ATSDR evaluation of health effects of chemicals. V. Xylenes: health effects, toxicokinetics, human exposure, and environmental fate

Case Report: Long segmental lesions of the spinal cord caused by exposure to xylene

Xylene has the potential to cause nervous system disturbances since it is a lipophilic substance with high affinity for lipid-rich tissue, such as the brain. Involvement in the spinal cord, especially long segmental spinal cord lesions that permeate almost the entire cervical and thoracic spinal cord, is extremely rare. We report two cases of occupational exposure to excessive xylene, both of which presented with severe and rapidly progressive numbness and weakness in the limbs that, more importantly, led to poor outcomes: one died and the other was left severely disabled. In both, spinal magnetic resonance imaging showed long segmental lesions in the cervicothoracic spinal cord. These findings may provide some insights into the effects of xylene as an isolated agent on the spinal cord injury.

Protective effect of Lycium barbarum polysaccharide on di-(2-ethylhexyl) phthalate-induced toxicity in rat liver

Di-(2-ethylhexyl)-phthalate (DEHP) is the most commonly used plasticizer and it has been a ubiquitous environmental contaminant which affects health. The purpose of this study was to investigate the protective effect of the Lycium barbarum polysaccharide (LBP) at dosages of 100, 200, and 300 mg/kg bw on DEHP-induced (3000 mg/kg) toxicity in rat liver through a 28-day animal experiment. The results showed that LBP attenuated oxidative stress slightly by lowering the production of ROS and improving the activity of SOD and GSH-Px in liver and serum of DEHP treatment rats. At the same time, the levels of PXR, CYP450, CYP2E1, CYP3A1, UGT1, and GST were reduced after LBP treatment. Moreover, LBP decreased the mRNA expression of PXR, UGT1, and GST significantly. These findings suggested that LBP might ameliorate DEHP-induced liver injury by down-regulating the expression of PXR in liver, further down-regulating the downstream phase I and II detoxification enzymes, thus reducing the damage caused by DEHP. Therefore, LBP may have the potential to become an auxiliary therapeutic agent as a natural ingredient of health food.

Adsorption of chromium (VI) from aqueous solution by sugar beet bagasse-based activated charcoal

Chromium (VI) is known to be potentially carcinogenic and mutagenic in humans. A low-cost industrial solid bioadsorbent, bagasse-based activated charcoal (BAC), has been investigated for removal of chromium from aqueous solution. All the experiments were carried out in batch process with laboratory-prepared samples to study the effects of adsorbent dose, contact time, pH and initial concentration of Cr(VI). The removal of chromium ion was found to be highly dependent on the pH of the solution, adsorbent dose and contact time. Also the equilibrium adsorption was analyzed by the Freundlich and Langmuir isotherm models. It was found that the Freundlich isotherm model best described the sorption of chromium by sugar beet bagasse-based activated charcoal (r2 > 0.9927). Experimental data of kinetic studies were fitted to pseudo-first-order, pseudo-second-order and modified pseudo-first-order models. The results showed pseudo-second order kinetics was best fitted to the collected data (r2 > 0.9893). Optimum conditions for adsorption were determined at pH 2 and a contact time of 180 minutes (92.7% removal). These retention capacities suggest that BAC can provide a simple, effective, and cheap method for removing Cr(VI) ions from effluents and water resources.

Ototoxicity in rats exposed to ethylbenzene and to two technical xylene vapours for 13 weeks

Male Sprague-Dawley rats were exposed to ethylbenzene (200, 400, 600 and 800 ppm) and to two mixed xylenes (250, 500, 1,000 and 2,000 ppm total compounds) by inhalation, 6 h/day, 6 days/week for 13 weeks and sacrificed for morphological investigation 8 weeks after the end of exposure. Brainstem auditory-evoked responses were used to determine auditory thresholds at different frequencies. Ethylbenzene produced moderate to severe ototoxicity in rats exposed to the four concentrations studied. Increased thresholds were observed at 2, 4, 8 and 16 kHz in rats exposed to 400, 600 and 800 ppm ethylbenzene. Moderate to severe losses of outer hair cells of the organ of Corti occurred in animals exposed to the four concentrations studied. Exposure to both mixed xylenes produced ototoxicity characterized by increased auditory thresholds and losses of outer hair cells. Ototoxicity potentiation caused by ethylbenzene was observed. Depending on the mixed xylene studied and the area of the concentration-response curves taken into account, the concentrations of ethylbenzene in mixed xylenes necessary to cause a given ototoxicity were 1.7-2.8 times less than those of pure ethylbenzene. Given the high ototoxicity of ethylbenzene, the safety margin of less or equal to two (LOAEL/TWA) might be too small to protect workers from the potential risk of ototoxicity. Moreover, the enhanced ototoxicity of ethylbenzene and para-xylene observed in mixed xylenes should encourage the production of mixed xylenes with the lowest possible concentrations of ethylbenzene and para-xylene.

A physiologically based toxicokinetic model of inhalation exposure to xylenes in Caucasian men

Widespread exposure to the volatile aromatic hydrocarbons, ortho-, meta-, and para-xylene occurs in many industries including the manufacture of plastics, pharmaceuticals, and synthetic fibers. This paper describes the development of a physiologically based toxicokinetic model using biomonitoring data to quantify the kinetics of ortho-, meta-, and para-xylenes. Serial blood concentrations of deuterium-labeled xylene isomers were obtained over 4 days after 37 controlled, 2h inhalation exposures to different concentrations of the isomers. Peak toxicant concentrations in blood occurred in all subjects at the termination of exposure. Systemic clearance averaged 116 L/h+/-34 L/h, 117 L/h+/-23 L/h, and 129 L/h+/-33 L/h for ortho-, para-, and meta-xylene, respectively. The half-life of each toxicant in the terminal phase (>90 h post-exposure) was fit by the model, yielding values of 30.3+/-10.2 h for para-xylene, 33.0+/-11.7 h for meta-xylene and 38.5+/-18.2 h for ortho-xylene. Significant isomeric differences were found (p<0.05) for toxicant half-life, clearance and extrahepatic metabolism. Inter-individual variability seen in this study suggests that airborne concentration guidelines may not protect all workers. A Biological Exposure Index is preferred for this purpose since it is integrative and reflective of inter-individual kinetic variability.