Effects of inhaled combined Benzene, Toluene, Ethylbenzene, and Xylenes (BTEX): Toward an environmental exposure model

Combined environmental exposures to the volatile organic compounds (VOCs) Benzene, Toluene, Ethylbenzene, and Xylene (BTEX) pose clear risks to public health. Research into these risks is under-studied even as BTEX levels in the atmosphere are predicted to rise. This review focuses on the available literature using single- and combined-BTEX component inhaled solvent exposures in animal models, necessarily also drawing on findings from models of inhalant abuse and occupational exposures. Health effects of these exposures are discussed for multiple organ systems, but with particular attention on neurobehavioral outcomes such as locomotor activity, impulsivity, learning, and psychopharmacological responses. It is clear that animal models have significant differences in the concentrations, durations and patterns of exposure. Experimental evidence of the deleterious health and neurobehavioral consequences of exposures to the individual components of BTEX were found, but these effects were typically assessed using concentrations and exposure patterns not characteristic of environmental exposure. Future studies with animal models designed appropriately to explore combined BTEX will be necessary and advantageous to discovering health outcomes and more subtle neurobehavioral impacts of long-term environmental exposures.

Association of benzene exposure with insulin resistance, SOD, and MDA as markers of oxidative stress in children and adolescents

Benzene is a ubiquitous environmental pollutant with various health effects. It is reported that benzene exposure might be associated with insulin resistance in elderly adults. The aim of this study is to investigate the association between urinary benzene metabolite, trans, trans-muconic acid (t,t-ma) and markers of oxidative stress and insulin resistance in children and adolescents. This cross-sectional study was conducted in 2017 among 86 children and adolescents, aged 6-18 years, living in Isfahan, Iran. t,t-ma was measured as urinary benzene metabolite and homeostasis model assessment (HOMA-IR) was determined as an index of insulin resistance. Moreover, malondialdehyde (MDA) and superoxide dismutase (SOD) were assessed as oxidative stress markers. We found significant association between insulin resistance, fasting blood glucose, and fasting blood insulin with t,t-ma (p values = 0.002, 0.03, and 0.001, respectively). Results of this study indicate that benzene metabolite in higher concentrations in comparison with lower concentrations is associated with increased risk of insulin resistance. Moreover, after adjustment for age, sex, and household passive smoking, statistically significant increase were documented in SOD and MDA (4.49- and 3.54-fold, respectively) in intermediate levels of t,t-ma vs. low levels of t,t-ma (p values = 0.01 and 0.034, respectively). To the best of our knowledge, this is the first study in its kind in the pediatric age group. It showed that benzene exposures, even in environmental levels, might be associated with insulin resistance and oxidative stress in children and adolescents. Further longitudinal studies are necessary to assess the clinical impacts of this finding.

In vitro human skin permeation of benzene in gasoline: Effects of concentration, multiple dosing and skin preparation

In vitro human skin benzene permeation was measured from gasoline formulations with benzene concentrations ranging from 0.8 to 10 vol% and from neat benzene. Steady-state fluxes (JSS), permeability coefficients (kp) and lag times (tlag) were calculated from infinite dose exposures. Permeation of benzene from small gasoline doses administered over a two-day period was also studied. The thermodynamic activity of benzene in gasoline at 30 °C was determined and the solution is near-ideal over the range from 0.8 to 100 vol%. JSS through human epidermal membranes were linear (R2=0.92) with concentration over the range from 0.8 to 10 vol%. JSS (μg/cm2/h) from gasoline (0.8 vol% benzene=6.99 mg/ml) through epidermis and full-thickness skin were 9.37±1.41 and 1.82±0.44, respectively. Neat benzene JSS was 566±138. Less than 0.25% of the total applied benzene mass from finite doses (10 μl/cm2) of gasoline was detected in receptor cells, and a small reduction of barrier function was observed from six total doses administered over 2 days. Application of these results to dermal exposure assessment examples demonstrates a range of systemic benzene uptakes that can be expected from occupational and consumer dermal exposures to gasoline, depending on the type and extent of exposure.

Validation of Armadillo officinalis Dumèril, 1816 (Crustacea, Isopoda, Oniscidea) as a bioindicator: in vivo study of air benzene exposure

This study tests the potential for using Armadillo officinalis as a bioindicator of exposure to and activation of benzene metabolic pathways using an in vivo model. A. officinalis specimens collected in a natural reserve were divided into a control and three test groups exposed to 2.00, 5.32 or 9.09 µg/m(3) benzene for 24h. Three independent tests were performed to assess model reproducibility. Animals were dissected to obtain three pooled tissue samples per group: hepatopancreas (HEP), other organs and tissues (OOT), and exoskeleton (EXO). Muconic acid (MA), S-phenylmercapturic acid (S-PMA), two human metabolites of benzene, and changes in mtDNA copy number, a human biomarker of benzene exposure, were determined in each sample; benzene was determined only in EXO. MA was measured by high-performance liquid chromatography (HPLC) with ultraviolet (UV) detection, S-PMA by triple quadrupole mass spectrometer liquid chromatography with electro spray ionization (LC-MS-ESI-TQD), mtDNA by real-time quantitative PCR and end-point PCR, and benzene by quadrupole mass spectrometer head-space gas chromatography (HSGC-MS). MA and S-PMA levels rose both in HEP and OOT; EXO exhibited increasing benzene concentrations; and mtDNA copy number rose in HEP but not in OOT samples. Overall, our findings demonstrate that A. officinalis is a sensitive bioindicator of air benzene exposure and show for the first time its ability to reproduce human metabolic dynamics.

Assessing human variability in kinetics for exposures to multiple environmental chemicals: a physiologically based pharmacokinetic modeling case study with dichloromethane, benzene, toluene, ethylbenzene, and m-xylene

The objective of this study was to compare the magnitude of interindividual variability in internal dose for inhalation exposure to single versus multiple chemicals. Physiologically based pharmacokinetic models for adults (AD), neonates (NEO), toddlers (TODD), and pregnant women (PW) were used to simulate inhalation exposure to "low" (RfC-like) or "high" (AEGL-like) air concentrations of benzene (Bz) or dichloromethane (DCM), along with various levels of toluene alone or toluene with ethylbenzene and xylene. Monte Carlo simulations were performed and distributions of relevant internal dose metrics of either Bz or DCM were computed. Area under the blood concentration of parent compound versus time curve (AUC)-based variability in AD, TODD, and PW rose for Bz when concomitant "low" exposure to mixtures of increasing complexities occurred (coefficient of variation (CV) = 16-24%, vs. 12-15% for Bz alone), but remained unchanged considering DCM. Conversely, AUC-based CV in NEO fell (15 to 5% for Bz; 12 to 6% for DCM). Comparable trends were observed considering production of metabolites (AMET), except for NEO's CYP2E1-mediated metabolites of Bz, where an increased CV was observed (20 to 71%). For "high" exposure scenarios, Cmax-based variability of Bz and DCM remained unchanged in AD and PW, but decreased in NEO (CV= 11-16% to 2-6%) and TODD (CV= 12-13% to 7-9%). Conversely, AMET-based variability for both substrates rose in every subpopulation. This study analyzed for the first time the impact of multiple exposures on interindividual variability in toxicokinetics. Evidence indicates that this impact depends upon chemical concentrations and biochemical properties, as well as the subpopulation and internal dose metrics considered.

[Interstitial endocrine apparatus of testes of experimental animals in conditions of chromium-benzene intoxication]

With the use of histological, morphometric and statistical methods there was shown a gonadotropic effect of chromium, benzene and also their mixtures in male mice (CBA x C57Bl6) F1. The established structural changes in the testes of exposed animals showed the suppression of their germinative and endocrine functions. The response of Leydig cells in the chromium group expresses a development of the compensatory process in the relation with the destruction of seminiferous epithelium.

Risk assessment of volatile organic compounds benzene, toluene, ethylbenzene, and xylene (BTEX) in consumer products

Exposure and risk assessment was performed by evaluating levels of volatile organic compounds (VOC) benzene, toluene, ethylbenzene, and xylene (BTEX) in 207 consumer products. The products were categorized into 30 different items, consisting of products of different brands. Samples were analyzed for BTEX by headspace-gas chromatography/mass spectrometry (headspace-GC/MS) with limit of detection (LOD) of 1 ppm. BTEX were detected in 59 consumer products from 18 item types. Benzene was detected in whiteout (ranging from not detected [ND] to 3170 ppm), glue (1486 ppm), oil-based ballpoint pens (47 ppm), and permanent (marking) pens (2 ppm). Toluene was detected in a leather cleaning product (6071 ppm), glue (5078 ppm), whiteout (1130 ppm), self-adhesive wallpaper (15-1012 ppm), shoe polish (806 ppm), permanent pen (609 ppm), wig adhesive (372 ppm), tapes (2-360 ppm), oil-based ballpoint pen (201 ppm), duplex wallpaper (12-52 ppm), shoes (27 ppm), and air freshener (13 ppm). High levels of ethylbenzene were detected in permanent pen (ND-345,065 ppm), shoe polish (ND-277,928 ppm), leather cleaner (42,223 ppm), whiteout (ND-2,770 ppm), and glue (ND-792 ppm). Xylene was detected in permanent pen (ND-285,132 ppm), shoe polish (ND-87,298 ppm), leather cleaner (12,266 ppm), glue (ND-3,124 ppm), and whiteout (ND-1,400 ppm). Exposure assessment showed that the exposure to ethylbenzene from permanent pens ranged from 0 to 3.11 mg/kg/d (men) and 0 to 3.75 mg/kg/d (women), while for xylene, the exposure ranges were 0-2.57 mg/kg/d and 0-3.1 mg/kg/d in men and women, respectively. The exposure of women to benzene from whiteout ranged from 0 to 0.00059 mg/kg/d. Hazard index (HI), defined as a ratio of exposure to reference dose (RfD), for ethylbenzene was 31.1 (3.11 mg/kg/d/0.1 mg/kg/d) and for xylene (2.57 mg/kg/d/0.2 mg/kg/d) was 12.85, exceeding 1 for both compounds. Cancer risk for benzene was calculated to be 3.2 × 10(-5) based on (0.00059 mg/kg/d × 0.055 mg/kg-d(-1), cancer potency factor), assuming that 100% of detected levels in some products such as permanent pens and whiteouts were exposed in a worst-case scenario. These data suggest that exposure to VOC via some consumer products exceeded the safe limits and needs to be reduced.

The use of biomonitoring data in exposure and human health risk assessment: benzene case study

Abstract A framework of "Common Criteria" (i.e. a series of questions) has been developed to inform the use and evaluation of biomonitoring data in the context of human exposure and risk assessment. The data-rich chemical benzene was selected for use in a case study to assess whether refinement of the Common Criteria framework was necessary, and to gain additional perspective on approaches for integrating biomonitoring data into a risk-based context. The available data for benzene satisfied most of the Common Criteria and allowed for a risk-based evaluation of the benzene biomonitoring data. In general, biomarker (blood benzene, urinary benzene and urinary S-phenylmercapturic acid) central tendency (i.e. mean, median and geometric mean) concentrations for non-smokers are at or below the predicted blood or urine concentrations that would correspond to exposure at the US Environmental Protection Agency reference concentration (30 µg/m(3)), but greater than blood or urine concentrations relating to the air concentration at the 1 × 10(-5) excess cancer risk (2.9 µg/m(3)). Smokers clearly have higher levels of benzene exposure, and biomarker levels of benzene for non-smokers are generally consistent with ambient air monitoring results. While some biomarkers of benzene are specific indicators of exposure, the interpretation of benzene biomonitoring levels in a health-risk context are complicated by issues associated with short half-lives and gaps in knowledge regarding the relationship between the biomarkers and subsequent toxic effects.

Association between environmental exposure to benzene and oxidative damage to nucleic acids in children

OBJECTIVES

To evaluate the association between environmental exposure to benzene and oxidative damage to nucleic acids in children, also considering the role of Environmental Tobacco Smoke (ETS).

METHODS

396 children living in central Italy were recruited in districts with different urbanization and air pollution. All biomarkers were determined in spot urine samples by mass spectrometric techniques to assess exposure [benzene (U-Benz), and its metabolites (t,t-muconic and S-phenylmercapturic acids, t,t-MA and S-PMA, respectively), cotinine] and nucleic acid oxidation [8-oxo-7, 8-dibydro-2'-deoxyguanosine (8-oxodGuo), 8-oxo-7, 8-dihydroguanosine (8-oxoGuo), and 8-oxo-7, 8-dihydroguanine (8-oxoGua)].

RESULTS

Biomarkers of exposure and nucleic acid oxidation increased with urbanization and were correlated with each other (r > 0.18, p < 0.005). In a multiple linear regression model, benzene exposure, assessed by S-PMA and t,t-MA, was associated (p < 0.0001) with both 8-oxodGuo (R2 = 0.392) and 8-oxoGuo (R2 = 0.193) in all areas of residence, with similar slopes.

CONCLUSIONS

(i) Biomarkers of exposure to benzene increased as a function of environmental air pollution and urbanization level; (ii) U-Benz clearly distinguished both exposure to ETS and areas of residence, whereas benzene metabolites were associated only with the latter; (iii) the variance of 8-oxodGuo and 8-oxoGuo was accounted for by environmental benzene exposure, thus suggesting that benzene is a good tracer of other components of complex mixtures of pollutants causing oxidative damage to nucleic acids.

Biological monitoring of low-level exposure to benzene

INTRODUCTION

Conflicting opinions exist about the reliability of biomarkers of low-level exposure to benzene. We compared the ability of the urinary excretion of trans,trans-muconic acid (t,t-MA), s-phenilmercapturic acid (s-PAMA) and urinary benzene (U-Benz) to detect low level occupational and environmental exposure to benzene.

METHODS

We monitored airborne benzene by personal air sampling, and U-Benz, s-PMAI, t,t-MA and cotinine (U-Cotinine) in spot urine samples, collected at 8 am and 8 pm, in 32 oil refinery workers and 65 subjects, randomly selected among the general population of urban and suburban Cagliari, Italy. Information on personal characteristics, diet and events during the sampling day was acquired through in person interviews.

RESULTS

The median concentration of airborne benzene was 25.2 microg/m3 in oil refinery workers, and 8.5 microg/m3 in the general population subgroup. U-Benz in morning and evening samples was significantly more elevated among oil refinery workers than the general population subgroup (p = 0.012, and p = 7.4 x 10(-7), respectively) and among current smokers compared to non-smokers (p = 5.2 x 10(-8), and p = 5.2 x 10(-5) respectively). Benzene biomarkers and their readings in the two sampling phases were well correlated to each other. The Spearman's correlation coefficient with airborne benzene was significant for U-Benz in the evening sample, while no correlation was seen with t,t-MA and s-PMA readings in either samplings. The two benzene metabolites were frequently below limit of detection (LOD), particularly among the general population study subjects (17-9% and 39%, for t,t-MA and s-PMA respectively). Morning U-Cotinine excretion showed a good correlation with U-Benz in the morning and in the evening sampling (p < 0.001), and with s-PMA in the evening sample (p < 0.001), but not with t,t-MA in either samplings. t,t-MA in the evening sample was the only biomarker showing a moderate inverse correlation with BMI (p < 0.05). The multiple regression analysis adjusting by BMI and number of cigarettes smoked during the day confirmed the results of the univariate analysis.

DISCUSSION

Our results suggest that unmetabolized U-Benz would allow a more reliable biomonitoring of low-level exposure to benzene than s-PMA and t,t-MA.

Pilot study of aromatic hydrocarbon adsorption characteristics of disposable filtering facepiece respirators that contain activated carbon

Disposable filtering facepiece respirators (FFRs) used by health care workers are not designed to reduce the inhalation of volatile organic compounds (VOCs). Smoke-generating surgical procedures release VOCs and have been associated with the following complaints: foul smell, headaches, nausea, irritated throat and lungs, and asthma. Organic vapor FFRs that contain activated carbon are used by industrial workers to provide odor relief. These respirators remove irritating odors but are not marketed as respirators that provide respiratory protection against a gas or vapor. This study investigated the aromatic hydrocarbon adsorption capabilities of nuisance organic vapor (OV) FFRs. Three OV FFR models were tested to determine the 10% breakthrough time of three aromatic hydrocarbons at ambient room temperature and relative humidity. All respirator models were exposed to each vapor separately in three duplicate tests (n = 27). The respirator was sealed with silicone to an AVON-ISI headform that was placed in a chamber and exposed to VOC-laden air (20 ppm, 37 L/min). Periodically, gas samples were directed to an SRI gas chromatograph (Model 8610C) for analysis. All respirators performed similarly. The average 10% breakthrough values for all tests were at least 64 min, 96 min, and 110 min for benzene, toluene, and xylene, respectively. Respirators were tested with challenge concentrations at nuisance levels (20 ppm) and did not exceed 10% breakthrough values for at least 61 min. While the results of this pilot study hold promise, there is a need for further investigation and validation to determine the effectiveness of nuisance FFRs in mitigating organic vapors such as benzene, toluene, and xylene.

Benzene absorption in animals and man: an overview

Benzene is a widespread, naturally occurring substance of environmental concern as systemic exposure in humans is proven to be carcinogenic. Dermal exposure is a common and significant route of systemic entry and percutaneous absorption is critical in exposure risk assessment. This article reviews the scientific principles, methodologies, and research behind the multiple steps of the percutaneous absorption of benzene in animals and man and the application of this information to optimize exposure risk assessments. A focus on occupational exposures to benzene is made with an exploration of the limitations of current preventative measures and hazard assessments. Finally, recommendations for future research to fill existing knowledge gaps are made.

Assessment of xenobiotic biotransformation including reactive oxygen species generation in the embryo using benzene as an example

Quantification of embryonic metabolic capacity is an important tool in developmental toxicology research. Bioactivation of xenobiotics into reactive intermediates often contributes to embryo toxicity; thus, identification and quantification of these toxic metabolites is essential to gain further understanding of developmental toxicity. This chapter uses the environmental chemical benzene as a model xenobiotic to describe the detection of both metabolites and reactive oxygen species (ROS) in fetal liver. Briefly, mice are bred and the presence of a vaginal plug in a female mouse indicates gestational day 1. On the desired gestational day, pregnant dams are exposed to benzene followed by sacrifice at the desired time-point after exposure. Using gas chromatography coupled to mass spectrometry, the detection of benzene metabolites can be achieved. Additionally, we describe the measurement of ROS by flow cytometry using the fluorescent probe 5-(and-6)-chloromethyl-2',7'-dichlorofluorescein diacetate, which readily diffuses into cells and, upon oxidation by any ROS, is converted to the highly fluorescent, negatively charged carboxydichlorofluorescein, which remains trapped within the cells.

A mechanistic modeling framework for predicting metabolic interactions in complex mixtures

BACKGROUND

Computational modeling of the absorption, distribution, metabolism, and excretion of chemicals is now theoretically able to describe metabolic interactions in realistic mixtures of tens to hundreds of substances. That framework awaits validation.

OBJECTIVES

Our objectives were to a) evaluate the conditions of application of such a framework, b) confront the predictions of a physiologically integrated model of benzene, toluene, ethylbenzene, and m-xylene (BTEX) interactions with observed kinetics data on these substances in mixtures and, c) assess whether improving the mechanistic description has the potential to lead to better predictions of interactions.

METHODS

We developed three joint models of BTEX toxicokinetics and metabolism and calibrated them using Markov chain Monte Carlo simulations and single-substance exposure data. We then checked their predictive capabilities for metabolic interactions by comparison with mixture kinetic data.

RESULTS

The simplest joint model (BTEX interacting competitively for cytochrome P450 2E1 access) gives qualitatively correct and quantitatively acceptable predictions (with at most 50% deviations from the data). More complex models with two pathways or back-competition with metabolites have the potential to further improve predictions for BTEX mixtures.

CONCLUSIONS

A systems biology approach to large-scale prediction of metabolic interactions is advantageous on several counts and technically feasible. However, ways to obtain the required parameters need to be further explored.

The impact of saturable metabolism on exposure-response relations in 2 studies of benzene-induced leukemia

Enzymatic saturation of metabolic pathways is one factor that potentially contributes to the nonlinear exposure-response relations that are frequently reported in occupational epidemiologic studies. The authors propose an approach to explore the contribution of saturable metabolism to previously reported exposure-response relations by integrating predictive models of relevant biomarkers of exposure into the epidemiologic analysis. The approach is demonstrated with 2 studies of leukemia in benzene-exposed workers, one conducted in the Australian petroleum industry (1981-1999) and one conducted in a US rubber hydrochloride production factory in Ohio (1940-1996). The studies differed greatly in their magnitudes and durations of exposure. Substitution of biomarker levels for external estimates of benzene exposure reduced the fold difference of the log relative risk of leukemia per unit of cumulative exposure between the 2 studies by 11%-44%. Nevertheless, a considerable difference in the log relative risk per unit of cumulative exposure remained between the 2 studies, suggesting that exposure misclassification, differences in study design, and potential confounding factors also contributed to the heterogeneity in risk estimates.

A biomarker approach to estimate the daily intake of benzene in non-smoking and smoking individuals in Germany

Owing to its carcinogenic properties, benzene is one of the most important environmental air pollutants. We have applied a simple pharmacokinetic model to estimate the individual daily exposure of persons of the general population to benzene using their urinary excretion of S-phenylmercapturic acid as biomarker of exposure. On the basis of a non-representative convenience sample of the general population, spontaneous urine samples of 43 non-smoking persons, 13 persons with exposure to environmental tobacco smoke (ETS) (as determined by urinary cotinine) and 72 smokers were analyzed for S-phenylmercapturic acid, and benzene exposure was back calculated on the basis of the results. The pharmacokinetic model was based either on estimated daily urinary volume or creatinine excretion. Median daily exposure of non-smokers was calculated to be 47 microg/day (volume-based model) and 63 microg benzene/day (creatinine-based model). ETS-exposed persons had a slightly higher median daily exposure of 65 microg/day (volume-based model) and 72 microg benzene/day (creatinine-based model). The daily exposure of smokers was significantly higher with median values of 491 microg benzene/day (volume-based model) and 693 microg benzene/day (creatinine-based model). Our biomarker-based model gave plausible results for daily benzene exposure that were in good agreement with exposure estimations published earlier. As it is purely based on the determination of individual internal dose, our model provides a powerful tool for the risk assessment of environmental benzene.

Nutrient removal as a function of benzene supply within vertical-flow constructed wetlands

The role of benzene, macrophytes and temperature in terms of nutrient removal within constructed wetlands is unknown. Therefore, a research study over approximately 30 months was conducted to assess the potential of vertical-flow constructed wetlands to treat nutrients and to examine the effect of benzene concentration, presence of Phragmites australis (Cav.) Trin. ex Steud (common reed), and temperature control on nutrient removal. Experimental wetlands removed between 72% and 90% of benzene at an influent concentration of 1000 mg L(-1). A statistical analysis indicated that benzene is linked to increased effluent chemical oxygen demand and biochemical oxygen demand concentrations. However, there was no significant relationship between benzene treatment and both nitrogen and phosphorus removal. Phragmites australis played a negligible role in organic matter (chemical oxygen demand, biochemical oxygen demand, nitrogen and phosphorus) removal. Control of temperature favoured biochemical oxygen demand removal. However, no significant difference in chemical oxygen demand, and nitrogen and phosphorus removal was detected. Only the combination of the benzene and temperature variables had a significant impact on biochemical oxygen demand removal. The effluent biochemical oxygen demand concentrations in temperature-controlled benzene treatment wetlands were much lower than those located in the natural environment. However, any other combination between benzene, P. australis and the environmental control variables had no significant effect on biochemical oxygen demand, chemical oxygen demand, or nitrogen and phosphorus removal.

Transplacental benzene exposure increases tumor incidence in mouse offspring: possible role of fetal benzene metabolism

Childhood cancer is the leading cause of disease-related death in children aged 1-14 years in Canada and the USA and it has been hypothesized that transplacental exposure to environmental carcinogens such as benzene may contribute to the etiology of these cancers. Our objectives were to determine if transplacental benzene exposure increased tumor incidence in mouse offspring and assess fetal benzene metabolism capability. Pregnant CD-1 and C57Bl/6N mice were given intraperitoneal injections of corn oil, 200 mg/kg, or 400 mg/kg benzene on gestational days 8, 10, 12 and 14. A significant increase in tumor incidence was observed in CD-1, but not C57BL/6N, 1-year-old offspring exposed transplacentally to 200 mg/kg benzene. Hepatic and hematopoietic tumors were predominantly observed in male and female CD-1 offspring, respectively. Female CD-1 offspring exposed transplacentally to 200 mg/kg benzene had significantly suppressed bone marrow CD11b(+) cells 1 year after birth, correlating with reduced colony-forming unit granulocyte/macrophage numbers in 2-day-old pups. CD-1 and C57Bl/6N maternal blood benzene levels and fetal liver benzene, t, t-muconic acid, hydroquinone and catechol levels were analyzed by gas chromatography/mass spectrometry. Significant strain-, gender- and dose-related differences were observed. Male CD-1 fetuses had high hydroquinone levels, whereas females had high catechol levels after maternal exposure to 200 mg/kg benzene. This is the first demonstration that transplacental benzene exposure can induce hepatic and hematopoietic tumors in mice, which may be dependent on fetal benzene metabolism capability.

[Effects of chromium and benzene on cell immunological parameters and the content of trace elements in rats]

The effects of potassium bichromate, benzene, and their mixture on cell immunological parameters and the blood content of trace elements were studied in Wistar rats. Oral administration of benzene, potassium bichromate, and their mixture to Wistar rats was found to result in reductions in cell immunological parameters (the count of leukocytes, thymocytes, splenocytes, myelokaryocytes, the level of phagocytic indices) and the levels of copper, iron, nickel, and, on the contrary, increases in the concentrations of zinc and chromium in blood.

Processes impacting on benzene removal in vertical-flow constructed wetlands

The overall aim of this research project was to reduce low molecular weight hydrocarbons such as benzene in produced wastewaters. Over 30 months of research was conducted to test the treatment performance in terms of benzene removal in vertical-flow constructed wetlands. Based on an influent concentration of 1 g L(-1) benzene, the results show mean benzene removal efficiencies between 88.71% and 89.77%, and 72.66% and 80.46% for indoor and outdoor constructed wetlands, respectively. A statistical analysis indicated that the five days at 20 degrees C N-allylthiourea biochemical oxygen demand (BOD(5)), chemical oxygen demand (COD), nitrate-nitrogen (NO(3)-N), dissolved oxygen (DO) and electric conductivity (EC) values of the effluent were positively correlated with the effluent benzene concentrations following the order COD>DO>EC>NO(3)-N>BOD(5), and negatively correlated according to the order pH>redox potential (redox)>temperature (T)>turbidity. No strong relationships between benzene and the variables ortho-phosphate-phosphorus (PO(4)(3-)) and ammonia-nitrogen (NH(4)-N) were recorded.

The effect of benzene on the activity of adenosine deaminase in tissues of rats

Swiss Albino (Rat rattus norvegicus) rats were intraperitoneally injected with a 100 mg kg(-1) dosage of benzene, a toxic and carcinogenic agent widely used for industrial purposes. Changes in the adenosine deaminase (ADA) activity in the liver, kidney and serum of rats were investigated at 0, 2, 4, 8, 16, 32 and 64 h following injection. Serum physiological was administered to each control group. Enzyme activities were measured spectrophotometrically. Our purpose was to further investigations of some diseases caused by benzene, and present evidence of variations in the activity of ADA enzyme effected by benzene. While benzene caused significant inhibitions in ADA activity in the liver at 16 and 32 h and at 0.05 probability level, no significant inhibition or activation occurred at other test periods (hours). ADA activity did not present any significant variation in the kidneys. It was observed that ADA activity displayed similar patterns in the control groups. Comparisons of ADA activities in the two groups showed a statistically significant decrease between 4(th) and 64(th) hours (p< 0.05), demonstrating a direct correlation between benzene and its effects on ADA enzymes.

Estimation of interindividual pharmacokinetic variability factor for inhaled volatile organic chemicals using a probability-bounds approach

The derivation of reference concentrations (RfCs) for systemically acting volatile organic chemicals (VOCs) uses a default factor of 10 to account for the interindividual variability in pharmacokinetics (PK) and pharmacodynamics (PD). The magnitude of the PK component of the interindividual variability factor (IVF; also referred to as human kinetic adjustment factor (HKAF)) has previously been estimated using Monte Carlo approaches and physiologically based pharmacokinetic (PBPK) models. Since the RfC derivation considers continuous lifetime human exposure to VOCs in the environment, algorithms to compute steady-state internal dose (SS-ID), such as steady-state arterial blood concentration (Ca) and the steady-state rate of amount metabolized (RAM), can be used to derive IVF-PKs. In this context, probability-bounds (P-bounds) approach is potentially useful for computing an interval of probability distribution of SS-ID from knowledge of population distribution of input parameters. The objective of this study was therefore to compute IVF-PK using the P-bounds approach along with an algorithm for SS-ID in an adult population exposed to VOCs. The existing steady-state algorithms, derived from PBPK models, were rewritten such that SS-ID could be related, without any interdependence, to the following input parameters: alveolar ventilation (Qp), hepatic blood flow (Ql), intrinsic clearance (CL(int)) and blood:air partition coefficient (Pb). The IVF-PK was calculated from the P-bounds of SS-ID corresponding to the 50th and 95th percentiles. Following either specification of probability distribution-free bounds (characterized by minimal, maximal, and mean values) or distribution-defined values (mean, standard deviation and shape of probability distribution where: Qp=lognormal, Ql=lognormal, CL(int)=lognormal and Pb=normal) in RAMAS Risk Calc software version 3.0 (Applied Biomathematics, Setauket, NY), the P-bound estimates of SS-ID for benzene, carbon tetrachloride, chloroform and methyl chloroform were obtained for low level exposures (1ppm). Using probability distribution-defined inputs, the IVF-PK for benzene, carbon tetrachloride, chloroform and methyl chloroform were, respectively, 1.18, 1.28, 1.24, and 1.18 (based on P-bounds for Ca), and 1.31, 1.58, 1.30, and 1.24 (based on P-bounds for RAM). A validation of the P-bounds computation was performed by comparing the results with those obtained using Monte Carlo simulation of the steady-state algorithms. In data-poor situations, when the statistical distributions for all input parameters were not known or available, the P-bounds approach allowed the estimation of IVF-PK. The use of P-bounds method along with steady-state algorithms, as done in this study for the first time, is a practical and scientifically sound way of computing IVF-PKs for systemically acting VOCs.

Genetic polymorphisms involved in toxicant-metabolizing enzymes and the risk of chronic benzene poisoning in Chinese occupationally exposed populations

Benzene is a recognized haematotoxin and leukaemogen, but its mechanism of action and the role of genetic susceptibility are still unclear. Cytochrome P450 2E1 (CYP2E1) and myeloperoxidase (MPO) are involved in benzene activation; and NAD (P)H:quinine oxidoreductase 1 (NQO1), glutathione S-transferase theta 1 (GSTT1) and glutathione S-transferase mu 1 (GSTM1) participate in benzene detoxification. The common, well-studied single-nucleotide polymorphisms (SNPs) were analysed in these genes drawn from the toxicant-metabolizing pathways. A total of 100 workers with chronic benzene poisoning (CBP) and 90 controls were enrolled in China. There was a 2.82-fold (95% CI = 1.42-5.58) increased risk of CBP in the subjects with the NQO1 609C > T mutation genotype (T/T) compared with those carrying heterozygous (C/T) and wild-type (C/C). The subjects with the GSTT1 null genotype had a 1.91-fold (95% CI = 1.05-3.45) increased risk of CBP compared with those with GSTT1 non-null genotype. There was no association of CYP2E1 and MPO genotype with CBP. A three genes' interaction showed that there was a 20.41-fold (95% CI = 3.79-111.11) increased risk of CBP in subjects with the NQO1 609C > T T/T genotype and with the GSTT1 null genotype and the GSTM1 null genotype compared with those carrying the NQO1 609C > T C/T and C/C genotype, GSTT1 non-null genotype, and GSTM1 non-null genotype. The study provides evidence of an association of a gene-gene interaction with the risk of CBP.