Health risk assessment of exposure to benzene, toluene, ethyl benzene, and xylene in shoe industry-related workplaces

Benzene, toluene, ethyl benzene, and xylene (BTEX) are prevalent pollutants in shoe industry-related workplaces. The aim of this study was to assess exposure to BTEX and their carcinogenic and non-carcinogenic risks in shoe-industry-related workplaces. This study was carried out at different shoe manufactures, small shoe workshop units, shoe markets, and shoe stores in Tabriz, Iran in 2021. Personal inhalation exposure to BTEX was measured using the National Institute for Occupational Safety and Health (NIOSH) 1501 method. Carcinogenic and non-carcinogenic risks due to inhalation exposure to BTEX were estimated by United States Environmental Protection Agency (U.S. EPA) method based on Mont Carlo simulation. Results showed that the concentrations of benzene and toluene were higher than the threshold limit value (TLV) in both gluing and non-gluing units of shoe manufactures. The total carcinogenic risk (TCR) due to exposure to benzene and ethyl benzene was considerable in all shoe industry-related workplaces. Also, the hazard index (HI) as a non-carcinogenic index was higher than standard levels in all shoe industry-related workplaces. Therefore, shoe industry-related workers are at cancer and non-cancer risks due to exposure to BTEX. Prevention measures need to be implemented to reduce the concentration of BTEX in shoe industry-related workplaces.

Assessment of health safety of pigs taking natural sorbents with feed

BACKGROUND

The study assessed the effect of smectites (bentonite and zeolite) used as natural sorbents in the diet of pigs on feed digestibility, health parameters, the severity of anatomo-histological changes in organs, and the accumulation of volatile pollutants in organs.

MATERIAL AND METHODS

The study was conducted using fattening pigs (crossbreds from multiple breeds) assigned to three groups - a control (C) and two experimental groups (A and B), with 240 pigs in each group (3 replicates × 80). The animals in group C received a standard complete diet, while groups A and B received diets with 1.5% composed smectite sorbents. The feed and faeces were analysed for content of dry matter, crude ash, crude protein, ether extract, and crude fibre. The content of P was determined using a Helios Alpha UV-VIS spectrophotometer. Whole blood was analysed for haematological parameters and serum for biochemical parameters. Tissue samples were collected for analysis of volatile substances and histological analysis. After slaughter, samples of the lungs, liver, kidneys and jejunum were collected for morphological evaluation, and samples of the perirenal fat, liver, kidneys, lungs and brain for headspace gas chromatography (GC) to determine the levels of volatile toxic substances.

RESULTS

A statistical increase in the digestibility of crude fibre and an increase in that of P were observed in both experimental groups (A and B) in comparison to the control. The whole blood and serum of the pigs from the control group had statistically significantly higher levels of creatinine, urea, and Mg and a higher WBC count compared to both experimental groups (A and B).

CONCLUSIONS

The feed additives were not shown to have a negative effect on the health parameters analysed or on accumulation of pollutants in selected tissues. No significant effect on the digestibility of most nutrients was observed; only an increase in the digestibility of crude fibre and a decrease in P digestibility were noted in the experimental groups.

Evaluation of the human hazard of the liver and lung tumors in mice treated with permethrin based on mode of action

The non-genotoxic synthetic pyrethroid insecticide permethrin produced hepatocellular adenomas and bronchiolo-alveolar adenomas in female CD-1 mice, but not in male CD-1 mice or in female or male Wistar rats. Studies were performed to evaluate possible modes of action (MOAs) for permethrin-induced female CD-1 mouse liver and lung tumor formation. The MOA for liver tumor formation by permethrin involves activation of the peroxisome proliferator-activated receptor alpha (PPARα), increased hepatocellular proliferation, development of altered hepatic foci, and ultimately liver tumors. This MOA is similar to that established for other PPARα activators and is considered to be qualitatively not plausible for humans. The MOA for lung tumor formation by permethrin involves interaction with Club cells, followed by a mitogenic effect resulting in Club cell proliferation, with prolonged administration producing Club cell hyperplasia and subsequently formation of bronchiolo-alveolar adenomas. Although the possibility that permethrin exposure may potentially result in enhancement of Club cell proliferation in humans cannot be completely excluded, there is sufficient information on differences in basic lung anatomy, physiology, metabolism, and biologic behavior of tumors in the general literature to conclude that humans are quantitatively less sensitive to agents that increase Club cell proliferation and lead to tumor formation in mice. The evidence strongly indicates that Club cell mitogens are not likely to lead to increased susceptibility to lung tumor development in humans. Overall, based on MOA evaluation it is concluded that permethrin does not pose a tumorigenic hazard for humans, this conclusion being supported by negative data from permethrin epidemiological studies.

Whole-body inhalation exposure to 2-ethyltoluene for two weeks produced nasal lesions in rats and mice

OBJECTIVE

Ethyltoluenes are isolated during crude oil refinement for use in gasoline and commercial products and are ubiquitous in the environment. However, minimal toxicity data are available. Previously, we identified 2-ethyltoluene (2-ET) as the most potent isomer via nose-only inhalation exposure in rodents. Here, we expanded the hazard characterization of 2-ET in two rodent models using whole-body inhalation exposure and evaluated the role of prenatal exposure.

METHODS

Time-mated Hsd:Sprague Dawley^® SD^® rats were exposed to 0, 150, 300, 600, 900, or 1200 ppm 2-ET via inhalation starting on gestation day 6 until parturition. Rat offspring (n = 8/exposure/sex) were exposed to the same concentrations as the respective dams for 2 weeks after weaning. Adult male and female B6C3F1/N mice (n = 5/exposure/sex) were exposed to the same concentrations for 2 weeks.

RESULTS AND DISCUSSION

Exposure to ≥600 ppm 2-ET produced acute toxicity in rats and mice characterized by large decreases in survival, body weight, adverse clinical observations, and diffuse nasal olfactory epithelium degeneration (rats) or necrosis (mice). Due to the early removal of groups ≥600 ppm, most endpoint evaluations focused on lower exposure groups. In 150 and 300 ppm exposure groups, reproductive performance and littering were not significantly changed and body weights in exposed rats and mice were 9-18% lower than controls. Atrophy of the olfactory epithelium and nerves was observed in all animals exposed to 150 and 300 ppm. These lesions were more severe in mice than in rats.

CONCLUSION

Nasal lesions were observed in all animals after whole-body exposure up to 600 ppm 2-ET for 2 weeks. Future studies should focus on 2-ET metabolism and distribution to better understand species differences and refine hazard characterization of this understudied environmental contaminant.

Technical note: Residues of gaseous air pollutants in rabbit (Oryctolagus cuniculus) tissues

The modern consumer is concerned not only for meat quality, but also about animal welfare and the environment. Studies were conducted to determine the concentration of gaseous residues in the tissues of rabbits. For this purpose, gaseous air pollutants were measured at the height of rabbit cages. Immediately after slaughter, samples were taken for analysis to determine the level of residual pollutants in the tissues (blood, perirenal fat and lung). Headspace gas chromatography was performed on the tissue samples to test for volatile toxic substances. Gas residues of 11 compounds were determined in the samples of blood, perirenal fat and lungs. The same chemicals were present in the air of the farm and the animal tissues, which may indicate their capacity for bioaccumulation. We recommend that the results should be used to develop guidelines regarding the welfare of meat rabbits and requirements for laboratory rabbits.

Development of a Novel AOP for Cyp2F2-Mediated Lung Cancer in Mice

Traditional methods for carcinogenicity testing rely heavily on the rodent bioassay as the standard for identification of tumorigenic risk. As such, identification of species-specific outcomes and/or metabolism are a frequent argument for regulatory exemption. One example is the association of tumor formation in the mouse lung after exposure to Cyp2F2 ligands. The adverse outcome pathway (AOP) framework offers a theoretical platform to address issues of species specificity that is consistent, transparent, and capable of integrating data from new approach methodologies as well as traditional data streams. A central premise of the AOP concept is that pathway progression from the molecular initiating event (MIE) implies a definable “response-response” (R-R) relationship between each key event (KE) that drives the pathway towards a specific adverse outcome (AO). This article describes an AOP for lung cancer in the mouse from an MIE of Cyp2F2-specific reactive metabolite formation, advancing through KE that include protein and/or nucleic acid adducts, diminished Club Cell 10 kDa (CC10) protein expression, hyperplasia of CC10 deficient Club cells, and culminating in the AO of mixed-cell tumor formation in the distal airways. This tumor formation is independent of route of exposure and our AOP construct is based on overlapping mechanistic events for naphthalene, styrene, ethyl benzene, isoniazid, and fluensulfone in the mouse. This AOP is intended to accelerate the explication of an apparent mouse-specific outcome and serve as a starting point for a quantitative analysis of mouse-human differences in susceptibility to the tumorigenic effects of Cyp2F2 ligands.

LC-high resolution-MS/MS for identification of 69 metabolites of the new psychoactive substance 1-(4-ethylphenyl-)-N-[(2-methoxyphenyl)methyl] propane-2-amine (4-EA-NBOMe) in rat urine and human liver S9 incubates and comparison of its screening power with further MS techniques

4-EA-NBOMe (N-(2-methoxybenzyl)-4-ethylamphetamine, 1-(4-ethylphenyl-)-N-[(2-methoxyphenyl)methyl]propane-2-amine) is an amphetamine-derived new psychoactive substance (NPS) of the N-methoxybenzyl (NBOMe) group first seized by German custom authorities. In contrast to the phenethylamine NBOMes, studies on the pharmacological, toxicological, or metabolic properties are not yet published. The aims of the presented work were the use of LC-HR-MS/MS for identification of the phase I and II metabolites of 4-EA-NBOMe in rat urine and pooled human S9 fraction (pS9) incubations, to compare metabolite formation in both models, to identify involved monooxygenases, and to elucidate its detectability in standard urine screening approaches (SUSAs) using GC-MS, LC-MSⁿ, and LC-HR-MS/MS. 4-EA-NBOMe was mainly metabolized by oxidation of the ethyl group to phenyl acetaldehyde, to benzoic acid, or to phenylacetic acid, by hydroxylation, and all combined with O-demethylation as well as by glucuronidation and sulfation of the main phase I metabolites in rats. With the exception of the oxidation to benzoic acid, all main metabolic reactions could be confirmed in the incubations with pS9. In total, 36 phase I and 33 phase II metabolites could be identified. Monooxygenase activity screenings revealed the general involvement of cytochrome-P450 (CYP) 1A2, CYP2B6, and CYP3A4. An intake of 4-EA-NBOMe was detectable only via its metabolites by all SUSAs after low-dose administration. The main targets for both LC-MS screenings should be the phenylacetic acid derivative, the mandelic acid derivative both with and without additional O-demethylation, and, for GC-MS, the hydroxy metabolite after conjugate cleavage.

Roles of oxidative stress, apoptosis, and heme oxygenase-1 in ethylbenzene-induced renal toxicity in NRK-52E cells

Ethylbenzene is an important industrial chemical, but its potential toxicity is a recent concern. Our previous study investigated the renal toxicity of ethylbenzene in vivo. Rat renal epithelial cells (NRK-52E cells) were incubated with 0, 30, 60, and 90 µmol/L of ethylbenzene for 24 h in vitro to investigate ethylbenzene-induced oxidative stress, apoptosis, and the expression of heme oxygenase 1 (HO-1) and nuclear factor (erythroid 2)-related factor 2 (Nrf2). The cell survival rate in the ethylbenzene-treated groups was significantly lower than the control group. Ethylbenzene significantly increased intracellular reactive oxygen species and apoptosis. Malondialdehyde levels were significantly elevated compared with the control group, while glutathione levels and glutathione peroxidase activities were decreased in ethylbenzene-treated groups. The activities of catalase and superoxide dismutase were also markedly reduced. A significant dose-dependent increase in HO-1 and Nrf2 messenger RNA expression levels was observed in ethylbenzene-treated groups compared with the control group. Similarly, ethylbenzene treatment enhanced protein expression of HO-1 and Nrf2 in a dose-dependent manner. Our results indicated that ethylbenzene induced oxidative stress, apoptosis, and upregulation of HO-1 and Nrf2 in NRK-52E cells, which contributes to ethylbenzene-induced renal toxicity.

Risk assessments for chronic exposure of children and prospective parents to ethylbenzene (CAS No. 100-41-4)

Potential chronic health risks for children and prospective parents exposed to ethylbenzene were evaluated in response to the Voluntary Children's Chemical Evaluation Program. Ethylbenzene exposure was found to be predominately via inhalation with recent data demonstrating continuing decreases in releases and both outdoor and indoor concentrations over the past several decades. The proportion of ethylbenzene in ambient air that is attributable to the ethylbenzene/styrene chain of commerce appears to be relatively very small, less than 0.1% based on recent relative emission estimates. Toxicity reference values were derived from the available data, with physiologically based pharmacokinetic models and benchmark dose methods used to assess dose-response relationships. An inhalation non-cancer reference concentration or RfC of 0.3 parts per million (ppm) was derived based on ototoxicity. Similarly, an oral non-cancer reference dose or RfD of 0.5 mg/kg body weight/day was derived based on liver effects. For the cancer assessment, emphasis was placed upon mode of action information. Three of four rodent tumor types were determined not to be relevant to human health. A cancer reference value of 0.48 ppm was derived based on mouse lung tumors. The risk characterization for ethylbenzene indicated that even the most highly exposed children and prospective parents are not at risk for non-cancer or cancer effects of ethylbenzene.

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.

A review of the electrophilic reaction chemistry involved in covalent DNA binding

The need to assess the ability of a chemical to act as a mutagen or a genotoxic carcinogen (collectively termed genotoxicity) is one of the primary requirements in regulatory toxicology. Several pieces of legislation have led to an increased interest in the use of in silico methods, specifically the formation of chemical categories for the assessment of toxicological endpoints. A key step in the development of chemical categories for genotoxicity is defining the organic chemistry associated with the formation of a covalent bond between DNA and an exogenous chemical. This organic chemistry is typically defined as structural alerts. To this end, this article has reviewed the literature defining the structural alerts associated with covalent DNA binding. Importantly, this review article also details the mechanistic organic chemistry associated with each of the structural alerts. This information is extremely important in terms of meeting regulatory requirements for the acceptance of the chemical category approach. The structural alerts and associated mechanistic chemistry have been incorporated into the Organisation for Economic Co-operation and Development (OECD) (Q)SAR Application Toolbox.