Fumonisin B1 causes multiple lesions in common carp (Cyprinus carpio)

Year-1 carp were fed ratios containing 100mg/kg and 10 mg/kg of added fumonisin B1 for 42 days. The experimental and control fish were examined clinically during the experiment and at the end all fish were necropsied and histological changes recorded. Blood vessels, liver, exocrine and endocrine pancreas, excretory and haematopoietic kidney, heart and brain were sensitive both to 100 and 10mg/kg of FB1 in the diet and the rodlet cell (RC) frequency was considerably increased in and around damaged tissues. Many damaged blood vessels contained stacks of RCs above the endothelium. Other changes subsequent to fumonisin exposure that have not been previously reported include scattered lesions in the exocrine and endocrine pancreas, and interrenal tissue, probably due to ischemia and/or increased endothelial permeability. Presented findings indicate the need for more intensive studies of fumonisin-induced toxicity in cultured fish.

Structural Basis for Catalytic Differences between α Class Human Glutathione Transferases hGSTA1-1 and hGSTA2-2 for Glutathione Conjugation of Environmental Carcinogen Benzo[a]pyrene-7,8-diol-9,10-epoxide

The ultimate diol epoxide carcinogens derived from polycyclic aromatic hydrocarbons, such as benzo[a]pyrene (BP), are metabolized primarily by glutathione (GSH) conjugation reaction catalyzed by GSH transferases (GSTs). In human liver and probably lung, the alpha class GSTs are likely to be responsible for the majority of this reaction because of their high abundance. The catalytic efficiency for GSH conjugation of the carcinogenic (+)-anti-benzo[a]pyrene-7,8-diol-9,10-epoxide [(+)-anti-BPDE] is more than 5-fold higher for hGSTA1-1 than for hGSTA2-2. Here, we demonstrate that mutation of isoleucine-11 of hGSTA2-2, a residue located in the hydrophobic substrate-binding site (H-site) of the enzyme, to alanine (which is present in the same position in hGSTA1-1) results in about a 7-fold increase in catalytic efficiency for (+)-anti-BPDE-GSH conjugation. Thus, a single amino acid substitution is sufficient to convert hGSTA2-2 to a protein that matches hGSTA1-1 in its catalytic efficiency. The increased catalytic efficiency of hGSTA2/I11A is accompanied by greater enantioselectivity for the carcinogenic (+)-anti-BPDE over (-)-anti-BPDE. Further remodeling of the H-site of hGSTA2-2 to resemble that of hGSTA1-1 (S9F, I11A, F110V, and S215A mutations, SIFS mutant) results in an enzyme whose catalytic efficiency is approximately 13.5-fold higher than that of the wild-type hGSTA2-2, and about 2.5-fold higher than that of the wild-type hGSTA1-1. The increased activity upon mutations can be rationalized by the interactions of the amino acid side chains with the substrate and the orientation of the substrate in the active site, as visualized by molecular modeling. Interestingly, the catalytic efficiency of hGSTA2-2 toward (-)-anti-BPDE was increased to a level close to that of hGSTA1-1 upon F110V, not I11A, mutation. Similar to (+)-anti-BPDE, however, the SIFS mutant was the most efficient enzyme for GSH conjugation of (-)-anti-BPDE.

Inter-individual differences in the ability of human milk-fat extracts to enhance the genotoxic potential of the procarcinogen benzo[a]pyrene in MCF-7 breast cells

Environmental factors are believed to play an important role in cancer aetiology. Whether environmental pollutants act in isolation or in combination within mixtures remains unclear. Four human milk-fat extracts (from resident U.K. women) were screened for levels of organochlorinated and brominated compounds prior to being tested (1-50 mg-equiv) for micronucleus (MN)-forming activity in MCF-7 cells. Using the cytokinesis-block micronucleus assay, micronuclei (MNi) were scored in 1000 binucleate cells per treatment. Cell viability (% plating efficiency) and immunohistochemical detection of p53 induction were also measured. The effects of treatment with 1 mg-equiv of extract in combination with benzo[a]pyrene (BP) were also examined. BP-DNA adducts were detected and quantified by 32P-postlabeling analysis. Dose-related increases in MNi independent of pollutant concentrations were induced by milk-fat extracts. All four extracts elevated the percentage of p53 positive cells, although not always in a dose-related fashion. Some combinations resulted in profound low-dose-induced increases in MNi and significant elevations in the percentage of p53 positive cells, which occurred without further reduction in cell viability or mitotic rate. When one particular extract was combined with BP, a 100-fold increase in BP-DNA adducts was detected as compared with the levels induced by BP alone; an effect not induced by other extracts. This adduct-enhancing extract was fractionated into 14 fractions that were subsequently tested (1 mg-equiv of original extract) in combination with 0.01 microM BP. Fraction 1, into which nonpolar pollutants mostly eluted, enhanced MN-forming activity with BP. Surprisingly, the more polar and less likely to contain fat-soluble pollutants fractions 5 and 8 also enhanced MN-forming activity. No identifiable pollutants were present in these fractions. The results suggest that different environmental pollutants present in human tissue may influence the susceptibility of target cells to initiating events.

Dose responses for the formation of hemoglobin adducts and urinary metabolites in rats and mice exposed by inhalation to low concentrations of 1,3-[2,3-(14)C]-butadiene

Blood and urine were obtained from male Sprague-Dawley rats and B6C3F1 mice exposed to either a single 6 h or multiple daily (5 x 6 h) nose-only doses of 1,3-[2,3- (14)C]-butadiene at atmospheric concentrations of 1, 5 or 20 ppM. Globin was isolated from erythrocytes of exposed animals and analyzed for total radioactivity and also for N-(1,2,3-trihydroxybut-4-yl)-valine adducts. The modified Edman degradation procedure coupled with GC-MS was used for the adduct analysis. Linear relationships were observed between the exposures to 1,3-[2,3-(14)C]-butadiene and the total radioactivity measured in globin and the level of trihydroxybutyl valine adducts in globin. A greater level of radioactivity (ca. 1.3-fold) was found in rat globin compared with mouse globin. When analyzed for specific amino acid adducts, higher levels of trihydroxybutyl valine adducts were found in mouse globin compared with rat globin. Average levels of trihydroxybutyl valine adduct measured in globin from rats and mice exposed for 5 x 6 h at 1, 5 and 20 ppM 1,3-[2,3-(14)C]-butadiene were, respectively, for rats: 80, 179, 512 pM/g globin and for mice: 143, 351, 1100 pM/g globin. The profiles of urinary metabolites for rats and mice exposed at the different concentrations of butadiene were obtained by reverse phase HPLC analysis on urine collected 24 h after the start of exposure and were compared with results of a previous similar study carried out for 6 h at 200 ppM butadiene. Whilst there were qualitative and quantitative differences between the profiles for rats and mice, the major metabolites detected in both cases were those representing products of epoxide hydrolase mediated hydrolysis and glutathione (GSH) conjugation of the metabolically formed 1,2-epoxy-3-butene. These were 4-(N-acetyl-l-cysteine-S-yl)-1,2-dihydroxy butane and (R)-2-(N-acetyl-l-cystein-S-yl)-1-hydroxybut-3-ene, 1-(N-acetyl-l-cystein-S-yl)-2-(S)-hydroxybut-3-ene, 1-(N-acetyl-l-cystein-S-yl)-2-(R)-hydroxybut-3-ene, (S)-2-(N-acetyl-l-cystein-S-yl)-1-hydroxybut-3-ene, respectively. The former pathway showed a greater predominance in the rat. The profiles of metabolites were similar at exposure concentration in the range 1-20 ppM. There were however some subtle differences compared with results of exposure to the higher 200 ppM concentrations. Overall the results provide the basis for cross species comparison of low exposures in the range of occupational exposures, with the wealth of data available from high exposure studies.

Dose responses for DNA adduct formation in tissues of rats and mice exposed by inhalation to low concentrations of 1,3-[2,3-[(14)C]-butadiene

Male Sprague-Dawley rats and B6C3F1 mice were exposed to either a single 6h or a multiple (5) daily (6h) nose-only dose of 1,3-[2,3-(14)C]-butadiene at exposure concentrations of nominally 1, 5 or 20 ppm. The aim was to compare the results with those from a similar previous study at 200 ppm. DNA isolated from liver, lung and testis of exposed rats and mice was analysed for the presence of butadiene related adducts, especially the N7-guanine adducts. Total radioactivity present in the DNA from liver, lung and testis was quantified and indicated more covalent binding of radioactivity for mouse tissue DNA than rat tissue DNA. Following release of the depurinating DNA adducts by neutral thermal hydrolysis, the liberated depurinated DNA adducts were measured by reverse phase HPLC coupled with liquid scintillation counting. The guanine adduct G4, assigned as N7-(2,3,4-trihydroxybutyl)- guanine, was the major adduct measured in liver, lung and testis DNA in both rats and mice. Higher levels of G4 were detected in all mouse tissues compared with rat tissue. The dose-response relationship for the formation of adduct G4 was approximately linear for all tissues studied for both rats and mice exposed in the 1-20 ppm range. The formation of G4 in liver tissue was about three times more effective for mouse than rat in this exposure range. Average levels of adduct G4 measured in liver DNA of rats and mice exposed to 5 x 6 h 1, 5 and 20 ppm 1,3-[2,3-(14)C]-butadiene were, respectively, for rats: 0.79 +/- 0.30, 2.90 +/- 1.19, 16.35 +/- 4.8 adducts/10(8) nucleotides and for mice: 2.23 +/- 0.71, 12.24 +/- 2.15, 48.63 +/- 12.61 adducts/10(8) nucleotides. For lung DNA the corresponding values were for rats: 1.02 +/- 0.44, 3.12 +/- 1.06, 17.02 +/- 4.07 adducts/10(8) nucleotides, and for mice: 3.28 +/- 0.32, 14.04 +/- 1.55, 42.47 +/- 13.12 adducts/10(8) nucleotides. Limited comparative data showed that the levels of adduct G4 formed in liver and lung DNA of mice exposed to a single exposure to butadiene in the present 20 ppm study and earlier 200 ppm study were approximately directly proportional across dose, but this was not observed in the case of rats. From the available evidence it is most likely that adduct G4 was formed from a specific isomer of the diol-epoxide metabolite, 3,4-epoxy-1,2-butanediol rather than the diepoxide, 1,2,3,4-diepoxybutane. Another adduct G3, possibly a diastereomer of N7-(2,3,4-trihydroxybutyl)-guanine or most likely the regioisomer N7-(1-hydroxymethyl-2,3-dihydroxypropyl)-guanine, was also detected in DNA of mouse tissues but was essentially absent in DNA from rat tissue. Qualitatively similar profiles of adducts were observed following exposures to butadiene in the present 20 ppm study and the previous 200 ppm study. Overall the DNA adduct levels measured in tissues of both rats and mice were very low. The differences in the profiles and quantity of adducts seen between mice and rats were considered insufficient to explain the large difference in carcinogenic potency of butadiene to mice compared with rats.

Kinetics and mechanism of the reduction of CrVI and CrV by d-lactobionic acid

The oxidation of D-lactobionic acid by Cr(VI) yields the 2-ketoaldobionic acid and Cr(3+) as final products when a 20-times or higher excess of the aldobionic acid over Cr(VI) is used. The redox reaction takes place through a complex multistep mechanism, which involves the formation of intermediate Cr(IV) and Cr(V) species. Cr(IV) reacts with lactobionic acid much faster than Cr(V) and Cr(VI) do, and cannot be directly detected. However, the formation of CrO(2)(2+), observed by the first time for an acid saccharide/Cr(VI) system, provides indirect evidence for the intermediacy of Cr(IV) in the reaction path. Cr(VI) and the intermediate Cr(V) react with lactobionic acid at comparable rates, being the complete rate laws for the Cr(VI) and Cr(V) consumption expressed by: -d[Cr(VI)]/dt=[k(I)+k(II)[H(+)]][lactobionicacid][Cr(VI)], where k(I)=(4.1+/-0.1) x 10(-3) M(-1) s(-1) and k(II)=(2.1+/-0.1) x 10(-2) M(-2) s(-1); and -d[Cr(V)]/dt=[k(III)[H(+)]+(k(IV)+k(V)[H(+)])[lactobionicacid]] [Cr(V)], where k(III)=(1.8+/-0.1) x 10(-3) M(-1) s(-1), k(IV)=(1.1+/-0.1) x 10(-2) M(-1) s(-1) and k(V)=(1.0+/-0.1) x 10(-2) M(-2) s(-1), at 33 degrees C. The Electron Paramagnetic Resonance (EPR) spectra show that five-co-ordinate oxo-Cr(V) bischelates are formed at pH 1-5 with the aldobionic acid bound to Cr(V) through the alpha-hydroxyacid group.

Metabolic activation of polycyclic aromatic hydrocarbons to carcinogens by cytochromes P450 1A1 and 1B1

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitously distributed environmental chemicals. PAHs acquire carcinogenicity only after they have been activated by xenobiotic-metabolizing enzymes to highly reactive metabolites capable of attacking cellular DNA. Cytochrome P450 (CYP) enzymes are central to the metabolic activation of these PAHs to epoxide intermediates, which are converted with the aid of epoxide hydrolase to the ultimate carcinogens, diol-epoxides. Historically, CYP1A1 was believed to be the only enzyme that catalyzes activation of these procarcinogenic PAHs. However, recent studies have established that CYP1B1, a newly identified member of the CYP1 family, plays a very important role in the metabolic activation of PAHs. In CYP1B1 gene-knockout mice treated with 7,12-dimethylbenz[a]anthracene and dibenzo[a,l]pyrene, decreased rates of tumor formation were observed, when compared to wild-type mice. Significantly, gene expression of CYP1A1 and 1B1 is induced by PAHs and polyhalogenated hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin through the arylhydrocarbon receptor. Differences in the susceptibility of individuals to the adverse action of PAHs may, in part, be due to differences in the levels of expression of CYP1A1 and 1B1 and to genetic variations in the CYP1A1 and 1B1 genes.

Exposure biomarkers for the study of toxicological impact on carcinogenic processes

Exposure biomarkers for carcinogens in humans include the measurement of the genotoxin or its active metabolite in blood, urine or other tissues, and the determination of the interaction products (adducts) of the carcinogen with protein or DNA. The latter approach may indicate the amount of genotoxically active material that has reached the tissue under study and provides invaluable information for molecular epidemiological studies. Protein adducts are not repaired and are considered primarily as exposure monitors, but DNA adducts may give further information about the mutagenic significance of the exposure. The techniques available for measurement of protein and DNA adducts include mass spectrometry, immunoassay, high performance liquid chromatography with UV, fluorescence or electrochemical detection, 32P-postlabelling (for DNA only) and accelerator mass spectrometry. The lowest limits of sensitivity of the protein adduct measurements is less than 1 pmol adduct/g protein, and the procedures for DNA adduct determination have sensitivities ranging from of 1 adduct in 10(8) to 1 in 10(11) nucleotides. All these techniques are capable of measuring environmental, occupational and dietary exposures to a variety of genotoxic compounds, as exemplified in this review.

Chromate reduction at low sulphate concentration in hydrogen-fed bioreactors

Aimed at developing a bioremediation process to treat Cr(VI)-bearing water at low sulphate concentration in order to reduce excess sulphide production, the highly toxic, mutagenic, and soluble Cr(VI) was reduced to the less toxic and insoluble Cr(III) in 2-litre fixed-bed reactors inoculated with the sulphate-reducing bacterium (SRB) Desulfomicrobium norvegicum, capable of performing direct enzymatic Cr(VI) reduction. H2 was used as the electron source. The fixed-films were developed on three different supports: a PVC cross-flow material, a pozzolana, and a ceramic granulate. The phased experiments began with a progressive increase of the Cr(VI) concentration in the feed to the column reactors, followed by a progressive decrease of the sulphate concentration. Inhibition by Cr(VI) was less pronounced with pozzolana than with the other supports; when the pozzolana column was fed with a medium containing 100 mg l(-1) Cr(VI) and only 250 mg l(-1) sulphate, the lowest residence time that could be applied for complete Cr(VI) reduction was 16 h. The molar ratio between the sulphate and Cr(VI) reduction rates was decreased down to 1.5, suggesting that indirect reaction with HS was not the sole mechanism of Cr(VI) reduction.

Use of two-surfactants mixtures to attain specific HLB values for assisted TPH-diesel biodegradation

In a surfactant assisted biodegradation process, the choice of surfactant(s) is of crucial importance. The question is: does the type of surfactant (i.e. chemical family) affect the biodegradation process at fixed hidrophillic-lypofillic balance (HLB) values? Microcosm assessments were developed using contaminated soil, with around of 5000 mg/kg of hydrocarbons as TPH-diesel. Mixtures of three nonionic surfactants were employed to get a wide range of specific HLB values. Tween20 and Span20 were mixed in the appropriate proportions to get HLB values between 8.6 and 16.7. Tween/Span60 mixtures reached HLB values between 4.7 and 14.9. Finally, Tween/Span80 combinations yielded HLB values between 4.3 and 15. TPH-diesel biodegradation was measured at the beginning, and after 8 weeks, as well as the FCU/gr(soil), as a measure of microorganisms' development during the biodegradation period. A second aim of this work was to assess the use of guar gum as a biodegradation enhancer instead of synthetic products. The conclusions of this work are that surfactant chemical family, and not only the HLB value clearly affects the assisted biodegradation rate. Surfactant's synergism was clearly observed. Regarding the use of guar gum, no biodegradation enhancement was observed for the three assessed concentrations, i.e., 2, 20, and 200 mg/kg, respectively. On the contrary, TPH-diesel removal was lower as the gum concentration increased. It is quite possible that guar gum was used as a microbial substrate.

Electron spin resonance study of chromium(V) formation and decomposition by basalt-inhabiting bacteria

Bacterial reduction of Cr(VI) to Cr(III) compounds may produce reactive intermediates Cr(V) and Cr(IV), which can affect the mobility and toxicity of chromium in environments. To address this important subject, we conducted an electron spin resonance (ESR) study to understand the kinetics of the formation and decomposition of Cr(V) during Cr(VI) reduction by different gram-positive Cr(VI)-tolerant bacteria, which were isolated from polluted basalts from the United States of America and the Republic of Georgia. Results from our batch experiments show that during Cr(VI) reduction, the macromolecules at the cell wall of these bacteria could act as an electron donor to Cr(VI) to form a stable square-pyramidal Cr(V) complexes, which were reduced further probably via a one-electron transfer pathway to form Cr(IV) and Cr(III) compounds. The Cr(V) peak at the ESR spectrum possessed superhyperfine splitting characteristic of the Cr(V) complexes with diol-containing molecules. It appears that the kinetics of Cr(V) formation and decomposition depended on the bacterial growth phase and on the species. Both formation and decomposition of Cr(V) occurred more quickly when Cr(VI) was added at the exponential phase. In comparison with other gram-positive bacteria from the republic of Georgia, the formation and decomposition of Cr(V) in Arthrobacter species from the Unites States was significantly slower.

Cometabolism of Cr(VI) by Shewanella oneidensis MR-1 produces cell-associated reduced chromium and inhibits growth

Microbial reduction is a promising strategy for chromium remediation, but the effects of competing electron acceptors are still poorly understood. We investigated chromate (Cr(VI)) reduction in batch cultures of Shewanella oneidensis MR-1 under aerobic and denitrifying conditions and in the absence of an additional electron acceptor. Growth and Cr(VI) removal patterns suggested a cometabolic reduction; in the absence of nitrate or oxygen, MR-1 reduced Cr(VI), but without any increase in viable cell counts and rates gradually decreased when cells were respiked. Only a small fraction (1.6%) of the electrons from lactate were transferred to Cr(VI). The 48-h transformation capacity (Tc) was 0.78 mg (15 micromoles) Cr(VI) reduced. [mg protein](-1) for high levels of Cr(VI) added as a single spike. For low levels of Cr(VI) added sequentially, Tc increased to 3.33 mg (64 micromoles) Cr(VI) reduced. [mg protein](-1), indicating that it is limited by toxicity at higher concentrations. During denitrification and aerobic growth, MR-1 reduced Cr(VI), with much faster rates under denitrifying conditions. Cr(VI) had no effect on nitrate reduction at 6 microM, was strongly inhibitory at 45 microM, and stopped nitrate reduction above 200 microM. Cr(VI) had no effect on aerobic growth at 60 microM, but severely inhibited growth above 150 microM. A factor that likely plays a role in Cr(VI) toxicity is intracellular reduced chromium. Transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) of denitrifying cells exposed to Cr(VI) showed reduced chromium precipitates both extracellularly on the cell surface and, for the first time, as electron-dense round globules inside cells.

In situ reduction of chromium(VI) in heavily contaminated soils through organic carbon amendment

Chromium has become an important soil contaminant at many sites, and facilitating in situ reduction of toxic Cr(VI) to nontoxic Cr(III) is becoming an attractive remediation strategy. Acceleration of Cr(VI) reduction in soils by addition of organic carbon was tested in columns pretreated with solutions containing 1000 and 10 000 mg L(-1) Cr(VI) to evaluate potential in situ remediation of highly contaminated soils. Solutions containing 0,800, or 4000 mg L(-1) organic carbon in the form of tryptic soy broth or lactate were diffused into the Cr(VI)-contaminated soils. Changes in Cr oxidation state were monitored through periodic micro-XANES analyses of soil columns. Effective first-order reduction rate constants ranged from 1.4 x 10(-8) to 1.5 x 10(-7) s(-1), with higher values obtained for lower levels of initial Cr(VI) and higher levels of organic carbon. Comparisons with sterile soils showed that microbially dependent processes were largely responsible for Cr(VI) reduction, except in the soils initially exposed to 10 000 mg L(-1) Cr(VI) solutions that receive little (800 mg L(-1)) or no organic carbon. However, the microbial populations (< or = 2.1 x 10(5) g(-1)) in the viable soils are probably too low for direct enzymatic Cr(VI) reduction to be important. Thus, synergistic effects sustained in whole soil systems may have accounted for most of the observed reduction. These results show that acceleration of in situ Cr(VI) reduction with addition of organic carbon is possible in even heavily contaminated soils and suggest that microbially dependent reduction pathways can be dominant.

Screening toxicity study in young carp (Cyprinus carpio L.) on feed amended with fumonisin B1

Fumonisin B1 (FB1) is one of several mycotoxins produced by Fusarium moniliforme, a major fungal pathogen of corn and widely spread throughout the world. FB1 produces a wide range of biological effects, some of which are specific for particular organs or species and some are common to all investigated animals. In this study we have evaluated subchronic toxicosis features in young carp (Cyprinus carpio L.) exposed to 0.5 and 5.0 mg FB1 kg(-1) body weight for 42 days through nutritionally balanced diet. During the trial we observed loss of body weight in both treated groups, together with higher incidence of infective bacterial dermatological lesions erythrodermatitis cyprini (Aeromonas salmonicida subsp. nova) in the group treated with the higher FB1 dose. Several hematological parameters (erythrocyte count, platelet count) and serum chemical concentrations (creatinin, total bilirubin) and activities (aspartate aminotransferase, AST and alanine aminotransferase, ALT) were greater in the fumonisin treated groups than in the control group. Our results indicate that long-term dietary exposure to 0.5 and 5.0 mg FB1 kg(-1) body weight is not lethal to young carp, but can produce adverse physiological effects. These findings also suggest that primary target organs of FB1 in the carp are kidney and liver, as it has already been observed in other animal species tested. Specifically changed red blood cell- parameters reveal that FB1 probably causes erythrocyte membrane defect or interferes with carp's respiratory process.

Chromate reduction by chromium-resistant bacteria isolated from soils contaminated with dichromate

Extensive use of hexavalent chromium [Cr(VI)] in various industrial applications has caused substantial environmental contamination. Chromium-resistant bacteria isolated from soils can be used to remove toxic Cr(VI) from contaminated environments. This study was conducted to isolate chromium-resistant bacteria from soils contaminated with dichromate and describes the effects of some environmental factors such as pH, temperature, and time on Cr(VI) reduction and resistance. We found that chromium-resistant bacteria can tolerate 2500 mg L(-1) Cr(VI), but most of the isolates tolerated and reduced Cr(VI) at concentrations lower than 1500 mg L(-1). Chromate reduction activity of whole cells was detected in five isolates. Most of these isolates belong to the genus Bacillus as identified by the 16S rRNA gene sequencing. Maximal Cr(VI) reduction was observed at the optimum pH (7.0-9.0) and temperature (30 degrees C) of growth. One bacterial isolate (Bacillus sp. ES 29) was able to aerobically reduce 90% of Cr(VI) in six hours. The Cr(VI) reduction activity of the whole cells of five isolates had a K(M) of 0.271 (2.61 mM) to 1.51 mg L(-1) (14.50 mM) and a V(max) of 88.4 (14.17 nmol min(-1)) to 489 mg L9-1) h(-1) (78.36 nmol min(-1)). Our consortia and monocultures of these isolates can be useful for Cr(VI) detoxification at low and high concentrations in Cr(VI)-contaminated environments and under a wide range of environmental conditions.

Microbiological reduction of chromium(VI) in presence of pyrolusite-coated sand by Shewanella alga Simidu ATCC 55627 in laboratory column experiments

Hexavalent chromium (Cr(VI)) was reduced to non-toxic trivalent chromium (Cr(III)) by a dissimilatory metal reducing bacteria, Shewanella alga Simidu (BrY-MT) ATCC 55627. A series of dynamic column experiments were conducted to provide an understanding of Cr(VI) reduction by the facultative anaerobe BrY-MT in the presence of pyrolusite (beta-MnO(2)) coated sand and uncoated-quartz sand. All dynamic column experiments were conducted under growth conditions using Cr(VI) as the terminal electron acceptor and lactate as the electron donor and energy source. Reduction of Cr(VI) was rapid (within 8 h) in columns packed with uncoated quartz sand and BrY-MT, whereas Cr(VI) reduction by BrY-MT was delayed (57 h) in the presence of beta-MnO(2)-coated sand. The role of beta-MnO(2) in this study was to provide oxidation of trivalent chromium (Cr(III)). BrY-MT attachment was higher on beta-MnO(2)-coated sand than on uncoated quartz sand at 10, 60, and 85.5 h. Results have shown that this particular strain of Shewanella did not appreciably reduce Mn(IV) to Mn(II) species nor biosorbed Cr and Mn during its metabolic activities.

Primary DNA damage in chrome-plating workers

In order to evaluate the primary DNA damage due to occupational exposure to chromium (VI), DNA strand-breaks and apoptosis in peripheral lymphocytes were measured in a group of 19 chrome-plating workers. DNA strand-breaks was assessed by alkaline (pH>13) single-cell microgel electrophoresis ('comet') assay, while apoptosis was measured by flow-cytometry after propidium iodide staining of the cells. Concentrations of chromium in urine, erythrocytes and lymphocytes were investigated as biological indicators of exposure. A group of 18 hospital workers (control group I) and another 20 university personnel (control group II) without exposure to chromium were also studied as controls. The results of the study show that chrome-plating workers have higher levels of chromium in urine, erythrocytes and lymphocytes than unexposed workers. Comet tail moment values, assumed as index of DNA damage, are increased in chromium-exposed workers and results are significantly correlated to chromium lymphocyte concentrations. No difference emerged in the percentage of apoptotic nuclei in exposed and unexposed workers. The study confirms that measurements of chromium in erythrocytes and lymphocytes may provide useful information about recent and past exposure to hexavalent chromium at the workplace. The increase in DNA strand-breaks measured by comet assay suggests this test is valid for the biological monitoring of workers exposed to genotoxic compounds such as chromium (VI).

Combined slurry and solid-phase bioremediation of diesel contaminated soils

This work investigates, at a laboratory and pilot-scale, the influence of various operating parameters on the combined slurry and solid-phase bioremediation technique for a diesel contaminated soil. For slurry-phase bioreactors (SPB), it has been found that, as far as famine conditions are attained at the end of the react cycle, a low hydraulic retention time and a low slurry recycle ratio allows for a better utilization of the reactor volume. A 7-day slurry-phase bioreactor treatment has been shown to provide enough contaminant removal allowing the soil drawn from the slurry-phase bioreactors to be fed effectively to the solid-phase bioreactors (SoPB) for completing the soil cleanup. However, an important improvement of the solid-phase bioreactor performance has been found using soil additives, namely sand and surfactants. While the first soil additive improves pile porosity and consequently oxygen diffusion, the latter increases contaminant bioavailability.

Nonsmoking-related arylamine exposure and bladder cancer risk

Roughly one-half of bladder cancer incidence in the United States can be attributed to known causes, mainly cigarette smoking, and it has been hypothesized that the aromatic amines in tobacco smoke are important etiological agents. Nonsmokers are also exposed, through unknown sources, to many of the same carcinogenic aromatic amines that are present in cigarette smoke. Previous epidemiological studies have not tested whether either of these aromatic amine exposures are associated with cancer risk. We conducted a population-based case-control study in Los Angeles County, California, involving 761 case patients with bladder cancer and 770 individually matched control subjects. In-person interviews provided information on tobacco smoking and other potential risk factors. Quantitative analysis of hemoglobin adducts of 4- and 3-aminobiphenyl (ABP) was used to assess aromatic amine exposure. Adducts of both aminobiphenyls were significantly higher in cases than in controls, independent of cigarette smoking at the time of blood collection and lifetime smoking history. Adjustment for other risk factors as well as for metabolic differences did not materially alter the associations. Our findings strengthen the connection between exposure to aromatic amines in tobacco smoke and cigarette smoking-related bladder cancer and suggest that environmental exposure to arylamines may account for a significant proportion of nonsmoking-related bladder cancer in the general population.

Issues in the epidemiological analysis and interpretation of intermediate biomarkers

We critically reviewed the validity and interpretation of two analytical approaches that have been used in the molecular epidemiological literature to investigate the role of gene-environment (GxE) interactions in disease (D) causation. Several studies have attempted to use biomarkers of biologically effective dose (BBED) such as polycyclic aromatic hydrocarbon-DNA and alfatoxin-albumin adducts to assess possible GxE interactions. To truly determine whether BBED results from a GxE interaction that is causally implicated in disease development would require data on G, E, BBED, and D, and thus far, few studies have had data on each of these components. In the absence of data on an antecedent E, one approach has been to assess interactions between G and BBED on D and to interpret the results as providing information on the presence of GxE interactions. In the absence of data on G, another approach has been to control for E in analyses of BBED and D and to interpret nonnull risk estimates for BBED as reflecting the role of G. We show that neither approach is valid. Analyses of interactions between G and BBED cannot be used to draw conclusions about the presence or absence of GxE interactions. Similarly, analyses of BBED and D, controlling for E, do not provide insight into the role of G. We discuss how differences in the risk estimate for BBED, with and without control for E may be interpreted.

Microbiological evaluation of toxicity of three polycyclic aromatic hydrocarbons and their decomposition products formed by advanced oxidation processes

The toxicity of benzo[a]pyrene, chrysene, and fluorene and their decomposition products formed by advanced oxidation processes (AOPs) was investigated using biotests with Escherichia coli and Vibrio fischeri. The polycyclic aromatic hydrocarbons (PAHs) were not highly toxic to either bacterial strain; the toxicity of their degradation products depended on the method of chemical processing. Inhibition of more than 27% was observed with products formed by oxidation of the PAHs, by AOP methods without hydrogen peroxide. Toxicity as high as 100% was observed after the combined action of hydrogen peroxide and other oxidizing agents.

Extending the understanding of mutagenicity: structural insights into primer-extension past a benzo[a]pyrene diol epoxide-DNA adduct

DNA polymerase enzymes employ a number of innate fidelity mechanisms to ensure the faithful replication of the genome. However, when confronted with DNA damage, their fidelity mechanisms can be evaded, resulting in a mutation that may contribute to the carcinogenic process. The environmental carcinogen benzo[a]pyrene is metabolically activated to reactive intermediates, including the tumorigenic (+)-anti-benzo[a]pyrene diol epoxide, which can attack DNA at the exocyclic amino group of guanine to form the major (+)-trans-anti-[BP]-N(2)-dG adduct. Bulky adducts such as (+)-trans-anti-[BP]-N(2)-dG primarily block DNA replication, but are occasionally bypassed and cause mutations if paired with an incorrect base. In vitro standing-start primer-extension assays show that the preferential insertion of A opposite (+)-trans-anti-[BP]-N(2)-dG is independent of the sequence context, but the primer is extended preferentially when dT is positioned opposite the damaged base in a 5'-CG*T-3' sequence context. Regardless of the base positioned opposite (+)-trans-anti-[BP]-N(2)-dG, extension of the primer past the lesion site poses the greatest block to polymerase progression. In order to gain insight into primer-extension of each base opposite (+)-trans-anti-[BP]-N(2)-dG, we carried out molecular modeling and 1.25 ns unrestrained molecular dynamics simulations of the adduct in the +1 position of the template within the replicative pol I family T7 DNA polymerase. Each of the four bases was modeled at the 3' terminus of the primer, incorporated opposite the adduct, and the next-to-be replicated base was in the active site with its Watson-Crick partner as the incoming nucleotide. As in our studies of nucleotide incorporation, (+)-trans-anti-[BP]-N(2)-dG was modeled in the syn conformation in the +1 position, with the BP moiety on the open major groove side of the primer-template duplex region, leaving critical protein-DNA interactions intact. The present work revealed that the efficiency of primer-extension past this bulky adduct opposite each of the four bases in the 5'-CG*T-3' sequence can be rationalized by the stability of interactions between the polymerase protein, primer-template DNA and incoming nucleotide. However, the relative stabilization of each nucleotide opposite (+)-trans-anti-[BP]-N(2)-dG in the +1 position (T > G > A > or = C) differed from that when the adduct and partner were the nascent base-pair (A > T > or = G > C). In addition, extension past (+)-trans-anti-[BP]-N(2)-dG may pose a greater block to a high fidelity DNA polymerase than does nucleotide incorporation opposite the adduct because the presence of the modified base-pair in the +1 position is more disruptive to the polymerase-DNA interactions than it is within the active site itself. The dN:(+)-trans-anti-[BP]-N(2)-dG base-pair is strained to shield the bulky aromatic BP moiety from contact with the solvent in the +1 position, causing disruption of protein-DNA interactions that would likely result in decreased extension of the base-pair. These studies reveal in molecular detail the kinds of specific structural interactions that determine the function of a processive DNA polymerase when challenged by a bulky DNA adduct.

Distribution of chromium contamination and microbial activity in soil aggregates

Biogeochemical transformations of redox-sensitive chemicals in soils can be strongly transport-controlled and localized. This was tested through experiments on chromium diffusion and reduction in soil aggregates that were exposed to chromate solutions. Reduction of soluble Cr(VI) to insoluble Cr(II) occurred only within the surface layer of aggregates with higher available organic carbon and higher microbial respiration. Sharply terminated Cr diffusion fronts develop when the reduction rate increases rapidly with depth. The final state of such aggregates consists of a Cr-contaminated exterior, and an uncontaminated core, each having different microbial community compositions and activity. Microbial activity was significantly higher in the more reducing soils, while total microbial biomass was similar in all of the soils. The small fraction of Cr(VI) remaining unreduced resides along external surfaces of aggregates, leaving it potentially available to future transport down the soil profile. Using the Thiele modulus, Cr(VI) reduction in soil aggregates is shown to be diffusion rate- and reaction rate-limited in anaerobic and aerobic aggregates, respectively. Thus, spatially resolved chemical and microbiological measurements are necessary within anaerobic soil aggregates to characterize and predict the fate of Cr contamination. Typical methods of soil sampling and analyses that average over redox gradients within aggregates can erase important biogeochemical spatial relations necessary for understanding these environments.