An overview of environmental and toxicological aspects of aromatic hydrocarbons. I. Benzene

Rapid screening of volatile chemicals in surface water samples from the East Palestine, Ohio chemical disaster site with proton transfer reaction mass spectrometry

The increasing prevalence of hazardous chemical incidents in the United States necessitates the implementation of analytically robust, rapid, and reliable screening techniques for toxicant mixture analysis to understand short- and long-term health impacts of environmental exposures. A recent chemical disaster in East Palestine, Ohio has underscored the importance of thorough contamination assessment. On February 03, 2023, a Norfolk Southern train derailment prompted a chemical spill and fires. An open burn involving over 100,000 gal of vinyl chloride was conducted three days later. Hazardous compounds were released into air, water, and soil. To provide time-sensitive exposure data for emergency response, this study outlines a novel methodology for rapid characterization of chemical contamination of environmental media to support disaster response efforts. A controlled static headspace sampling system, in conjunction with a high-resolution proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS), was developed to characterize volatile organic compounds (VOCs) in surface water samples collected near the East Palestine train derailment site. Spatial variations were observed in the chemical composition of surface water samples collected at different locations. Hydrocarbons were found to be the most abundant chemical group of all surface water samples, contributing 50 % to 97 % to the total headspace VOC mass. Compounds commonly detected in surface water samples, including benzene, styrene, xylene, and methyl tert-butyl ether (MTBE) were also observed in most surface water samples, with aqueous concentrations typically at ng/L levels. This study demonstrated the potential of the proposed methodology to be applied for rapid field screening of volatile chemicals in water samples in order to enable fast emergency response to chemical disasters and environmental hazards.

High-efficiency organic solar cells processed from a real green solvent

The fabrication of organic solar cells (OSCs) depends heavily on the use of highly toxic chlorinated solvents, which are incompatible with industrial manufacturing. The reported alternative solvents such as non-halogenated aromatic hydrocarbons and cyclic ethers are also not really "green" according to the "Globally Harmonized System of Classification and Labelling of Chemicals" of the United Nations. Therefore, processing from real green solvents such as water, alcohols, or anisole will constitute a big breakthrough for OSCs. However, it is fundamentally challenging to obtain high-performance photovoltaic materials processable from these solvents. Herein, we propose the incorporation of a B-N covalent bond, which has a dipole moment of 1.84 Debye, into the conjugated backbone of polymer donors to fabricate high-efficiency OSCs from anisole, a real green and eco-compatible solvent recommended by the United Nations. Based on a newly developed B-N-based polymer, the OSCs with a record-high efficiency of 15.65% in the 0.04 cm² device and 14.01% in the 1.10 cm² device have thus been realized via real green processing.

Vacuum ultraviolet photoionization and dissociative photoionization of toluene: Experimental and theoretical insights

The photoionization and dissociative photoionization of toluene have been studied using synchrotron radiation vacuum ultraviolet light with photon energy in the range of 8.50-25.50 eV. The ionization energies (8.82 eV) and double ionization energies (23.80 eV) of toluene as well as the appearance energies for its major fragments C₇H₇⁺ (11.17/10.71 eV), C₆H₅⁺ (13.73 eV), C₅H₆⁺ (13.58/12.50 eV), C₅H₅⁺ (16.23 eV), C₄H₅⁺ (15.64 eV), C₄H₄⁺ (16.10 eV) and C₄H₃⁺ (17.11 eV) are determined, respectively by using photoionization efficiency spectrometry. With the help of experimental and theoretical results, seven dissociative photoionization channels have been proposed: C₇H₇⁺ + H, C₆H₅⁺ + CH₃, C₅H₆⁺ + C₂H₂, C₅H₅⁺ + C₂H₂ + H, C₄H₅⁺ + C₃H₃, C₄H₄⁺ + C₃H₄ and C₄H₃⁺ + C₃H₄ + H. In addition, the geometries of the intermediates, transition states and products involved in these photoionization and dissociative photoionization processes have been performed at the B3LYP/6-311++G(d, p) level. The mechanisms of dissociative photoionization of toluene and the intermediates and transition states involved are discussed in detail. Generally speaking, the experimental results are in agreement with theoretical calculations in this work and published literature results. Especially the mechanisms of dissociative photoionization to C₄H₅⁺, C₄H₄⁺ and C₄H₃⁺ were discussed for the first time in this work. This investigation may provide useful information on understanding the photoionization and dissociative photoionization of toluene.

Quantification of gasoline-ethanol blend emissions effects

Emissions levels from current gasoline spark-ignited engines are low, and emissions changes associated with the blending of ethanol into gasoline are small and difficult to quantify. Addition of ethanol, with a high blending octane number, allows a reduction in aromatics in market gasoline. Blending behavior of ethanol is nonlinear, altering the distillation curve, including the 50% temperature point, T50. Increase in gasoline direct injection (GDI) engine technology in the fleet challenges ability of older models based on port fuel injection (PFI) results to predict the overall air quality impact of ethanol blending. Five different models derived from data collected through U.S. Environmental Protection Agency Energy Policy Act (EPAct) programs were used to predict LA92 Phase 1 particulate matter (PM) emissions for summer regular (SR) E0 (gasoline with 0% ethanol by volume), E10 (gasoline with 10% ethanol) and E15 (gasoline with 15% ethanol). Substantial reductions of PM for E10 and E15 relative to E0 were predicted when aromatics were displaced by ethanol to maintain octane rating. SR E0 and E10 were also matched to linear combinations of EPAct fuels and results showed a 35% PM reduction for SR E10 relative to SR E0. For GDI vehicles the Coordinating Research Council (CRC) E-94-3 study found that E10 had 23% or 29% PM increase. However, CRC E-129 found an E10 PM reduction of 10% when one E0 fuel and its splash blended (SB) E10 were compared. Both CRC project E-129 SB data and fuel triplets selected from the EPAct study showed variation for E15 emissions, although E-129 suggests that E15 in GDI offers about a 25% reduction of PM with respect to E0. Overall, data suggest that ethanol blending offers a modest to a substantial reduction of cold-start PM mass if aromatic levels of the finished products are reduced in response to ethanol addition. Implications: Studies of exhaust emissions effects of ethanol blending with gasoline vary in conclusions. Blending properties are nonlinear. Modeling of real-world emissions effects must consider all fuel composition adjustments and property changes associated with ethanol addition. Aromatics are reduced in E10 or E15, compared with E0, and distillation changes. PFI-derived models show reductions in cold-start PM for expected average E10 versus E0 pump fuel, due to reduced aromatic content. Relative emissions effects from older technology (PFI) engines do not predict newer engine (GDI) results reliably, but recent GDI data show reduced cold-start PM when ethanol displaces aromatics.

Exosomes derived from normal human bronchial epithelial cells down-regulate proliferation and migration of hydroquinone-transformed malignant recipient cells via up-regulating PTEN expression

The gene encoding the tumor suppressor, phosphatase and tensin homolog (PTEN), located on chromosome 10, is frequently expressed at low levels in various tumors, resulting in the stimulation of cell proliferation and migration. However, the role of exosomal PTEN in cell-cell communication during the progress of benzene-induced carcinogenesis remains unclear. The goal of this study was to explore whether exosomes derived from normal human bronchial epithelial cells (16HBE) could transmit PTEN to hydroquinone-transformed malignant recipient cells (16HBE-t) and its possible effects on cell proliferation and migration. Consistent with PTEN expression being down-regulated in transformed cells, we found that its expression was significantly decreased in 16HBE-t relative to 16HBE cells and that purified exosomes secreted by 16HBE, up-regulated PTEN levels in recipient 16HBE-t cells. Thus, down-regulating their proliferation and migration. Further, when exosomes derived from 16HBE cells that had been treated with the PTEN inhibitor SF1670, were incubated with recipient 16HBE-t cells, they exhibited decreased PTEN levels, with a corresponding increase in their proliferation and migration. In conclusion, our study demonstrates that exosomes derived from 16HBE cells can down-regulate proliferation and migration of recipient 16HBE-t cells via transferring PTEN.

Potential for city parks to reduce exposure to BTEX in air

Benzene, toluene, ethylbenzene, and xylenes (BTEX) are hazardous air pollutants commonly found in outdoor air. Several studies have explored the potential of vegetation to mitigate BTEX in outdoor air, but they are limited to a northern temperate climate and their results lack consensus. To investigate this subject in a subtropical climate, we deployed passive air samplers for two weeks in parks and outside nearby residences at four locations: three in an urban area and one in a rural area in Alabama, USA. All BTEX concentrations were below health-based guidelines and were comparable to those found in several other studies in populated settings. Concentrations of TEX, but not benzene, were 3-39% lower in parks than at nearby residences, and the differences were significant. Site type (park vs. residential) was a significant predictor of TEX concentrations, while distance to the nearest major road was a significant predictor of BTX concentrations. In and around two of the parks, toluene : benzene ratios fell outside the range expected for vehicular emissions (p < 0.01), suggesting that there were additional, industrial sources of benzene near these two locations. The ratio of m-,p-xylene : ethylbenzene was high at all locations except one residential area, indicating that BTEX were freshly emitted. Concentrations of individual BTEX compounds were highly correlated with each other in most cases, except for locations that may have been impacted by nearby industrial sources of benzene. Results of this study suggest that parks can help reduce exposure to TEX by a modest amount in some situations.

New Look at BTEX: Are Ambient Levels a Problem?

Benzene, toluene, ethylbenzene, and xylene (BTEX) are retrieved during fossil fuel extraction and used as solvents in consumer and industrial products, as gasoline additives, and as intermediates in the synthesis of organic compounds for many consumer products. Emissions from the combustion of gasoline and diesel fuels are the largest contributors to atmospheric BTEX concentrations. However, levels indoors (where people spend greater than 83% of their time) can be many times greater than outdoors. In this review we identified epidemiological studies assessing the noncancer health impacts of ambient level BTEX exposure (i.e., nonoccupational) and discussed how the health conditions may be hormonally mediated. Health effects significantly associated with ambient level exposure included sperm abnormalities, reduced fetal growth, cardiovascular disease, respiratory dysfunction, asthma, sensitization to common antigens, and more. Several hormones including estrogens, androgens, glucocorticoids, insulin, and serotonin may be involved in these health outcomes. This analysis suggests that all four chemicals may have endocrine disrupting properties at exposure levels below reference concentrations (i.e., safe levels) issued by the U.S. Environmental Protection Agency. These data should be considered when evaluating the use of BTEX in consumer and industrial products and indicates a need to change how chemicals present at low concentrations are assessed and regulated.

Association between intrafollicular concentration of benzene and outcome of controlled ovarian stimulation in IVF/ICSI cycles: a pilot study

BACKGROUND

Several studies have shown that exposure to benzene is associated to menstrual disorders, miscarriages and other disorders of the reproductive system. We performed an observational prospective pilot study to evaluate if levels of benzene in follicular fluid were correlated with response to controlled ovarian stimulation.

METHOD

Thirty-four normogonadotrophic women undergoing IVF were enrolled. Intra-follicular benzene levels were evaluated by chromatography/mass spectrometry. Based on median benzene level, we divided the study population in two groups: Group A with a "low" intra-follicular benzene concentration (n=19, benzene <0.54 ng/mL) and Group B with a "high" intra-follicular benzene concentration (n=15, benzene ≥ 0.54 ng/mL). The ovarian response to gonadotrophins and the outcome of IVF were analyzed in the two groups.

RESULTS

The two groups did not differ in terms of demographic or anthropometric characteristics. Group B had significantly higher basal FSH levels, lower estradiol peak concentration, and fewer oocytes retrieved and embryos transferred (p<0.05). Number of gonadotrophin vials, length of controlled ovarian stimulation and ongoing pregnancy rate were similar in the two groups.

CONCLUSION

In conclusion, ovarian response to endogenous and exogenous gonadotrophins appeared to be influenced by intra-follicular benzene levels.

Functional characterization of human cytochrome P4502E1 allelic variants: in vitro metabolism of benzene and toluene by recombinant enzymes expressed in yeast cells

Benzene and toluene are common organic solvents currently in worldwide industrial usage, which are metabolized mainly by hepatic cytochrome P450 2E1 (CYP2E1) in humans. Genetic polymorphism of CYP2E1 in 5'-flanking and coding regions has been found previously in Caucasian and Chinese populations. In this study, the effects of CYP2E1 alleles causing amino acid substitutions (CYP2E1*2, CYP2E1*3 and CYP2E1*4; wild-type, CYP2E1.1A) on benzene hydroxylation and toluene methylhydroxylation were studied using recombinant CYP2E1 enzymes of wild-type (CYP2E1.1) and variants (CYP2E1.2 having Arg76His, CYP2E1.3 having Val389Ile and CYP2E1.4 having Val179Ile) expressed in yeast cells. The K (m), V (max) and CL (int) values of CYP2E1.1 were 10.1 mM, 9.38 pmol/min/pmol CYP and 0.99 nL/min/pmol CYP for benzene hydroxylation, and 3.97 mM, 19.9 pmol/min/pmol CYP and 5.26 nL/min/pmol CYP for toluene methylhydroxylation, respectively. The K (m), V (max) and CL (int) values for benzene and toluene metabolism of CYP2E1.2, CYP2E1.3 and CYP2E1.4 were comparable to those of wild-type CYP2E1. These findings may mean that the polymorphic alleles of CYP2E1 causing amino acid substitutions are not directly associated with the metabolic activation of benzene and toluene. The information gained in this study should help to identify the variations in the toxicity of environmental pollutants.

The role of occupational and environmental exposures in the aetiology of acquired severe aplastic anaemia: a case control investigation

Aplastic anaemia is a rare but serious disorder with a high morbidity and mortality rate. The causes of aplastic anaemia are, for the most part, unknown. We report on the hypothesis that aplastic anaemia may be caused by occupational and/or environmental exposures to certain chemicals. The UK Aplastic Anaemia Study was an interview-based case-control study covering the whole of Great Britain. Those patients diagnosed between 1 July 1993 and 20 October 1997, aged < or =75 years and born and diagnosed in the UK were eligible for the study. Two hundred eligible cases of aplastic anaemia were compared with 387 age- and sex-matched controls. A number of occupational exposures showed increases in risk. In a multivariate model of these exposures the odds ratios (ORs) for solvents/degreasing agents, pesticides and radiation were >2 and statistically significant. Reported chemical treatment of houses within 5 years of diagnosis had a significantly raised risk for adults [OR = 2.51, 95% confidence interval (CI) 1.02-12.01], particularly for woodworm treatment (OR = 5.1, 95% CI 1.5-17.4). This study identified significant risks associated with self-reported exposure to solvents, radiation and pesticides in the workplace. Self-reported chemical treatment of houses was also associated with an increased risk of developing aplastic anaemia, in keeping with previous literature.

Performance characteristics and applications of a proton transfer reaction-mass spectrometer for measuring volatile organic compounds in ambient air

Data illustrating the performance characteristics of a proton transfer reaction-mass spectrometer (PTR-MS) under both laboratory and field conditions are presented. Under laboratory conditions, we demonstrate that PTR-MS measures (within 10%) a 2.6 ppbv concentration of gaseous dimethyl sulfide. Using a stepwise dilution of a gaseous isoprene standard, we demonstrate the linearity of the response of PTR-MS across 3 orders of magnitude of mixing ratios, from 100 ppbv to less than 100 pptv. By combining this data set with that of its monosubstituted 13C isotopic analogue, we demonstrate the ability of the instrumentto reliably measure concentrations as low as approximately 50 pptv and to detect concentrations at significantly lower levels. We conclude our laboratory characterization by investigating the components of the instrument noise signal (drift, mean, and range) and develop an expression (noise statistic) that reliably predicts the instrumental noise associated with any signal across a wide range of masses. In the field, we deployed a PTR-MS at a clean-air coastal site and an urban kerbside monitoring station to demonstrate the measurement of atmospheric dimethyl sulfide and benzene concentrations, respectively. At both sites, we were able to monitor diurnal variations in concentrations at unprecedented temporal resolutions (<5 min between successive measurements). We then demonstrate how the noise statistic can be applied to enable real fluctuations in atmospheric VOC concentrations to be reliably distinguished from instrument noise. We conclude by demonstrating how PTR-MS can be used to measure real-time VOC emission rate changes from vegetation in response to external forcing by examining the effect varying photon-flux density has upon emissions of isoprene from a Sitka spruce tree.

Ethylbenzene induces microsomal oxygen free radical generation: antibody-directed characterization of the responsible cytochrome P450 enzymes

Small aromatic hydrocarbons cause changes in oxidative metabolism by modulating the levels of cytochrome P450 enzymes, with the changes in these enzymes being responsible for qualitative changes in aromatic hydrocarbon metabolism. The goal of this study was to determine if exposure to the small alkylbenzene ethylbenzene (EB) leads to an increase in hepatic free radical production. Male F344 rats were treated with ip injections of EB (10 mmol/kg) and compared to corn oil controls. Hepatic free radical production was examined by measuring the conversion of 2',7'-dichlorofluorescin diacetate (DCFH-DA) to its fluorescent product 2',7'-dichlorofluorescein (DCF). A significant elevation of fluorescent DCF production was observed after treatment with EB, despite the lack of effect on overall cytochrome P450 levels. This process was shown to be inhibitable by metyrapone, an inhibitor of P450. DCF production was also inhibited by catalase, suggesting that hydrogen peroxide (H(2)O(2)) is one of the reactive oxygen intermediates involved in EB-mediated reactive oxygen species (ROS) formation. Interestingly, superoxide dismutase (SOD) did not inhibit DCF production in corn oil-treated rats but was an effective inhibitor in the EB-treated groups. In an effort to determine if the increase in ROS production was related to changes in specific P450 enzymes, DCF production was measured in the presence of anti-CYP2B, anti-CYP2C11, anti-CYP2E1, and anti-CYP3A2 inhibitory antibodies. Anti-CYP2B antibodies inhibited DCF production in EB-treated, but not corn oil groups, which is consistent with the low constitutive levels of this enzyme and its induction by EB. The data also demonstrate that CYP2B contributes to ROS production. Anti-CYP2C11 did not influence DCF production in either group. ROS formation in corn oil-treated rats as well as in ethylbenzene-treated rats was also inhibited with antibodies to anti-CYP2E1 and anti-CYP3A2. These results suggest that CYP2C11 does not appear to influence free radical production and that the increase in free radical production in EB treated rats is consistent with the EB-mediated elevation of CYP2B, CYP 2E1, and CYP3A2. Such alterations in free radical generation in response to hydrocarbon treatment may contribute to the toxicity of these compounds.

Benzene--a review of the literature from a health effects perspective

A literature review of the impact on human health of exposure to benzene was conducted. Special emphasis in this report is given to the health effects reported in excess of national norms by participants in the Benzene Subregistry of the National Exposure Registry--people having documented exposure to benzene through the use of benzene-contaminated water for domestic purposes. The health effects reported in excess (p < or = .01) by some or all of the sex and age groups studied were diabetes, kidney disease, respiratory allergies, skin rashes, and urinary tract disorders; anemia was also increased for females, but not significantly so.

Transport of organic environmental contaminants to animal products

A large number of chemical contaminants potentially may be present in agricultural environments, leading to exposure of animals and potential residues in animal products. The contamination may be either widespread, as a result of aerial transport of industrial emissions, or localized, as a result of accidental emissions and spills, improper waste disposal, contaminants in useful products, and areas of past use of products now banned. The halogenated hydrocarbons, including the polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), and persistent organochlorine insecticides remaining from past use, are the contaminants of most concern. Depending on the degree and pattern of chlorine substitution, these compounds are resistant to degradation and tend to accumulate in the fat of animals and their products. Other classes of environmental contaminants as exemplified by the PAHs, phthalate esters, acid phenolics, and nitrosamines also may occur widely in the environment. These compounds are unlikely to be transported to animal products because the compounds are water-soluble or can be metabolized to water-soluble products, which are excreted in the urine and thus do not bioaccumulate in products such as milk and meat. The points of entry of environmental contaminants into agricultural environments usually are plants and soils. Lipophilic compounds such as the halogenated hydrocarbons are not taken up and translocated by plants. Contamination of plants is mainly a surface phenomenon resulting from aerial deposition of emissions or deposition of compounds volatilized from the surface of contaminated soil. Thus, fibrous roughages used primarily in feeding cattle and other ruminants will be the most important pathway of animal exposure and transport to human foods. The second pathway of animal exposure is by ingestion of contaminated soil while grazing or when confined to unpaved facilities. As in the case of feed sources, cattle is the species most vulnerable to exposure by the soil ingestion pathway under most commercial management systems, but poultry and swine are more vulnerable in those infrequent situations in which these species have access to contaminated soil.

Benzene, toluene and xylenes in air, geographical distribution in the Piedmont region (Italy) and personal exposure

The objectives of this study were the determination of: (a) benzene (B), toluene (T) and xylene (X) air pollution in three sites of the Piedmont region (north-western Italy), (b) the relationship between BTX pollution in indoor, outdoor and personal air measured for a group of non-smoking university students, (c) the influence of environmental tobacco smoke on the level of BTX exposure for indoor air environments. Results indicate (i) a direct relationship between human density and level of contamination and higher toluene pollution, (ii) an indoor/outdoor ratio of > 1 for all the three aromatics, (iii) a similar level of personal and indoor air contamination. Human exposure to BTX air pollution has been found to depend principally on indoor air contamination, not only on home pollution, but also, probably on many other confined environments.

Relationship between hydrocarbon structure and induction of P450: effects on protein levels and enzyme activities

1. Treatment of male rat with the small aromatic hydrocarbons, benzene, toluene, ethylbenzene, n-propylbenzene, m-xylene, and p-xylene increased several P450-dependent activities, with ethylbenzene, m-xylene, and n-propylbenzene producing the greatest response. Hydrocarbon treatment differentially affected toluene metabolism, producing a response dependent on the metabolite monitored. In untreated rats, benzyl alcohol was the major hydroxylation product of toluene metabolism, comprising > 99% of the total metabolites formed. Hydrocarbon treatment increased the overall rate of toluene metabolism by dramatically increasing the amount of aromatic hydroxylation. Ethylbenzene, n-propylbenzene and m-xylene were the most effective inducers of aromatic hydroxylation of toluene. In contrast, production of the major toluene metabolite benzyl alcohol was increased only after treatment with m-xylene. 2. P450 2B1/2B2 levels were induced by each of the hydrocarbons examined, with the magnitude of induction increasing with increasing hydrocarbon size. P450 1A1 was also induced after hydrocarbon exposure; however, the degree of induction was smaller than that observed for P450 2B1/2B2. P450 2C11 levels were suppressed after treatment with benzene, ethylbenzene and n-propylbenzene. 3. Taken together these results display two induction patterns. The first generally corresponds to changes in the P450 2B subfamily, where activities (e.g. the aromatic hydroxylations of toluene) were most effectively induced by ethylbenzene, n-propylbenzene and m-xylene. In the second, induction was observed only after m-xylene treatment, a pattern that was found when the metabolism of the substrate was catalysed by both the P450 2B subfamily and P450 2C11. Hydrocarbons that both induced P450 2B1/2B2 and suppressed P450 2C11 (such as ethylbenzene and n-propylbenzene) showed little change in activities catalysed by both isozymes (e.g. aliphatic hydroxylation of toluene, and aniline hydroxylation); however, m-xylene treatment led to elevated P450 2B1/2B2 levels without significantly suppressing P450 2C11. m-Xylene produced significant increases in activities efficiently catalysed by both isozymes. Therefore, the unique induction pattern observed after m-xylene treatment can be accounted for by induction of P450 2B1/2B2 without concomitant suppression of P450 2C11.

Development of an immunoassay to detect hemoglobin adducts formed by benzene exposure

Polyclonal murine antibodies that recognize the adducts formed by benzene metabolites in hemoglobin (Hb) were prepared and used to develop immunoassays. In competitive inhibition assays, the concentration of competitor needed to reduce the signal by 50% (IC50) was less than 10 pmoles for hydroquinone-hemoglobin (HQHb) adducts and less than 1 pmole for 1,2,4 trihydroxybenzene-hemoglobin (TriOH Hb). Hemoglobin (Hb) incubated with either phenol or catechol (CAT) did not elicit antibodies suitable for quantitative immunoassays. The metabolite-directed immunoassays were tested using hemoglobin from mice previously administered [C14] benzene for two to four weeks. The most sensitive assay for hydroquinone measured 0.49 pmoles adduct/40 pmoles Hb (191 pmoles adduct/mg Hb) in mice treated with 200 mg/kg benzene (P < 0.05, Student's t test). TriOH Hb adducts were not detected.

Ethylbenzene-mediated induction of cytochrome P450 isozymes in male and female rats

Male and female Holtzman rats were exposed to ethylbenzene, and the effect on liver microsomal activities was studied. Hydrocarbon- and sex-dependent effects on P450-dependent metabolism of drugs and aromatic hydrocarbons were investigated. Hydrocarbon treatment produced two patterns of induction in cytochrome P450-dependent activities: (1) induction common to both sexes; and (2) induction exclusively in females. Benzphetamine N-demethylation, 7-ethoxycoumarin O-deethylation, p-nitroanisole O-demethylation and aromatic hydroxylation of toluene were induced in both sexes after rats were exposed to ethylbenzene. The rate of benzphetamine N-demethylation increased 4-fold in females and nearly doubled in males. The increase in O-deethylation of 7-ethoxycoumarin was 3-fold in females and doubled in males, while p-nitroanisole O-demethylation increased 4-fold in both sexes after exposure to ethylbenzene. Ethylbenzene had its greatest effect upon the formation of aromatic hydroxylated metabolites of toluene. Ethylbenzene exposure increased the rate of o-cresol formation by 4- and 9-fold in female and male rats, respectively. The formation rate of p-cresol was undetectable in either sex prior to hydrocarbon exposure; however, after the rats were given ethylbenzene, rates increased to 0.4 nmol/min/mg protein in females and to 0.9 nmol/min/mg protein in the males. Ethylbenzene exposure selectively induced aminopyrine demethylation, aniline hydroxylation, N,N-dimethylnitrosamine N-demethylation (DMNA) and aliphatic hydroxylation of toluene in females. Rates for aminopyrine, aniline, and DMNA were increased 50% over controls, while formation of benzyl alcohol from toluene was enhanced to 260% of control. Western immunoblotting indicated that ethylbenzene treatment induced cytochrome P450 2B1/2B2 to a greater extent in male rats and cytochrome P450 2E1 only in females. Ethylbenzene exposure did not affect significantly the level of cytochrome P450 1A1.

Hypothalamic-pituitary-adrenocortical axis activity and immune function after oral exposure to benzene and toluene

Benzene and toluene, commonly used solvents, possess neurotoxic and immunotoxic effects. Male CD-1 mice were continuously fed drinking water containing 0, 31, 166 and 790 mg/l benzene and 0, 17, 80 and 405 mg/l toluene, respectively. The concentrations of hypothalamic norepinephrine (NE) and its metabolite vanillylmandelic acid (VMA), circulating corticosterone and adrenocorticotropic hormone (ACTH), and lymphocyte-derived interleukin-2 (IL-2) activity were evaluated after 28 days of exposure to each solvent. Serum corticosterone was also measured at pretreatment, 2, 7, and 14 days of exposure. The concentrations of NE, VMA, ACTH and corticosterone were increased following exposure to these solvents. Benzene increased corticosterone levels in mice after 7 days (166 and 790 mg/l) and at 28 days (790 mg/l). Toluene elevated corticosterone levels at 14 and 28 days at the 405 mg/l exposure. IL-2 production by mouse T-lymphocytes was suppressed in the two higher benzene-treated groups, while toluene decreased IL-2 synthesis at the highest level only. Both benzene and toluene exposures stimulated hypothalamic-pituitary-adrenocortical (HPA) activity. Elevated corticosterone has been reported to inhibit IL-2 production and impair immunocompetence. Organic solvents may have, at least partially, an additive adverse effect on immune function via activated HPA status.

Subclinical effects of groundwater contaminants. IV. Effects of repeated oral exposure to combinations of benzene and toluene on regional brain monoamine metabolism in mice

Benzene and toluene are known neurotoxicants that may interact in vivo. The effect of combined treatment with benzene and toluene on the endogenous concentrations of the catecholamines norepinephrine (NE) and dopamine (DA), the catecholamine metabolites vanillylmandelic acid (VMA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), and the indoleamine serotonin (5-HT) and its metabolite 5-hydroxy-indoleacetic acid (5-HIAA), were investigated in six discrete brain regions of CD-1 mice. Groups of male, adult mice were continuously exposed to benzene (166 mg/l), toluene (80 and 325 mg/l), and combinations of benzene + toluene (80 or 325 mg/l) in drinking water for 4 weeks. Benzene produced increases of NE in the hypothalamus, cortex, midbrain and medulla oblongata, DA in the hypothalamus and corpus striatum, and 5-HT in all dissected brain regions except cerebellum. Elevated levels of various monoamine metabolites were also observed in these brain areas. Toluene ingestion alone also significantly increased the concentrations of NE, DA, 5-HT, and their metabolites in several brain regions. Mice given the combined treatments exhibited raised regional neurochemical levels when compared to the untreated controls. Increased concentrations of biogenic amine metabolites in several brain regions were greater in the combined exposures of benzene and toluene than when either chemical was used alone. The findings were different from those observed on immune parameters using similar treatment protocols, where simultaneous exposure to toluene prevented the immunotoxic effects of benzene.