni UCM B-400, B-401 have high destructive activity toward hexachlorobenzene. The highest (50 mg/L) initial concentration decreased to 41.5 and 43.8%, respectively, for C. testosteroni UCM B-400, B-401. The unadapted C. testosteroni UCM B-213 was tolerant to hexachlorobenzene (cell titers after cultivating with 10.0, 20.0, 50.0 mg/mL were higher compared to initial titer), but had a low-destructing activity level (two times less than B-400 and B-401). Conclusions: Bacterial strains C. testosteroni UCM B-400, B-401 can be seen as a potential soil bioremediation from hexachlorobenzene pollution.

Persistent organic pollutants: The trade-off between potential risks and sustainable remediation methods

Persistent Organic Pollutants (POPs) have become a very serious issue for the environment because of their toxicity, resistance to conventional degradation mechanisms, and capacity to bioconcentrate, bioaccumulate and biomagnify. In this review article, the safety, regulatory, and remediation aspects of POPs including aromatic, chlorinated, pesticides, brominated, and fluorinated compounds, are discussed. Industrial and agricultural activities are identified as the main sources of these harmful chemicals, which are released to air, soil and water, impacting on social and economic development of society at a global scale. The main types of POPs are presented, illustrating their effects on wildlife and human beings, as well as the ways in which they contaminate the food chain. Some of the most promising and innovative technologies developed for the removal of POPs from water are discussed, contrasting their advantages and disadvantages with those of more conventional treatment processes. The promising methods presented in this work include bioremediation, advanced oxidation, ionizing radiation, and nanotechnology. Finally, some alternatives to define more efficient approaches to overcome the impacts that POPs cause in the hydric sources are pointed out. These alternatives include the formulation of policies, regulations and custom-made legislation for controlling the use of these pollutants.

Chlordane exposure causes developmental delay and metabolic disorders in Drosophila melanogaster

The incidence of metabolic diseases is increasing every year, and several studies have highlighted the activity of persistent organic pollutants (POPs) in causing hyperlipidemia and diabetes, and these compounds are considered to be endocrine disrupting chemicals (EDCs). Chlordane is classified as an endocrine disruptor, but the mechanism of how it functions is still unclear. This study investigates the effects of chlordane exposure on Drosophila larvae. Drosophila was cultured in diet containing 0.01 μM, 0.1 μM, 1 μM, 5 μM, and 10 μM chlordane, and the toxicity of chlordane, the growth and development of Drosophila, the homeostasis of glucose and lipid metabolism and insulin signaling pathway, lipid peroxidation-related indicators and Nrf2 signaling pathway were evaluated. We here found that exposure to high concentrations of chlordane decreased the survival rate of Drosophila and that exposure to low concentrations of chlordane caused disruption of glucose and lipid metabolism, increased insulin secretion and impairment of insulin signaling. Notably, it also led to massive ROS production and lipid peroxidation despite of the activation of Nrf2 signaling pathway, an important pathway for maintaining redox homeostasis. Collectively, chlordane causes lipid peroxidation and disrupts redox homeostasis, which may be a potential mechanism leading to impaired insulin signaling and the metabolism of glucose and lipid, ultimately affects Drosophila development.

Persistent organic pollutants (POPs) in coastal wetlands: A review of their occurrences, toxic effects, and biogeochemical cycling

Coastal wetlands, such as mangroves, seagrass beds, and salt marshes, are highly threatened by increasing anthropic pressures, including chemical pollution. Persistent organic pollutants (POPs) have attracted attention in these particularly vulnerable ecosystems, due to their bioaccumulative, pervasive, and ecotoxic behavior. This article reviews and summarizes available information regarding current levels, biogeochemical cycling, and effects of POPs on coastal wetlands. Sediment POP levels were compared with international quality guidelines, revealing many areas where compounds could cause damage to biota. Despite this, toxicological studies on some coastal wetland plants and microorganisms showed a high tolerance to those levels. These taxonomic groups are likely to play a key role in the cycling of the POPs, with an active role in their accumulation, immobilization, and degradation. Toxicity and biogeochemical processes varied markedly along three main axes; namely species, environmental conditions, and type of pollutant. While more focused research on newly and unintentionally produced POPs is needed, mainly in salt marshes and seagrass beds, with the information available so far, the environmental behavior, spatial distribution, and toxicity level of the studied POPs showed similar patterns across the three studied ecosystems.

Ecological risk assessment of persistent organic pollutants (POPs) in surface sediments from aquaculture system

Organochlorinated pesticides (OCPs) and Polychlorinated biphenyls (PCBs) in the surface sediments from shrimp ponds in four regions of the northern part of the Central Java coast (namely Brebes, Tegal, Pemalang, and Pekalongan) were investigated. The highest concentration of ∑ OCPs was found in Brebes Regency, ranging from 68.1 ± 3.4 to 168.1 ± 9.8 μg kg^-1 dw. As indicated by the DDT ratio and chlordane ratio, the value suggested that those compounds may mainly originate from historical inputs rather than a recent application. The concentrations of Ʃ 7 indicator PCBs were determined, with the concentration ranged from 1.2 ± 0.7 μg kg^-1 dw (Pekalongan) to 2.2 ± 0.4 μg kg^-1 dw (Tegal). The most toxic PCB congener, PCB 118, was detected in all studied regions, with the highest proportion found in Tegal. Source analysis indicated that PCBs in the sediments mainly originated from Aroclor 1254 and Aroclor 1248. Compared to sediment quality guidelines (SQGs), some OCPs were found with concentrations which potentially posed an adverse effect. Our findings suggested that more attention should be paid to ensure sustainable shrimp culture facing such a risk of the OCPs and PCBs.

Assessment of persistent organic pollutants (POPs) in sediments of the Eastern Indian Ocean

The concentrations of persistent organic pollutants (POPs) in sediments from the Eastern Indian Ocean were analyzed by GC-MS/MS to explore the status of contamination, distribution and their potential sources and risk. The average (±SD) concentrations of total polycyclic aromatic hydrocarbons (∑₁₆PAHs), polybrominated diphenyl ethers (∑₁₀PBDEs), dechlorane plus (∑₂DP), organochlorine pesticides (∑₂₂OCPs) and polychlorinated biphenyls (∑₃₁PCBs) in sediments were 79,900 ± 31,400, 173 ± 62, 42 ± 24, 1051 ± 305 and 147 ± 24 pg g^-1 dw (or 11,200 ± 7200, 28 ± 26, 6 ± 6, 168 ± 121 and 24 ± 17 ng g^-1 organic carbon), respectively. The concentrations of POPs in sediments were generally at low to median levels compared to those recorded in other ocean sediments. Composition analyses suggest that PAHs originate from both petrogenic and pyrogenic sources, while dichlorodiphenyltrichloroethane (DDT) mainly comes from technical-DDT, hexachlorocyclohexane (HCH) from lindane, and chlordane from fresh inputs. The risk assessments show that the targeted chemicals except for chlordane and naphthalene in sediments do not pose potential biological effects to the organisms in the Eastern Indian Ocean. The present study contributes to the very rare data on PAHs, PBDEs, DP, OCPs and PCBs in the vast deep-ocean and will deepen our knowledge of the fate of POPs in ocean environments.

Eukaryal composition and diversity in anaerobic soils influenced by the novel chiral insecticide Paichongding

Paichongding (IPP) is a neonicotinoid chiral insecticide with independent intellectual property in China. IPP application can increase crop yield, and also lead to insecticide residue and pollution in soils, which will affect microbial population and community composition in soils. In this study, four different types of soils were employed to inquire into the impact of IPP on eukaryal community and species-group through pyrosequencing of 18S rRNA gene amplicons. Fungal population differed in different soils at different days after IPP treatment (DAT). Eukaryal community species in CK (control check) groups were more rich than that with Paichongding sprayed at 5 DAT, while eukaryal species in CK soils at 60 DAT was relatively slight. Shannon's H' analysis indicated fungal species in CK soils were also higher at 5 DAT and relative lower at 60 DAT, except in soil C. There are also differences in the phyla and genus levels of the eukaryotic communities in the soil. After IPP application, the relative abundance of Nectriaceae increased 3-4 times in soil C. In soil F, Phaeosphaeriaceae increased to 57.3% at 5 DAT. The genus of Guehomyces, Aspergillus and Alternaria increased from 3.1 to 9.7, 1.1 to 4.6, 1.5 to 6.7% in soil H, respectively.

Removal of a mixture of pesticides by a Streptomyces consortium: Influence of different soil systems

Although the use of organochlorine pesticides (OPs) is restricted or banned in most countries, they continue posing environmental and health concerns, so it is imperative to develop methods for removing them from the environment. This work is aimed to investigate the simultaneous removal of three OPs (lindane, chlordane and methoxychlor) from diverse types of systems by employing a native Streptomyces consortium. In liquid systems, a satisfactory microbial growth was observed accompanied by removal of lindane (40.4%), methoxychlor (99.5%) and chlordane (99.8%). In sterile soil microcosms, the consortium was able to grow without significant differences in the different textured soils (clay silty loam, sandy and loam), both contaminated or not contaminated with the OPs-mixture. The Streptomyces consortium was able to remove all the OPs in sterile soil microcosm (removal order: clay silty loam > loam > sandy). So, clay silty loam soil (CSLS) was selected for next assays. In non-sterile CSLS microcosms, chlordane removal was only about 5%, nonetheless, higher rates was observed for lindane (11%) and methoxychlor (20%). In CSLS slurries, the consortium exhibited similar growth levels, in the presence of or in the absence of the OPs-mixture. Not all pesticides were removed in the same way; the order of pesticide dissipation was: methoxychlor (26%)>lindane (12.5%)>chlordane (10%). The outlines of microbial growth and pesticides removal provide information about using actinobacteria consortium as strategies for bioremediation of OPs-mixture in diverse soil systems. Texture of soils and assay conditions (sterility, slurry formulation) were determining factors influencing the removal of each pesticide of the mixture.

Bioaccumulation of organochlorine pesticides and polychlorinated biphenyls by loaches living in rice paddy fields of Northeast China

The concentrations of 21 organochlorine pesticide (OCP) residues and 18 polychlorinated biphenyl (PCB) congeners were measured in two loach species (Misgurnus mohoity and Paramisgurnus dabryanus) and the soils of their inhabiting rice paddies from three typical rice production bases of Northeast China to explore the main factors influencing the bioaccumulation. The concentrations of ∑18PCBs and ∑21OCPs in loaches were determined to be in the ranges of 0.14-0.76 ng g(-1) wet weight (ww) and 1.19-78.53 ng g(-1) ww, respectively. Most of loaches showed the considerably high contamination levels of dichlorodiphenyltrichloroethane (DDT), hexachlorocyclohexane (HCH), hexachlorobenzene (HCB), which accounted for over 97% of the total OCPs. The much lower maximum allowable loach consumption rates (<15 g d(-1)) indicated a high carcinogenic risk that results from the consumption of rice-field loaches. The field biota-soil accumulation factor (BSAF) was calculated as a main measure of bioaccumulation potential. The comparisons of BSAF values and the results of multivariate analysis indicated that habitat-specific environmental conditions, mainly the paddy soil contamination levels and average temperature, decisively affected the bioaccumulation of organochlorine contaminants. When the influence of lipid contents was offset, M. mohoity loaches were found to have a higher potential to accumulation PCBs and OCPs than P. dabryanus loaches, while the bioaccumulation potentials did not exhibit significant differences between juvenile and adult loaches and between male and female loaches. The octanol-water partition coefficient (KOW) was the main chemical factor influencing bioaccumulation potentials. The BSAF values presented an increasing tendency with increasing log KOW values from 6.0 to approximately 7.0, followed by a decreasing tendency with a continuous increase in log KOW values. Moreover, loaches exhibited an isomeric-selective bioaccumulation for p,p'-chlorinated DDTs, α-HCH, β-HCH, δ-HCH and cis-chlordane.

Impact of the novel neonicotinoid insecticide Paichongding on bacterial communities in yellow loam and Huangshi soils

Insecticides are widely sprayed in modern agriculture for ensuring the crop yield, which could also lead to contamination and insecticide residue in soils. Paichongding (IPP) is a novel neonicotinoid insecticide and was developed recently in China. Soil bacterial community, diversity, and community composition vary widely depending on environmental factors. As for now, little is known about bacterial species thriving, bacterial community diversity, and structure in IPP-spraying soils. In present study, IPP degradation in yellow loam and Huangshi soils was investigated, and bacterial communities and diversity were examined in soil without IPP spray and with IPP spray through pyrosequencing of 16S ribosomal RNA (rRNA) gene amplicons. The degradation ratio of IPP at 60 days after treatment (DAT) reached 51.22 and 34.01 % in yellow loam and Huangshi soil, respectively. A higher richness of operational taxonomic units (OTUs) was found in yellow loam soil (867 OTUs) and Huangshi soil (762 OTUs) without IPP spray while OUTs were relatively low in IPP-spraying soils. The community composition also differed both in phyla and genus level between these two environmental conditions. Proteobacteria, Firmicutes, Planctomycetes, Chloroflexi, Armatimonadetes, and Chlorobi were stimulated to increase after IPP application, while IPP inhibited the phyla of Bacteroidetes, Actinobacteria, and Acidobacteria.

Polychlorinated biphenyls and organochlorine pesticides in atmospheric particulate matter of Northern China: distribution, sources, and risk assessment

The objectives of this work are to track the contamination levels, distribution characteristics, and sources of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in atmospheric particulate matter (APM) of Northern China and to provide more comprehensive and fundamental data for risk assessment of organochlorine contaminants (OCs) in environments. Samples were extracted and purified by the microwave-assisted extraction and solid-phase extraction system, respectively. PCBs and OCPs were analyzed by gas chromatograph-mass spectrometer. The concentrations of ΣPCBs and ΣOCPs ranged from 0.73 to 112.65 ng/g and 0.14 to 34.73 ng/g, respectively. PCBs in atmospheric particulates collected from Shijiazhuang City had the highest concentration, whereas OCP congeners were at the relatively low levels. However, the highest concentration of OCPs occurred in Yongning City. The principal component analysis indicated that the predominant compositions of PCBs in most of samples were tetrachlorobiphenyl (Tetra-CB), pentachlorobiphenyl (Penta-CB), hexachlorobiphenyl (Hexa-CB), and heptachlorbiphenyl (Hepta-CB), while hexachlorocyclohexanes (HCHs), DDTs, chlordanes, and endosulfans were the dominant components of OCPs, which was attributed to their application characteristics. OCs in those particles were further used to assess a potential cancer risk to humans via ingestion, dermal contact, and inhalation. Cancer risk was evaluated in airborne particles caused by PCBs and OCPs. TEQPCBs values suggested that the representative areas were subject to different pollution degrees. However, the pollution of OCPs in certain areas should be a concern due to 41.6% of the high risk, which could pose a potential risk to organisms.

Polyphasic characterization of an anaerobic hexachlorobenzene-dechlorinating microbial consortium with a wide dechlorination spectrum for chlorobenzenes

An anaerobic consortium that was capable of reductively dechlorinating hexachlorobenzene (HCB) to benzene was enriched from contaminated sediment. The consortium was capable of dechlorinating all chlorobenzene isomers except 1,4-dichlorobenzene. Singly and doubly flanked chlorines, as well as unflanked meta-substituted chlorines, were dechlorinated, although doubly flanked chlorines were preferred. Formate, acetate and lactate (but not ethanol) could be utilized as optimum electron donors for reductive dechlorination. Alternative electron acceptors, including nitrate and sulfate, completely inhibited HCB degradation, whereas amorphous iron oxide (FeOOH) did not suppress dechlorination activity. No degradation was found in chloramphenicol-treated consortium; however, vancomycin, molybdate, and 2-bromoethanesulfonate did not inhibit HCB dechlorination. The results of inhibitory treatments suggested that the dechlorinators were non-sulfate-reducing gram-negative or vancomycin resistant gram-positive bacteria. In addition to physiological characterization, analyses of 16S rRNA gene library of the consortium and quantitative PCR of 16S rRNA genes suggested that Dehalococcoides sp. was involved in the reductive dechlorination of HCB, and Geobacter sp. may serve as a dechlorinating candidate.

Studies on the anoxic dissipation and metabolism of pyribambenz propyl (ZJ0273) in soils using position-specific radiolabeling

Pyribambenz propyl (ZJ0273) is a polycyclic herbicide with increasing use, although studies show that it tends to be persistent in soil and pose phytotoxicity to rotational crops. This study employed an improved ring-specific (14)C labeling method to characterize its anoxic metabolism, with (14)C positioned on the benzoate, pyrimidyl or benzyl rings. Separation and identification of the metabolites were achieved by liquid chromatography (LC), ultralow-level liquid scintillation spectrometry, and LC-mass spectrometry (MS). Results show that the anoxic degradation follows first-order kinetics and the half-lives are approximately 38.7, 50.2 and 70.7d for loamy, saline and clayey soils, respectively. A total of five radioactive intermediates (M1-M5) were detected, and due to the loss of radiolabels, different radiochromatograms were obtained from different labels, i.e., radioactive M5 was only detected for pyrimidinyl-(14)C; M3 and M4 were only detected for pyrimidinyl-(14)C and benzyl-(14)C, while M1 and M2 were detected for all labels. Based on their appearance pattern and fragmentations from LC-MS, the structures of M1-M5 were identified, and they were proposed to form by reactions such as de-estering, hydrolysis, acylation, CN cleavage, and demethylation. All metabolites have been previously detected in aerobic soils except M4, which is a demethylation product from M3, and identified as 2-(4-hydroxy-6-methoxypyrimidin-2-yloxy)benzoic acid. The results show that ZJ0273 is more persistent in anoxic soils, and its degradation pathways and intermediates are different from aerobic metabolism and differ with the soil types, suggesting that soil-specific and farming practices may be important considerations in the use of this herbicide. The ring-specific labeling provides full molecular information about the referred compound and guarantees the reliability of the results, and can be used as an effective tool for metabolite profiling of polycyclic compounds.

Residues and enantiomeric profiling of organochlorine pesticides in sediments from Xinghua Bay, southern East China Sea

The spatial distribution and chiral signatures of organochlorine pesticides (OCPs) in the surface sediments of Xinghua Bay, southern East China Sea, were investigated. The total OCP concentrations ranged from 9.15 to 40.5 ng/g dry weight, with a predominance of hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs). The isomer ratios of α-HCH/γ-HCH (less than 1.0) and the predominant β-HCH implied that HCH residues were derived not only from historical technical HCH use but also from the additional use of lindane in this area. The isomer ratios of p,p'-DDT/(p,p'-DDD + p,p'-DDE) and o,p'-DDT/p,p''-DDT, and a strong correlation (R = 0.83, P < 0.001) between p,p'-DDE and o,p'-DDT depicted a cocktail input pattern of dicofol-type DDT and technical DDT. Moreover, the fact that only cis-chlordane was detectable for all sampling stations suggested the past application of technical chlordane. Based on the sediment quality guidelines (SQG), γ-HCH is the main OCP species of ecotoxicological concern in Xinghua Bay. Enantiomeric analysis showed that the (+)-enantiomers of α-HCH and o,p'-DDT were more prevalent than the (-)-enantiomers in most samples, whereas both racemic and nonracemic residues existed for o,p'-DDD. These results implied that the SQG of chiral OCPs should be reassessed using concentrations of their individual enantiomers.

Modification to degradation of hexazinone in forest soils amended with sewage sludge

Influences of one sewage sludge on degradation of hexazinone and formation of its major metabolites were investigated in four forest soils (A, B, C and D), collected in Zhejiang Province, China. In non-amended forest soils, the degradation half-life of hexazinone was 21.4, 30.4, 19.4 and 32.8 days in forest soil A, B, C and D, respectively. Degradation could start in soil A and C without lag period because the two soils had been contaminated by this herbicide for a long time, possibly leading to completion of acclimation period of hexazinone-degrading bacteria. In forest soils amended with sewage sludge, the degradation rate constant increased by 17.3% in soil A, 48.2% in soil B, 8.1% in soil C and 51.6% in soil D, respectively. The higher degradation rates (soil A and C) in non-amended soils accord with the lower rate increase in sewage sludge-amended soils. Under non-sterile conditions, biological mechanism accounted for 51.8-62.4% of hexazinone degradation in four soils. Under sterile conditions, the four soils had the similar chemical degradation capacity for hexazinone. In non-amended soil B, only one metabolite (B) was detected, while two metabolites (B and C) were found in sewage sludge-amended soil B. Similarly situated in agricultural soils, N-demethylation at 6-position of triazine ring, hydroxylation at the 4-positon of cyclohexyl group, and removal of the dimethylamino group with formation of a carbonyl group at 6-position of triazine ring appear to be the principal mechanism involved in hexazinone degradation in sewage sludge-amended forest soils. These data will improve understanding of the actual pollution risk as a result of forest soil fertilization with sewage sludge.

Chlorobenzenes and organochlorinated pesticides in vegetable soils from an industrial site, China

Organochlorinated compounds are ubiquitous contaminants in the environment, especially in industrial sites. The objective of the work was to investigate whether a vegetable field near an industrial site is safe for vegetable production. The residues of chlorobenzenes (CBs), hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs) in a vegetable field which was near a chemical plant in China were characterized. Point estimate quotient was used for ecological risk assessment of the investigated site. The results showed that all CBs except monochlorobenzene (MCB) were detected in soils. The total concentrations of sigmaCBs ranged from 71.06 to 716.57 ng/g, with a mean concentration of 434.93 ng/g. The main components of CBs in soil samples were dichlorobenzenes (DCBs), trichlorobenzenes (TCBs) and tetrachlorobenzenes (TeCBs), while for single congeners, 1,2,4-TCB had the highest concentration, which ranged from 13.21 to 210.35 ng/g with a mean concentration of 111.89 ng/g. Residues of hexachlorobenzene (HCB) in soil samples ranged from 0.9 to 11.79 ng/g, significantly lower than sigmaDCB, sigmaTCB and sigmaTeCB. Concentrations of sigmaHCHs and sigmaDDTs in soils ranged from 11.32 to 55.24 ng/g and from 195.63 to 465.58 ng/g, respectively, of which the main components were alpha-HCH and p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE). Ecological risk assessment for the investigated site showed that the most potential risks were from TCBs and TeCBs, based on the hazard quotients. The higher residues of CBs and DDTs compared to the target values and the higher than 1 hazard quotients indicated that this area is not safe for vegetable production and thus soil remediation is needed.

Role of "Dehalococcoides" spp. in the anaerobic transformation of hexachlorobenzene in European rivers

The diffuse pollution by chlorinated organic compounds in river basins is a concern, due to their potential adverse effects on human health and the environment. Organohalides, like hexachlorobenzene (HCB), are recalcitrant to aerobic microbial degradation, and "Dehalococcoides" spp. are the only known microorganisms capable of anaerobic transformation of these compounds coupled to their growth. In this study, sediments from four European rivers were studied in order to determine their HCB dechlorination capacities and the role of Dehalococcoides spp. in this process. Only a weak correlation was observed between Dehalococcoides species abundance and HCB transformation rates from different locations. In one of these locations, in the Ebro River sediment, HCB dechlorination could be linked to Dehalococcoides species growth and activity by 16S rRNA-based molecular methods. Furthermore, HCB dechlorination activity in this sediment was found over the full range of ambient temperatures that this sediment can be exposed to during different seasons throughout the year. The sediment contained several reductive dehalogenase (rdh) genes, and analysis of their transcription revealed the dominance of cbrA, previously shown to encode a trichlorobenzene reductive dehalogenase. This study investigated the role of Dehalococcoides spp. in HCB dechlorination in river sediments and evaluated if the current knowledge of rdh genes could be used to assess HCB bioremediation potential.

Anaerobic degradation of chlorothalonil in four paddy soils

Degradation of Chlorothalonil (CTN) was investigated in four different paddy soils under anaerobic conditions. The CTN biodegradation is strongly affected by the properties of the paddy soils. Soils associating with rich total carbon (TC), repeated CTN application, and neutral pH have shown the high capacity to biodegrade CTN. Additionally, anaerobic CTN biodegradation was accompanied by the methane generation and a drop of oxidation-reduction potential (ORP). The initial CTN concentration had a significant effect on CTN removal efficiency, and increase in the initial CTN concentration resulted in the decreasing of CTN removal percentage. However, it is believed that the inhibitory effect on anaerobic biodegradation of CTN is negligible in natural environment due to the much lower concentration of CTN in natural environment (at ng g(-1) or pg g(-1) level) than the one (10 μg g(-1)) investigated in this study. The 4-hydroxy-2,5,6- trichloroisophthalonitrile (HTI), one of the major metabolites of CTN degradation, has shown the significant inhibitation to the anaerobic CTN biodegradation when its residual level is over 0.1 μg g(-1).

Hexachlorobenzene dechlorination as affected by nitrogen application in acidic paddy soil

Batch incubation experiments were conducted to study the effects of different nitrogen (N) fertilizers (NH(4)HCO(3), CO(NH(2))(2), and NaNO(3)) on hexachlorobenzene (HCB) dechlorination in an acidic paddy soil. Results showed that NH(4)HCO(3) and CO(NH(2))(2) had similar effects on HCB dechlorination, and their application amount was a crucial factor on reductive dechlorination. The addition of a proper amount of 0.14 g NH(4)HCO(3)- or CO(NH(2))(2)-N to 500 g soil promoted HCB dechlorination, however, the application of a high amount (0.84 g) of NH(4)HCO(3)- or CO(NH(2))(2)-N inhibited HCB dechlorination. Additional NaNO(3) served as an electron acceptor and led to lower soil pH, thus inhibited HCB dechlorination. Detected dechlorinated products showed that the dominant pathway of HCB dechlorination was HCB-->pentachlorobenzene (PeCB)-->1,2,3,5-tetrachlorobenzene (TeCB)-->1,3,5-trichlorobenzene (TCB), and PeCB was the main metabolite. The role of methanogenic bacteria in HCB dechlorination was uncertain and conditions-dependent.

Development of a sample preparation method for the analysis of current-use pesticides in sediment using gas chromatography

Pyrethroid insecticides have been implicated as the cause of sediment toxicity to Hyalella azteca in both agricultural and urban areas of California; however, for a subset of these toxic sediments (approximately 30%), the cause of toxicity remains unidentified. This article describes the analytical method development for seven additional pesticides that are being examined to determine if they might play a role in the unexplained toxicity. A pressurized liquid extraction method was optimized to simultaneously extract diazinon, methyl parathion, oxyfluorfen, dicofol, fenpropathrin, pyraclostrobin, and indoxacarb from sediment, and the extracts were cleaned using a two-step solid-phase extraction procedure. The final extract was analyzed for the target pesticides by gas chromatography/nitrogen-phosphorus detector (GC/NPD), and gas chromatography/electron capture detector (GC/ECD), after sulfur was removed by shaking with copper and cold crystallization. Three sediments were used as reference matrices to assess method accuracy and precision. Method detection limits were 0.23-1.8 ng/g dry sediment using seven replicates of sediment spiked at 1.0 ng/g dry sediment. Recoveries ranged from 61.6 to 118% with relative standard deviations of 2.1-17% when spiked at 5.0 and 50 ng/g dry sediment. The three reference sediments, spiked with 50 ng/g dry weight of the pesticide mixture, were aged for 0.25, 1, 4, 7, and 14 days. Recoveries of the pesticides in the sediments generally decreased with increased aging time, but the magnitude of the decline was pesticide and sediment dependent. The developed method was applied to field-collected sediments from the Central Valley of California.

Hexachlorobenzene dechlorination as affected by organic fertilizer and urea applications in two rice planted paddy soils in a pot experiment

Reductive dechlorination is a crucial pathway for HCB degradation, the applications of organic materials and nitrogen can alter microbial activity and redox potential of soils, thus probably influence HCB dechlorination. To evaluate hexachlorobenzene (HCB) dechlorination as affected by organic fertilizer (OF) and urea applications in planted paddy soils, a pot experiment was conducted in two types of soils, Hydragric Acrisols (Ac) and Gleyi-Stagnic Anthrosols (An). After 18 weeks of experiment, HCB residues decreased by 28.2-37.5% of the initial amounts in Ac, and 42.1-70.9% in An. The amounts of HCB metabolites showed that dechlorination rates in An were higher than in Ac, which was mainly attributed to the higher pH and dissolved organic carbon (DOC) content of An. Both in Ac and An, the additions of 1% and 2% OF had negative effect on HCB dechlorination, which was probably because excessive nitrogen in OF decreased degraders' activity and the degradation of organic carbon in OF accepted electrons. The application of 0.03% urea could enhance HCB dechlorination rates slightly, while 0.06% urea accelerated HCB dechlorination significantly both in Ac and An. It could be assumed that urea served as an electron donor and stimulated degraders to dechlorinate HCB. In addition, the methanogenic bacteria were involved in dechlorination process, and reductive dechlorination in planted paddy soil might be impeded for the aerenchyma and O(2) supply into the rhizosphere. Results indicated that soil types, rice root system, methanogenic bacteria, OF and urea applications all had great effects on dechlorination process.

Transcripts level responses in a marine medaka (Oryzias javanicus) exposed to organophosphorus pesticide

The differential expression of a set of genes encoding antioxidant enzymes and stress-responsive proteins was investigated by real-time quantitative PCR in intestine, liver, and muscle tissues extracted from Oryzias javanicus after exposure to the organophosphorus pesticide, Iprobenfos (IBP). After IBP exposure, transcriptional changes in all the tested genes were prominent in the liver and moderate in the intestine, but unpredictable in the muscle. In the liver, CAT transcription increased after exposure to IBP at all concentrations (P<0.05). CYP1A mRNA was induced in the intestine and liver at the two higher concentrations. G6PD transcription was induced in the liver at the three higher IBP concentrations, but was suppressed in muscle at the same concentrations. GPx expression in the liver increased at three higher concentrations of IBP. In the intestine and liver, GR expression was induced at two higher and three higher concentrations, respectively. However, no significant changes were observed in the muscle. GST and SOD transcription was induced in the liver at all IBP concentrations. IBP exposure induced UB expression in the intestine and liver in a concentration-dependent manner. The transcriptional changes in these genes in the liver could be good biomarkers for stress levels in O.javanicus, and be used as critical biomarkers for environmental quality assessment.

Biodegradability and toxicity assessment of trans-chlordane photochemical treatment

The removal of trans-chlordane (C(10)H(6)Cl(8)) from aqueous solutions was studied using UV, UV/H(2)O(2), UV/H(2)O(2)/Fe(2+), UV/TiO(2), or UV/TiO(2)/H(2)O(2) treatment using either UV/Vis blue lamps or UVC lamps (254 nm). H(2)O(2), FeSO(4) and TiO(2) were added at 1700, 456, and 2500 mgL(-1), respectively. trans-Chlordane was not significantly removed in non-irradiated controls and in samples irradiated with UV/Vis. It was also not removed in the absence of surfactant Triton X-114 added at 250 mgL(-1). In the presence of the surfactant, trans-chlordane concentration was reduced by 95-100% after 48 h of UVC and UVC/H(2)O(2) treatments and 70-80% after UVC/H(2)O(2)/Fe(2+), UVC/TiO(2) and UVC/H(2)O(2)/TiO(2) treatments. Based on these results, UVC, UVC/H(2)O(2) and UVC/TiO(2) treatments were further investigated. UVC treatment supported the highest pollutant removal (100% in 48 h), dechlorination efficiency (81% in 48 h), and detoxification to Lepidium sativum seed germination and activated sludge respiration although irradiated samples remained toxic to Chlorella vulgaris. Biodegradation of the UVC irradiated samples removed the source of algae toxicity but this could not be clearly attributed to the removal of trans-chlordane photoproducts because the surfactant interfered with the chemical and biological assays. Evidence was found that trans-chlordane was photodegraded through photolysis causing its successive dechlorination. trans-Chlordane removal was well described by a first order kinetic model at a rate of 0.21±0.01h(-1) at the 95% confidence interval.

Tracing the behaviour of hexachlorobenzene in a paddy soil-rice system over a growth season

Hexachlorobenzene (HCB), a persistent organic pollutant (POP), has been found in paddy soils. To improve the understanding of HCB contamination in paddy soils, a laboratory simulative study was carried out to investigate the behavior of HCB in a paddy soil and rice plants. This study was divided into three experiments. First, an experiment aimed to examine the evaporation of HCB in paddy soil. In the second experiment, rice was planted in 10 mg/kg HCB contaminated soil and after pot culture at 3, 6, 9, and 27 weeks (at maturity), both soil and plant samplings were scheduled to be sampled. The soil samples comprised rhizosphere soil, nonrhizosphere soil, and unplanted contaminated soil, whereas plant samples included shoots, roots, and rice grains (dehusked). Lastly, in this part, HCB in xylem saps was designed to be examined. The results showed that (1) the HCB translocation from paddy soil to rice by vaporization; (2) the HCB concentration in rice grains was surprisingly high; (3) the observed HCB decrease in rice rhizosphere offers a potential means for in situ HCB degradation; (4) HCB might not be transported along transpiration in rice.

Environmental toxicology and health effects associated with hexachlorobenzene exposure

The synthetic industrial chemical hexachlorobenzene (HCB) is a white crystalline solid compound. The substance is a bioaccumulative, persistent, and toxic pollutant. Historically HCB was commonly used as a pesticide and fungicide. Although HCB production and use has ceased in many countries, the compound is still generated inadvertently, as a byproduct and/or impurity in the manufacture of various chlorinated compounds, and released into the environment. Hexachlorobenzene is ubiquitous in air, water, soil, and biological matrices, as well as in major environmental compartments. Exposure to this substance is a public health concern because of its association with a wide range of adverse health effects. The International Agency for Research on Cancer and the United States Environmental Protection Agency classify HCB as a probable human carcinogen. Although globally the consumption of HCB-contaminated food is the principal source of environmental exposure, exposure can also occur through the inhalation of HCB-contaminated air, by dermal contact, or through in utero exposure and breast milk. In addition to cancer, the human health effects associated with HCB exposure involve systemic impairment (thyroid, liver, bone, skin), as well as damage to the kidneys and blood cells and the immune, endocrine, developmental, and nervous systems. In this review, we discuss the sources of HCB and the potential for human exposure, as well as systemic, carcinogenic, and teratogenic health effects.