In vitro studies of the genotoxic effects of bitumen and coal-tar fume condensates: comparison of data obtained by mutagenicity testing and DNA adduct analysis by 32P-postlabelling

Influence of GSTM1 and GSTT1 genotypes and confounding factors on the frequency of sister chromatid exchange and micronucleus among road construction workers

In the present study, we have investigated the influence of polymorphism of GSTM1 and GSTT1 genes and confounding factors such as age, sex, exposure duration and consumption habits on cytogenetic biomarkers. Frequency of sister chromatid exchanges (SCEs), high frequency cell (HFC) and cytokinesis blocked micronuclei (CBMN) were evaluated in peripheral blood lymphocytes of 115 occupationally exposed road construction workers and 105 unexposed individuals. The distribution of null and positive genotypes of glutathione-S transferase gene was evaluated by multiplex PCR among control and exposed subjects. An increased frequency of CBMN (7.03±2.08); SCE (6.95±1.76) and HFC (6.28±1.69) were found in exposed subjects when compared to referent (CBMN - 3.35±1.10; SCE - 4.13±1.30 and HFC - 3.98±1.56). These results were found statistically significant at p<0.05. When the effect of confounding factors on the frequency of studied biomarkers was evaluated, a strong positive interaction was found. The individuals having GSTM1 and GSTT1 null genotypes had higher frequency of CBMN, SCE and HFC. The association between GSTM1 and GSTT1 genotypes and studied biomarkers was found statistically significant at p<0.05. Our findings suggest that individuals having null type of GST are more susceptible to cytogenetic damage by occupational exposure regardless of confounding factors. There is a significant effect of polymorphism of these genes on cytogenetic biomarkers which are considered as early effects of genotoxic carcinogens.

Genotoxic effects of fumes from asphalt modified with waste plastic and tall oil pitch

As the use of recycled materials and industrial by-products in asphalt mixtures is increasing, we investigated if recycled additives modify the genotoxicity of fumes emitted from asphalt. Fumes were generated in the laboratory at paving temperature from stone-mastic asphalt (SMA) and from SMA modified with waste plastic (90% polyethylene, 10% polypropylene) and tall oil pitch (SMA-WPT). In addition, fumes from SMA, SMA-WPT, asphalt concrete (AC), and AC modified with waste plastic and tall oil pitch (AC-WPT) were collected at paving sites. The genotoxicity of the fumes was studied by analysis of DNA damage (measured in the comet assay) and micronucleus formation in human bronchial epithelial BEAS 2B cells in vitro and by counting mutations in Salmonella typhimurium strains TA98 and YG1024. DNA damage was also assessed in buccal leukocytes from road pavers before and after working with SMA, SMA-WPT, AC, and AC-WPT. The chemical composition of the emissions was analysed by gas chromatography/mass spectrometry. The SMA-WPT fume generated in the laboratory induced a clear increase in DNA damage in BEAS 2B cells without metabolic activation. The laboratory-generated SMA fume increased the frequency of micronucleated BEAS 2B cells without metabolic activation. None of the asphalt fumes collected at the paving sites produced DNA damage with or without metabolic activation. Fumes from SMA and SMA-WPT from the paving sites increased micronucleus frequency without metabolic activation. None of the asphalt fumes studied showed mutagenic activity in Salmonella. No statistically significant differences in DNA damage in buccal leukocytes were detected between the pre- and post-shift samples collected from the road pavers. However, a positive correlation was found between DNA damage and the urinary metabolites of polycyclic aromatic hydrocarbons (PAHs) after work shift, which suggested an association between occupational exposures during road paving and genotoxic effects. Our results indicate that fumes from SMA and SMA-WPT contain direct-acting genotoxic components.

Assessment of DNA Damage in WBCs of Workers Occupationally Exposed to Fumes and Aerosols of Bitumen

We conducted a cross-shift study with 66 bitumen-exposed mastic asphalt workers and 49 construction workers without exposure to bitumen. Exposure was assessed using personal monitoring of airborne bitumen exposure, urinary 1-hydroxypyrene (1-OHP), and the sum of 1-, 2 + 9-,3-,4-hydroxyphenanthrene (OHPH). Genotoxic effects in WBC were determined with nonspecific DNA adduct levels of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) and the formation of DNA strand breaks and alkali-labile sites. Concentration of fumes and aerosols of bitumen correlated significantly with the concentrations of 1-OHP and OHPH after shift (r(s) = 0.27; P = 0.03 and r(s) = 0.55; P < 0.0001, respectively). Bitumen-exposed workers had more DNA strand breaks than the reference group (P < 0.0001) at both time points and a significant correlation with 1-OHP and OHPH in the postshift urines (r(s) = 0.32; P = 0.001 and r(s) = 0.27; P = 0.004, respectively). Paradoxically, we measured higher levels of DNA strand breaks, although not significant, in both study groups before shift. 8-OxodGuo adduct levels did not correlate with DNA strand breaks. Further, 8-oxodGuo levels were associated neither with personal exposure to bitumen nor with urinary metabolite concentrations. Significantly more DNA adducts were observed after shift not only in bitumen-exposed workers but also in the reference group. Only low-exposed workers had significantly elevated 8-oxodGuo adduct levels before as well as after shift (P = 0.0002 and P = 0.02, respectively). Our results show that exposure to fumes and aerosols of bitumen may contribute to an increased DNA damage assessed with strand breaks.

Genotoxic effects of bitumen fumes in Big Blue transgenic rat lung

Road paving workers are exposed to bitumen fumes (CAS No. 8052-42-4), a complex mixture of volatile compounds and particles containing carcinogenic and non-carcinogenic polycyclic aromatic hydrocarbons. However, epidemiological and experimental animal studies failed to draw unambiguous conclusions concerning their toxicity. In order to gain better insights on their genotoxic potential, we used an experimental design able to generate bitumen fumes at road paving temperature (temperature: 170 degrees C, total particulate matter: 100mg/m3) and perform a nose-only exposure of Big Blue transgenic rodents 6h/day for five consecutive days. The mutagenic properties of bitumen fumes were determined by analyzing the mutation frequency and spectrum of the neutral reporter gene cII inserted into the rodent genome. We previously observed in mouse lung, that bitumen fumes did not induce an increase of cII mutants, a modification of the mutation spectrum, nor the formation of DNA adducts. Since DNA adducts were found in the lungs of rats exposed to asphalt fumes in similar conditions, we decided to carry out an analogous experiment with Big Blue rats. A DNA adduct was detected 3 and 30 days after the end of treatment suggesting that these genetic alterations were quite steady. Thirty days after exposure, the cII mutant frequency was similar in control and exposed rats. In addition, a slight but not significant modification of the mutation spectrum associated with an increase of G:C to T:A and A:T to C:G transversions was noticeable in the treated animals. Then, these data failed to demonstrate a pulmonary mutagenic potential for bitumen fumes generated at road paving temperature in our experimental conditions despite the presence of a DNA adduct. These results may provide information concerning the pulmonary mechanism of action of this aerosol and may contribute to the occupational health hazard assessment.

Effects of paving asphalt fume exposure on genotoxic and mutagenic activities in the rat lung

Asphalt fumes are complex mixtures of aerosols and vapors containing various organic compounds, including polycyclic aromatic hydrocarbons (PAHs). Previously, we have demonstrated that inhalation exposure of rats to asphalt fumes resulted in dose-dependent induction of CYP1A1 with concomitant down-regulation of CYP2B1 and increased phase II enzyme quinone reductase activity in the rat lung. In the present study, the potential genotoxic effects of asphalt fume exposure due to altered lung microsomal enzymes were studied. Rats were exposed to air or asphalt fume generated under road paving conditions at various concentrations and sacrificed the next day. Alveolar macrophages (AM) were obtained by bronchoalveolar lavage and examined for DNA damage using the comet assay. To evaluate the systemic genotoxic effect of asphalt fume, micronuclei formation in bone marrow polychromatic erythrocytes (PCEs) was monitored. Lung S9 from various exposure groups was isolated from tissue homogenates and characterized for metabolic activity in activating 2-aminoanthracene (2-AA) and benzo[a]pyrene (BaP) mutagenicity using the Ames test with Salmonella typhimurium YG1024 and YG1029. This study showed that the paving asphalt fumes significantly induced DNA damage in AM, as revealed by DNA migration in the comet assay, in a dose-dependent manner, whereas the micronuclei formation in bone marrow PCEs was not detected even at a very high exposure level (1733 mg h/m3). The conversion of 2-AA to mutagens in the Ames test required lung S9-mediated metabolic activation in a dose-dependent manner. In comparison to the controls, lung S9 from rats exposed to asphalt fume at a total exposure level of 479+/-33 mg h/m3 did not significantly enhance 2-AA mutagenicity with either S. typhimurium YG1024 or YG1029. At a higher total asphalt fume exposure level (1150+/-63 mg h/m3), S9 significantly increased the mutagenicity of 2-AA as compared to the control. However, S9 from asphalt fume-exposed rats did not significantly activate the mutagenicity of BaP in the Ames test. These results show that asphalt fume exposure, which significantly altered both phases I and II metabolic enzymes in lung microsomes, is genotoxic to AM and enhances the metabolic activation of certain mutagens through altered S9 content.

Mutagenicity of bitumen and asphalt fumes

The mutagenicity of asphalt fumes was tested with the Salmonella bioassays. The aim was to investigate if recycled additives modify the genotoxicity of emissions. Recycling of old asphalt is increasing, and we studied also the mutagenicity of emissions sampled during the re-use of asphalt. The composition of vapours and fumes were analysed by gas chromatography and by liquid chromatography. Bitumens containing coal fly ash (CFA) or waste plastics were heated to the paving temperatures in the laboratory. In the field, bitumen fumes were collected during paving of stone mastic asphalts (lime or CFA as a filler), remixing of stone mastic asphalt (lime or CFA as a filler), and of asphalt concrete. All the lab-generated vapour fractions were non-mutagenic. The particulate fractions were mutagenic with TA98 in the presence of the S9 activation. In addition, the lab-fumes from bitumen containing waste plastics were positive with both strains without S9. Only particulate fractions sampled in the field were tested. They were mutagenic with and without metabolic activation with both strains. The mutagenic potency of the field samples was higher than that of the lab-generated fumes without S9, and the remixing fumes were more mutagenic than the normal paving and lab-generated fumes with S9. The use of inorganic additive, CFA, did not change the mutagenicity of the fumes, whereas the organic additive, waste plastics, increased the mutagenicity of the laboratory emissions significantly.

Bitumen fumes: review of work on the potential risk to workers and the present knowledge on its origin

Bitumens fumes contain polycyclic aromatic compounds (PAC). There is a possibility of long-term health effects following chronic exposure by inhalation or skin contamination in asphalt road pavers and highway maintenance workers. Epidemiological and experimental studies on this topic are reviewed and the possible causes of cancer discussed with a primary focus on heterocyclic polyaromatic compounds. In 2001, the results of the IARC epidemiological study confirmed an excess of lung cancer despite a lower cancer mortality. In vitro genotoxicity and mechanistic studies demonstrated a mutagenic effect of bitumen fume condensates (BFC) and some data suggested that the polycyclic aromatic hydrocarbons (PAH) analysed were not the major genotoxic compounds in bitumen fume condensates. Other compounds such as nitrogen-, sulfur- and/or oxygen-containing PAH or their alkyl substituted analogues, mutagenic in the Ames mutation assay, may be involved in the genotoxic effect of BFC. After skin painting with BFC, DNA adducts were found in skin, lung and lymphocytes of all the treated animals. Differences in the adduct patterns were also observed, but a more polar adduct was common to the three tissues and not observed in those from rats treated with coal-tar fume condensates (CTFC). Rat inhalation experiments with bitumen fumes confirmed the presence of a DNA-adduct in the lungs with the same Rf as the previous polar adduct. This adduct therefore merits further investigation as a potential biomarker in lymphocyte DNA to follow exposed workers. All the analytical data and the mechanistic data are complementary and suggest the potential role of thiophenes in the genotoxicity of bitumen fumes. Some thiophenes have lower mutagenic activity than their isosteric PAH, whereas others are very potent carcinogens. Generally, the sulfur analogues of PAH (SPAH) in bitumen fumes have a higher concentration than the PAH of similar molecular weight, whereas the SPAH in coal-tar fumes have a much lower concentration than the corresponding PAH. This may explain why the more polar adducts have been detected only in animals exposed to bitumen fume. In a skin carcinogenicity study of condensed asphalt roofing fumes, it has been demonstrated that the most active fractions were those containing a variety of aromatic SPAH. In conclusion to this review, there is an interest in determining the chemical identity of the major DNA adducts induced by BFC. This would allow experimental studies on the carcinogenic potency of these compounds and their validation as potential biomarkers. These compounds could thus merit further analytical investigation in preference to the PAH included in the list of the US Environmental Protection Agency that are currently being analysed by the industry in field studies.

Lack of genotoxicity of bitumen fumes in transgenic mouse lung

During hot application of bitumen containing materials, e.g. in hot paving or roofing, fumes are emitted that contain polycyclic aromatic compounds. Previous studies with rodents exposed to bitumen and coal-tar fume condensates showed formation of DNA adducts. In order to clarify the genotoxicity of bitumen fumes, we designed a study by using mice carrying a reporter gene for mutagenesis analysis and exposed by nose-only to a constant and reproducible aerosol of bitumen fumes. We analyzed the genotoxic activity of inhaled bitumen fumes generated under those controlled conditions through the induction of mutation and DNA adducts in Big Blue mice. Mice were exposed to bitumen fumes (100 mg/m(3) total particulate matter) 6 h per day during 5 days by nose-only in an inhalation chamber designed in our laboratory. Following a 30-day fixation period, the experiment was terminated and lung DNA was extracted for mutant frequency and adduct determinations. The mutant frequency was determined using the cII and the lacI mutant analysis systems. In, addition, 61 and 54 mutants were sequenced in control and exposed groups, respectively. The study did not show any mutation or adduct induction in the exposed group compared to the control group: cII mutant frequencies were 11.0+/-4.5x10(-5) and 11.0+/-4.8x10(-5) in control and exposed lungs, respectively. Identically, using the lacI mutation detection system, the mutant frequencies were 6.4+/-3.1x10(-5) and 5.8+/-2.0x10(-5). The mutation spectra of both series were quite similar with regard to transition and transversion frequencies. The absence of genotoxicity in the group exposed to 100 mg/m(3) bitumen is discussed with regard to dosage of inhaled polycyclic aromatic compounds and species.

Enhancement of DNA damage and involvement of reactive oxygen species after exposure to bitumen with UVA irradiation

This study was carried out to evaluate whether bitumen cytotoxicity is enhanced when bitumen treatment is combined with UVA exposure. We also evaluated the oxidative processes in bitumen-induced DNA damage, and attempted to identify the DNA damage caused by bitumen and UVA exposures, either alone or in combination. The effects of bitumen and UVA on cell proliferation were examined using HL 60 cells. DNA-protein crosslinks (DPCs) were assessed using a K-SDS assay, and reactive oxygen species formation was detected by 8-OH-dG formation. We evaluated the formations of double-strand breaks (DSB) using lambdaDNA/HindIII and single-strand breaks (SSB) using PM2 DNA. The cytotoxicity assay showed enhanced suppression of cell proliferation when bitumen exposure and UVA exposure were combined. Combined exposure caused significant increases in DPCs over either exposure alone. Incubation of deoxyguanosine (dG) with bitumen or UVA showed an increase in 8-hydroxy-2'-deoxyguanosine (8-OH-dG) levels when compared with controls, and combined exposure enhanced this effect. An evaluation of agarose gel bands showed that DSB and SSB were not formed following exposure to bitumen and UVA. This fact indicates that bitumen and UVA may be involved in genotoxic processes by producing oxygen free radicals and that combined exposure enhances these effects.

Cytogenetic biomonitoring of workers exposed to bitumen fumes

Bitumen samples and fumes consist essentially of polycyclic hydrocarbons (PAH) and their derivatives, some of which are known to be carcinogenic or co-carcinogenic in animals. The level of total PAH is low when compared with coal-tar products. There is very limited data on possible health risk from exposure to bitumen fumes in workers. In this study, sister-chromatid exchange (SCE), micronuclei (MN) and high frequency of SCE cells (HFCs) were determined for 28 workers exposed to bitumen fumes and 28 control subjects. Urinary 1-hydroxypyrene (1-OHP) excretion was used as a biomarker of occupational exposure to PAH. The mean value of 1-OHP excretion of workers was 0.78+/-0.46 micromol/mol creatinine and for controls 0.52+/-0.44 micromol/mol creatinine (p<0.05). The mean values of SCE per cell and the frequency ( per thousand) of MN in peripheral lymphocytes from the workers and controls were 5.13+/-0. 64, 4.71+/-0.67, and 2.25+/-0.42, 1.79+/-0.32 respectively (p<0.05, p<0.0001). The mean value of HFCs for workers and controls were 7. 85+/-2.3 and 7.05+/-3.16, respectively (p>0.05). Our data reveal that bitumen fumes during road paving operations are absorbed by workers and that bitumen fume exposure is able to significantly induce cytogenetic damage in peripheral lymphocytes of workers after controlling some possible confounding factors, such as age, sex and smoking habits.

Implication of cytochrome P-450 1A isoforms and the AH receptor in the genotoxicity of coal-tar fume condensate and bitumen fume condensates

During the hot application of bitumen- or coal-tar-containing materials, fumes are emitted that contain polycyclic aromatic compounds. Although workers' exposure to these fumes is low, it might lead to health problems. No study has reported the metabolic pathways involved in the genotoxicity of coal tar or bitumen fume condensates (CTFC, BFCs). We have therefore studied the DNA adducts formed by incubation of CTFC or BFCs with liver microsomes from several type of mice and with yeast microsomes expressing individual human CYP enzymes. Our results demonstrates that: (1) the aryl hydrocarbon receptor (AHR) plays an important role in the biotransformation of BFCs and to a lesser extent of CTFC; (2) for CTFC, both cytochrome P450 (CYP) 1A isoforms are involved in the formation of genotoxic compounds, and the reactive metabolites formed via CYP 1A1, are substrates for epoxide hydrolase (mEH); (3) for BFCs, the genotoxicity is partially dependent upon CYP 1A1 and the reactive metabolites are not substrates for mEH; (4) CYP 1A isoforms are not exclusively responsible for the genotoxicity of the CTFC and BFCs as other CYPs and also enzymes of the [AH] gene battery, may play an important role.