Mixture Of Benzo Research Articles

The detoxification responses, damage effects and bioaccumulation in the scallop Chlamys farreri exposed to single and mixtures of benzo[a]pyrene and chrysene

This study aimed to investigate the detoxification responses, damage effects and biotransformation in scallop Chlamys farreri exposed to benzo[a]pyrene (BaP) (0.1, 1μg/L), chrysene (CHR) (0.1, 1μg/L) and BaP+CHR (0.1+0.1, 1+1μg/L) for 15days. Results demonstrated that BaP and CHR concentration (BaP<CHR) in tissues increased rapidly in a time and dose effect. The mRNA expression of aryl hydrocarbon receptor (AhR), cytochrome P450 1A1 (CYP1A1), CYP1B1, multidrug resistance protein 1 (MRP1/ABCC1), breast cancer resistance protein (BCRP/ABCG2) and P-glycoprotein (P-gp) were induced especially in the mixtures of BaP and CHR. Heat shock protein 90 (HSP90) and aryl hydrocarbon receptor nuclear translocator (ARNT) mRNA expression was significantly elevated at days 1, 10 and 15. Detoxification enzymes of 7-ethoxyresorufin O-deethylase (EROD), uridine-diphosphate-glucuronyl-transferase (UGT) and sulfotransferase (SULT) were significantly induced and then became stable gradually while glutathione-S-transferase (GST) was inhibited in the mixtures of BaP and CHR at days 10 and 15. Superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT) and glutathione (GSH) were all stimulated especially in the mixtures of BaP and CHR. The levels of DNA strand breaks, lipid peroxidation (LPO) and protein carbonyl (PC) contents showed damage effects exposed BaP and CHR. All the results indicated that BaP and CHR have similar induced effect and a majority of the biomarkers pointed to a more toxic effect when BaP and CHR were mixed. These will provide a solid foundation for the study of PAHs detoxification mechanism in bivalves and valuable information for marine pollution monitoring.

Mixtures of benzo(a)pyrene, dichlorodiphenyltrichloroethane and tributyltin are more toxic to neotropical fish Rhamdia quelen than isolated exposures

The effects of benzo(a)pyrene (BaP), dichlorodiphenyltrichloroethane (DDT) and tributyltin (TBT) association were investigated through a multi-biomarker approach. Ten Rhamdia quelen fish per group were exposed through intraperitoneal injections either to BaP (0.3; 3 or 30mgkg−1), DDT or TBT (0.03; 0.3 or 3mgkg−1) or BaP/DDT, BaP/TBT, DDT/TBT or BaP/DDT/TBT on their lowest doses. The experiments were divided in acute (one dose, 5-day) and sub-chronic (3 doses, 15-day). Control groups received an equal volume of PBS or canola oil (1mlkg−1). The three tested contaminants altered AChE activity in brain and muscle in similar ways; the mixtures antagonized the increase evoked by the contaminants alone. BaP and TBT increased GSH content and mixtures reduced it. GPx activity was increased by DDT and TBT in the 15-day experiment and reduced by the mixtures. BaP increased GST activity in sub-chronic experiment while TBT reduced it in the acute experiment. BaP/TBT increased GST activity compared to all groups; the other mixtures reduced it compared to BaP or DDT in the 5-day experiment. BaP, DDT and TBT increased δ-ALAd activity mainly in acute exposure; the mixtures also increased δ-ALAd compared to DDT or TBT in 5 and 15-day. BaP, TBT and BaP/DDT decreased LPO in the acute experiment. In the sub-chronic experiment DDT/TBT increased LPO when compared to TBT. None of the contaminants alone altered PCO, but all mixtures increased it compared to one or another contaminant. Contaminants isolated had a more acute effect in ALT plasma level; their lowest dose, which had no effect alone, in combination has led to an increase of this enzyme, especially after 15 days. DDT increased AST in the acute and sub-chronic experiments, while TBT did the same in the latter. DDT/TBT decreased AST opposing the effect of the contaminants alone in the 5-day experiment. Hepatic lesions index could be explained by a more acute effect of the contaminants alone or combined and by activation of cell defenses after the sub-chronic exposure. TBT increased melanomacrophages counting in the 5-day experiment and the mixtures increased it in the 5 and 15-day experiments. Overall, the majority of the biomarkers pointed to a more toxic effect when these contaminants were combined, leading to unexpected toxicities compared to individual exposure scenarios. These findings are relevant considering environmental exposure conditions, since organisms are often exposed to different combinations of contaminants.

Abstract 1789: Effects of benzo(a)pyrene-7,8-dione and cadmium on early response to DNA damage in primary human bronchoepithelial cells.

Abstract Polycyclic aromatic hydrocarbons (PAHs) and heavy metals often co-exist in the environment, but despite their significant toxicities little is known about their combined effects. Cadmium (Cd), a known human carcinogen, interferes with cellular responses to DNA damage, through inhibition of DNA repair systems, disturbance of tumor suppressor functions, or increased resistance to apoptosis. Cd has been linked to lung cancer in humans and the most common exposure scenarios in humans involve co-exposure with PAHs. However, studies on combined effects of Cd and PAHs are mostly limited to marine invertebrates or soil bacteria. Both PAHs and Cd induce formation of reactive oxygen species (ROS) in the cell. Mitochondria are the main target for oxidative DNA damage and also play an important role in programmed cell death. Cytochrome c is an important component of apoptosis and its translocation from mitochondria to the cytosol is an indicator of apoptotic activity in intact cells. Another indicator of the early response to apoptotic signals is the phosphorylation of H2AX, which also reflects DNA damage. Here, we propose that the exposure of primary human bronchoepithelial cells (hBEC) to the mixture of benzo(a)pyrene-7,8-dione (BaPD) and cadmium chloride (CdCl2) will significantly augment DNA damage and disrupt mitochondrial functions involving apoptosis. Methods: Cytotoxicity was analyzed by the WST-8 assay. hBEC were exposed to CdCl2 (5 μg/ml) and BaPD (10 μg/ml) for 24h. Levels of 8-hydroxy-2’-deoxyguanosine (8-OHdG) and cytochrome c were quantified using ELISA. Quantification of H2AX phosphorylation (Ser139, γ-H2AX) was performed by western blotting. Statistical tests were conducted using GraphPad Prism software at a significance level of 0.05. Mean levels across treatment groups were compared using analysis of variance (ANOVA). Results: IC50 values at 24h for CdCl2 and BaPD were 8.7 and 12.5 μg/ml, respectively. Levels of 8-OHdG in nuclear DNA were significantly higher in hBEC exposed to CdCl2 or BaPD when compared to controls. We observed an increased release of cytochrome c during the first few hours after exposure to CdCl2 and BaPD, followed by significant reductions at 24h. Furthermore, cytochrome c levels in cells exposed to the combination of BaPD and CdCl2 were substantially lower than those observed with either treatment alone. Phosphorylation of H2AX increased in hBEC exposed to CdCl2 or BaPD, with higher levels observed in cells treated with BaPD. Conclusion: Our results suggest increased DNA damage in hBEC after 24h of exposure to Cd and BaPD. We also observed decreased cytochrome c levels after exposure to BaPD and/or Cd, suggesting disruption of mitochondrial functions. This effect was more pronounced in cells exposed to the mixture. Citation Format: Jibanananda Mishra, Berrin Serdar. Effects of benzo(a)pyrene-7,8-dione and cadmium on early response to DNA damage in primary human bronchoepithelial cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1789. doi:10.1158/1538-7445.AM2013-1789

The role of the characteristics of humic substances in binding with benzo[h]quinoline

The binding constants (K(DOC)) of the mixture of benzo[h]quinoline and its protonated analog, benzo[h]quinolinium, to four types of humic substances obtained from the International Humic Substances Society were determined by the fluorescence quenching method. A simple mixing model was used to eliminate the fluorescent interference from the minor analog in the solution and to deduce K(mix), which represents the overall binding as the sum of that for the individual analogs. The characteristics of humic substances, especially their hydrophobicity and aromaticity, established by principal component analysis of structural and elemental compositions, were the main determinants of the binding affinity with both benzo[h]quinoline and benzo[h]quinolinium (K(BQ) and K (BQH+) across a range of pH values. The strongest overall affinity of benzo[h]quinoline for humic substances is observed near pH 4 and with more hydrophobic humic substances, which suggests possible choices in attempts at remediation of benzo[h]quinoline containing particles with humic substances.

Transcriptional responses in neonate and adult Daphnia magna in relation to relative susceptibility to genotoxicants

Little information is available on the responses of lower animals to genotoxic chemicals or on their sensitivity for detecting genotoxic chemicals, especially at different life-stages, despite the established use of the water flea Daphnia magna in ecotoxicity testing. Comet assay methodology was developed and applied to daphnid cells but only limited, non-statistically significant responses to the genotoxicants sodium dichromate (0.2–1 μM), chrysoidine (0.1–2 μM), and mixtures of benzo- a-pyrene (BaP) and sodium dichromate were found (from 0.01 μM BaP & 0.1 μM sodium dichromate to 0.25 μM BaP & 0.75 μM sodium dichromate). Transcriptomic analyses using Agilent D. magna oligonucleotide microarrays were undertaken to assess the effect of a mixture of sodium dichromate and BaP (designed to produce both adducted and oxidised DNA) on gene transcription. Neonates (<24 h) and adults (day 7) were exposed for 6 h and 24 h at two combination concentration levels (0.02 μM BaP & 0.15 μM sodium dichromate and 0.1 μM BaP & 0.75 μM sodium dichromate). The greatest differences in transcriptional profile occurred between adults and neonates. Subsets of the transcriptional profiles distinguished genotoxicant-exposed animals from controls, both for neonates and adults. Higher transcript levels of DNA repair genes were found in adults and adults also displayed significant induction of DNA repair gene transcripts in response to exposure whereas neonates did not. Transcriptional changes in response to genotoxicant exposure proved more sensitive than measurement of DNA strand breaks by the Comet assay and the extensive differences in transcription between adults and neonates emphasized the importance of life stage in toxicant testing with Daphnia.

Biochemical biomarkers in Oreochromis niloticus exposed to mixtures of benzo[a]pyrene and diazinon

Biochemical biomarkers in Oreochromis niloticus exposed to mixtures of benzo[a]pyrene and diazinon

Approaches to benzo[b]thiophenes by gas-phase pyrolysis of methyl 2-(alkylthio)cinnamates

Flash vacuum pyrolysis (FVP) of 3-[2-(t-butylthio)phenyl]propenoate 7 at 700 °C (0.01 Torr) unexpectedly gave a mixture of benzo[b]thiophene derivatives 5 (15%) and 8 (21%), and thiocoumarin 9 (28%). Control experiments show that thiophenoxyls (e.g. 15) cyclise efficiently to benzo[b]thiophene 5 under similar conditions. It follows that FVP of S-t-butyl derivatives of thiophenols, is not an efficient means of generating thiophenoxyl radicals owing to competing hydrogen capture processes.

Bile fluorescence, heme oxygenase induction, and increased biliverdin excretion by mixtures of environmental toxicants

The measurement of bile fluorescence has become a popular biomarker to demonstrate the exposure of fish to polycyclic aromatic hydrocarbons. Conflicting data has been published on how to normalize bile fluorescence. To investigate if normalization to biliverdin is a suitable method, experiments were performed to study the mechanisms related to biliverdin excretion in fish. In two separate experiments channel catfish ( Ictalurus punctatus) were dosed with mixtures of benzo[a]pyrene with cadmium, chlorinated phenols or borneol. The results showed linear relationships between bile protein and biliverdin for each treatment group, but the slope of this relationship was significantly increased when fish received more chemical stress. Thus, under increasing toxicant stress, more biliverdin was excreted per amount of protein. To investigate if the increased biliverdin excretion was related to increased heme degradation, enzymatic activity of heme oxygenase (HO) was measured in liver homogenates of the dosed fish. The fish dosed with chemical mixtures had a significantly higher HO activity than the control fish, and in both experiments a significant correlation was observed between HO activity and biliverdin concentration in the bile. It is concluded that mixtures of environmental pollutants can induce HO activity and that this chemical stress leads to increased biliverdin excretion. The elucidation of this mechanistic pathway warrants that bile fluorescence should not be expressed per biliverdin absorption, and that expression per bile protein would be a more reliable method.

Heme oxygenase induction and biliverdin excretion: Implications for the bile fluorescence biomarker

The measurement of bile fluorescence has become a popular biomarker to demonstrate the exposure of fish to polycyclic aromatic hydrocarbons. Conflicting data have been published on how to normalize bile fluorescence. To investigate if normalization to biliverdin is a suitable method, experiments were performed to study the mechanisms related to biliverdin excretion in fish. Channel catfish (Ictalurus punctatus) were dosed with mixtures of benzo[a]pyrene and cadmium, chlorinated phenols or borneol. The results showed that under increasing toxicant stress, more biliverdin was excreted per amount of protein. To investigate if the increased biliverdin excretion was related to increased heme degradation, enzymatic activity of heme oxygenase (HO) was measured in liver homogenates. The fish dosed with chemical mixtures had significantly higher HO activity than the control fish, and a significant correlation was observed between HO activity and biliverdin concentration in the bile. It is concluded that chemical mixtures of environmental pollutants can induce HO activity and that this chemical stress leads to increased biliverdin excretion. The elucidation of this mechanistic pathway warrants that bile fluorescence is better expressed per amount of bile protein than per biliverdin absorption.

Kordiimonas gwangyangensis gen. nov., sp. nov., a marine bacterium isolated from marine sediments that forms a distinct phyletic lineage (Kordiimonadales ord. nov.) in the ‘Alphaproteobacteria’

A marine bacterium, designated strain GW14-5(T), capable of degrading high-molecular-mass polycyclic aromatic hydrocarbons was isolated from the sediments of Gwangyang Bay, Republic of Korea, after enrichment culture for 2 years with a mixture of benzo[a]pyrene and pyrene. Phylogenetic analysis based on 16S rRNA gene sequences indicated that the isolate forms a phyletic lineage that is distinct from the seven known orders within the 'Alphaproteobacteria'. 16S rRNA gene sequence similarity of strain GW14-5(T) to all recognized bacterial species was not greater than 92%. The dominant fatty acids of the isolate were i-17:1 (46.2%), i-15:0 (15.1%) and i-17:0 (12.6%). The major respiratory quinone was MK-5, and the DNA G+C content was 39.3 mol%. Cells of strain GW14-5(T) were Gram-negative, motile, catalase-positive, oxidase-positive and weakly halophilic. Glucose, N-acetylglucosamine and maltose were utilized as sole carbon sources. The strain was positive for beta-glucosidase activity. Optimal growth of strain GW14-5(T) was at pH 7.0 and 37-40 degrees C and required the presence of 2% (w/v) NaCl. On the basis of this evidence, strain GW14-5(T) represents a novel genus and species in the 'Alphaproteobacteria' for which the name Kordiimonas gwangyangensis gen. nov., sp. nov. is proposed. The novel order Kordiimonadales is proposed for the distinct phyletic line represented by the genus Kordiimonas. The type strain is GW14-5(T) (=KCCM 42021(T)=JCM 12864(T)).

Exposure and time dependent DNA strand breakage in hepatopancreas of green-lipped mussels ( Perna viridis) exposed to Aroclor 1254, and mixtures of B[ a]P and Aroclor 1254

Green-lipped mussels ( Perna viridis) were exposed to Aroclor 1254 (0.5, 5 and 50 μg l −1) and a mixture of benzo[ a]pyrene (B[ a]P) and Aroclor 1254 (0.3 + 0.5 and 3 + 5 μg l −1) for 12 days. On day 0, 1, 3, 6 and 12, the levels of DNA strand breaks in the mussel hepatopancreas were monitored using an alkaline unwinding assay. The results were compared to the findings of a previous study in which the levels of DNA strand breakage in the same species were measured following exposure to various concentrations of B[ a]P (0.3, 3 and 30 μg l −1). The results indicated that Aroclor 1254 at a concentration ⩽50 μg l −1 did not cause any increase in DNA strand breaks while B[ a]P at concentrations ranging from 0.3 to 3 μg l −1 caused an increase in strand breaks after one day of exposure, followed by an apparent rapid recovery. In contrast, exposure to 30 μg l −1 B[ a]P caused no increase in DNA strand breaks over the exposure period. This was postulated to be due to an early elicitation of the DNA repair system by the relatively high exposure level of B[ a]P. This hypothesis was tested in the present study, and the results suggest that exposure to the high B[ a]P concentration might have elicited the defense mechanism within the mussels, resulting in no observed increase in DNA strand breaks. An increase in strand breaks was, however, evident when the mussels were exposed to lower B[ a]P levels. The levels of DNA strand breaks were correlated with the body burden of B[ a]P and Aroclor 1254 but no significant relationship was observed, possibly owing to the rapid metabolism of the toxicant and/or an effective DNA repair mechanism. As a result, DNA strand breakage in the hepatopancreas of green-lipped mussels may not be a suitable biomarker of exposure to the above toxicants in the marine environment. Our findings also suggest that it would be instructive to investigate (1) the role of DNA repair enzymes in the exposed mussels; and (2) the correlation between the activity of these enzymes and the body burden of specific toxicants.

Effects of benzyl isothiocyanate and 2-phenethyl isothiocyanate on benzo[a]pyrene and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone metabolism in F-344 rats.

A mixture of dietary benzyl isothiocyanate (BITC) and 2-phenethyl isothiocyanate (PEITC) inhibits lung tumorigenesis by a mixture of benzo[a]pyrene (B[a]P) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in A/J mice. Previous studies indicated that inhibition of 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB) releasing DNA adducts of NNK by PEITC in the lung was responsible for inhibition of tumorigenicity. We have now extended these investigations to F-344 rats treated with 2 p.p.m. B[a]P in the diet and 2 p.p.m. NNK in the drinking water. The effects of BITC (1 micromol/g diet), PEITC (3 micromol/g diet), and a mixture of BITC plus PEITC (1 and 3 micromol/g diet) on DNA and hemoglobin (Hb) adducts of B[a]P and NNK, and on two urinary metabolites of NNK, were examined. DNA adducts were quantified after 8 and 16 weeks of treatment. Hb adducts were quantified in blood samples withdrawn every 2 weeks. 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) and its glucuronide NNAL-Gluc were measured in urine every 4 weeks. PEITC or BITC plus PEITC significantly reduced levels of HPB releasing DNA adducts of NNK in lung at 8 and 16 weeks, but there was no effect of BITC. There were no effects of any of the treatments on levels of HPB releasing DNA adducts of NNK in liver, or on DNA adducts of B[a]P in either lung or liver. PEITC or BITC plus PEITC significantly inhibited the formation of Hb adducts of NNK from 2-12 weeks of treatment while there were no effects on Hb adducts of B[a]P. There was a significant increase in levels of NNAL and NNAL-Gluc in the urine of the rats treated with PEITC or BITC plus PEITC. These results demonstrate that dietary PEITC, or a mixture of BITC plus PEITC, inhibit the formation of HPB releasing adducts of NNK in the rodent lung, leading to inhibition of tumorigenesis.

Effects of benzyl isothiocyanate and phenethyl isothiocyanate on DNA adduct formation by a mixture of benzo[a]pyrene and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in A/J mouse lung.

Dietary phenethyl isothiocyanate (PEITC) and a mixture of dietary PEITC and benzyl isothiocyanate (BITC) inhibit lung tumorigenesis in A/J mice induced by a mixture of the tobacco smoke carcinogens benzo[a]pyrene (B[a]P) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). In this study, we tested the hypothesis that inhibition of tumorigenesis by these isothiocyanates was due to inhibition of DNA adduct formation. We quantified the following pulmonary DNA adducts: N2-[7,8,9-trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene-10-yl]deoxyguanosine (BPDE-N2-dG) from B[a]P; and O(6)-methylguanine (O(6)-mG) and 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB)-releasing adducts from NNK. Initial experiments demonstrated that there were no effects of B[a]P on NNK-DNA adduct formation, or vice versa, and established by way of a time course study the appropriate sacrifice intervals for the main experiment. Dietary PEITC, or dietary BITC plus PEITC, inhibited the formation of HPB-releasing DNA adducts of NNK at several of the time points examined. There were no effects of dietary isothiocyanates on levels of O(6)-mG or BPDE-N2-dG. These results, which are consistent with previous studies in rats and with tumor inhibition data in mice, support a role for inhibition of HPB-releasing DNA adducts of NNK as a mechanism of inhibition of tumorigenesis by dietary PEITC and BITC plus PEITC. However, the observed inhibition was modest, suggesting that other effects of isothiocyanates are also involved in chemoprevention in this model.

Interaction Analyses of Binary Mixtures of Carcinogenic PAHs Using Morphological Cell Transformation of C3H10T1/2CL8 Mouse Embryo Fibroblasts in Culture

Studies of defined mixtures of carcinogenic polycyclic aromatic hydrocarbons (PAH) have identified three major categories of interactions: antagonism; synergism; and additivity depending on the biological model, tissue, route of exposure, and specific PAH. To understand the bases of these interactions we studied binary mixtures of benzo[a]pyrene (B[a]P) and dibenz[a,h]anthracene (DBA) in transformable C3H10T1/2C18 (C3H10T1/2) mouse embryo fibroblast cells in culture. C3H10T1/2 cells treated with binary mixtures of B[a]P and DBA gave less than additive morphological cell transformation based on response additivity. These results were consistent with those reported in mice and rats on the antagonistic effects of B[a]P and DBA on tumorigenesis. 32P-Postlabeling DNA adduct studies revealed that DBA reduced B[a]P-DNA adduct levels by 47% with no effect on DBA-DNA adduct levels. This suggests that one mechanism for the inhibition of morphological cell transformation of binary mixtures of B[a]P and DBA is due to alterations in the metabolic activation of B[a]P.

Chemoprevention of lung tumorigenesis induced by a mixture of benzo(a)pyrene and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone by the organoselenium compound 1,4-phenylenebis(methylene)selenocyanate

We evaluated the chemopreventive efficacy of the organoselenium compound 1,4-phenylenebis(methylene)selenocyanate (p-XSC) against the development of tumors of the lung and forestomach induced by a mixture of benzo(a)pyrene (B(a)P) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), two of the major lung carcinogens present in tobacco smoke. A/J mice (20 mice/group) were given intragastric doses of a mixture of B(a)P (3 μmol/mouse) and NNK (3 μmol/mouse) in cottonseed oil (0.1 ml) once a week for eight consecutive weeks. Mice were fed either AIN-76A control diet or control diet containing p-XSC (10 ppm selenium), either during or after carcinogen administration. Dietary p-XSC significantly reduced lung tumor multiplicity, regardless of whether it was given during or after carcinogen administration. p-XSC was also an effective inhibitor of tumor development in the forestomach. To provide some biochemical insights into the protective role of p-XSC, its effect on selected phase I and II enzyme activities involved in the metabolism of NNK and B(a)P was also examined in vivo in this animal model. Dietary p-XSC significantly inhibited the activities of the phase I enzymes, methoxyresorufin O-dealkylase (MROD) and N-nitrosodimethylamine N-demethylase (NDMAD), in mouse liver, but it had no effect on ethoxyresorufin O-dealkylase (EROD), pentoxyresorufin O-dealkylase (PROD), and erythromycin N-demethylase (ERYTD). Total glutathione S-transferase (GST) enzyme activity, as well as GST-π and GST-μ enzyme activities, were significantly induced by dietary p-XSC in both the lung and liver. Glutathione peroxidase (GPX) activity was also induced by p-XSC in mouse lung, but not in the liver. Dietary p-XSC had no effect on selenium-dependent glutathione peroxidase (GPXSe), GST-α, and UDP-glucuronosyl transferase (UDPGT) enzyme activities in either the lung or the liver. These studies suggest that the chemopreventive efficacy of p-XSC, when fed during carcinogen administration, may be, in part, due to the inhibition of certain phase I enzymes involved in the metabolic activation of these carcinogens, and the induction of specific phase II enzymes involved in their detoxification. The mechanisms that account for the effect of p-XSC when fed after carcinogen administration remain to be determined.

Stimulated Raman Scattering as an Excitation Source for Time-Resolved Excitation-Emission Fluorescence Spectroscopy with Fiber-Optical Sensors

For a fiber-optical sensor system based on time-resolved excitation-emission (TEE) fluorescence spectroscopy, stimulated Raman scattering (SRS) was used to generate simultaneously several excitation wavelengths between 250 and 400 nm. For a frequency-quadrupled Nd:YAG laser and a hydrogen–methane mixture as the Raman medium, an optimum pressure and mixing ratio was identified. The observed pulse energies in the micro-Joule range were sufficient for remote sensing with fiber lengths on the order of 50 m. The TEE probe is comprised of eight independent fiber-optical sensors and was interfaced to an intensified charge-coupled device (CCD) camera with an imaging spectrograph. The system permitted a nanosecond time resolution and parts-per-billion detection limits, for pyrene and fluorescein. The preliminary study of a binary mixture of benzo( a)pyrene and benzo( k)fluoranthene indicates a gain in selectivity for TEE spectra compared to time-resolved emission spectra.

Identification and quantification of overlapped peaks in liquid chromatography with UV diode array detection using an adaptive Kalman filter

A method for the identification and quantification of overlapped peaks in liquid chromatography with UV diode array detection is reported. The adaptive Kalman filter, which is optimized using simplex optimization, can detect low levels of isomeric impurities. The filter optimization is based on the maximum information yield from the filtering procedure, and is capable of compensating the model errors. This approach is combined with the commercially available software to result in a complete method for chromatographic peak analysis. A mixture of two isomers, chrysene and benz(a)anthracene, has been evaluated. This method can detect as low as 1 μM benz(a)anthracene in a 121 μM chrysene solution, and 1 μM chrysene in a 106 μM benz(a)anthracene solution. Both, identification and quantification of the major and minor components have been achieved. For the overall method, the prediction errors are within 2% for the major components and within 10% for the minor components. If the reference spectrum of the minor component is unavailable, this filter can also predict the concentration of the major component within an error of 7%. The reliability of this method has been tested by the second isomeric system, a mixture of benzo(k)fluoranthene and benzo(b)fluoranthene. This method is valid for highly overlapped peaks even when the chromatographic resolution is zero, but an overlap-free region is required in the spectra.

Mutagenic potential of binary mixtures of nitro-polychlorinated dibenzo-p-dioxins and related compounds.

The mutagenic potential of binary mixtures of nitro-polychlorinated dibenzo-p-dioxins and other environmentally related compounds was determined using Salmonella typhimurium strain TA98 in the standard plate incorporation assay. Samples tested included binary mixtures of 4-nitro-4'-chlorobiphenyl with 6-nitro-4,2',3',4',5'-pentachlorobiphenyl, 4-nitrobenzo-p-dioxin with 4-nitro-2,3,8-trichlorodibenzo-p-dioxin, and benzo[a]pyrene with either nitropentachlorobiphenyl or nitrotrichlorodibenzo-p-dioxin. Inhibition was the primary interaction observed for the mixtures of polyhalogenated dioxins or biphenyls with the direct-acting mutagens nitrodibenzo-p-dioxin or nitrochlorobiphenyl. At the highest dose tested, nitrotrichlorodibenzo-p-dioxin inhibited the bacterial mutagenicity of nitrodibenzo-p-dioxin by almost 50%, while pentachlorobiphenyl inhibited the mutagenicity of nitrobiphenyl by 34%. Conversely, synergism was the primary interaction observed for mixtures of halogenated aromatics with the promutagen benzo[a]pyrene. The addition of nitrotrichlorodioxin to benzo[a]pyrene enhanced the mutagenicity of the latter compound by as much as 70%, while the mutagenic potential of a mixture of benzo[a]pyrene and nitropentachlorobiphenyl was approximately 50% greater than the mutagenicity of benzo[a]pyrene alone. In summary, mixtures of nonmutagenic nitropolyhalogenated biphenyls or dibenzo-p-dioxins appear to inhibit the mutagenicity of direct-acting mutagens, while these same compounds seem to enhance the mutagenic potential of the promutagen benzo[a]pyrene.

Partly quenched, synchronously excited fluorescence emission spectra in the characterisation of complex mixtures

Non-linear quenching of mixed fluorescences at low concentrations of quencher, and linear variation at increased concentrations, depend on the Stern-Volmer coefficients and on the proportions of the components in a manner that can be predicted from the Stern-Volmer equation. The variation with quencher concentration of emission intensities synchronously excited from mixtures of benzo[a]pyrene and perylene at intervals of 45 nm is quantitatively interpreted in this way.A variety of examples is used to show that in the qualitative characterisation of complex mixtures the specificity of synchronously excited spectra is enhanced by the use of varyingly quenched conditions. The high resolution afforded by the synchronous excitation technique readily demonstrates the widely differing relative sensitivities of components of fluorescent mixtures to quenching effects; and reveals new emissions that are obscured under non-quenching conditions.