Biodegradation of hexachlorocyclohexane (HCH) by microorganisms

The mode of action of different organochlorine pesticides families in mammalians

Organochlorine pesticides (OCPs) show differences in their chemical structure, mechanism of toxicity, and target organisms. However, OCPs also have some common characteristics such as high persistence in the environment, bioaccumulation, and toxicity which lead to health issues. Nowadays, the toxicity of OCPs is well known, but we still do not know all the specific molecular mechanisms leading to their toxicity in mammalians. Therefore, this review aims to collect data about the mode of action of various classes of OCPs, highlighting their differences and common behavioural reactions in the human and animal body. To discuss the OCPs molecular pathways and fate in different systems of the body, three organochlorine insecticides were selected (Dichlorodiphenyltrichloroethane, Hexachlorocyclohexane and Chlordecone), regarding to their widespread use, with consequent effects on the ecosystem and human health. Their common biological responses at the molecular scale and their different interactions in human and animal bodies were highlighted and presented.

Exploring the potential of horse amendment for the remediation of HCHs-polluted soils

This study assessed for the first time the bioremediation potential of an organic horse amendment in soils contaminated with solid wastes of the obsolete pesticide lindane (α-hexachlorocyclohexane (α-HCH) = 80 mg kg-1, β-HCH = 40 mg kg-1, γ,δ,ε-HCH≈10 mg kg-1) searching for a self-sufficient bio-based economy. Four treatments were implemented: polluted (PS, ΣHCHs = 130 mg kg-1) and control (CS, ΣHCHs = 1.24 mg kg-1) soils and the respective amended soils (APS and ACS). A commercial amendment, coming from organic wastes, was used for soil biostimulation (5% dry weight), and the temporal evolution of the enzymatic activity (dehydrogenase, β-glucosidase activity, phenoloxidase, arylamidase, phosphatase, and urease) and HCHs concentration of the soils was evaluated over 55 days under controlled humidity and temperature conditions. The horse amendment positively influenced the physicochemical properties of the soil by reducing pH (from 8.3 to 8) and increasing the organic matter (TOC from 0.5 to 3.3%) and nutrient content (P and NH4+ from 24.1 to 13.7 to 142.1 and 41.2 mg kg-1, respectively). Consequently, there was a notable enhancement in the soil biological activity, specifically in the enzymatic activity of dehydrogenase, phenol-oxidase, phosphatase, and urease and, therefore, in HCH degradation, which increased from <1 to 75% after the incubation period. According to the chlorine position on the cyclohexane ring, the following ranking has been found for HCHs degradation: β-HCH (46%) < ε-HCH (57%) < α-HCH (91%) ≈ δ-HCH (91%) < γ-HCH (100%). Pentachlorocyclohexene (PCCH) and 1,2,4-trichlorobenzene (1,2,4-TCB) were identified as HCHs degradation metabolites and disappeared at the end of the incubation time. Although further research is required, these preliminary findings suggest that organic amendments represent a sustainable, harmless, and cost-effective biostimulation approach for remediating soils contaminated with recalcitrant HCHs, boosting the circular economy.

Transgenic Arabidopsis thaliana plants expressing bacterial γ-hexachlorocyclohexane dehydrochlorinase LinA

BACKGROUND

γ-Hexachlorocyclohexane (γ-HCH), an organochlorine insecticide of anthropogenic origin, is a persistent organic pollutant (POP) that causes environmental pollution concerns worldwide. Although many γ-HCH-degrading bacterial strains are available, inoculating them directly into γ-HCH-contaminated soil is ineffective because of the low survival rate of the exogenous bacteria. Another strategy for the bioremediation of γ-HCH involves the use of transgenic plants expressing bacterial enzyme for γ-HCH degradation through phytoremediation.

RESULTS

We generated transgenic Arabidopsis thaliana expressing γ-HCH dehydrochlroninase LinA from bacterium Sphingobium japonicum strain UT26. Among the transgenic Arabidopsis T2 lines, we obtained one line (A5) that expressed and accumulated LinA well. The A5-derived T3 plants showed higher tolerance to γ-HCH than the non-transformant control plants, indicating that γ-HCH is toxic for Arabidopsis thaliana and that this effect is relieved by LinA expression. The crude extract of the A5 plants showed γ-HCH degradation activity, and metabolites of γ-HCH produced by the LinA reaction were detected in the assay solution, indicating that the A5 plants accumulated the active LinA protein. In some A5 lines, the whole plant absorbed and degraded more than 99% of γ-HCH (10 ppm) in the liquid medium within 36 h.

CONCLUSION

The transgenic Arabidopsis expressing active LinA absorbed and degraded γ-HCH in the liquid medium, indicating the high potential of LinA-expressing transgenic plants for the phytoremediation of environmental γ-HCH. This study marks a crucial step toward the practical use of transgenic plants for the phytoremediation of POPs.

Assessing HCH isomer uptake in Alnus glutinosa: implications for phytoremediation and microbial response

Although the pesticide hexachlorocyclohexane (HCH) and its isomers have long been banned, their presence in the environment is still reported worldwide. In this study, we investigated the bioaccumulation potential of α, β, and δ hexachlorocyclohexane (HCH) isomers in black alder saplings (Alnus glutinosa) to assess their environmental impact. Each isomer, at a concentration of 50 mg/kg, was individually mixed with soil, and triplicate setups, including a control without HCH, were monitored for three months with access to water. Gas chromatography-mass spectrometry revealed the highest concentrations of HCH isomers in roots, decreasing towards branches and leaves, with δ-HCH exhibiting the highest uptake (roots-14.7 µg/g, trunk-7.2 µg/g, branches-1.53 µg/g, leaves-1.88 µg/g). Interestingly, α-HCH was detected in high concentrations in β-HCH polluted soil. Phytohormone analysis indicated altered cytokinin, jasmonate, abscisate, and gibberellin levels in A. glutinosa in response to HCH contamination. In addition, amplicon 16S rRNA sequencing was used to study the rhizosphere and soil microbial community. While rhizosphere microbial populations were generally similar in all HCH isomer samples, Pseudomonas spp. decreased across all HCH-amended samples, and Tomentella dominated in β-HCH and control rhizosphere samples but was lowest in δ-HCH samples.

Biodiversity in wetland+ system: a passive solution for HCH dump effluents

The hexachlorocyclohexane isomers (HCH) are long-banned pesticides. Even though their use has been prohibited for decades, their presence in the environment is still reported worldwide. Wetland + is a registered trademark of the remedial treatment technology consisting of an aerobic sedimentary tank, a permeable reactive barrier, a biosorption system, and an aerobic wetland. This proven method combines a reductive treatment known from PRBs with the natural wetland self-cleaning processes. The average efficiency of the system is 96.8% for chlorobenzenes (ClB) and 81.7% for HCH, during the first 12 months of the system operation. The presence of the genes encoding enzymes involved in the degradation of the HCH compounds indicates that the removal of HCH and ClB occurs not only by chemical removal but also through aerobic and anaerobic combining biodegradation. Changes in abundance and the composition of the diatom community were found to be suitable indicators of the water quality and of the impact of the Wetland + operation on the water ecosystem. The system's annual operation exhibited a markedly higher number of diatom species in the closing profiles of the Ostrovský Creek, the Wetland + effluent recipient.

Deciphering the kinetics and pathway of lindane biodegradation by novel soil ascomycete fungi for its implication in bioremediation

Lindane, an organochlorine pesticide, negatively affects living beings and the ecosystem. In this study, the potential of 9 Ascomycetes fungi, isolated from an hexachlorocyclohexane dumpsite soil, was tested for biodegradation of lindane. The strain Pleurostoma richardsiae (FN5) showed lindane biodegradation rate constant (K value) of 0.144 d-1 and a half-life of 4.8d. The formation of intermediate metabolites upon lindane degradation including γ-pentachlorocyclohexene, 2,4-dichlorophenol, phenol, benzene, 1,3- cyclohexadiene, and benzoic acid detected by GC-MS and the potential pathway adopted by the novel fungal strain FN5 for lindane biodegradation has been elucidated. The study of gene profiles with reference to linA and linB in strain FN5 confirmed the same protein family with the reported heterologs from other fungal strains in the NCBI database. This study for the first time provides a thorough understanding of lindane biodegradation by a novel soil-borne Ascomycota fungal strain for its possible application in field-scale bioremediation.

Competitive formation of molecular inclusion complexes of chlordecone and β-hexachlorocyclohexane with natural cyclodextrins: DFT and molecular dynamics study

CONTEXT

Chlordecone (CLD) and β-hexachlorocyclohexane (β-HCH) are chlorinated pesticides that coexist as persistent organic pollutants in the groundwater of several countries in the Caribbean, being an environmental issue. This work evaluates theoretically the competitive formation of host-guest complexes pesticides@cyclodextrines (CDs) as an alternative for water purification and selective separation of pesticides.

METHODS

Quantum mechanical calculations based on density functional theory (DFT) and classical molecular dynamics (MD) simulations were used to achieve information on geometries, energies, structure, and dynamics of guest-host complexes in the gas phase, implicit solvent medium, and in aqueous solutions.

RESULTS

DFT studies showed that interactions of both pesticides with CDs are mediated by steric factors and guided by maximization of the hydrophobic interactions either with the other pesticide or with the CD cavity's inner atoms. MD results corroborate the formation of stable complexes of both pesticides with the studied CDs. α-CD exhibited a preference for the smaller β-HCH molecule over the CLD that could not perturb the formed complex.

CONCLUSIONS

The simulation of competitive formation with γ-CD illustrated that this molecule could accommodate both pesticides inside its cavity. These results suggest that CDs with smaller cavity sizes such as α-CD could be used for selective separation of β-HCH from CLD in water bodies, while γ-CD could be used for methods that aim to remove both pesticides at the same time.

Mycelial nutrient transfer promotes bacterial co-metabolic organochlorine pesticide degradation in nutrient-deprived environments

Biotransformation of soil organochlorine pesticides (OCP) is often impeded by a lack of nutrients relevant for bacterial growth and/or co-metabolic OCP biotransformation. By providing space-filling mycelia, fungi promote contaminant biodegradation by facilitating bacterial dispersal and the mobilization and release of nutrients in the mycosphere. We here tested whether mycelial nutrient transfer from nutrient-rich to nutrient-deprived areas facilitates bacterial OCP degradation in a nutrient-deficient habitat. The legacy pesticide hexachlorocyclohexane (HCH), a non-HCH-degrading fungus (Fusarium equiseti K3), and a co-metabolically HCH-degrading bacterium (Sphingobium sp. S8) isolated from the same HCH-contaminated soil were used in spatially structured model ecosystems. Using ¹³C-labeled fungal biomass and protein-based stable isotope probing (protein-SIP), we traced the incorporation of ¹³C fungal metabolites into bacterial proteins while simultaneously determining the biotransformation of the HCH isomers. The relative isotope abundance (RIA, 7.1-14.2%), labeling ratio (LR, 0.13-0.35), and the shape of isotopic mass distribution profiles of bacterial peptides indicated the transfer of ¹³C-labeled fungal metabolites into bacterial proteins. Distinct ¹³C incorporation into the haloalkane dehalogenase (linB) and 2,5-dichloro-2,5-cyclohexadiene-1,4-diol dehydrogenase (LinC), as key enzymes in metabolic HCH degradation, underpin the role of mycelial nutrient transport and fungal-bacterial interactions for co-metabolic bacterial HCH degradation in heterogeneous habitats. Nutrient uptake from mycelia increased HCH removal by twofold as compared to bacterial monocultures. Fungal-bacterial interactions hence may play an important role in the co-metabolic biotransformation of OCP or recalcitrant micropollutants (MPs).

Remedial trial of sequential anoxic/oxic chemico-biological treatment for decontamination of extreme hexachlorocyclohexane concentrations in polluted soil

During production of γ-hexachlorocyclohexane (γ-HCH), thousands of tons of other isomers were synthesized as byproducts, and after dumping represent sources of contamination for the environment. Several microbes have the potential for aerobic and anaerobic degradation of HCHs, and zero-valent iron is an effective remediation agent for abiotic dechlorination of HCHs, whereas the combination of the processes has not yet been explored. In this study, a sequence of anoxic/oxic chemico-biological treatments for the degradation of HCHs in a real extremely contaminated soil (10-30 g/kg) was applied. Approximately 1500 kg of the soil was employed, and various combinations of reducing and oxygen-releasing chemicals were used for setting up the aerobic and anaerobic phases. The best results were obtained with mZVI/nZVI, grass cuttings, and oxygen-releasing compounds. In this case, 80 % removal of HCHs was achieved in 129 days, and 98 % degradation was achieved after 1106 days. The analysis of HCHs and their transformation products proved active degradation when slight accumulation of the transformation product during the anaerobic phase was followed by aerobic degradation. The results document that switching between aerobic and anaerobic phases, together with the addition of grass, also created suitable conditions for the biodegradation of HCHs and monochlorobenzene/benzene by microbes.

Degradation Characteristics and Remediation Ability of Contaminated Soils by Using β-HCH Degrading Bacteria

Three degradation strains that can utilize β-Hexachlorocyclohexanes (β-HCH) as the sole carbon source were isolated from the soil substrate of constructed wetland under long-term β-HCH stress, and they were named A1, J1, and M1. Strains A1 and M1 were identified as Ochrobactrum sp. and strain J1 was identified as Microbacterium oxydans sp. by 16S rRNA gene sequence analysis. The optimum conditions for degradation with these three strains, A1, J1, and M1, were pH = 7, 30 °C, and 5% inoculum amount, and the degradation rates of 50 μg/L β-HCH under these conditions were 58.33%, 51.96%, and 50.28%, respectively. Degradation characteristics experiments showed that root exudates could increase the degradation effects of A1 and M1 on β-HCH by 6.95% and 5.82%, respectively. In addition, the degradation bacteria A1 and J1 mixed in a ratio of 1:1 had the highest degradation rate of β-HCH, which was 69.57%. An experiment on simulated soil remediation showed that the compound bacteria AJ had the best effect on promoting the degradation of β-HCH in soil within 98 d, and the degradation rate of β-HCH in soil without root exudates was 60.22%, whereas it reached 75.02% in the presence of root exudates. The addition of degradation bacteria or degradation bacteria-root exudates during soil remediation led to dramatic changes in the community structure of the soil microorganisms, as well as a significant increase in the proportion of aerobic and Gram-negative bacterial groups. This study can enrich the resources of β-HCH degrading strains and provided a theoretical basis for the on-site engineering treatment of β-HCH contamination.

Diversity-triggered bottom-up trophic interactions impair key soil functions under lindane pollution stress

A growing amount of evidence suggests that microbial diversity loss may have negative effects on soil ecosystem function. However, less attention has been paid to the determinants of the relationship between community diversity and soil functioning under pollution stress. Here we manipulated microbial diversity to observe how biotic and abiotic factors influenced soil multi-functions (e.g. lindane degradation, soil respiration and nutrient cycling). Results showed that protist community was more sensitive to dilution, pollution stress, and sodium acetate addition than bacterial and fungal community. Acetate addition accelerated the lindane removal. Any declines in microbial diversity reduced the specialized soil processes (NO₃-N production, and N₂O flux), but increased soil respiration rate. Dilution led to a significant increase in consumers-bacterial and fungi-bacterial interaction as evidenced by co-occurrence network, which possibly played roles in maintaining microbiome stability and resilience. Interestingly, pollution stress and resource availability weaken the relationship between microbial diversity and soil functions through the bottom-up trophic interaction and environmental preference of soil microbiome. Overall, this work provides experimental evidence that loss in microbial diversity, accompanied with changes in trophic interactions mediated biotic and abiotic factors, could have important consequences for specialized soil functioning in farmland ecosystems.

Enhanced biodegradation of hexachlorocyclohexane (HCH) isomers by Sphingobium sp. strain D4 in the presence of root exudates or in co-culture with HCH-mobilizing strains

Lindane and other 1,2,3,4,5,6-hexachlorocyclohexane (HCH) isomers are persistent organic pollutants highly hydrophobic, which hampers their availability and biodegradation. This work aimed at (i) investigating genes encoding enzymes involved in HCH degradation in the bacterium Sphingobium sp. D4, (ii) selecting strains, from a collection of environmental isolates, able to mobilize HCHs from contaminated soil, and (iii) analysing the biodegradation of HCHs by strain D4 in co-culture with HCH-mobilizing strains or when cultivated with root exudates. Fragments of the same size and similar sequence to linA and linB genes were successfully amplified. Two isolates, Streptomyces sp. M7 and Rhodococcus erythropolis ET54b able to produce emulsifiers and to mobilize HCH isomers from soil were selected. Biodegradation of HCH isomers by strain D4 was enhanced when co-inoculated with HCH mobilizing strains or when cultivated with root exudates. The degrader strain D4 was able to decompose very efficiently HCHs isomers, reducing their concentration in soil slurries by more than 95% (from an average initial amount of 50 ± 8 mg HCH kg^-1 soil) in 9 days. The combination of HCH-degrading and HCH-mobilizing strains can be considered a promising inoculum for future soil bioremediation studies using bioaugmentation techniques or in combination with plants in rhizodegradation assays.

The Toxic Effects of Lindane via the Impact of pH and Dissolved Organic Matter on Microcystis aeruginosa

The toxic effects of Lindane (γ-BHC) on Microcystis aeruginosa were studied under lab culture conditions. Total protein levels, as well as malondialdehyde (MDA) levels and superoxide dismutase (SOD) enzyme activity, in algal cells, were determined after exposure to different concentrations of Lindane. The bioaccumulation of Lindane, as well as the influence of pH and dissolved organic matter (DOM) on the toxic effects, was also evaluated in algal cells. The growth of M. aeruginosa was inhibited by the Lindane treatment (96 h), resulting in a 50% maximal effect (EC50) concentration of 442 μg/L. In addition, the lowest observed effect concentration (LOEC) was found to be 120 μg/L; the no observed effect concentration (NOEC) was found to be 60 μg/L, and the maximum acceptable toxicant concentration (MATC) was 85 μg/L. With increasing concentrations of Lindane and exposure time, M. aeruginosa growth was significantly inhibited; in addition, the total protein levels and SOD activity significantly decreased. MDA concentration, however, showed an insignificant increase after 96 h. Lindane has the potential for bioaccumulation in algal cells with a bioconcentration factor (BCF) of 340. Furthermore, the toxic effects of Lindane on M. aeruginosa were influenced by environmental factors, such as pH and DOM. The toxic effects decreased with increasing pH and humic acid concentrations. Ultrastructure cell images were used to depict Lindane-induced apoptosis.

Enhancing soil vapor extraction with EKSF for the removal of HCHs

This paper evaluates the combination of electrokinetic soil flushing (EKSF) with soil vapor extraction (SVE) for the removal of four hexachlorocyclohexane (HCH) isomers contained in a real matrix. Results demonstrate that the combination of EKSF and SVE can be positive, but it is required the application of high electric fields (3 V cm^-1) in order to promote a higher temperature in the system, which improves the volatilization of the HCH contained in the system. Electrokinetic transport is also enhanced with the application of higher electric gradients, but these transport processes are slower than the volatilization processes, which are the primary in this system. Hence collection of species in the electrolyte wells is negligible as compared to the compound dragged with air by the SVE but the temperature increase demonstrates a good performance. Combination of EKSF with SVE can efficiently exhaust the four HCH isomers reaching a removal of more than 90% after 15 days of treatment (20% more than values attained by SVE) but it is required the application of high electric fields to promote a higher temperature in the system (to improve the volatilization) and EK transport (to improve the dragging). 1-D transport model can be easily used to estimate the average pore water velocity and the effective diffusion of each compound under the different experimental conditions tested.

Genome evolution related to γ-hexachlorocyclohexane metabolic function in the soil microbial population

γ-Hexachlorocyclohexane (γ-HCH)-degrading strain, Sphingobium sp. TA15, was newly isolated from an experimental field soil from which the archetypal γ-HCH-degrading strain, S. japonicum UT26, was isolated previously. Comparison of the complete genome sequences of these 2 strains revealed that TA15 shares the same basic genome backbone with UT26, but also has the variable regions that are presumed to have changed either from UT26 or from a putative common ancestor. Organization and localization of lin genes of TA15 were different from those of UT26. It was inferred that transposition of IS6100 had played a crucial role in these genome rearrangements. The accumulation of toxic dead-end products in TA15 was lower than in UT26, suggesting that TA15 utilizes γ-HCH more effectively than UT26. These results suggested that genome evolution related to the γ-HCH metabolic function in the soil microbial population is ongoing.

Integrated soil washing and bioreactor systems for the treatment of hexachlorocyclohexane contaminated soil: A review on enhanced degradation mechanisms, and factors affecting soil washing and bioreactor performances

Investigations about the remediation of Hexachlorocyclohexane (HCH), a persistent organic pollutant of global concern, have been extensively reported to treat the HCH contaminated soil. The difficulty arising due to desorption and long ageing procedures of this hydrophobic organic compound in the soil, make it necessary to exploit techniques like soil washing or addition of surfactants, for enhancing the mass transfer rate of hydrophobic compounds. However, this technique gives rise to the generation of a large quantity of waste solution containing the pollutant and various other toxic substances. Moreover, it is challenging to deal with the complex soil washing solution, and thus a follow-up treatment of such washing solution is essentially required before its discharge. This follow-up treatment could be the bioreactor system to efficiently treat the pollutant in the wash solution, thereby reducing the amount of contaminated soil that has to be treated. Among many suggested remediation methods and treatment technologies, integrated soil washing and post-treatment with the bioreactor system could be an environmentally viable method for the remediation of HCH contaminated sites. This review focuses on the soil washing procedures applied so far for the HCH contaminated soil and various factors affecting the efficiency of separation of the target pollutant. Furthermore, the environmental and reactor design-related factors are also discussed for degradation of HCH in the reactor system. Finally, advantages and environmental feasibility of this proposed combined technology and the challenges that need to be encountered are envisaged.

Current research scenario for biological effect of exogenous factors on microcystin synthesis

In natural water bodies, numerous cyanobacteria have the potential to intracellularly synthesize cyanotoxins, among which microcystin (MC) is the ubiquitous toxin that has been well known to be carcinogenic for hepatocytes. MC synthesis is a complex process, which involves about 10 non-ribosomal proteins encoded by the mcy gene cluster. In the natural environments containing MC-producing cyanobacteria, a variety of external factors can affect the generation of MC by mediating the expression of synthesizing genes. These factors can be generally divided into biotic factors (e.g., daphnia, virioplankton, MC-degrading bacteria, algicidal bacteria) and abiotic factors (e.g., nutrients, physical factors, chemicals, phytochemicals, essential trace elements), which are of great significance to the effective reduction of MC. Furthermore, comparison of MC-synthesizing genes in different cyanobacterial strains was performed, and the related factors affecting MC synthesis were summarized. Then, the problems and gaps regarding the biological effect of exogenous factors on microcystin synthesis were discussed. This review article may provide new ideas for addressing the challenges and bottlenecks of MC management.

Organochlorine pesticides in immature scalloped hammerheads Sphyrna lewini from the western coast of the Gulf of California, Mexico: Bioaccumulation patterns and human exposure

Despite the intensive use of organochlorine pesticides (OCPs) in the proximity of the Gulf of California, there is no information regarding their levels in predatory shark species, which could be exposed to relatively high concentrations. In this area, neonates and juveniles of the critically endangered scalloped hammerhead Sphyrna lewini are caught for consumption, so the examination of the accumulation of OCPs is necessary for future conservation, as well as to assess the exposure to humans. Levels and accumulation patterns of 29 OCPs were analyzed in the liver and muscle of 20 immature scalloped hammerheads. Twenty-three compounds were detected in liver and 17 OCPs were found in muscle. In the latter tissue, only p,p'-DDE presented concentrations above the detection limit in all samples (0.59 ± 0.21 ng/g w.w.), while in the liver, DDTs were also the main group of pesticides (215 ± 317 ng/g w.w.), followed by ∑Chlordanes > ∑Chlorobenzenes > Mirex > HCBD > Others. One of the two analyzed neonates presented high concentrations of OCPs in the liver (1830 ng/g w.w.), attributed to a bioamplification process. No differences in accumulation of OCPs were found between juveniles of both sexes, where an increase in the concentration of various compounds related with size and age was observed. Additionally, juveniles under 2 years of age may undergo a growth dilution process. Our results suggest that the consumption of this species does not imply risks to human health (chronic or carcinogenic effects) associated with OCPs. Likewise, we recommend further monitoring due to the possible recent inputs of some OCPs (e.g. dicofol, median of ratio o, p'-DDT/p, p'-DDT = 0.7) into the environment.

Toxicokinetics of hydrophobic organic compounds in oligochaeta: A critical review

Toxicokinetic studies appertain to the fundamental research of soil bioavailability. However, the research outcomes of aspects influencing uptake and elimination of hydrophobic organic compounds have not been summarized so far. In our review, a recapitulation of available toxicokinetic data (i.e. experimental conditions, if the steady state was reached, uptake and elimination rate constants, and bioaccumulation factors) is presented in well-arranged tables. Further, toxicokinetic models are overviewed in the schematic form. In the review, the required information could be quickly found and/or the experimental gaps easily identified. Generally a little is known about the effects of soil properties other than soil organic matter. Limited or no data are available about soil treatment, food supply during laboratory exposure, and metabolization in oligochaeta. The impact of these factors might be important especially for arable soils with typically low organic matter content but high consequences on humans. Besides these circumstances, other uncertainties between published studies have been found. Firstly, the scientific results are provided in heterogenous units: bioaccumulation factors as well as the rate constants are reported in dry or wet weight of soil and earthworms. The steady state is another critical factor because the time to reach the equilibrium is influenced not only by soil and compound characteristics but for example also by aging. Nevertheless, toxicokinetic studies bring irreplaceable information about the real situation in soil and our review help to define missing knowledge and estimate the scientific priorities.

Lake Superior Has Lost over 90% of Its Pesticide HCH Load since 1986

The time trend of α- and γ-hexachlorocyclohexane (HCH) isomers in Lake Superior water was followed from 1986 to 2016, the longest record for any persistent organic pollutant (POP) in Great Lakes water. Dissipation of α-HCH and γ-HCHs was first order, with halving times (t1/2) of 5.7 and 8.5 y, respectively. Loss rates were not significantly different starting a decade later (1996-2016). Concentrations of β-HCH were followed from 1996-2016 and dissipated more slowly (t1/2 = 16 y). In 1986, the lake contained an estimated 98.8 tonnes of α-HCH and 13.2 tonnes of γ-HCH; by 2016, only 2.7% and 7.9% of 1986 quantities remained. Halving times of both isomers in water were longer than those reported in air, and for γ-HCH, they were longer in water than those reported in lake trout. Microbial degradation was evident by enantioselective depletion of (+)α-HCH, which increased from 1996 to 2011. Volatilization was the main removal process for both isomers, followed by degradation (hydrolytic and microbial) and outflow through the St. Mary's River. Sedimentation was minor. Major uncertainties in quantifying removal processes were in the two-film model for predicting volatilization and in microbial degradation rates. The study highlights the value of long-term monitoring of chemicals in water to interpreting removal processes and trends in biota.

A critical review on the formation, fate and degradation of the persistent organic pollutant hexachlorocyclohexane in water systems and waste streams

The environmental impacts of persistent organic pollutants (POPs) is an increasingly prominent topic in the scientific community. POPs are stable chemicals that are accumulated in living beings and can act as endocrine disruptors or carcinogens on prolonged exposure. Although efforts have been taken to minimize or ban the use of certain POPs, their use is still widespread due to their importance in several industries. As a result, it is imperative that POPs in the ecosystem are degraded efficiently and safely in order to avoid long-lasting environmental damage. This review focuses on the degradation techniques of hexachlorocyclohexane (HCH), a pollutant that has strong adverse effects on a variety of organisms. Different technologies such as adsorption, bioremediation and advanced oxidation process have been critically analyzed in this study. All 3 techniques have exhibited near complete removal of HCH under ideal conditions, and the median removal efficiency values for adsorption, bioremediation and advanced oxidation process were found to be 80%, 93% and 82% respectively. However, it must be noted that there is no ideal HCH removal technique and the selection of removal method depends on several factors. Furthermore, the fates of HCH in the environment and challenges faced by HCH degradation have also been explained in this study. The future scope for research in this field has also received attention.

Deep seafloor plastics as the source and sink of organic pollutants in the northern South China Sea

Large plastic litter (as opposed to microplastics and plastic pellets) could adsorb organic pollutants and thus pose a serious threat to the marine environment. We report high levels of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) adsorbed to plastic litter sampled from depths of 1800-3100 m in the Xisha Trough region of the northern South China Sea (NSCS). ∑PCBs on plastics ranged from 126.9-142.1 ng/g, with tri-PCBs accounting for 92-97% of the total PCB concentrations in all samples. Levels of ∑OCPs varied from 4280 to 5351 ng/g (average 4690 ng/g), with a total of 19 compounds detected in the seven samples. While no parent DDT (dichlorodiphenyltrichloroethane) was detected, op'-DDE (metabolite of DDT) was most abundant, with concentrations ranging from 947.5-1551.7 ng/g. ∑CHLs (heptachlor + heptachlor epoxide A + heptachlor epoxide B + cis-chlordane + trans-chlordane) ranged from 1083.1-1263.7 ng/g (mean 1153 ng/g) and accounted for 24% of ∑OCPs. Various compositional ratios of HCH (hexachlorocyclohexane) and DDT metabolites improved our understanding of the sources and transport pathways of OCPs. The total absence of DDT may be a "ghost indicator" of no recent DDT inputs into the oceans. There could well be inputs of DDT, but only as the degraded metabolites DDE and DDD when they are adsorbed to seafloor plastic litter. A comparison of HCH isomer ratios in seafloor plastics with technical HCH ratios revealed that HCHs were possibly not from early residues but from later inputs. An ecological risk assessment of the contaminants indicated a high risk from ∑DDTs, p,p-DDE, and γ-HCH in all the sampled locations. Finally, we propose a descriptive model depicting the movements and transportation of PCBs and OCPs from the ocean surface to seafloor plastics in the NSCS.

Biodegradation of Lindane (γ-Hexachlorocyclohexane) To Nontoxic End Products by Sequential Treatment with Three Mixed Anaerobic Microbial Cultures

The γ isomer of hexachlorocyclohexane (HCH), also known as lindane, is a carcinogenic persistent organic pollutant. Lindane was used worldwide as an agricultural insecticide. Legacy soil and groundwater contamination with lindane and other HCH isomers is still a big concern. The biotic reductive dechlorination of HCH to nondesirable and toxic lower chlorinated compounds such as monochlorobenzene (MCB) and benzene, among others, has been broadly documented. Here, we demonstrate that complete biodegradation of lindane to nontoxic end products is attainable using a sequential treatment approach with three mixed anaerobic microbial cultures referred to as culture I, II, and III. Biaugmentation with culture I achieved dechlorination of lindane to MCB and benzene. Culture II was able to dechlorinate MCB to benzene, and finally, culture III carried out methanogenic benzene degradation. Distinct Dehalobacter populations, corresponding to different 16S rRNA amplicon sequence variants in culture I and culture II, were responsible for lindane and MCB dechlorination, respectively. This study continues to highlight key roles of Dehalobacter as chlorobenzene- and HCH -respiring bacteria and demonstrates that sequential treatment with specialized anaerobic cultures may be explored at field sites in order to address legacy soil and groundwater contamination with HCH.

Examination of barnacles' potential to be used as bioindicators of persistent organic pollutants in coastal ecosystem: A Malaysia case study

Barnacles are ubiquitous in coastal ecosystems of different geographical regions worldwide. This is the first study attempting to assess the suitability of barnacles as bioindicators of persistent organic pollutants (POPs) in coastal environments. Barnacles were collected from the coasts around Peninsular Malaysia and analyzed for POPs including polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and organochlorine pesticides (OCPs). Among POPs, PCBs showed the highest concentrations with elevated contributions of CB28 and CB153. As for PBDEs, BDE47 was the most frequently detected congener, while BDE209 was detected in barnacles from two stations in Port Klang and the levels reached up to >70% of total PBDE concentrations. Concentrations of OCPs detected in barnacles were in the order of CHLs > DDTs > HCHs > HCB and 4,4'-DDE and cis- and trans-chlordane were the predominant OCP compounds. A comparison with previous studies in Malaysia showed consistent levels of POPs. Green mussels collected from selected barnacles' habitats, for the sake of a comparison, showed almost similar profiles but lower concentrations of POPs. The spatial distribution of POPs observed in barnacles and comparison of POP levels and profiles with mussels indicated that barnacles can be useful bioindicators for monitoring POPs contamination in the coastal ecosystems.

Microbial catabolism of lindane in distinct layers of acidic paddy soils combinedly affected by different water managements and bioremediation strategies

The environmental fate of the recalcitrant organic chlorine insecticide lindane and its removal from contaminated soils are still of great concern. However, the key factors influencing microbial removal of lindane from paddy soils with intermittent flooding and draining remain largely unknown. Here, we conducted laboratory experiments to investigated lindane biodegradation in different layers of typical acidic paddy soils under different water managements and bioremediation strategies, together with the changes of functional bacterial consortium, key genes and metabolic pathways. It was found that under flooded conditions, lindane spiking significantly stimulated the growth of some bacterial genera with potential anaerobic catabolic functions in both top- (0-20 cm depth) and subsoil (20-40 cm depth), leading to the shortest half-life of lindane with 7.6-9.0 d in the topsoil. In contrary, lindane spiking dramatically stimulated the growth of bacterial members with aerobic catabolic functions under drained conditions, exhibiting half-lives of lindane with 85-131 d and 18-23 d in the top- and subsoil, respectively. Overall, biostimulation coupled with flooding management would be the better combination for increased lindane bioremediation. Functional genes involved in lindane degradation and retrieved from metagenomic data further supported the anaerobic and aerobic biodegradation of lindane under flooded and drained conditions, respectively. Moreover, the integrated network analysis suggested water management and organic matter were the primary factors shaped the assembly of functional bacteria in lindane degradation, among which Clostridium and Rhodanobacter were the key anaerobic and aerobic functional genera, respectively. Taken together, our study provides a comprehensive understanding of lindane biodegradation in distinct layers of acidic paddy soils that were combinedly affected by different water managements and bioremediation strategies.

In vivo comparison of the proangiogenic properties of chlordecone and three of its dechlorinated derivatives formed by in situ chemical reduction

In situ chemical reduction (ISCR) has been identified as a possible way for the remediation of soils contaminated by chlordecone (CLD). Evidences provided by the literature indicate an association between the development of prostate cancer and CLD exposure (Multigner et al. 2010). In a previous in vitro study, we demonstrated that the two main dechlorinated CLD derivatives formed by ISCR, CLD-1Cl, and CLD-3Cl have lower cytotoxicity and proangiogenic properties than CLD itself (Legeay et al. 2017). By contrast, nothing is known on the in vivo proangiogenic effect of these dechlorinated derivatives. Based on in vitro data, the aims of this study were therefore to evaluate the in vivo influence of CLD and three of its dechlorinated metabolites in the control of neovascularization in a mice model of prostate cancer. The proangiogenic effect of CLD and three of its dechlorinated derivatives, CLD-1Cl, CLD-3Cl, and CLD-4Cl, was evaluated on a murine model of human prostate tumor (PC-3) treated, at two exposure levels: 33 μg/kg and 1.7 μg/kg respectively reflecting acute and chronic toxic exposure in human. The results of serum measurements show that, for the same ingested dose, the three metabolite concentrations were significantly lower than that of CLD. Dechlorination of CLD lead therefore to molecules that are biologically absorbed or metabolized, or both, faster than the parent molecule. Prostate tumor growth was lower in the groups treated by the three metabolites compared to the one treated by CLD. The vascularization measured on the tumor sections was inversely proportional to the rate of dechlorination, the treatment with CLD-4Cl showing no difference with control animals treated with only the vehicle oil used for all substances tested. We can therefore conclude that the proangiogenic effect of CLD is significantly decreased following the ISCR-resulting dechlorination. Further investigations are needed to elucidate the molecular mechanisms by which dechlorination of CLD reduces proangiogenic effects in prostate tumor.

Physico-chemical and agronomic results of soil remediation by In Situ Chemical Reduction applied to a chlordecone-contaminated nitisol at plot scale in a French Caribbean banana plantation

The In Situ Chemical Reduction (ISCR) process was tested in a nitisol in a French Caribbean banana plantation using five different soil amendments. The addition of 2.8% or 4.0% of Zero Valent Iron (ZVI; dw/dw, 2 different trial plots) in the 0-40-cm soil layer lowered the initial chlordecone (CLD) concentration by up to 74% or 69% in 37 days or 94 days, with 75% of the decrease achieved after only 21 or 24 days of treatment depending on the trial plot. The addition of commercially available Daramend® was also tested by applying the 6% dose (dw/dw) recommended by the manufacturer and using either the regular alfalfa-based product or a bagasse-based product specifically formulated for the study. Both significantly lowered CLD concentrations, but to a lesser extent than with the ZVI-only amendment. A bagasse-ZVI mixture prepared on site produced results slightly better than the two Daramend®. The percentage decreases in CLD concentrations were correlated with the negative redox potentials achieved. In all the trial plots, dechlorinated transformation products appeared in the soil and soil water as the CLD concentrations decreased, with H atoms replacing up to 4 and 7 of the 10 Cl atoms, respectively. None of these degradation products appeared to accumulate in the soil or soil water during the treatment. Instead, the reverse occurred, with an overall downward trend in their concentrations over time. The effects of ISCR treatment on agronomic and human health-related parameters were measured in three different crops. The radishes produced with some treatments were visually of lower quality or smaller in size than those grown in the control plots. Lower yields were observed for the cucumbers and sweet potatoes grown after applying the bagasse-based amendments. Mortality among cucumber seedlings was observed after treatment with ZVI only. Simple operational solutions should suffice to remedy these negative agronomic effects. As regards human health-related effects, the CLD concentrations in radishes grown with three of the amendments were significantly lower than in the two control plots and well below the maximum residue level (MRL), which was substantially exceeded in the radishes grown on untreated soil. For cucumbers, the treatments with regular Daramend® and with a local bagasse-ZVI mixture produced fruits with CLD below the MRL and also below the concentrations in one of the two control plots. As for the sweet potatoes, adding a bagasse-ZVI mixture had a significant positive effect by decreasing contamination below the levels in the two control plots and below the MRL.

Guest-host complexes of 1-iodochlordecone and β-1-iodo-pentachlorocyclohexane with cyclodextrins as radiotracers of organochlorine pesticides in polluted water

The chlordecone (CLD) and the β-hexachlorocyclohexane (β-HCH) are persistent organic pollutants with a great environmental stability that cause severe affectations to health. The concentration of these pesticides in the environment is low, which represent a problem for their determination, even for the modern analytical methods. The labeling of these compounds with an iodine radioisotope for their use as radiotracers is a potential solution to this problem. The present work studies the interaction of 1-iodochlordecone (I-CLD) and β-1-iodo-pentachlorocyclohexane (I-β-HCH) with cyclodextrins (CDs), during the formation of molecular inclusion complexes pesticide@CDs. The methodology of multiple minima hypersurfaces, quantic calculations based on density functional theory and a topologic study of electronic density were used to corroborate the stability of I-CLD@CDs and I-β-HCH@CDs complexes. Three main types of guest-host complexes in relation to the occlusion grade were observed: with total occlusion, with partial occlusion and external interaction without occlusion. The more stable complexes are obtained when the γ-CD is the host molecule. The formed complexes with radiolabelled pollutants are analogous with the ones reported in previous works. These results confirm the utility of these complexes for the removal of organochlorine pesticides from polluted water and, also, demonstrate the possibility of using the I-CLD and the I-β-HCH as possible radiotracers for these pollutants in further studies with environmental proposes.

Dual C-Cl Isotope Analysis for Characterizing the Reductive Dechlorination of α- and γ-Hexachlorocyclohexane by Two Dehalococcoides mccartyi Strains and an Enrichment Culture

Hexachlorocyclohexanes (HCHs) are persistent organic contaminants that threaten human health. Microbial reductive dehalogenation is one of the most important attenuation processes in contaminated environments. This study investigated carbon and chlorine isotope fractionation of α- and γ-HCH during the reductive dehalogenation by three anaerobic cultures. The presence of tetrachlorocyclohexene (TeCCH) indicated that reductive dichloroelimination was the first step of bond cleavage. Isotope enrichment factors (ε_C and ε_Cl) were derived from the transformation of γ-HCH (ε_C, from -4.0 ± 0.5 to -4.4 ± 0.6 ‰; ε_Cl, from -2.9 ± 0.4 to -3.3 ± 0.4 ‰) and α-HCH (ε_C, from -2.4 ± 0.2 to -3.0 ± 0.4 ‰; ε_Cl, from -1.4 ± 0.3 to -1.8 ± 0.2 ‰). During α-HCH transformation, no enantioselectivity was observed, and similar ε_c values were obtained for both enantiomers. The correlation of ¹³C and ³⁷Cl fractionation (Λ = Δδ¹³C/Δδ³⁷Cl ≈ ε_C/ε_Cl) of γ-HCH (from 1.1 ± 0.3 to 1.2 ± 0.1) indicates similar bond cleavage during the reductive dichloroelimination by the three cultures, similar to α-HCH (1.7 ± 0.2 to 2.0 ± 0.3). The different isotope fractionation patterns during reductive dichloroelimination and dehydrochlorination indicates that dual-element stable isotope analysis can potentially be used to evaluate HCH transformation pathways at contaminated field sites.

Uptake kinetics of four hydrophobic organic pollutants in the earthworm Eisenia andrei in aged laboratory-contaminated natural soils

Laboratory studies of pollutant uptake kinetics commonly start shortly after experimental soil contamination when it is not clear if the processes between soil and chemicals are equilibrated and stabilized. For instance, when the concentration in soil quickly decreases due to initial biodegradation, bioaccumulation may show a peak-shape accumulation curve instead of conventional first order kinetics with a plateau at the end. The results of such experiments with soil freshly contaminated in the laboratory are then hardly comparable to bioaccumulation observed in soils from historically contaminated sites. Therefore, our study focused on the uptake kinetics of four hydrophobic organic compounds (pyrene, lindane, p,p'-DDT and PCB 153) in two laboratory-contaminated natural soils with different soil properties (e.g. total organic carbon content of 1.6 and 9.3%) aged for 203 days to mimic long-term contamination. For pyrene, the results surprisingly showed peak-shape accumulation curves despite long aging. It seems compound biodegradation might be significant in aged soils when the conditions change (e.g. by distribution to the experimental vessels) and this should be also considered when testing historically contaminated soils. For lindane, longer aging seems to guarantee stability of the soil-compound-earthworm system and the steady state was reached after 5 days of exposure. Furthermore, although concentrations of p,p'-DDT and PCB 153 in earthworms after 11-15-day exposure did not statistically differ, which is a commonly-used indicator that a steady state was reached, they continuously increased until the end of the exposure. Therefore, despite the aging, longer exposure was probably needed to reach the true equilibrium between concentrations in earthworms and soil. In summary, aging does not warranty the conventional first order kinetic curve with the equilibrium at the end of the exposure but may have diverse effects for compounds with different environmental properties and should be taken into account in the bioaccumulation factor calculation and the risk assessment.

Potency of Phlebia species of white rot fungi for the aerobic degradation, transformation and mineralization of lindane

The widespread use of the organochlorine insecticide lindane in the world has caused serious environmental problems. The main purpose of this paper is to investigate the potency of several Phlebia species of white rot fungi to degrade, transform and mineralize lindane, and to provide the feasibility of using white rot fungi for bioremediation at contaminated sites. Based on tolerance experiment results, Phlebia brevispora and Phlebia lindtneri had the highest tolerance to lindane and were screened by degradation tests. After 25 days of incubation, P. brevispora and P. lindtneri degraded 87.2 and 73.3% of lindane in low nitrogen medium and 75.8 and 64.9% of lindane in high nitrogen medium, respectively. Several unreported hydroxylation metabolites, including monohydroxylated, dehydroxylated, and trihydroxylated products, were detected and identified by GC/MS as metabolites of lindane. More than 10% of [¹⁴C] lindane was mineralized to ¹⁴CO₂ by two fungi after 60 days of incubation, and the mineralization was slightly promoted by the addition of glucose. Additionally, the degradation of lindane and the formation of metabolites were efficiently inhibited by piperonyl butoxide, demonstrating that cytochrome P450 enzymes are involved in the fungal transformation of lindane. The present study showed that P. brevispora and P. lindtneri were efficient degraders of lindane; hence, they can be applied in the bioremediation process of lindane-contaminated sites.

Crop-dependent root-microbe-soil interactions induce contrasting natural attenuation of organochlorine lindane in soils

Plant-specific root-microbe-soil interactions play an indisputable role in microbial adaptation to environmental stresses. However, the assembly of plant rhizosphere microbiomes and their feedbacks in modification of pollution alleviation under organochlorine stress condition is far less clear. This study examined the response of root-associated bacterial microbiomes to lindane pollution and compared the dissipation of lindane in maize-cultivated dry soils and rice-cultivated flooded soils. Results showed that lindane pollution dramatically altered the microbial structure in the rhizosphere soil of maize but had less influence on the microbial composition in flooded treatments regardless of rice growth, when the reductive dechlorination of lindane was actively coupled with natural redox processes under anaerobic conditions. After 30 days of plant growth, lindane residues dissipated much faster in anaerobic than in aerobic environments, with only 1.08 mg kg^-1 lindane remaining in flooded control compared to 12.79 mg kg^-1 in dry control soils. Compared to the corresponding unplanted control, maize growth significantly increased, but rice growth slightly decreased the dissipation of lindane. Our study suggests that opposite impacts would lead to the self-purification of polluted soils during the growth of xerophytic maize and hygrocolous rice. This was attributed to the contrasting belowground micro-ecological processes regarding protection of root tissues and thereby assembly of rhizosphere microbiomes shaped by the xerophytic and hygrocolous crops under different water managements, in response to lindane pollution.

Microbial Communities Associated with Sustained Anaerobic Reductive Dechlorination of α-, β-, γ-, and δ-Hexachlorocyclohexane Isomers to Monochlorobenzene and Benzene

Intensive historical and worldwide use of pesticide formulations containing hexachlorocyclohexane (HCH) has led to widespread contamination. We derived four anaerobic enrichment cultures from HCH-contaminated soil capable of sustainably dechlorinating each of α-, β-, γ-, and δ-HCH isomers stoichiometrically to benzene and monochlorobenzene (MCB). For each isomer, the dechlorination rates, inferred from production rates of the dechlorinated products, MCB and benzene, increased progressively from <3 to ∼12 μM/day over 2 years. The molar ratio of benzene to MCB produced was a function of the substrate isomer and ranged from β (0.77 ± 0.15), α (0.55 ± 0.09), γ (0.13 ± 0.02), to δ (0.06 ± 0.02) in accordance with pathway predictions based on prevalence of antiperiplanar geometry. Data from 16S rRNA gene amplicon sequencing and quantitative PCR revealed significant increases in the absolute abundances of Pelobacter and Dehalobacter, most notably in the α-HCH and δ-HCH cultures. Cultivation with a different HCH isomer resulted in distinct bacterial communities, but similar archaeal communities. This study provides the first direct comparison of shifts in anaerobic microbial communities induced by the dechlorination of distinct HCH isomers. It also uncovers candidate microorganisms responsible for the dechlorination of α-, β-, γ-, and δ-HCH, a key step toward better understanding and monitoring of natural attenuation processes and improving bioremediation technologies for HCH-contaminated sites.

Restoring HCHs polluted land as one of the priority activities during the UN-International Decade on Ecosystem Restoration (2021-2030): A call for global action

The United Nations General Assembly has recently declared 2021-2030 as the 'International Decade on Ecosystem Restoration' for facilitating the restoration of degraded and destroyed terrestrial and marine systems for regaining biodiversity and ecosystem services, creating job opportunities and also to fight against climate change. One of the prime focus is the restoration of ~350 mha of degraded land across the world for attaining the UN-Sustainable Development Goals. Pesticides are one of the major causes of land pollution and hexachlorocyclohexanes (HCHs, including technical-HCH and γ-HCH) is one of the widely used organochlorine pesticides during the past seven decades before α-, β-, and γ-HCH was listed in the Stockholm Convention in 2009. The widespread pollution of HCHs has been reported from every sphere of the environment and ~7 Mt of HCHs residues have been dumped worldwide near the production sites. HCHs isomers have higher volatility, water solubility and long-range atmospheric transport ability which further facilitates its entry into various environmental compartments. Therefore, the restoration and management of HCHs polluted land is urgently required. Despite various pilot-scale studies have been reported for the remediation of HCHs polluted land, they are not successfully established under the field conditions. This is mainly due to the high concentration of HCHs residues in the contaminated soil and also due to its toxicity and highly persistent nature, which increases the complexity of the onsite remediation. Here we provide a novel approach i.e. sequential and integrated remediation approach (SIRA) for the restoration of HCHs contaminated land by the integrated use of agroresidues along with the application of HCHs degrading microorganisms and chemical amendments followed by the plant-based clean-up techniques using grasses, herbs, shrubs and trees in a sequential manner. SIRA provides cost effective solution with enhanced ecological and socioeconomic benefits for the sustainable restoration of HCHs contaminated sites.

Hexachlorocyclohexane exposure alters the microbiome of colostrum in Chinese breastfeeding mothers

Breast milk, especially colostrum, is not just a source of nutrients and immune factors for the newborn, but also accumulates environmental persistent pollutants and its diverse microbes affect the early colonization of the newborn's gut. Little is known about associations between environmental pollutants and the microbial composition of human colostrum. We assessed the influence of hexachlorocyclohexane (HCH), a persistent organic pollutant (POP), in colostrums on the microbial composition of human colostrum samples. HCH concentrations in 89 colostrum samples collected from a population living on the easternmost island of China were measured via gas chromatography equipped with mass spectrometer (GC-MS), HCH exposure risks for infants via dietary intake of breast milk were assessed, and for 29 colostrum samples the microbiota were profiled using 16S rRNA gene pyrosequencing to assess the association with HCH exposure levels. Our study confirmed high colostrum exposure levels of total HCHs (12.19 ± 13.68 μg L^-1) in this Chinese population. We predominantly identified Proteobacteria (67.6%) and Firmicutes (25.1%) in colostrum and microbial diversity at the genus level differed between samples with different HCH levels; e.g., Pseudomonas which contains several HCH degrading strains was found in significantly higher abundance in γ-HCH rich samples. Also, microbes that were statistically significantly associated with HCH levels were also highly correlated with each other (false discovery rate (FDR)＜0.01) and clustered in network analysis. Microbial diversity is associated with HCH levels in human colostrum and these associations might be attributable to their HCH degrading ability. These finding provide first insights into the role that environmental persistent pollutants may play in the microbial composition of human colostrum and the colonization of the infant gut.

Risk assessment of organochlorine pesticides in drinking water source of the Yangtze River

Organochlorine pesticides have been banned for many years, but the residual trace amount of organochlorine in water may still pose ecotoxicological risk. Meanwhile, the potential risk of organochlorine pesticides released from sediments, especially into drinking water sources, is receiving increasing attention. The present study assessed the pollution and potential risk of drinking water sources along the midstream and downstream Yangtze River. Residues of organochlorine pesticides (OCPs) in water, suspended particle matter (SPM), and sediment were evaluated with isotope dilution HRGC/HRMS. The results indicated that OCPs in water, SPM, and sediment ranged in 0.52-92.97 ng/L, 0.10-4.10 ng/L, and 0.038-11.36 ng/g, respectively. The predominant OCPs in water, SPM, and sediment were β-HCH, p,p'-DDE and PeCB. At site Y1, 8, 13, 18, β-HCH has a higher proportion in sediment samples, while, α-HCH has a higher proportion in SPM samples. The industrial use of HCHs in the history was the main HCHs source for most water and sediment samples, which indicated an absence of fresh inputs of industrial HCHs. Meanwhile, the abundance of p,p'-DDE in water, sediment and SPM samples could be attributed to long-term aerobic degradation of DDTs. The values of ffsw of HCHs, DDTs and PeCB indicate the transfer from water to sediment. Risk assessment showed that HCHs and DDTs posed low ecotoxicological risk to the Yangtze River.

Lessons from the genomes of lindane-degrading sphingomonads

Bacterial strains capable of degrading man-made xenobiotic compounds are good materials to study bacterial evolution towards new metabolic functions. Lindane (γ-hexachlorocyclohexane, γ-HCH, or γ-BHC) is an especially good target compound for the purpose, because it is relatively recalcitrant but can be degraded by a limited range of bacterial strains. A comparison of the complete genome sequences of lindane-degrading sphingomonad strains clearly demonstrated that (i) lindane-degrading strains emerged from a number of different ancestral hosts that have recruited lin genes encoding enzymes that are able to channel lindane to central metabolites, (ii) in sphingomonads lin genes have been acquired by horizontal gene transfer mediated by different plasmids and in which IS6100 plays a role in recruitment and distribution of genes, and (iii) IS6100 plays a role in dynamic genome rearrangements providing genetic diversity to different strains and ability to evolve to other states. Lindane-degrading bacteria whose genomes change so easily and quickly are also fascinating starting materials for tracing the bacterial evolution process experimentally in a relatively short time period. As the origin of the specific lin genes remains a mystery, such genes will be useful probes for exploring the cryptic 'gene pool' available to bacteria.

Chemical oxidation and reduction of hexachlorocyclohexanes: A review

Lindane (γ-hexachlorocyclohexane) and its isomers (HCH) are some of the most common and most easily detected organochlorine pesticides in the environment. The widespread distribution of lindane is due to its use as an insecticide, accompanied by its persistence and bioaccumulation, whereas HCH were disposed of as waste in unmanaged landfills. Unfortunately, certain HCH (especially the most reactive ones: γ- and α-HCH) are harmful to the central nervous system and to reproductive and endocrine systems, therefore development of suitable remediation methods is needed to remove them from contaminated soil and water. This paper provides a short history of the use of lindane and a description of the properties of HCH, as well as their determination methods. The main focus of the paper, however, is a review of oxidative and reductive treatment methods. Although these methods of HCH remediation are popular, there are no review papers summarising their principles, history, advantages and disadvantages. Furthermore, recent advances in the chemical treatment of HCH are discussed and risks concerning these processes are given.

Assembly of root-associated microbiomes of typical rice cultivars in response to lindane pollution

Organochlorine pesticides have been extensively used for many years to prevent insect diseases of rice (Oryza sativa L.), but little is known about their residual impacts on the underground micro-ecology in anaerobic environment. In this glasshouse study, we characterized the lindane effects on the assembly of root-associated microbiomes of commonly used indica, japonica and hybrid rice cultivars, and their feedback in turn, in modifying lindane anaerobic dissipation during 60 days' rice production. The results showed that rice growth inhibited the anaerobic dissipation of lindane, but was not affected apparently by lindane at initial spiked concentration of 4.62 and 18.54 mg kg^-1 soil. Suppressed removal of lindane in rice planted treatments as compared with that in unplanted control was likely due to inhibited reductive dechlorination induced by a comprehensive effect of radial O₂ secretion of rice root and co-occurring Fe(III) reduction that consumed electron competitively in rice rhizosphere. However, the hybrid cultivar exhibited a less suppression than the conventional cultivars in high polluted soils. Bacteria was more sensitively responded to lindane pollution than fungal taxa, and Actinobacteria, Chloroflexi, Verrucomicrobia and Proteobacteria were the main different phyla between hybrid and conventional cultivars, with a more stable community structure exhibited in the hybrid rice under lindane stress. Our study highlights the assembly and variation of root-associated microbiomes in responses of lindane pollution, and suggests that hybrid rice cultivar might be most competent for cultivation in paddy fields polluted by lindane and other organochlorine pesticides, especially in the area with high residual levels.

Evaluation of the molecular inclusion process of β-hexachlorocyclohexane in cyclodextrins

The present work aimed to study the guest-host complexes of β-hexachlorocyclohexane (β-HCH), a pesticide with high environmental stability that can cause severe health problems, with the most common cyclodextrins (α-, β-, and γ-CDs). The formation reactions of these molecular inclusion complexes were addressed in this research. The multiple minima hypersurface methodology, quantum calculations based on density functional theory and a topological exploration of the electron density based on the quantum theory of atoms in molecules approach were used to characterize the interaction spaces of the pollutant with the three CDs. Additionally, charge distribution, charge transfer and dual descriptor analyses were employed to elucidate the driving forces involved in the formation of these molecular inclusion complexes. Three types of fundamental interactions were observed: total occlusion, partial occlusion and external interaction (non-occlusion). Finally, experiments were performed to confirm the formation of the studied complexes. The most stable complexes were obtained when γ-CD was the host molecule. The interactions between the pesticide and CDs have fundamentally dispersive natures, as was confirmed experimentally by spectroscopic results. All the obtained results suggest the possibility of using CDs for the purification and treatment of water polluted with β-HCH.

Dissipation, dehalogenation, and denitration of chloroaromatic compounds by Nocardioides sp. strain PD653: Characterization of the substrate specificity

The substrate range of Nocardioides sp. strain PD653, capable of mineralizing hexachlorobenzene, was investigated based on the dissipation of substrates and the liberation of halogen ions. Strain PD653 dehalogenated 10 out of 18 halophenol congeners; however, it could dehalogenate only hexachlorobenzene out of seven halobenzene congeners tested. Moreover, dehalogenation activities were shown for chloronitrobenzenes, along with an increase in the number of substituted chlorine atoms except for 2,3,4,5-tetrachloro-1-nitrobenzene. These results suggested that this strain might be applicable to remediate soil contaminated with these persistent chloroaromatic compounds.

Occurrence and Toxicological Risk Evaluation of Organochlorine Pesticides from Suburban Soils of Kenya

The use of organic chemicals in agriculture and manufacturing has raised concerns about the dangers of organochlorine pesticides (OCPs) in the environment. By examining OCPs occurrence in the suburban soils from Kenya, this study revealed the distribution, concentrations, and the threat posed to the environment and human health. A gas chromatography electron capture detector was used to test the pesticides. The hexachlorocyclohexane (HCH) and dichlorodiphenyltrichloroethane (DDT) studied in soils of Kapsabet, Voi, and Nyeri towns showed concentrations ranging from 0.03-52.7, 0.06-22.3, and 0.24-24.3 ng/g respectively. The highest concentration of HCHs was in Kapsabet (0.03-48.1 ng/g), whereas the highest DDTs concentration was in Voi (n.d.-15.5 ng/g). Source identification revealed OCPs pollution originated from recent usage of DDT pesticides to control insect-borne diseases and from the use of lindane in agriculture. Correlation test revealed that total organic carbon influenced the presence of pesticides in the soils. The enantiomeric ratios of α-HCH/γ-HCH were <3 indicating the use of lindane while the ratios of DDE/DDT were <1 suggesting recent input of DDT. The cancer risk assessment showed values close to the set risk level of 10^-6, suggesting the likelihood of exposure to cancer was not low enough, and control measures need to be established.

Understanding fungal potential in the mitigation of contaminated areas in the Czech Republic: tolerance, biotransformation of hexachlorocyclohexane (HCH) and oxidative stress analysis

The study of the soil microbial community represents an important step in better understanding the environmental context. Therefore, biological characterisation and physicochemical integration are keys when defining contaminated sites. Fungi play a fundamental role in the soil, by providing and supporting ecological services for ecosystems and human wellbeing. In this research, 52 soil fungal taxa were isolated from in situ pilot reactors installed to a contaminated site in Czech Republic with a high concentration of hexachlorocyclohexane (HCH). Among the identified isolates, 12 strains were selected to evaluate their tolerance to different isomers of HCH by using specific indices (Rt:Rc; T.I.) and to test their potential in xenobiotic biotransformation. Most of the selected taxa was not significantly affected by exposure to HCH, underlining the elevated tolerance of all the tested fungal taxa, and different metabolic intermediates of HCH dechlorination were observed. The oxidative stress responses to HCH for two selected species, Penicillium simplicissimum and Trichoderma harzianum, were investigated in order to explore their toxic responses and to evaluate their potential functioning in bioremediation of contaminated environments. This research suggests that the isolated fungal species may provide opportunities for new eco-friendly, integrated and cost-effective solutions for environmental management and remediation, considering their efficient adaptation to stressful conditions.

A proteomic approach to investigate enhanced responsiveness in rechallenged adult rats prenatally exposed to lindane

Proteomic analysis was carried out in substantia nigra (SNi) and hippocampus (Hi) isolated from rat offspring born to mothers exposed to lindane (orally; 0.25 mg/kg) from gestation day 5 (GD5) to GD 21 and subsequently rechallenged (orally; 2.5 mg/kg X 21 days) at adulthood (12 weeks). 2D gel electrophoresis revealed no significant differences in the expression of proteins in brain regions isolated from prenatally exposed offspring at adulthood. Significantly greater magnitude of alterations was observed in the expression of proteins related to mitochondrial and energy metabolism, ubiquitin-proteasome pathway, structural and axonal growth leading to increased oxidative stress in Hi and SNi isolated from rechallenged offspring when compared to control offspring treated postnatally with lindane. Western blotting and DNA laddering showed a greater magnitude of increase in apoptosis in the Hi and SNi of rechallenged offspring. Ultrastructural analysis demonstrated disrupted mitochondrial integrity, synaptic disruption and necrotic structures in the brain region of rechallenged offspring. Neurobehavioral studies also demonstrated a greater magnitude of alterations in cognitive and motor functions in rechallenged rats. The data suggest that prenatal exposure of lindane induces persistent molecular changes in the nervous system of offspring which are unmasked leading to neurodegeneration following rechallenge at adulthood.

Porous zeolite imidazole framework-wrapped urchin-like Au-Ag nanocrystals for SERS detection of trace hexachlorocyclohexane pesticides via efficient enrichment

A core-shell configuration of the zeolite imidazole framework (ZIF-8) wrapped urchin-like Au-Ag alloyed nanocrystals (UAANs) were designed and fabricated via adding the pre-formed plasmonic nanoparticles into the ZIF-8 precursor solution with hexadecyltrimethyl ammonium bromide (CTAB). The UAANs are about 100 nm in size with high-density tips. The ZIF-8 shell layer is nanoporous and can be controlled in thickness from 10 nm to 40 nm by the CTAB concentration. Importantly, such ZIF-8 wrapped UAANs can be used as the highly efficient surface enhanced Raman scattering (SERS) substrates for detection of the trace hexachlorocyclohexane (HCH) molecules. The ZIF-8 shell layer with an appropriate thickness (-∼20 nm) can evidently increase the SERS performance of the UAANs to the trace γ-HCH and α-HCH. Such wrapping-enhanced SERS effect significantly increases, by a power function, with the decreasing HCH concentration, especially in the concentration below 10^-6 M, which is attributed to the ever-increasing enrichment effect to the HCH molecules. The detection limit is down below 1.5 ppb. This work presents a highly efficient substrate for the SERS-based detection of the trace HCH, and also displays the potential application in the SERS detection of volatile small molecules.

Organochlorinated pesticides expedite the enzymatic degradation of DNA

Extracellular DNA in the environment may play important roles in genetic diversity and biological evolution. However, the influence of environmental persistent organic contaminants such as organochlorinated pesticides (e.g., hexachlorocyclohexanes [HCHs]) on the enzymatic degradation of extracellular DNA has not been elucidated. In this study, we observed expedited enzymatic degradation of extracellular DNA in the presence of α-HCH, β-HCH and γ-HCH. The HCH-expedited DNA degradation was not due to increased deoxyribonuclease I (DNase I) activity. Our spectroscopic and computational results indicate that HCHs bound to DNA bases (most likely guanine) via Van der Waals forces and halogen bonds. This binding increased the helicity and accumulation of DNA base pairs, leading to a more compact DNA structure that exposed more sites susceptible to DNase I and thus expedited DNA degradation. This study provided insight into the genotoxicity and ecotoxicity of pesticides and improved our understanding of DNA persistence in contaminated environments.

Response of microbial communities to different organochlorine pesticides (OCPs) contamination levels in contaminated soils

Understanding microbial community structure and diversity in contaminated soils helps optimize the bioremediation strategies and performance. This study investigated the roles of environmental variables and contamination levels of organochlorine pesticides (OCPs) in shaping microbial community structure at an abandoned aged insecticide plant site. In total, 28 bacterial phyla were identified across soils with different physiochemical properties and OCPs levels. Proteobacteria, Bacterioidetes and Firmicutes represented the dominant lineages, and accounted for 60.2%-69.2%, 5.6%-9.7% and 6.7%-9.4% of the total population, respectively. The overall microbial diversities, in terms of phylogenetic diversity and phylotype richness, were correlated with the contents of hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs) in soils, as well as other soil properties including total nitrogen, dissolved organic carbon, pH and vegetation. The multivariate regression tree (MRT) analysis revealed that the soil microbial diversity was significantly impacted by vegetation, which explained 31.8% of the total variation, followed by OCPs level (28.3%), total nitrogen (12.4%), dissolved organic carbon (6.3%) and pH (2.4%). Our findings provide new insights and implications into the impacts on soil microbial community by OCPs contamination and other environmental variables, and offer potential strategic bioremediation for the management of OCPs contaminated sites.