Low-level Benzene Exposure Research Articles

Leukemia risk assessment of exposure to low-levels of benzene based on the linearized multistage model.

To assess leukemia risk in occupational populations exposed to low levels of benzene. Leukemia incidence data from the Chinese Benzene Cohort Study were fitted using the Linearized multistage (LMS) model. Individual benzene exposure levels, urinary S-phenylmercapturic acid (S-PMA) and trans, trans-muconic acid (t, t-MA) were measured among 98 benzene-exposed workers from factories in China. Subjects were categorized into four groups by rounding the quartiles of cumulative benzene concentrations (< 3, 3-5, 5-12, ≥12 mg/m3·year, respectively). The risk of benzene-induced leukemia was assessed using the LMS model, and the results were validated using the EPA model and the Singapore semi-quantitative risk assessment model. The leukemia risks showed a positive correlation with increasing cumulative concentration in the four exposure groups (excess leukemia risks were 4.34, 4.37, 4.44 and 5.52 × 10-4, respectively; Ptrend < 0.0001) indicated by the LMS model. We also found that the estimated leukemia risk using urinary t, t-MA in the LMS model was more similar to those estimated by airborne benzene compared to S-PMA. The leukemia risk estimated by the LMS model was consistent with both the Singapore semi-quantitative risk assessment model at all concentrations and the EPA model at high concentrations (5-12, ≥12 mg/m3·year), while exceeding the EPA model at low concentrations (< 3 and 3-5 mg/m3·year). However, in all four benzene-exposed groups, the leukemia risks estimated by these three models exceeded the lowest acceptable limit for carcinogenic risk set by the EPA at 1 × 10-6. This study demonstrates the utility of the LMS model derived from the Chinese benzene cohort in assessing leukemia risk associated with low-level benzene exposure, and suggests that leukemia risk may occur at cumulative concentrations below 3 mg/m3·year.

Adult-Onset Transcriptomic Effects of Developmental Exposure to Benzene in Zebrafish (Danio rerio): Evaluating a Volatile Organic Compound of Concern.

Urban environments are afflicted by mixtures of anthropogenic volatile organic compounds (VOCs). VOC sources that drive human exposure include vehicle exhaust, industrial emissions, and oil spillage. The highly volatile VOC benzene has been linked to adverse health outcomes. However, few studies have focused on the later-in-life effects of low-level benzene exposure during the susceptible window of early development. Transcriptomic responses during embryogenesis have potential long-term consequences at levels equal to or lower than 1 ppm, therefore justifying the analysis of adult zebrafish that were exposed during early development. Previously, we identified transcriptomic alteration following controlled VOC exposures to 0.1 or 1 ppm benzene during the first five days of embryogenesis using a zebrafish model. In this study, we evaluated the adult-onset transcriptomic responses to this low-level benzene embryogenesis exposure (n = 20/treatment). We identified key genes, including col1a2 and evi5b, that were differentially expressed in adult zebrafish in both concentrations. Some DEGs overlapped at the larval and adult stages, specifically nfkbiaa, mecr, and reep1. The observed transcriptomic results suggest dose- and sex-dependent changes, with the highest impact of benzene exposure to be on cancer outcomes, endocrine system disorders, reproductive success, neurodevelopment, neurological disease, and associated pathways. Due to molecular pathways being highly conserved between zebrafish and mammals, developmentally exposed adult zebrafish transcriptomics is an important endpoint for providing insight into the long term-effects of VOCs on human health and disease.

Let-7e-5p, a promising novel biomarker for benzene toxicity, is involved in benzene-induced hematopoietic toxicity through targeting caspase-3 and p21

Benzene is a common industrial chemical and environmental pollutant. However, the mechanism of hematotoxicity caused by exposure to low doses of benzene is unknown. Let-7e-5p pathway regulatory networks were constructed by bioinformatics analysis using a benzene-induced aplastic anemia (BIAA) mouse model. The MTT assay, EdU staining, flow cytometric analysis, dual luciferase reporter gene assay, and RIP assay were utilized to evaluate the effects of benzoquinone (1,4-BQ) on let-7e-5p pathway. This study consisted of 159 workers with a history of low-level benzene exposure and 159 workers with no history of benzene exposure. After the confounding factors were identified, the associations between let-7e-5p expression and hematotoxicity were assessed by multiple linear regression. Furthermore, we used four machine learning algorithms (decision trees, neural network, Bayesian network, and support vector machines) to construct a predictive model for detecting benzene-causing hematotoxicity in workers. In this study, compared with respective controls, let-7e-5p expression was decreased in BIAA mice and benzene-exposed workers. After 1,4-BQ exposure, let-7e-5p overexpression negatively regulated caspase-3 and p21 expression, protected cells from apoptosis, and facilitated cell proliferation. RIP assays, and dual luciferase reporter gene assays confirmed that let-7e-5p could target p21 and caspase-3 and regulate the cell cycle and apoptosis. The support vector machines classifier achieved the best prediction of benzene-induced hematotoxicity (prediction accuracy = 88.27, AUC = 0.83) by statistically characterizing the internal dose of benzene exposure and the oxidative stress index, as well as the expression levels of let-7e-5p pathway-related genes in benzene-exposed workers. Let-7e-5p may be a potential therapeutic target of benzene-induced hematotoxicity, provide a basis for evaluating the health hazards of long-term and low-dose benzene exposure in workers, and supply a reference for revising occupational health standards.

Meta-analysis of the effect of low-level occupational benzene exposure on human peripheral blood leukocyte counts in China

To investigate the effect of low-level occupational benzene exposure on human peripheral blood leukocyte counts of the workers, domestic and foreign published research data on the change of human peripheral blood leukocyte counts under low-level occupational benzene exposure from January 1990 to December 2020 were collected and analyzed. According to the literature inclusion and exclusion criteria, 18 independent studies from 12 publications were selected for meta-analysis to explore the effect of low-level occupational benzene exposure on human peripheral blood leukocyte counts. The results showed that the peripheral blood leukocyte counts abnormal rates of low-level occupational benzene exposure group were higher than those of the control group, and the difference was statistically significant. Low-level occupational benzene exposure could result in a relatively higher abnormal rate of peripheral blood leukocyte counts in the exposed population, indicating that low-level occupational benzene exposure at workplaces specified by the current benzene occupational exposure limit in China would affect the peripheral blood leukocyte counts of the workers, thus benzene with concentrations under the limit in the ambient air of workplace could be still harmful to the health of the exposed workers. The results of this study could provide a scientific basis for future revision of the benzene occupational exposure limit in China, and could also be a reference for the formulation of environmental standard concerning benzene in China in the future.

A SIMPLE AND SENSITIVE LC-MS/MS METHOD FOR THE DETERMINATION OF S-PHENYLMERCAPTURIC ACID IN HUMAN URINE

Benzene is an important environmental and occupational pollutant, and recognized as human carcinogen. S-phenylmercapturic acid (SPMA) is a highly specific biomarker of exposure to benzene, applied in occupational toxicology to assess low levels of benzene exposure. The objective of this study was to develop and validate a one-step liquid extraction bioanalytical method for the quantification of SPMA in urine by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The method was applied to the evaluation of benzene exposure in an occupational setting. The assay was linear from 0.5 to 500 ng mL-1 (r>0.99), accurate (91.4-105.2%) and precise, with CV% between 4.73 and 9.96%. SPMA was stable in urine for 90 days at -20 °C. Airborne benzene concentrations, urinary levels of SPMA and t,t-MA were significantly higher in gas station workers (n=30) in comparison to outdoor workers (n=14) and individuals non-occupationally exposed to benzene (n=34). Benzene airborne levels had higher correlation with urinary SPMA (r=0.532, p<0.001) than with t,t-MA (r=0.338, p=0.04), demonstrating the applicability of this biomarker for monitoring low levels of benzene exposure.

Enhanced H3K4me3 modifications are involved in the transactivation of DNA damage responsive genes in workers exposed to low-level benzene

In this study, we explore whether altered global histone modifications respond to low-level benzene exposure as well as their association with the hematotoxicity. We recruited 147 low-level benzene-exposed workers and 122 control workers from a petrochemical factory in Maoming City, Guangdong Province, China. The internal exposure marker level, urinary S-phenylmercapturic acid (SPMA), in benzene-exposed workers was 1.81-fold higher than that of the controls (P<0.001). ELISA method was established to examine the specific histone modifications in human peripheral blood lymphocytes (PBLCs) of workers. A decrease in the counts of white blood cells (WBC), neutrophils, lymphocytes, and monocytes appeared in the benzene-exposed group (all P<0.05) compared to the control group. Global trimethylated histone 3 lysine 4 (H3K4me3) modification was enhanced in the benzene-exposed group (P<0.05) and was positively associated with the concentration of urinary SPMA (β=0.103, P=0.045) and the extent of DNA damage (% Tail DNA: β=0.181, P=0.022), but was negatively associated with the leukocyte count (WBC: β=-0.038, P=0.023). The invitro study revealed that H3K4me3 mark was enriched in the promoters of several DNA damage responsive (DDR) genes including CRY1, ERCC2, and TP53 in primary human lymphocytes treated with hydroquinone. Particularly, H3K4me3 modification was positively correlated with the expression of CRY1 in the PBLCs of benzene-exposed workers. These observations indicate that H3K4me3 modification might mediate the transcriptional regulation of DDR genes in response to low-dose benzene exposure.

Evidence for non-linear metabolism at low benzene exposures? A reanalysis of data

The presence of a high-affinity metabolic pathway for low level benzene exposures of less than one part per million (ppm) has been proposed although a pathway has not been identified. The variation of metabolite molar fractions with increasing air benzene concentrations was suggested as evidence of significantly more efficient benzene metabolism at concentrations <0.1 ppm The evidence for this pathway is predicated on a rich data set from a study of Chinese shoe workers exposed to a wide range of benzene concentrations (not just “low level”). In this work we undertake a further independent re-analysis of this data with a focus on the evidence for an increase in the rate of metabolism of benzene exposures of less than 1 ppm.The analysis dataset consisted of measurements of benzene and toluene from personal air samplers, and measurements of unmetabolised benzene and toluene and five metabolites (phenol hydroquinone, catechol, trans, trans-muconic acid and s-phenylmercapturic acid) from post-shift urine samples for 213 workers with an occupational exposure to benzene (and toluene) and 139 controls. Measurements from control subjects were used to estimate metabolite concentrations resulting from non-occupational sources, including environmental sources of benzene. Data from occupationally exposed subjects were used to estimate metabolite concentrations as a function of benzene exposure. Correction for background (environmental exposure) sources of metabolites was achieved through a comparison of geometric means in occupationally exposed and control populations. The molar fractions of the five metabolites as a function of benzene exposure were computed.A supra-linear relationship between metabolite concentrations and benzene exposure was observed over the range 0.1–10 ppm benzene, however over the range benzene exposures of between 0.1 and 1 ppm only a modest departure from linearity was observed. The molar fractions estimated in this work were near constant over the range 0.1–10 ppm. No evidence of high affinity metabolism at these low level exposures was observed. Our reanalysis brings in to question the appropriateness of the dataset for commenting on low dose exposures and the use of a purely statistical approach to the analysis.

Promoter methylation status in genes related with inflammation, nitrosative stress and xenobiotic metabolism in low-level benzene exposure: Searching for biomarkers of oncogenesis

Exposure to low levels of benzene may cause acute myeloid leukemia in humans. Epigenetic effects in benzene exposure have been studied for tumor suppressor genes and oxidative stress-related genes, but other cellular pathways must be explored. Here, we studied promoter DNA methylation of IL6, CYP2E1 and iNOS in blood cells from three groups of workers: a) gas station attendants (GS) exposed to low levels of benzene; b) plastic shoe factory workers (PS) exposed to other solvents different to benzene and c) administrative workers as a reference group with no solvent exposure (C). Results: IL6 promoter methylation was higher in GS workers (p < 0.05). Also in GS, CYP2E1 promoter methylation negatively correlated with benzene levels (r = −0.47, p < 0.05); iNOS promoter methylation positively correlated with CYP2E1 promoter methylation (r = 0.29, p < 0.05), cumulative time of exposure (r = 0.31, p < 0.05) as well as with urinary levels of S- Phenyl mercapturic acid (SPMA), (r = 0.55, p < 0.05). Our results demonstrate alterations in the inflammation pathway at the epigenetic level associated with exposure to benzene. Correlations between iNOS methylation with both CYP2E1 methylation and urinary SPMA levels represent novel evidence about CYP2E1 epigenetic regulation and activity related with nitrosative stress, making promoter methylation status of these genes a potential biomarker in early stages of oncogenesis.

Urinary Trans, Trans-Muconic Acid is Not a Reliable Biomarker for Low-level Environmental and Occupational Benzene Exposures.

BackgroundBenzene is a known occupational and environmental pollutant. Its urinary metabolite trans, trans-muconic acid (tt-MA) has been introduced by some environmental and occupational health regulatory associations as a biological index for the assessment of benzene exposure; however, recently, doubts have been raised about the specificity of tt-MA for low-level benzene exposures. In the present study, we investigated the association between urinary levels of tt-MA and inhalational exposure to benzene in different exposure groups.MethodsBenzene exposure was assessed by personal air sampling. Collected benzene on charcoal tube was extracted by carbon disulfide and determined by a gas chromatograph (gas chromatography with a flame ionization detector). Urinary tt-MA was extracted by a strong anion-exchange column and determined with high-performance liquid chromatography–UV.ResultsUrinary levels of tt-MA in intensive benzene exposure groups (chemical workers and police officers) were significantly higher than other groups (urban and rural residents), but its levels in the last two groups with significant different exposure levels (mean = 0.081 ppm and 0.019 ppm, respectively) showed no significant difference (mean = 388 μg/g creatinine and 282 μg/g, respectively; p < 0.05). Before work shift, urine samples of workers and police officers showed a high amount of tt-MA and its levels in rural residents’ samples were not zero.ConclusionOur results suggest that tt-MA may not be a reliable biomarker for monitoring low-level (below 0.5 ppm) benzene exposures.

Incidence of Myelodysplastic Syndrome in UK Petroleum Distribution and Oil Refinery Workers, 1995-2011.

The incidence of myelodysplastic syndrome (MDS) experienced by cohorts of 16,467 petroleum distribution workers and 28,554 oil refinery workers has been investigated. Study subjects were all those male employees first employed at one of 476 UK petroleum distribution centres or eight UK oil refineries in the period 1946–1974; all subjects had a minimum of twelve months employment with some employment after 1st January, 1951. Observed numbers (Obs) of MDS cases were compared with expectations based on national incidence rates for the period 1995–2011. The overall standardised registration ratio (SRR) was 73 (Obs = 17) in petroleum distribution workers for the age-range 15–84 years, and 77 (Obs = 21) for the age-range 15–99 years. The overall SRR was 81 (Obs = 29) in oil refinery workers for the age-range 15–84 years, and 83 (Obs = 36) for the age-range 15–99 years. More detailed analyses were carried out in terms of year of registration, period from hire, decade of hire, and duration of employment. The overall SRR findings did not provide clear evidence for the presence of an occupational cancer hazard, and provide no support for the hypothesis that low-level benzene exposure has an important effect on the risks of MDS.

DNA damage and repair capacity in workers exposed to low concentrations of benzene.

DNA damage and cellular repair capacity were studied in 18 male fuel tanker drivers and 13 male filling-station attendants exposed to low and very low concentrations of benzene, respectively, and compared to 20 males with no occupational exposure (controls). Exposure to airborne benzene was measured using passive personal samplers, and internal doses were assayed through the biomarkers t,t-muconic acid, S-phenylmercapturic acid and urinary benzene. DNA damage was evaluated using tail intensity (TI) determined by the comet assay in peripheral lymphocytes. Urinary 7-hydro-8-oxo-2'-deoxyguanosine (8-oxodG) was measured as a biomarker of oxidative damage. DNA repair kinetics were assessed using the comet assay in lymphocytes sampled 20 and 60 min post H2O2 exposure. Benzene exposure differed significantly between the drivers (median 246.3 µg/m(3)), attendants (median 13.8 µg/m(3)), and controls (median 4.1 µg/m(3)). There were no differences in TI and 8-oxodG among the three groups, or between smokers and non-smokers. DNA repair kinetics were similar among the drivers, attendants and controls, although the comet assay on H2 O2 -damaged lymphocytes after 60 min revealed significantly lower levels of TI only in drivers. The DNA repair process in smokers was similar to that observed in drivers. In conclusion, this study found no relationship between low levels of benzene exposure and DNA damage, although there was evidence that exposure interferes with DNA repair kinetics. The biological impact of this finding on the onset of genotoxic effects in exposed workers has still to be ascertained.

The relationship between low-level benzene exposure and blood cell counts in Korean workers

ObjectivesBenzene is a well-known haematological toxin causing aplastic anaemia and leukaemia. Some recent studies have shown that low-level benzene exposure (<1 ppm) disturbs the haematopoietic system. However, other studies showed...

0159 The relationship between low level benzene exposure and blood cell counts in Korean workers

ObjectivesBenzene is a well-known haematological toxin causing aplastic anaemia and leukaemia. Recent studies showed that low level benzene less than 1ppm disturbs the hematopoietic system. However, other studies did not...

Characterization of changes in gene expression and biochemical pathways at low levels of benzene exposure.

Benzene, a ubiquitous environmental pollutant, causes acute myeloid leukemia (AML). Recently, through transcriptome profiling of peripheral blood mononuclear cells (PBMC), we reported dose-dependent effects of benzene exposure on gene expression and biochemical pathways in 83 workers exposed across four airborne concentration ranges (from <1 ppm to >10 ppm) compared with 42 subjects with non-workplace ambient exposure levels. Here, we further characterize these dose-dependent effects with continuous benzene exposure in all 125 study subjects. We estimated air benzene exposure levels in the 42 environmentally-exposed subjects from their unmetabolized urinary benzene levels. We used a novel non-parametric, data-adaptive model selection method to estimate the change with dose in the expression of each gene. We describe non-parametric approaches to model pathway responses and used these to estimate the dose responses of the AML pathway and 4 other pathways of interest. The response patterns of majority of genes as captured by mean estimates of the first and second principal components of the dose-response for the five pathways and the profiles of 6 AML pathway response-representative genes (identified by clustering) exhibited similar apparent supra-linear responses. Responses at or below 0.1 ppm benzene were observed for altered expression of AML pathway genes and CYP2E1. Together, these data show that benzene alters disease-relevant pathways and genes in a dose-dependent manner, with effects apparent at doses as low as 100 ppb in air. Studies with extensive exposure assessment of subjects exposed in the low-dose range between 10 ppb and 1 ppm are needed to confirm these findings.

Aberrant Hypomethylated KRAS and RASGRF2 as a Candidate Biomarker of Low Level Benzene Hematotoxicity

Benzene is an important industrial chemical and an environmental contaminant. The mechanisms of low level benzene-induced hematotoxicity are unresolved. Aberrant DNA methylation, which may lead to genomic instability and the altered gene expression, is frequently observed in hematological cancers. The purpose of the present study was to conduct a genome-wide investigation to examine comprehensively whether low level benzene induces DNA methylation alteration in the benzene-exposed workers. Infinium 450K methylation array was used to compare methylation levels of the low level benzene-exposed individuals and health controls and the differentially expressed DNA methylation pattern critical for benzene hematotoxicity were screened. Signal net analysis showed that two key hypomethylated KRAS and RASGRF2 associated with low level benzene exposure were identified. Further, the hypomethylated RASGRF2 gene played central roles through regulation of Rho protein, MAPK, small GTPase mediated signal transduction. While the hypomethylated KRAS gene played important roles through small GTPase, Ras protein, MAPK cascade, Gap junction, Axon guidance, Tight junction, GnRH, T cell receptor signaling pathway, Acute myeloid leukemia, B cell receptor signaling pathway, Chronic myeloid leukemia, ErbB signaling pathway. Our preliminary study indicated that aberrant hypomethylated KRAS and RASGRF2 might be a potential methylated biomarker of low level benzene hematotoxicity.

Increased Mitochondrial DNA Copy Number in Occupations Associated with Low-Dose Benzene Exposure

Background: Benzene is an established leukemogen at high exposure levels. Although low-level benzene exposure is widespread and may induce oxidative damage, no mechanistic biomarkers are available to detect biological dysfunction at low doses.Objectives: Our goals were to determine in a large multicenter cross-sectional study whether low-level benzene is associated with increased blood mitochondrial DNA copy number (mtDNAcn, a biological oxidative response to mitochondrial DNA damage and dysfunction) and to explore potential links between mtDNAcn and leukemia-related epigenetic markers.Methods: We measured blood relative mtDNAcn by real-time polymerase chain reaction in 341 individuals selected from various occupational groups with low-level benzene exposures (> 100 times lower than the Occupational Safety and Health Administration/European Union standards) and 178 referents from three Italian cities (Genoa, Milan, Cagliari).Results: In each city, benzene-exposed participants showed higher mtDNAcn than referents: mtDNAcn was 0.90 relative units in Genoa bus drivers and 0.75 in referents (p = 0.019); 0.90 in Milan gas station attendants, 1.10 in police officers, and 0.75 in referents (p-trend = 0.008); 1.63 in Cagliari petrochemical plant workers, 1.25 in referents close to the plant, and 0.90 in referents farther from the plant (p-trend = 0.046). Using covariate-adjusted regression models, we estimated that an interquartile range increase in personal airborne benzene was associated with percent increases in mtDNAcn equal to 10.5% in Genoa (p = 0.014), 8.2% (p = 0.008) in Milan, 7.5% in Cagliari (p = 0.22), and 10.3% in all cities combined (p < 0.001). Using methylation data available for the Milan participants, we found that mtDNAcn was associated with LINE-1 hypomethylation (–2.41%; p = 0.007) and p15 hypermethylation (+15.95%, p = 0.008).Conclusions: Blood MtDNAcn was increased in persons exposed to low benzene levels, potentially reflecting mitochondrial DNA damage and dysfunction.

Hematological changes among Beninese motor-bike taxi drivers exposed to benzene by urban air pollution

Exposure to high-concentration of benzene in polluted air has been associated with bone marrow deficiency, aplastic anemia and leukemia. However, epidemiological studies have reported conflicting data following human exposure to benzene levels below 1 ppm (that is, 3.2 mg/m3). Therefore we investigated the influence of outdoor air benzene on peripheral blood cells among exposed motor-biketaxi drivers (MBTD) in which specific IgG antibodies against reactive benzene metabolites, such as hydroquinone (HQ) and para-benzoquinone (p-BQ) are identified and quantified for further use as biomarker of exposure. We compared 144 MBTD with 30 unexposed age and sex-matched controls. The mean age ± SD (95% CI) were: MBTD 39.5 ± 7.82 (38.2 - 40.7) and village residents 40.3 ± 10.56 (39.1-43.0). Personal benzene exposure was assessed using GABIE diffusive samplers. The levels of specific IgG antibodies to HQ and p-BQ were determined by ELISA. The peripheral blood cells were counted by an automated analyzer. Benzene, Toluene and Xylene levels were much higher in MBTD in comparison to the control group. Benzene exposure levels ranged from 0.012 to 0.550 ppm in MBTD. Their average exposure level per one week was 0.126±0.206 ppm. Accordingly, MBTD had significantly higher levels of specific IgG antibodies to HQ and p-BQ compared to the controls (p< 0.001). WBC, lymphocytes, eosinophils and platelets were significantly decreased in MBTD, whereas RBC and other blood cell numbers remained unchanged. Total WBC, lymphocytes and eosinophils counts were decreased among exposed MBTD compared to unexposed controls. We suggest the use of these blood parameters together with specific IgG antibodies to HQ and p-BQ as biomarkers in biological monitoring of low level benzene exposure. Larger studies are however required to validate this new approach of health survey in workers exposed to benzene. Key words: Benzene, motor-bike-taxi drivers, specific immune responses, peripheral blood cell count.

Risk of leukemia as a result of community exposure to gasoline vapors: A follow-up study

Objectives To assess the temporal and spatial relationship of risk for total leukemia and AML (acute myelogenous leukemia) among community residents of an area in northeastern (NE) Pennsylvania (PA) affected by the Tranguch Gasoline Spill which occurred in the early 1990s. Methods Standardized incidence ratios (SIR) were calculated for total leukemia and AML among 625 residents affected by the gasoline spill in relation to both PA and local county cancer incidence rates. The risk of total leukemia and AML among the gasoline exposed population was evaluated for the period prior to the spill, 1985–1989; during the time surrounding the spill, 1990–1994; and for a period subsequent to the spill, 1995–2001. Results The incidence of total leukemia and AML was significantly elevated subsequent to the spill for the entire period 1990–2001 and was highest for the period 1995–2001, whether comparison was made to PA or local county leukemia rates. Based on comparison to PA rates, the SIRs for total leukemia and AML were 7.69 (95% CI=1.58–22.46) and 11.54 (95% CI=2.38–33.69) for the 1995–2001 period, respectively. Prior to the spill, 1985–1989, and during the period of the spill, 1990–1994, no cases of leukemia were identified among the affected residents. Conclusions These results suggest a possible association between chronic low level benzene exposure and increased risk of leukemia among residents of the Tranguch Spill Site in NE PA. Our study provides additional support to the growing body of evidence implicating low level benzene exposure and cancer risk. We recommend that other communities contaminated with gasoline vapor through leaking underground storage vessels be monitored for elevated risk of leukemia.

Low occupational exposure to benzene in a petrochemical plant: Modulating effect of genetic polymorphisms and smoking habit on the urinary t,t-MA/SPMA ratio

The identification of reliable biomarkers is critical for the assessment of occupational exposure of benzene: S-phenylmercapturic acid (SPMA) and trans,trans-muconic acid (t,t-MA) are the most currently used. t,t-MA is an open-ring metabolite, but it is also a metabolite of the food preservative sorbic acid, while SPMA is formed by conjugation with glutathione, and several studies suggested that the genetic polymorphism of glutathione S-transferases modulates its production. This study compared the ability of these metabolites to assess the benzene exposure in a big group of petrochemical workers. Furthermore, investigated how genetic polymorphism of glutathione S-transferase theta 1 (GSTT1), glutathione S-transferase mu 1 (GSTM1), glutathione S-transferase pi 1 (GSTP1) and smoking habits, may influence their excretion. Results showed that occupational exposure to benzene was negligible compared to that from smoking and confirmed the modulating effect of the genetic polymorphism of GSTT1 on the urinary excretion of SPMA, but not of t, t-MA, even at very low levels of benzene exposure. The same effect was found for GSTM1, but only for smokers. The t,t-MA/SPMA ratio was not a constant value and resulted to be higher than the corresponding Biological Exposure Index (BEI) ratio, which is currently equal to 20. Higher values of metabolite have been associated with the GSTT1 or GSTM1 null genotype and these are responsible for increase health risk. We suggest that this ratio could be used as a marker of individual susceptibility for subjects with benzene exposure.

Abstract 3450: Changes in mitochondrial DNA copy number in subjects exposed to low-dose benzene

Abstract BACKGROUND: Benzene is a recognized hematotoxic and leukemogenic agent at high exposures, but whether low benzene levels found nowadays in the environment and selected occupational settings cause any hematotoxicity is unresolved. Exposure to benzene at very high doses has been recently shown to increase mitochondrial DNA copy number (mtDNAcn), as a mechanism to compensate for damaged mitochondria. OBJECTIVES: To evaluate whether low-dose benzene exposure was related with mtDNAcn in blood from 527 subjects from three Italian cities. METHODS: We measured mtDNAcn in blood leukocytes from 366 subjects exposed to benzene in working environments (petrochemical workers, airport refuelling workers, bus drivers, gas station attendants and traffic police officers) and 161 referent office workers in Milan, Cagliari, and Genoa. Individual exposure to benzene was determined by means of a Chromosorb 106 passive sampler, worn by the study subjects near the breathing zone during the work shift. Benzene concentrations were 53.3 μg/m3 (95% CI: 42.1 - 64.5 μg/m3) in the exposed subjects and 11.4 μg/m3 (95% CI: 8.4 - 14.4 μg/m3) in the referents. Benzene levels were almost twice as high in Milan and Cagliari (mean = 51.9 μg/m3 and 51.6 μg/m3, respectively) as in Genoa (mean = 20.5 μg/m3). Relative mtDNAcn was measured by a quantitative real-time PCR assay determining the ratio of mtDNAcn to single copy nuclear gene (human beta-globin) copy number in experimental samples. Statistical analyses included univariate analysis with non-parametric tests for differences among exposure categories and multivariate linear regression analyses, adjusting for main confounders of interest (sex, age, city of origin, educational level, smoking habit, alcohol consumption). RESULTS: mtDNAcn increased in association with increasing exposures due to different occupations. In Cagliari, mtDNAcn was 1.88 in petrochemical workers (highest exposure), 1.80 in airport refuelling workers (intermediate exposure), 1.71 in subjects living near a petrochemical plant (low exposure), and 1.21 in referent subjects (p-trend = 0.0001). In Genoa, mtDNAcn was 0.98 in bus drivers (exposed group), and 0.83 in referent subjects (p-trend = 0.0121). In Milan, mtDNAcn was 0.92 in gas station attendants (high exposure), 1.19 in traffic police officers (intermediate exposure), and 0.82 in referent subjects (p-trend = 0.0001). In the entire study population, personal airborne benzene levels were positively associated with mtDNAcn (β = 0.055, 95% CI: 0.015 - 0.096; p = 0.008). CONCLUSIONS: Benzene exposure may induce mtDNA amplification at low-doses, a potential response to oxidative stress caused by benzene-induced production of reactive oxygen species. Our results indicate potential toxicity of low-level benzene exposures due to mitochondrial dysfunction. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3450.