Corporate influence on threshold limit values

Investigations into the historical development of specific Threshold Limit Values (TLVs) for many substances have revealed serious shortcomings in the process followed by the American Conference of Governmental Industrial Hygienists. Unpublished corporate communications were important in developing TLVs for 104 substances; for 15 of these, the TLV documentation was based solely on such information. Efforts to obtain written copies of this unpublished material were mostly unsuccessful. Case studies on the TLV Committee's handling of lead and seven carcinogens illustrate various aspects of corporate influence and interaction with the committee. Corporate representatives listed officially as "consultants" since 1970 were given primary responsibility for developing TLVs on proprietary chemicals of the companies that employed them (Dow, DuPont). It is concluded that an ongoing international effort is needed to develop scientifically based guidelines to replace the TLVs in a climate of openness and without manipulation by vested interests.

The vinyl chloride DNA derivative N2,3-ethenoguanine produces G----A transitions in Escherichia coli

Vinyl chloride is a known human and rodent carcinogen that forms several cyclic base derivatives in DNA. The mutagenic potential of these derivatives has been examined in vitro but not in vivo. One of these derivatives, N2,3-ethenoguanine (epsilon G), is known to base pair with both cytosine and thymine during in vitro DNA synthesis, which would result in G----A transitions. To determine the base pairing specificity of this labile guanine derivative in Escherichia coli, we have developed a genetic reversion assay for guanine derivatives. The assay utilizes DNA polymerase-mediated analogue insertion into a bacteriophage vector, M13G*1, which detects all single-base substitutions at position 141 of the lacZ alpha gene by change in plaque color. After the insertion of a single epsilon G opposite the template cytosine at position 141 by use of epsilon dGTP and DNA polymerase and further extension with all four normal dNTPs, the DNA was transfected into E. coli. Transfection of M13G*1 containing epsilon G at the target site yielded 135 mutants among 26,500 plaques, 134 of which represented G----A transitions. The uncorrected mutation frequency was 0.5%, as compared with the control value, approximately 0.02%; when corrected for epsilon G content and penetrance, the calculated mutagenic potential of epsilon G (mutations/analogue) was about 13%. We thus conclude that epsilon G specifically induces G----A transitions during DNA replication in E. coli. The M13G*1 assay may permit the testing of other labile guanine derivatives not otherwise amenable to mutagenesis studies.

Occupational risk factors for multiple myeloma among Danish men

A large population-based case-control study evaluated occupational exposures in 1,098 Danish males diagnosed with multiple myeloma from 1970 to 1984 and in 4,169 age- and gender-matched controls alive at the time of case-diagnosis. Industrial histories were obtained from the Supplementary Pension Fund which, since 1964, has recorded employments of adult Danes; occupation came from subjects' most recent tax records. Four industrial hygienists created a job-exposure matrix for 47 substances based on 15,000 unique industry/occupation combinations in subjects' histories. Risk of myeloma was significantly elevated among road and railroad workers, precision metalworkers, and workers in the transportation and communication industries. Risk increased significantly with duration of employment in: production of synthetic yarns, plastic packaging, and miscellaneous chemical compounds; fabricating structural metal and stationary tanks; body factories; electrical plants; and retail sale of paint and wallpaper. Risks of myeloma were elevated, though statistically nonsignificantly, in all categories of exposure to gasoline and engine exhausts. Risks rose with likelihood and duration of exposure to phthalates, and were statistically significant and nearly fivefold with probable exposure to vinyl chloride for five or more years. After adjusting for multiple exposures and disregarding exposures within 10 years of diagnosis (or selection as a control), probable exposure to vinyl chloride was associated with increased risk of myeloma, which rose to fivefold with longer exposure. Associations with gasoline, engine exhausts, and phthalates persisted, but were inconsistent with duration and probability of exposure. Previously reported associations with agriculture were not confirmed by these data.

Characteristics of cases of angiosarcoma of the liver among vinyl chloride workers in the United States

A total of 13 cases of ASL have been documented to date among VC workers in four different plants in the United States. In this particular industrial population, this number of cases represents at least a 400-fold increase over expected incidence for this extremely rare tumor. The first case occurred in 1961. Average age at diagnosis is 48.2 years. Average length of time between initial VC work and diagnosis has been 20.3 years. A detailed review of 7 cases associated with one plant revealed that clinical features varied from little or no overt illness prior to diagnosis to advanced liver disease with portal hypertension and marked splenomegaly. Portal fibrosis was present in all 7 of these ASL cases as well as in 4 additional cases with non-malignant liver disease among VC workers at the same plant. These findings suggest that exposure to VCM in industrial settings can produce hepatic fibrosis with angiosarcoma as a late manifestation. Conventional liver function tests may not be sensitive indicators of such liver impairment, at least in its early stages.

Bioremediation of typical chlorinated hydrocarbons by microbial reductive dechlorination and its key players: A review

Chlorinated hydrocarbon contamination in soils and groundwater has a severe negative impact on the human health. Microbial reductive dechlorination is a major degradation pathway of chlorinated hydrocarbon in anaerobic subsurface environments, has been extensively studied. Recent progress on the diversity of the reductive dechlorinators and the key enzymes of chlororespiration has been well reviewed. Here, we present a thorough overview of the studies related to bioremediation of chloroethenes and polychlorinated biphenyls based on enhanced in situ reductive dechlorination. The major part of this review is to provide an up-to-date summary of functional microorganisms which are either detected during in situ biostimulation or applied in bioaugmentation strategies. The applied biostimulants and corresponding reductive dechlorination products are also summarized and the future research needs are finally discussed.

Lung cancer mortality of workers employed in chromate pigment factories. A multicentric European epidemiological study

This study was designed in an attempt to quantify the mortality from cancer and other diseases among workers of European factories producing chromate pigments. The prevailing mixed exposures to zinc as well as lead chromate pigment--although the latter was produced predominantly over the whole period of time made it impossible to distinguish those persons exposed to lead chromate pigment. This report deals with cancer of the respiratory tract and lung cancer in particular. The total workforce of each factory included in the study was followed up, more successfully when they were employed before 1960 than after that time owing to the rising number of foreign nationals. Observed deaths from five factories were compared with expected deaths calculated on the basis of mortality figures for the region in which a given factory was located. Further analysis concerned data of relevant cohorts, which comprised only persons observed for a minimum of 10 years (i.e., exposure beginning before 1965), certainty of complete records for the entire staff to assure a complete cohort instead of prevailing healthy survivors, and exclusion of all foreign nationals. As a result, the overall mortality did not deviate from the expected rates. Lung-cancer rates were always in excess of expected numbers, although only in one cohort to a statistically significant extent. The pattern of duration of exposure indicates that the lung-cancer risk does not show a clear dose-response effect with time of employment. Due to the mixed nature of exposure, conclusions must be limited with the effect that the results obtained are consistent with the hypothesis that working in a chrome-processing plant environment is associated with an increased incidence of lung cancer and with a higher probability of dying from lung cancer compared with the general population.

Ethyl vinyl chloride vapocoolant spray fails to decrease pain associated with intravenous cannulation in children

The purpose of the study was to determine the effect of ethyl vinyl chloride vapocoolant spray on pain reported by children undergoing intravenous cannulation. A randomized, double-blinded, placebo-controlled trial was conducted on eligible children between the ages of 9 and 18 years seen in a pediatric emergency department and requiring intravenous cannulation. Informed consent was obtained, and children were randomized to receive ethyl vinyl chloride spray, isopropyl alcohol spray, or no spray (control group). Patient demographics and information pertaining to each intravenous cannulation were recorded. Children indicated the degree of pain associated with intravenous cannulation on a 100-mm visual analog scale (VAS) compared to a baseline pain score of "zero." Statistical analysis was performed by using Stata version 7. One hundred twenty-seven subjects were enrolled: 37 received ethyl vinyl chloride vapocoolant spray, 48 received isopropyl alcohol spray (placebo), and 42 received no pretreatment. Mean VAS scores for pain experienced during cannulation were 34, 33, and 31 mL for each group, respectively. Ethyl vinyl chloride vapocoolant spray failed to measurably reduce pain associated with intravenous cannulation when compared to those pretreated with isopropyl alcohol spray or receiving no intervention.

Transformation yields of chlorinated ethenes by a methanotrophic mixed culture expressing particulate methane monooxygenase

Transformation yields for the aerobic cometabolic degradation of five chlorinated ethenes were determined by using a methanotrophic mixed culture expressing particulate methane monooxygenase (pMMO). Transformation yields (expressed as moles of chlorinated ethene degraded per mole of methane consumed) were 0.57, 0.25, 0.058, 0.0019, and 0.00022 for trans-1,2-dichloroethylene (t-DCE), vinyl chloride (VC), cis-1,2-dichloroethylene (c-DCE), trichloroethylene (TCE), and 1,1-dichloroethylene (1,1-DCE), respectively. Degradation of t-DCE and VC was observed only in the presence of formate or methane, sources of reducing energy necessary for cometabolism. The t-DCE and VC transformation yields represented 35 and 15%, respectively, of the theoretical maximum yields, based on reducing-energy availability from methane dissimilation to carbon dioxide, exclusive of all other processes that require reducing energy. The yields for t-DCE and VC were 20 times greater than the yields reported by others for cells expressing soluble methane monooxygenase (sMMO). Transformation yields for c-DCE, TCE, and 1,1-DCE were similar to or less than those for cultures expressing sMMO. Although methanotrophic biotreatment systems have typically been designed to incorporate cultures expressing sMMO, these results suggest that pMMO expression may be highly advantageous for degradation of t-DCE or VC. It may also be much easier to maintain pMMO expression in treatment systems, because pMMO is expressed by all methanotrophs whereas sMMO is expressed only by type II methanotrophs under copper-limited conditions.

Porphyrinurias and occupational disease

Pathologic porphyrinuria in man is based on a complex etiology and pathogenesis. In hepatic porphyrias, coproporphyrinuria is usually only one of the pathognomostic porphyrin parameters in the urine. Secondary coproporphyrinuria means that an increased excretion of coproporphyrin occurs as the biochemically dominant symptom of a disturbance in porphyrin and heme metabolism during an intoxication, individual condition, or basic disease. Certain foreign and environmental chemicals, such as hexachlorobenzene, polyhalogenated aromatic hydrocarbons, vinyl chloride, and dioxin, alter the heme pathway functionally. Increased porphyrinuria can follow as a toxic response that is differentiated into secondary coproporphyrinuria and chronic hepatic porphyria. This is characterized by a simultaneous increase in hepatic and urinary uroporphyrin and heptacarboxylic porphyrins, owing to inhibition of hepatic uroporphyrinogen decarboxylase. Most of the coproporphyrinurias observed in man are caused by alcohol ingestion. Dioxin, vinyl chloride, and polyhalogenated biphenyls induce an incipient subclinical stage of chronic hepatic porphyria in persons with normal red cell uroporphyrinogen decarboxylase. In contrast, exposure to dioxin on the part of persons with inherited uroporphyrinogen decarboxylase deficiency can cause latent chronic hepatic porphyria to develop into PCT. Coproporphyrinuria and latent chronic hepatic porphyria do not produce clinical symptoms. Secondary porphyrinuria with transition to chronic hepatic porphyria is a metabolic response following various toxic and pathologic conditions; it serves as a sensitive index for chemical exposure and occupational disease.

Normalized Quantitative PCR Measurements as Predictors for Ethene Formation at Sites Impacted with Chlorinated Ethenes

Quantitative PCR (qPCR) targeting Dehalococcoides mccartyi ( Dhc) biomarker genes supports effective management at sites impacted with chlorinated ethenes. To establish correlations between Dhc biomarker gene abundances and ethene formation (i.e., detoxification), 859 groundwater samples representing 62 sites undergoing monitored natural attenuation or enhanced remediation were analyzed. Dhc 16S rRNA genes and the vinyl chloride (VC) reductive dehalogenase genes bvcA and vcrA were detected in 88% and 61% of samples, respectively, from wells with ethene. Dhc 16S rRNA, bvcA, vcrA, and tceA (implicated in cometabolic reductive VC dechlorination) gene abundances all positively correlated with ethene formation. Significantly greater ethene concentrations were observed when Dhc 16S rRNA gene and VC RDase gene abundances exceeded 10⁷ and 10⁶ copies L^-1, respectively, and when Dhc 16S rRNA- and bvcA + vcrA-to-total bacterial 16S rRNA gene ratios exceeded 0.1%. Dhc 16S rRNA gene-to- vcrA/ bvcA ratios near unity also indicated elevated ethene; however, no increased ethene was observed in 19 wells where vcrA and/or bvcA gene copy numbers exceeded Dhc cell numbers 10- to 10 000-fold. Approximately one-third of samples with detectable ethene lacked bvcA, vcrA, and tceA, suggesting that comprehensive understanding of VC detoxification biomarkers has not been achieved. Although the current biomarker suite is incomplete, the data analysis corroborates the value of the available Dhc DNA biomarkers for prognostic and diagnostic groundwater monitoring at sites impacted with chlorinated ethenes.

Respiratory Vinyl Chloride Reductive Dechlorination to Ethene in TceA-Expressing Dehalococcoides mccartyi

Bioremediation of chlorinated ethenes in anoxic aquifers hinges on organohalide-respiring Dehalococcoidia expressing vinyl chloride (VC) reductive dehalogenase (RDase). The tceA gene encoding the trichloroethene-dechlorinating RDase TceA is frequently detected in contaminated groundwater but not recognized as a biomarker for VC detoxification. We demonstrate that tceA-carrying Dehalococcoides mccartyi (Dhc) strains FL2 and 195 grow with VC as an electron acceptor when sufficient vitamin B₁₂ (B₁₂) is provided. Strain FL2 cultures that received 50 μg L^-1 B₁₂ completely dechlorinated VC to ethene at rates of 14.80 ± 1.30 μM day^-1 and attained 1.64 ± 0.11 × 10⁸ cells per μmol of VC consumed. Strain 195 attained similar growth yields of 1.80 ± 1.00 × 10⁸ cells per μmol of VC consumed, and both strains could be consecutively transferred with VC as the electron acceptor. Proteomic analysis demonstrated TceA expression in VC-grown strain FL2 cultures. Resequencing of the strain FL2 and strain 195 tceA genes identified non-synonymous substitutions, although their consequences for TceA function are currently unknown. The finding that Dhc strains expressing TceA respire VC can explain ethene formation at chlorinated solvent sites, where quantitative polymerase chain reaction analysis indicates that tceA dominates the RDase gene pool.

The computed tomographic appearances of angiosarcoma of the liver

The computed tomographic (CT) appearances are described in five vinyl chloride workers with hepatic angiosarcoma subsequently confirmed at post-mortem. The tumour was multifocal in four patients. Non-enhanced scans were available in four cases showing hypodense masses relative to background liver. Dynamic scanning during intravenous contrast injection was performed in all five patients showing peripheral or central foci of enhancement within the tumour. On delayed post-contrast scans performed in three patients the angiosarcoma became wholly or partly isodense compared to normal liver. The CT appearances of angiosarcoma of the liver are non-specific but are consistent with a vascular tumour, and the differential diagnosis is discussed. Due to the vascularity of angiosarcoma, liver biopsy may be hazardous and can be avoided when there is a history of exposure to vinyl chloride monomer and the CT findings are consistent with the diagnosis.

Mechanistic Dichotomy in Bacterial Trichloroethene Dechlorination Revealed by Carbon and Chlorine Isotope Effects

Tetrachloroethene (PCE) and trichloroethene (TCE) are significant groundwater contaminants. Microbial reductive dehalogenation at contaminated sites can produce nontoxic ethene but often stops at toxic cis-1,2-dichloroethene ( cis-DCE) or vinyl chloride (VC). The magnitude of carbon relative to chlorine isotope effects (as expressed by Λ_C/Cl, the slope of δ¹³C versus δ³⁷Cl regressions) was recently recognized to reveal different reduction mechanisms with vitamin B₁₂ as a model reactant for reductive dehalogenase activity. Large Λ_C/Cl values for cis-DCE reflected cob(I)alamin addition followed by protonation, whereas smaller Λ_C/Cl values for PCE evidenced cob(I)alamin addition followed by Cl^- elimination. This study addressed dehalogenation in actual microorganisms and observed identical large Λ_C/Cl values for cis-DCE (Λ_C/Cl = 10.0 to 17.8) that contrasted with identical smaller Λ_C/Cl for TCE and PCE (Λ_C/Cl = 2.3 to 3.8). For TCE, the trend of small Λ_C/Cl could even be reversed when mixed cultures were precultivated on VC or DCEs and subsequently confronted with TCE (Λ_C/Cl = 9.0 to 18.2). This observation provides explicit evidence that substrate adaptation must have selected for reductive dehalogenases with different mechanistic motifs. The patterns of Λ_C/Cl are consistent with practically all studies published to date, while the difference in reaction mechanisms offers a potential answer to the long-standing question of why bioremediation frequently stalls at cis-DCE.

The astrocyte inhibition of peripheral nerve regeneration is reversed by Schwann cells

Schwann cell transplantation into the lesioned or demyelinated central nervous system (CNS) is being extensively explored as an approach to favorably influencing repair in the CNS. Under a variety of circumstances, however, the CNS glial microenvironment appears to offer an unfavorable terrain for the promotion of neurite elongation and for Schwann cell differentiation. Due to the heterogeneity of the cellular contents at injury sites, the specific role of each cell type present in limiting Schwann cell function is unclear. The damaged peripheral nervous system, a system capable of substantial regeneration (and free of the potentially negative influence of oligodendrocytes), represents a valuable model in which to specifically evaluate the influence of astrocytes on Schwann cell function. In the present study, purified cortical astrocyte populations were seeded into semipermeable guidance channels alone or in combination with adult Schwann cell populations to determine their effects on regeneration across an 8-mm gap in the transected sciatic nerve of the adult rat. Channels were prepared with (or without) a defined cellular content, implanted in inbred Lewis rats and evaluated after 3 weeks. Channels seeded with astrocytes alone impeded regeneration, regardless of the maturity of the astrocytes (7-8 days vs 28 days in culture) and their seeding density (40 vs 80 x 10(6) cells/ml). On the other hand, Schwann cells derived from adult sciatic nerve seeded at similar densities enhanced the regenerative process. Regenerative capacity was diminished when astrocytes were combined with Schwann cells; the rate of regeneration increased as the number of Schwann cells in the astrocyte/Schwann cell mixture increased. Immunostaining of the nerve stumps related to astrocyte-seeded channels and of the regenerated tissue in the astrocyte-Schwann cell-seeded channels indicated that astrocytes had migrated into the proximal nerve stump; only a few astrocytes remained within the regenerated cable. The present experiments show that although astrocytes alone inhibit nerve regeneration, Schwann cells are able to partially overcome this inhibition if they are provided in sufficient numbers. We believe these observations will be valuable in considering clinical strategies to use autologous Schwann cell transplantation to influence CNS regeneration.

Can aged microplastics be transport vectors for organic micropollutants? - Sorption and phytotoxicity tests

Microplastics have been investigated over the last decade as potential transport vectors for other pollutants. However, the specific role of plastic aging, in which plastics change their characteristics over time when exposed to environmental agents, has been overlooked. Therefore, sorption experiments were herein conducted using virgin and aged (by ozone treatment or rooftop weathering) microplastic particles of LDPE - low-density polyethylene, PET - poly(ethylene terephthalate), or uPVC - unplasticized poly(vinyl chloride). The organic micropollutants (OMPs) selected as sorbates comprise a diversified group of priority substances and contaminants of emerging concern, including pharmaceutical substances (florfenicol, trimethoprim, diclofenac, tramadol, citalopram, venlafaxine) and pesticides (alachlor, clofibric acid, diuron, pentachlorophenol), analyzed at trace concentrations (each ≤100 μg L^-1). Sorption kinetics and equilibrium isotherms were obtained, as well as the confirmation that the aging degree of microplastics plays a major role in their sorption capacities. The results show an increased sorption of several OMPs on aged microplastics when compared to pristine samples, i.e. the sorption capacity increasing from one or two sorbed substances (maximum 3 μg g^-1 per sorbate) up to nine after aging (maximum 10 μg g^-1 per sorbate). The extent of sorption depends on the OMP, polymer and the effectiveness of the aging treatment. The modifications (e.g. in the chemical structure) between virgin and aged microplastics were linked to the increased sorption capacity of certain OMPs, allowing to better understand the different affinities observed. Additionally, phytotoxicity tests were performed to evaluate the mobility of the OMPs sorbed on the microplastics and the potential effects (on germination and early growth) of the combo on two species of plants (Lepidium sativum and Sinapis alba). These tests suggest low or no phytotoxicity effect under the conditions tested but indicate a need for further research on the behavior of microplastics on soil-plant systems.

Relationships between the Abundance and Expression of Functional Genes from Vinyl Chloride (VC)-Degrading Bacteria and Geochemical Parameters at VC-Contaminated Sites

Bioremediation of vinyl chloride (VC) contamination in groundwater could be mediated by three major bacterial guilds: anaerobic VC-dechlorinators, methanotrophs, and ethene-oxidizing bacteria (etheneotrophs) via metabolic or cometabolic pathways. We collected 95 groundwater samples across 6 chlorinated ethene-contaminated sites and searched for relationships among VC biodegradation gene abundance and expression and site geochemical parameters (e.g., VC concentrations). Functional genes from the three major VC-degrading bacterial guilds were present in 99% and expressed in 59% of the samples. Etheneotroph and methanotroph functional gene abundances ranged from 10² to 10⁹ genes per liter of groundwater among the samples with VC reductive dehalogenase gene (bvcA and vcrA) abundances reaching 10⁸ genes per liter of groundwater. Etheneotroph functional genes (etnC and etnE) and VC reductive dehalogenase genes (bvcA and vcrA) were strongly related to VC concentrations (p < 0.001). Methanotroph functional genes (mmoX and pmoA) were not related to VC concentration (p > 0.05). Samples from sites with bulk VC attenuation rates >0.08 year^-1 contained higher levels of etheneotroph and anaerobic VC-dechlorinator functional genes and transcripts than those with bulk VC attenuation rates <0.004 year^-1. We conclude that both etheneotrophs and anaerobic VC-dechlorinators have the potential to simultaneously contribute to VC biodegradation at these sites.

Sustained Dechlorination of Vinyl Chloride to Ethene in Dehalococcoides-Enriched Cultures Grown without Addition of Exogenous Vitamins and at Low pH

Trichloroethene (TCE) bioremediation has been demonstrated at field sites using microbial cultures harboring TCE-respiring Dehalococcoides whose growth is cobalamin (vitamin B₁₂)-dependent. Bioaugmentation cultures grown ex situ with ample exogenous vitamins and at neutral pH may become vitamin-limited or inhibited by acidic pH once injected into field sites, resulting in incomplete TCE dechlorination and accumulation of vinyl chloride (VC). Here, we report growth of the Dehalococcoides-containing bioaugmentation culture KB-1 in a TCE-amended mineral medium devoid of vitamins and in a VC-amended mineral medium at low pH (6.0 and 5.5). In these cultures, Acetobacterium, which can synthesize 5,6-dimethylbenzimidazole (DMB), the lower ligand of cobalamin, and Sporomusa are dominant acetogens. At neutral pH, Acetobacterium supports complete TCE dechlorination by Dehalococcoides at millimolar levels with a substantial increase in cobalamin (∼20-fold). Sustained dechlorination of VC to ethene was achieved at pH as low as 5.5. Below pH 5.0, dechlorination was not stimulated by DMB supplementation but was restored by raising pH to neutral. Cell-extract assays revealed that vinyl chloride reductase activity declines significantly below pH 6.0 and is undetectable below pH 5.0. This study highlights the importance of cobamide-producing populations and pH in microbial dechlorinating communities for successful bioremediation at field sites.

Dehalococcoides mccartyi Strain GEO12 Has a Natural Tolerance to Chloroform Inhibition

Cocontamination by chloroform and chloroethenes often confounds bioremediation efforts. Here, we describe Dehalococcoides mccartyi strain GEO12 that dechlorinates trichloroethene to ethene in 14 μM (1.6 mg·L^-1) chloroform. The same chloroform concentration effectively inhibited dechlorination in Dehalococcoides strains ANAS2, 11a, and BAV1. Successive transfers of strain GEO12 in increasing concentrations of chloroform led to culture GEO12CF that tolerated 83 μM (10 mg·L^-1) chloroform. The genome of strain GEO12 revealed seven reductive dehalogenase homologous (rdh) genes, including tceA and vcrA. Transcriptional analyses showed that chloroform (45 μM; 5.3 mg·L^-1) in culture GEO12CF enhanced the transcription of tceA to a statistically significant degree (the median increase was 55.4 transcripts per 10⁴ 16S rRNA, CI_95% = [12.9, 125]). The increase of vcrA transcripts in the presence of chloroform (45 μM; 5.3 mg·L^-1) in culture GEO12CF was not statistically significant because the CI_95% range spanned 0 (the median increase was 109 transcripts per 10⁴ 16S rRNA, CI_95% = [-13.6, 246]). Inhibition of dehalogenation by chloroform is often seen in Dehalococcoides, but the mechanism remains unknown. Our results suggest that culture GEO12CF may overcome chloroform inhibition by rdh upregulation. The chloroform-adapted culture GEO12CF provides insights into the metabolic flexibility of Dehalococcoides and could be used to fight chloroethene contamination where chloroform is a cocontaminant.

Mutagenicity of waste products from vinyl chloride industries

The by-product from vinyl chloride production, EDC-tar, is a complex mixture of mainly short-chained chlorinated aliphatic hydrocarbons. This mixture has been tested for mutagenicity by means of Ames' Salmonella/mammalian microsome method. Since most of the components in the tar are poorly soluble in water, three agents were used as solvents or emulsifier: ethanol, DMSO, and Tween 80. The results with all these agents showed that EDC-tar contains direct as well as indirect mutagenic constitutents. It could be concluded that the mutagenic effect observed in the test could not be due to any significant extent to one of the main components, ethylene dichloride (1,2-dichloroethane). This substance showed a weak mutagenic effect, but only at higher concentrations than could be available in the highest concentration tested of the tar. Although the microsomal system enhanced the mutagenicity both of the EDC-tar and of 1,2-dichloroethane, this enhancement was dependent on NADPH in the case of EDC-tar but independent of NADPH with 1,2-dichloroethane. The Salmonella/mammalian microsome method seems to be a suitable tool for both mutagenicity screening of complex chemical mixtures and identification of mutagenic constituents in such mixtures.

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 XR_DCA and XR_TCA derived from river sediment dihaloeliminated 1,2-DCA to ethene and 1,1,2-TCA to vinyl chloride (VC), respectively. The XR_TCA culture subsequently converted VC to ethene via hydrogenolysis. Microbial community profiling demonstrated the enrichment of Geobacter 16S rRNA gene sequences in both the XR_DCA and XR_TCA cultures, and Dehalococcoides mccartyi (Dhc) sequences were only detected in the ethene-producing XR_TCA 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.