Spatio-temporal distribution of organochlorine pesticides in agricultural soils of southeast China during 2014-2019.

Organochlorine pesticides (OCPs) are organic pollutants that are persistent and undegradable in the environment. To investigate their residual concentrations, spatial and temporal distributions, and the relationship with the crops planted, 12 individual OCPs in 687 soil samples from Jiangsu, Zhejiang and Jiangxi provinces of southeast China were examined. The detection frequencies of OCPs in the studied areas were 1.89%-64.9%. The concentrations of dichloro-diphenyl-trichloroethanes (DDTs), hexachlorocyclohexanes (HCHs), and endosulfans ranged from 0.01 to 5659 µg/kg, 0.03-3.58 µg/kg, and 0.05-3235 µg/kg, respectively. Jiangsu was mainly contaminated by p,p'-DDT, p,p'-DDD and endosulfan sulfate, Zhejiang was more polluted by OCPs except δ-HCH, and Jiangxi was more vulnerable to the contamination of OCPs except o,p'-DDE. The partial least-squares discrimination analysis (PLS-DA) model with RX2 36.3-36.8% revealed that compounds with similar chemical properties tended to appear in the same year and month. All crop lands were polluted by DDTs and Endosulfans. The highest concentrations of DDTs and Endosulfans were found in citrus and vegetable fields, respectively. This study offers new insight into the layout and partitioning of OCPs in agricultural land and into insecticide management on public health and ecological safety.

Age at menarche and chemical exposure: per- and polyfluoroalkyl substances (PFAS), dichloro-diphenyl-trichloroethane (DDT), dichloro-diphenyl-dichloroethylene (DDE), and polychlorinated biphenyls (PCBs).

CONTEXT: Humans are now exposed to a multitude of chemicals throughout the life course, some of which may affect growth and development owing to their endocrine-like activity. OBJECTIVE: To assess the relationship of suspect toxicants to maturation, specifically to age at menarche. METHODS: We conducted two systematic reviews of age at menarche and PFOA, PFOS, PCBs and DDE/DDT based on publications indexed by pubmed. RESULTS: 16 unique reports were identified. Most studies of PFOA and PFOS reported either no association or delays in the age at menarche; only one reported an earlier age. Studies of DDT and DDE were more mixed. Reports on PCBs varied by PCB congener group with an equal number of them reporting delays and no association but one an acceleration. Sources of variation in results include the timing of exposure assessment (prenatal vs. postnatal), level of the toxicant, and sample size. No obvious pattern to the variation in results could be tied to those sources of variation. CONCLUSION: The absence of consistent evidence from multiple reports of earlier age at menarche suggests that these toxicants may not be responsible for accelerated sexual maturation in girls. However, human populations naturally vary in the variety and levels of exposure, making the comparison of studies difficult. Further, studies vary in methodology, complicating aggregation of results and generalisations.

Geobacter sp. Strain IAE Dihaloeliminates 1,1,2-Trichloroethane and 1,2-Dichloroethane.

Chlorinated ethanes, including 1,2-dichloroethane (1,2-DCA) and 1,1,2-trichloroethane (1,1,2-TCA), are widespread groundwater contaminants. Enrichment cultures XRDCA and XRTCA derived from river sediment dihaloeliminated 1,2-DCA to ethene and 1,1,2-TCA to vinyl chloride (VC), respectively. The XRTCA culture subsequently converted VC to ethene via hydrogenolysis. Microbial community profiling demonstrated the enrichment of Geobacter 16S rRNA gene sequences in both the XRDCA and XRTCA cultures, and Dehalococcoides mccartyi (Dhc) sequences were only detected in the ethene-producing XRTCA culture. The presence of a novel Geobacter population, designated as Geobacter sp. strain IAE, was identified by the 16S rRNA gene-targeted polymerase chain reaction and Sanger sequencing. Time-resolved population dynamics attributed the dihaloelimination activity to strain IAE, which attained the growth yields of 0.93 ± 0.06 × 107 and 1.18 ± 0.14 × 107 cells per µmol Cl- released with 1,2-DCA and 1,1,2-TCA as electron acceptors, respectively. In contrast, Dhc growth only occurred during VC-to-ethene hydrogenolysis. Our findings discover a Geobacter sp. strain capable of respiring multiple chlorinated ethanes and demonstrate the involvement of a broader diversity of organohalide-respiring bacteria in the detoxification of 1,2-DCA and 1,1,2-TCA.

Impact of Environmental Risk Factors on Mitochondrial Dysfunction, Neuroinflammation, Protein Misfolding, and Oxidative Stress in the Etiopathogenesis of Parkinson's Disease.

As a prevalent progressive neurodegenerative disorder, Parkinson's disease (PD) is characterized by the neuropathological hallmark of the loss of nigrostriatal dopaminergic (DAergic) innervation and the appearance of Lewy bodies with aggregated α-synuclein. Although several familial forms of PD have been reported to be associated with several gene variants, most cases in nature are sporadic, triggered by a complex interplay of genetic and environmental risk factors. Numerous epidemiological studies during the past two decades have shown positive associations between PD and several environmental factors, including exposure to neurotoxic pesticides/herbicides and heavy metals as well as traumatic brain injury. Other environmental factors that have been implicated as potential risk factors for PD include industrial chemicals, wood pulp mills, farming, well-water consumption, and rural residence. In this review, we summarize the environmental toxicology of PD with the focus on the elaboration of chemical toxicity and the underlying pathogenic mechanisms associated with exposure to several neurotoxic chemicals, specifically 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), rotenone, paraquat (PQ), dichloro-diphenyl-trichloroethane (DDT), dieldrin, manganese (Mn), and vanadium (V). Our overview of the current findings from cellular, animal, and human studies of PD provides information for possible intervention strategies aimed at halting the initiation and exacerbation of environmentally linked PD.

Long-Term Continuous Co-reduction of 1,1,1-Trichloroethane and Trichloroethene over Palladium Nanoparticles Spontaneously Deposited on H2-Transfer Membranes.

1,1,1-Trichloroethane (1,1,1-TCA) and trichloroethene (TCE) are common recalcitrant contaminants that coexist in groundwater. H2-induced reduction over precious-metal catalysts has proven advantageous, but its application to long-term continuous treatment has been limited due to poor H2-transfer efficiency and catalyst loss. Furthermore, catalytic reductions of aqueous 1,1,1-TCA alone or concomitant with TCE catalytic co-reductions are unstudied. Here, we investigated 1,1,1-TCA and TCE co-reduction using palladium nanoparticle (PdNP) catalysts spontaneously deposited on H2-transfer membranes that allow efficient H2 supply on demand in a bubble-free form. The catalytic activities for 1,1,1-TCA and TCE reductions reached 9.9 and 11 L/g-Pd/min, values significantly greater than that reported for other immobilized-PdNP systems. During 90 day continuous operation, removals were up to 95% for 1,1,1-TCA and 99% for TCE. The highest steady-state removal fluxes were 1.5 g/m2/day for 1,1,1-TCA and 1.7 g/m2/day for TCE. The major product was nontoxic ethane (94% selectivity). Only 4% of the originally deposited PdNPs were lost over 90 days of continuous operation. Documenting long-term continuous Pd-catalyzed dechlorination at high surface loading with minimal loss of the catalyst mass or activity, this work expands understanding of and provides a foundation for sustainable catalytic removal of co-existing chlorinated solvents.

A Synergistic Platform for Continuous Co-removal of 1,1,1-Trichloroethane, Trichloroethene, and 1,4-Dioxane via Catalytic Dechlorination Followed by Biodegradation.

Groundwater co-contaminated with 1,4-dioxane, 1,1,1-trichloroethane (TCA), and trichloroethene (TCE) is among the most urgent environmental concerns of the U.S. Department of Defense (DoD), U.S. Environmental Protection Agency (EPA), and industries related to chlorinated solvents. Inspired by the pressing need to remove all three contaminants at many sites, we tested a synergistic platform: catalytic reduction of 1,1,1-TCA and TCE to ethane in a H2-based membrane palladium-film reactor (H2-MPfR), followed by aerobic biodegradation of ethane and 1,4-dioxane in an O2-based membrane biofilm reactor (O2-MBfR). During 130 days of continuous operation, 1,1,1-TCA and TCE were 95-98% reductively dechlorinated to ethane in the H2-MPfR, and ethane served as the endogenous primary electron donor for promoting 98.5% aerobic biodegradation of 1,4-dioxane in the O2-MBfR. In addition, the small concentrations of the chlorinated intermediate from the H2-MPfR, dichloroethane (DCA) and monochloroethane (MCA), were fully biodegraded through aerobic biodegradation in the O2-MBfR. The biofilms in the O2-MBfR were enriched in phylotypes closely related to the genera Pseudonocardia known to biodegrade 1,4-dioxane.

Sex differences in the association of measures of sexual maturation to common toxicants: Lead, dichloro-diphenyl-trichloroethane (DDT), dichloro-diphenyl-dichloroethylene (DDE), and polychlorinated biphenyls (PCBs).

Many studies of human toxicant exposure examine the hypothesis that human sexual maturation can be affected through endocrine disruption. Within this body of literature there is significant variation in the findings. Variation may be related to the differential effects by toxicants between males and females as well as variation in sample size, toxicant levels, and the timing of exposure. We review sexual maturation outcomes between males and females when exposed to lead, dichlorodiphenyldichloroethylene (DDE), dichloro-diphenyl-trichloroethane (DDT), and polychlorinated biphenyls (PCBs) using a systematic process to gather peer-reviewed studies published from January 1994 through December 2019 on the NCBI website's PubMed search engine. The review includes 34 studies, some comprised of multiple analyses, to compare effects on sexual maturation by sex. The analysis shows that both boys and girls have delayed sexual maturation in relation to lead exposure. There are differences in the direction of effects associated with DDE/DDT and PCB exposure in boys and girls. PCBs exist as congeners of many structural forms, and that variation is considered in this review. Dioxin-like and non-dioxin-like PCBs exposure directionality differed between boys and girls as well. Future investigations into the basis of sex variation in DDE/DDT and PCB relationships to sexual maturation are warranted.

Polyacrylic acid-b-polyptyrene covered Ni/Fe nanoparticles to remove 1,1,1-trichloroethane in water.

A new material, polyacrylic acid-b-polyptyrene (PAA-b-PS) covered Ni/Fe nanoparticles (PAA-b-PS-nZVI-Ni), was developed and evaluated for the selective dechlorination of 1,1,1-trichloroethane (1,1,1-TCA) in the presence of potential interferents. The average size of the PAA-b-PS coated Fe/Ni bimetallic nanoparticles was approximately 50 nm, which resulted from agglomeration prevention by PAA-b-PS. The removal efficiency of 1,1,1-TCA by an optimal dose with a 1.0 g/L Fe/Ni (Ni/Fe = 2 wt%) and 0.5 g/L PAA-b-PS-coated concentration was higher (87.5%) than that of bare Fe/Ni (60%). The pseudo-first-order rate constant (Kobs) of 1,1,1-TCA removal by PAA-b-PS-nZVI-Ni was 0.0142 min-1 within 240 min. Comparatively, the Kobs values of 1,1,1-TCA removal by other materials (Fe, pure bimetallic Fe/Ni, PAA-b-PS-Fe) were only 0.003, 0.0052 and 0.0103 min-1, respectively. The 1,1,1-TCA removal efficacy by PAA-b-PS-nZVI-Ni showed no obvious gap regardless of pH or various common inorganic anions (NO3-, HCO3- and SO42-) at different concentrations. However, humic acid (HA) had great influence on the degradation of 1,1,1-TCA. In conclusion, PAA-b-PS-covered Ni/Fe nanoparticles with its selectivity high effectiveness could be used as one remedial agent for the degradation of 1,1,1-TCA in water.

Mosquitocidal activity of p,p'-difluoro-diphenyl-trichloroethane (DFDT).

New insecticides are urgently needed for the control of arthropod vectors of public health diseases. As resistance to many insecticides used for the control of public health pests is ubiquitous, all available chemistries should be evaluated for their potential to effectively control both insecticide-susceptible and insecticide-resistant strains of mosquitoes. This study aimed to evaluate p-p'-difluoro-diphenyl-trichloroethane (DFDT) as a mosquito control technology and relate its activity to that of DDT. We found that topical DFDT was significantly less toxic than DDT to both pyrethroid-susceptible and pyrethroid-resistant strains of Anopheles gambiae and Aedes aegypti. Direct nervous system recording from Drosophila melanogaster CNS demonstrated that DFDT is approximately 10-times less potent than DDT at blocking nerve firing, which may explain its relatively lower toxicity. DFDT was shown to be at least 4500 times more vapor-active than DDT, with an LC50 in a vapor toxicity screening assay of 2.2 µg/cm2. Resistance to DFDT was assessed in two mosquito strains that possess target-site mutations in the voltage-gated sodium channel and upregulated metabolic activity. Resistance ratios for Akdr (An. gambiae) and Puerto Rico (Ae. aegypti) strains were 9.2 and 12.2, respectively. Overall, this study demonstrates that DFDT is unlikely to be a viable public health vector control insecticide.

Employment characteristics and cause-specific mortality at automotive electronics manufacturing plants in Huntsville, Alabama.

BACKGROUND: This study was carried out in response to worker concerns over their exposure to lead solder and chlorinated solvents at automotive electronics manufacturing plants in Huntsville, Alabama. METHODS: A study of 4396 United Autoworkers members ever-employed at the plants between 1972 and 1993 was conducted with mortality follow-up through 2016. Poisson regression was used to estimate mortality rate ratios (RR) according to employment characteristics, including calendar period of employment. RESULTS: Pre-1977 hires exhibited elevated adjusted rates of all-cause (RR, 1.29; 95% confidence interval [CI], 1.09-1.52), cardiovascular (RR, 1.38; 95% CI, 1.03-1.86), and digestive system (RR, 2.31; 95% CI, 1.04-5.10) disease mortality relative to the most recent hire group (1984-1993). Never- versus ever-employment in a skilled trade job was associated with elevated adjusted rates of all-cause, all-cancer, and cardiovascular disease mortality. Nervous system disorder mortality was greatest among 1977-1983 hires. CONCLUSIONS: Elevated mortality among pre-1977 hires is consistent with worker concerns over greater exposure to hazards at the original plant building.

Natural attenuation mechanism and health risk assessment of 1,1,2-trichloroethane in contaminated groundwater.

1,1,2-trichloroethane (TCA) is a contaminant in many pesticide and chemical fields. This study mainly described the potential effectiveness of the natural attenuation of 1,1,2-TCA in groundwater in a typical pesticide-contaminated field in east China. In this study, six typical 1,1,2-TCA-contaminated sites (MW14, MW21, MW25, MW31, MW36 and MW41) were selected, and the field investigation results indicated that there was an obvious decline in the concentrations of 1,1,2-TCA over time in all selected sites. Furthermore, the attenuation rate of 1,1,2-TCA concentration in sites MW14, MW21, MW25, MW31 and MW41 followed the first-order kinetic equation, and the first-order attenuation rate constants were calculated. The health risks of 1,1,2-TCA and its degradation product dichloroethane (DCA) were assessed and compared in site MW14. The result showed that the health risks of 1,1,2-TCA were much higher than those of DCA, and 1,1,2-TCA was the contamination source in this site. 16S rRNA sequencing was also conducted to investigate the diversity of the bacterial community in 1,1,2-trichloroethane (TCA)-contaminated groundwater, and Geobacter, Thauera, Pseudomonas, Diaphorobacter were the main species in the bacterial community.

Effect of dose and exposure protocol on the toxicokinetics and first-pass elimination of trichloroethylene and 1,1,1-trichloroethane.

Trichloroethylene (TCE) and 1,1,1-trichloroethane (TRI) are frequent contaminants of drinking water and of groundwater at hazardous waste sites. There is relatively little information on the target organ deposition of TRI, despite its ingestion and common occurrence in humans. An important aim of the study was to delineate and contrast the toxicokinetics (TK) and bioavailability (F) of TRI and its well metabolized congener, TCE. Blood profiles were obtained from male Sprague-Dawley rats given aqueous emulsions of 6 or 48 mg TRI/kg and 10 or 50 mg TCE/kg as an oral bolus (po) or by gastric infusion (gi) over 2 h. TCE exhibited nonlinear TK, with a disproportionate increase in AUC and decrease in clearance and F with increase in dose. TRI exhibited linear TK. F did not vary significantly with TRI dose or dosage regimen. F values were substantially higher for TRI than for the respective TCE groups. TRI was distributed widely to tissues of rats gavaged with 6 mg TRI/kg, with accumulation in fat. This experiment yielded tissue uptake and elimination profiles and in vivo tissue:blood partition coefficients (PCs). Finally, additional rats were given 10 mg/kg of TCE and TRI po, ia and iv, so that first-pass hepatic (FPh) and pulmonary (FPp) elimination could be measured directly. Total and FPh elimination of TCE exceeded that of TRI. TRI, with its higher air:blood PC, exhibited the higher FPp. TCE and TRI, despite several common physical and chemical properties resulting in similar absorption and systemic distribution, displayed dissimilar dosage and dose rate effects on their TK.

Human Health Risk from Consumption of Marine Fish Contaminated with DDT and Its Metabolites in Maputo Bay, Mozambique.

Many countries with incidence of malaria, including those surrounding Maputo Bay, use dichloro-diphenyl-trichloroethane (DDT) to reduce mosquitoes. This study is the first to estimate the human health risk associated with consumption of marine fish from Maputo Bay contaminated with DDTs. The median for ∑DDTs was 3.8 ng/g ww (maximum 280.9 ng/g ww). The overall hazard ratio for samples was 1.5 at the 75th percentile concentration and 28.2 at the 95th percentile. These calculations show increased potential cancer risks due to contamination by DDTs, data which will help policy makers perform a risk-benefit analysis of DDT use in malaria control programs in the region.

Occupational solvent exposure and adult chronic lymphocytic leukemia: No risk in a population-based case-control study in four Nordic countries.

The aim of this study was to assess the effect of occupational solvent exposure on the risk of adult chronic lymphocytic leukemia (CLL). The current case-control study was nested in the Nordic Occupational Cancer Study (NOCCA) cohort. 20,615 CLL cases diagnosed in 1961-2005 in Finland, Iceland, Norway, and Sweden, and 103,075 population-based controls matched by year of birth, sex, and country were included. Occupational histories for cases and controls were obtained from census records in 1960, 1970, 1980/1981, and 1990. Exposure to selected solvents was estimated by using the NOCCA job-exposure matrix (NOCCA-JEM). Odds ratios (OR) and 95% confidence intervals (95% CI) were estimated by using conditional logistic regression models. Overall, nonsignificant CLL risk elevations were observed for methylene chloride, perchloroethylene, and 1,1,1-trichloroethane. Compared to unexposed, significantly increased risks were observed for cumulative perchloroethylene exposure ≤13.3 ppm-years (OR = 1.85, 95% CI 1.16-2.96) and average life-time perchloroethylene exposure ≤2.5 ppm (1.61, 95% CI 1.01-2.56) among women, and cumulative methylene chloride exposure ≤12.5 ppm-years (OR = 1.19, 95% CI 1.01-1.41) and 12.5-74.8 ppm-years (OR = 1.23, 95% CI 1.01-1.51) among men in an analysis with 5 years lag-time, though without dose-response pattern. Decreased CLL risk was observed for aliphatic and alicyclic hydrocarbon solvents and toluene. This study did not support associations for solvent exposure and CLL. Observed weak associations for methylene chloride, perchloroethylene, 1,1,1-trichloroethane exposures, aliphatic and alicyclic hydrocarbons and toluene were not consistent across sexes, and showed no gradient with amount of exposure.

Dehalogenimonas formicexedens sp. nov., a chlorinated alkane-respiring bacterium isolated from contaminated groundwater.

A strictly anaerobic, Gram-stain-negative, non-spore-forming bacterium designated NSZ-14T, isolated from contaminated groundwater in Louisiana (USA), was characterized using a polyphasic approach. Strain NSZ-14T reductively dehalogenated a variety of polychlorinated aliphatic alkanes, producing ethene from 1,2-dichloroethane, propene from 1,2-dichloropropane, a mixture of cis- and trans-1,2-dichloroethene from 1,1,2,2-tetrachloroethane, vinyl chloride from 1,1,2-trichloroethane and allyl chloride (3-chloro-1-propene) from 1,2,3-trichloropropane. Formate or hydrogen could both serve as electron donors. Dechlorination occurred between pH 5.5 and 7.5 and over a temperature range of 20-37 °C. Major cellular fatty acids included C18 : 1ω9c, C14 : 0 and C16 : 0. 16S rRNA gene sequence-based phylogenetic analysis indicated that the strain clusters within the class Dehalococcoidia of the phylum Chloroflexi, most closely related to but distinct from type strains of the species Dehalogenimonas alkenigignens (97.63 % similarity) and Dehalogenimonas lykanthroporepellens (95.05 %). A complete genome sequence determined for strain NSZ-14T revealed a DNA G+C content of 53.96 mol%, which was corroborated by HPLC (54.1±0.2 mol% G+C). Genome-wide comparisons based on average nucleotide identity by orthology and estimated DNA-DNA hybridization values combined with phenotypic and chemotaxonomic traits and phylogenetic analysis indicate that strain NSZ-14T represents a novel species within the genus Dehalogenimonas, for which the name Dehalogenimonas formicexedens sp. nov. is proposed. The type strain is NSZ-14T (=HAMBI 3672T=JCM 19277T=VKM B-3058T). An emended description of Dehalogenimonas alkenigignens is also provided.

Combination of zero-valent iron and anaerobic microorganisms immobilized in luffa sponge for degrading 1,1,1-trichloroethane and the relevant microbial community analysis.

1,1,1-Trichloroethane (1,1,1-TCA), a dense non-aqueous phase liquid (DNAPL), is relatively slow to remediate naturally; combination of zero-valent iron and immobilized microorganism is a potential means to accelerate DNAPL biodegradation. We first adopted high density luffa sponge (HDLS) as immobilized microorganism carrier. The experimental results demonstrated that (1) the supernatant liquid microorganisms were the optimal immobilized microorganisms for HDLS and (2) the combination of zero-valent iron and immobilized microorganisms accelerated 1,1,1-TCA transformation. Furthermore, in the long-term remediation process, anaerobic microorganisms produced reductant H2S which was beneficial to zero-valent iron PRBs. Through further study of the microbial community, we found that majority of the sulfate-reducing bacteria (SRB) perfectly adapted to the process of 1,1,1-TCA co-metabolism dechlorination. Desulfobulbus and Desulfococcus potentially were the special SRB that contributed significantly to TCA co-metabolism. Additionally, 1,1,1-TCA induced the generation of new SRB and stimulated the growth of majority of dominating methanogens. The results indicated that they played a constructive role in accelerating the dechlorination of 1,1,1-TCA, reduction of sulfate, and improving the production of CH4. Consequently, combination of zero-valent iron and immobilized microorganisms for remediating groundwater by contaminated 1,1,1-TCA is a sustainable and green remediation technology. Especially for groundwater of SO42- type contaminated by 1,1,1-TCA, in the long-term course of combination degradation, cyclic utilization of H2S to prolong the service life of zero-valent iron PRBs. H2 and CH4 generated to capture as potential energy resource. Based on this, a tentative reaction mechanism for Fe0 biodegradation of 1,1,1-TCA was proposed.

High-density natural luffa sponge as anaerobic microorganisms carrier for degrading 1,1,1-TCA in groundwater.

Anaerobic microorganisms were applied to degrade organic contaminants in groundwater with permeable reactive barriers (PRBs). However, anaerobic microorganisms need to select optimal immobilizing material as carrier. The potential of high-density natural luffa sponge (HDLS) (a new variety of luffa) for the immobilization and protection of anaerobic microorganisms was investigated. The HDLS has a dense structure composed of a complicated interwoven fibrous network. Therefore, the abrasion rate of HDLS (0.0068 g s-1) was the smallest among the four carriers [HDLS, ordinary natural luffa sponge (OLS), polyurethane sponge (PS), and gel carrier AQUAPOROUSGEL (APG)]. The results suggest that it also had the greatest water retention (10.26 H2O-g dry carrier-g-1) and SS retention (0.21 g dry carrier-g-1). In comparison to well-established commercialized gel carrier APG, HDLS was of much better mechanical strength, hydrophilicity and stability. Microbial-immobilized HDLS also had the best performance for the remediation of 1,1,1-TCA simulated groundwater. Analysis of the clone libraries from microorganism-immobilized HDLS showed the HDLS could protect microorganisms from the toxicity of 1,1,1-TCA and maintain the stability of microbial community diversity. The mechanism of HDLS immobilizing and protecting microorganisms was proposed as follows. The HDLS had a micron-scale honeycomb structure (30-40 µm) and an irregular ravine structure (4-20 µm), which facilitate the immobilization of anaerobic microorganisms and protect the anaerobic microorganisms.

Thermally activated persulfate oxidation of NAPL chlorinated organic compounds: effect of soil composition on oxidant demand in different soil-persulfate systems.

This study investigates the interaction of persulfate with soil components and chlorinated volatile organic compounds (CVOCs), using thermally activated persulfate oxidation in three soil types: high sand content; high clay content; and paddy field soil. The effect of soil composition on the available oxidant demand and CVOC removal rate was evaluated. Results suggest that the treatment efficiency of CVOCs in soil can be ranked as follows: cis-1,2-dichloroethene > trichloroethylene > 1,2-dichloroethane > 1,1,1-trichloroethane. The reactions of soil components with persulfate, shown by the reduction in soil phase natural organics and mineral content, occurred in parallel with persulfate oxidation of CVOCs. Natural oxidant demand from the reaction of soil components with persulfate exerted a large relative contribution to the total oxidant demand. The main influencing factor in oxidant demand in paddy-soil-persulfate systems was natural organics, rather than mineral content as seen with sand and clay soil types exposed to the persulfate system. The competition between CVOCs and soil components for oxidation by persulfate indicates that soil composition exhibits a considerable influence on the available oxidant demand and CVOC removal efficiency. Therefore, soil composition of natural organics and mineral content is a critical factor in estimating the oxidation efficiency of in-situ remediation systems.

Isolation and characterization of Dehalobacter sp. strain UNSWDHB capable of chloroform and chlorinated ethane respiration.

Dehalobacter sp. strain UNSWDHB can dechlorinate up to 4 mM trichloromethane at a rate of 0.1 mM per day to dichloromethane and 1,1,2-trichloroethane (1 mM, 0.1 mM per day) with the unprecedented product profile of 1,2-dichloroethane and vinyl chloride. 1,1,1-trichloroethane and 1,1-dichloroethane were slowly utilized by strain UNSWDHB and were not completely removed, with minimum threshold concentrations of 0.12 mM and 0.07 mM respectively under growth conditions. Enzyme kinetic experiments confirmed strong substrate affinity for trichloromethane and 1,1,2-trichloroethane (Km = 30 and 62 µM respectively) and poor substrate affinity for 1,1,1-trichloroethane and 1,1-dichloroethane (Km = 238 and 837 µM respectively). Comparison of enzyme kinetic and growth data with other trichloromethane respiring organisms (Dehalobacter sp. strain CF and Desulfitobacterium sp. strain PR) suggests an adaptation of strain UNSWDHB to trichloromethane. The trichloromethane RDase (TmrA) expressed by strain UNSWDHB was identified by BN-PAGE and functionally characterized. Amino acid comparison of homologous RDases from all three organisms revealed only six significant amino acid substitutions/deletions, which are likely to be crucial for substrate specificity. Furthermore, strain UNSWDHB was shown to grow without exogenous supply of cobalamin confirming genomic-based predictions of a fully functional cobalamin synthetic pathway.