Conditioned flavor aversion induced by inhaled p-xylene in rats

Interdisciplinary Approach to Assessing the Health Risk of Air Toxic Chemicals: An Overview

To assist the regulatory branch of the Environmental Protection Agency in addressing the risk assessment of air toxics, the Health Effects Research Laboratory initiated a comprehensive inhalation toxicology program to provide key health effects data missing from the current data base. A priority ranking of chemicals based on the potential for substantial human exposure and the need for health effects data was developed to identify candidate chemicals for toxicological research. The major goal of the program is to evaluate the concentration-response from acute, intermittent and subchronic inhalation exposures to developmental, genetic, hepatic, immunologic, neurologic, pulmonary and reproductive toxicity in a manner that provides data for the regulatory health assessment of air toxic chemicals. Extrapolation and dosimetry research is also conducted to improve the basis for human risk assessment. Determination of biological endpoints to be examined will be decided on a compound-by-compound basis, depending on the physical, chemical and structural characteristics of the chemical and evaluation of the existing health data base. Although the main emphasis is on inhalation as the primary route of exposure, some of the laboratories will compare inhalation to other routes, such as oral, to better understand the influence of route of exposure and hence the potential applicability of existing health data. Acute and intermittent exposures will be done for all compounds. Upon evaluation of the acute results, a decision will be made as to whether subchronic studies are needed. Endpoints that show unusual sensitivity may be investigated in greater detail. The total length of exposure will vary from 1 to 21 days. The daily length of exposure will range from 1 to 8 hr. If adverse effects are observed at ambient levels, the time to recovery after exposure will be investigated.

Behavioral effects following subacute inhalation exposure to m-xylene or trimethylbenzene in the rat: a comparative study

Trimethylbenzene (TMB), like xylene (dimethylbenzene), is a significant constituent of some industrial solvent mixtures. In earlier studies, we found that in the rat a subacute low-level inhalation exposure to some of the TMB isomers may result in behavioral alterations detectable weeks after the exposure [Neurotoxicol Teratol 19;1997:327; Int J Occup Med Environ Health 11;1998:319]. The purpose of the present study was to compare m-xylene (XYL) and each of the TMB isomers: 1,2,3-TMB (hemimellitene - HM), 1,2,4-TMB (pseudocumene - PS), and 1,3,5-TMB (mesitylene - MES) with respect to the ability for inducing behavioral effects in the rat. The rats (10-11 animals per group) were exposed repeatedly for 4 weeks (6 h per day, 5 days per week) to XYL (XYL group), HM (HM group), PS (PS group) or MES (MES group) at 100 ppm, or sham exposed (C group) in 1.3 cu/m dynamic inhalation chambers. Starting 2 weeks after exposure the following forms of rat's behavior were assessed: radial maze performance, spontaneous activity in an open field, learning and retention of passive and active (two-way) avoidance response, and heat-induced paw licking before and after a 2 min footshock (a test for assessment of the stress response). None of the solvent-exposed groups differed considerably from the control one with respect to the radial maze performance. Compared to control rats, the rats of the XYL, PS and MES groups, but not those of HM group, showed a significantly higher spontaneous locomotor activity in the open field, an impaired passive avoidance learning and significantly longer paw-lick latencies 24 h after footshock. Acquisition, but not retention, of the two-way active avoidance response was significantly impaired in all solvent-exposed groups. The XYL group did not differ significantly from PS, MES or HM group in any of the behavioral parameters. The above results show that a short-term exposure to any of the TMB isomers or m-xylene at concentration as low as 100 ppm may induce persistent behavioral alterations in the rat.

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

Xylenes, or dimethylbenzenes, are among the highest-volume chemicals in production. Common uses are for gasoline blending, as a solvent or component in a wide variety of products from paints to printing ink, and in the production of phthalates and polyester. They are often encountered as a mixture of the three dimethyl isomers, together with ethylbenzene. As part of its mandate, the Agency for Toxic Substances and Disease Registry (ATSDR) prepares toxicological profiles on hazardous chemicals found at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) National Priorities List (NPL) sites that are of greatest concern for public health purposes. These profiles comprehensively summarize toxicological and environmental information. This article constitutes the release of the bulk of this profile (ATSDR, 1995) into the mainstream scientific literature. An extensive listing of known human and animal health effects, organized by route, duration, and end point, is presented. Toxicological information on toxicokinetics, biomarkers, interactions, sensitive subpopulations, reducing toxicity after exposure, and relevance to public health is also included. Environmental information encompasses physical properties, production and use, environmental fate, levels seen in the environment, analytical methods, and a listing of regulations. ATSDR, as mandated by CERCLA (or Superfund), prepares these profiles to inform and assist the public.

Toxicological considerations in evaluating indoor air quality and human health: impact of new carpet emissions

This review article considers evidence regarding the toxicological impact of new carpet emissions on indoor air quality and human health. It compares emissions data from several studies and describes the dominant compounds found in those emissions. The toxicity of each these compounds is assessed for animal and human data, with a focus on inhalation exposure. Data for acute and chronic exposures are presented, and synergistic effects are considered. Differences and similarities between health responses caused by toxicity and/or by immunological reactions are discussed. Possible neurogenic pathways and associations between these and immune changes are considered as they might relate to inflammatory-based human reactions. Additionally, factors affecting human odor responses are described. The roles that a variety of psychological factors may also play in the etiology of potentially related phenomena, such as the sick building syndrome, pathogenic illness, and multiple chemical sensitivity, are considered. Gaps in the literature are identified within the article and suggestions for future research are offered. In particular, it is noted that few, if any, prior studies have evaluated both neurogenic and immune-mediated inflammation status within the same study. Based on the present information available, it is concluded that under normal environmental circumstances, VOC emissions from new carpets are sufficiently low such that they should not adversely affect indoor air quality or pose significant health risk to people.

Enhanced mortality and liver damage in virus-infected mice exposed to p-xylene

This study assessed effects of exposure to p-xylene, a ubiquitous air pollutant, on mice infected with murine cytomegalovirus (MCMV), a mouse model for a common human virus. It was postulated that adverse health effects could occur as a result of (1) enhanced infection due to xylene-induced immune suppression, (2) increased p-xylene toxicity due to viral suppression of cytochrome P-450 (P-450), and/or (3) additive or synergistic effects on liver function due to tissue injury by both p-xylene and MCMV. Mice were exposed to filtered air, 600 or 1200 ppm p-xylene 6 h/d for 4 d and infected with a sublethal dose of MCMV after the first exposure. No deaths occurred among uninfected, p-xylene-exposed mice or infected, air-exposed mice; 34% and 0% mortality occurred respectively in infected mice exposed to 1200 and 600 ppm p-xylene. Virus titers in the liver and splenic natural killer cell activity were unaffected by exposure to 1200 ppm p-xylene. Small but significant increases in serum aspartate aminotransferase, alanine aminotransferase, and lactate dehydrogenase activities, indicators of liver damage, were observed at 4 d postinfection. p-Xylene exposure had no effect on these serum enzyme activities in uninfected mice, but 1200 ppm potentiated this effect in infected mice. MCMV significantly suppressed and p-xylene significantly increased total P-450 levels in the liver, but there was no significant interaction between the two. Isozymes 1A1, 2B1/B2, and 2E1 were decreased to a similar degree, suggesting that the virus does not target specific isozymes. Enhanced mortality was not due to immune suppression. While p-xylene potentiated liver damage was caused by the virus, the magnitude of serum enzyme activities indicates that this damage was not a likely cause of death. The cause of deaths is unclear, results were consistent with the hypothesis that enhanced mortality was related to enhanced xylene toxicity due to suppression of P-450, although additive or synergistic damage to tissues other than liver cannot be ruled out.

Assessment of the hepatotoxicity of acute and short-term exposure to inhaled p-xylene in F-344 rats

Due to the ubiquitous presence of p-xylene in air and the existing uncertainty regarding its hepatotoxic potential, we examined the effect of acute and short-term exposure to inhaled p-xylene on the liver. Male F-344 rats were exposed to 0 or to 1600 ppm p-xylene, 6 h/d, for 1 or 3 d. Exposure to inhaled p-xylene caused no histopathological evidence of hepatic damage and had little or no effect on the serum levels of aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, ornithine carbamyl transferase, alkaline phosphatase, and total bilirubin. Exposure to p-xylene for 1 or 3 d resulted in an increase in relative liver weight on d 1 post-exposure. The concentration of hepatic cytochrome P-450 was increased by both p-xylene exposure regimens on d 1 postexposure and had returned to control levels by d 3 following the single p-xylene exposure and by d 2 following the 3-d exposure. These observations provide consistent evidence that acute and short-term exposure to 1600 ppm p-xylene by inhalation did not produce overt hepatotoxicity but resulted in a significant increase in the concentration of hepatic cytochrome P-450, the principal enzyme system involved in the metabolic biotransformation of xenobiotics.