Toxicity studies on trans-1,2-dichloroethylene

The Acute and Subchronic Toxicity in Rats of Trans-1,2-Dichloroethylene in Drinking Water

Trans-1,2-dichloroethylene was administered either by gavage (acute studies) or in drinking water (subchronic studies) to male and female Sprague-Dawley derived Charles River rats. The acute oral LD50 was 7902 mg/kg for males and 9939 mg/kg for females. Decreased activity, ataxia, and depressed respiration preceded death. In the subchronic study, rats received theoretical daily doses of 500, 1500, and 3000 mg trans-1,2-dichloroethylene/kg body weight/day for 90 consecutive days. The actual daily doses were 402, 1314, and 3114 mg/kg for males and 353, 1257, and 2809 mg/kg for females. There were no compound-related deaths. There were no consistently significant compound-related dose-dependent adverse effects on any of the hematological, serological, or urinary parameters evaluated. There were dose-dependent increases in kidney weights and ratios in treated females. There were no compound-related gross or histological effects. No specific organ site toxicity could be identified in these studies. These data suggest that the toxicity from exposure to trans-1,2-dichloroethylene in drinking water apparently is low and probably does not constitute a serious health hazard.

Health effects classification and its role in the derivation of minimal risk levels: Hepatic effects

The Agency for Toxic Substances and Disease Registry (ATSDR) derives health based guidance values called minimal risk levels (MRLs) to assist with assessment of risks posed by exposures to hazardous chemicals. Current MRLs are posted on ATSDR's web site (www.atsdr.cdc.gov). From the total 326 MRLs currently posted, 79 MRLs are based on hepatic endpoints. The paper reports on endpoints used for the derivation of these MRLs and the use of uncertainty factors. It also describes the ranking of effects into less serious and serious categories as described in ATSDR's Guidance for Developing Toxicological Profiles.

Health effects of environmental contaminant exposure: an intrafile comparison of the Trichloroethylene Subregistry

The establishment of the National Exposure Registry represents the first major effort toward longitudinal surveillance of general populations exposed long-term to low levels of specific substances in the environment. The authors investigated the National Exposure Registry's Trichloroethylene Subregistry intrasubregistry differences with respect to health outcomes and the possible relationships with types and levels of chemical exposure. Investigators divided the 4041 living members of the Trichloroethylene Subregistry into 4 subgroups, by type(s) of exposures (chemicals) and duration and level of exposures. The authors compared the reporting rates for 25 health outcomes across subgroups. The authors used logistic regression, in which age, sex, education, smoking history, and occupational history were the covariates. Statistically significant increases in reporting rates were seen with (a) increased maximum trichloroethylene exposures for the outcome stroke, (b) increased cumulative chemical exposure for respiratory allergies, and (c) duration of exposure for hearing impairment. Consistently elevated reporting rates across the exposure subgroups were seen for hearing impairment, speech impairment, asthma and emphysema, respiratory allergies, and stroke. Reporting rates for urinary tract disorders were related only to cumulative chemical levels. The authors noted that there appeared to be a relationship between trichloroethylene and reporting rates for speech impairment, hearing impairment, and stroke and between volatile organic compounds and asthma and emphysema, respiratory allergies, and urinary tract disorders.

Humoral and cell-mediated immune status of mice exposed to trans-1,2-dichloroethylene

This study assessed possible adverse immunological effects of trans-1,2-dichloroethylene (DCE) on random-bred CD-1 mice following 14 and 90 days of exposure. A 14-day range-finding study was performed on male mice by gavage at doses 1/10 and 1/100 the LD50 (210 and 21 mg/kg). No alterations in either humoral or cell-mediated immunity were observed following this exposure. A 90-day study was conducted in which DCE was administered in the drinking water of male and female mice. The levels of DCE in the drinking water were calculated to deliver levels equivalent to, and higher than, those delivered for 14 days (17, 175, and 387 mg/kg for males and 23, 224, and 452 mg/kg for females). No changes were observed in the cell-mediated immune status of either sex or in the humoral immune status of females. However, a marked suppression in humoral immune status was observed in male mice exposed to all three levels of DCE, as indicated by a decreased ability of spleen cells to produce antibody against sheep erythrocytes (sRBC). Macrophage function was depressed only in females, as indicated by the decreased ability of thioglycollate-recruited peritoneal exudate cells (PEC) to phagocytize sRBC.

Toxicology of trans-1,2-dichloroethylene in the mouse

Trans-1,2-dichloroethylene (DCE) was administered to male and female CD-1 mice in order to evaluate its effects on standard toxicological parameters. Following an acute LD50 determination (2122 mg/kg in males and 2391 mg/kg in females) and a 14-day range-finding study, a 90-day drinking water study was performed using levels of DCE calculated to deliver approximately 1/100, 1/10, and 1/5 the LD50. Various toxicological assessments were made, including body and organ weights, hematology, serum chemistries, and hepatic microsomal activities. Few alterations were observed in either sex following 90 days of exposure. The most noteworthy changes occurred in the males exposed to the highest level of DCE, where there was a significant decrease in glutathione levels, and in the females exposed to all three DCE levels, where there was a significant decrease in aniline hydroxylase activity. These data served as background for the immunotoxicological evaluation presented in the following manuscript.

Comparative genetic activity of cis- and trans-1,2-dichloroethylene in yeast

The cis and trans isomers of 1,2-dichloroethylene were tested for mutagenic effects in a diploid strain (D7) of the yeast Saccharomyces cerevisiae in suspension tests with and without a mammalian microsomal activation system, an S9 mouse liver fraction, and by an in vivo intrasanguineous host mediated assay. The effects of the same agents on aminopyrine N-demethylase activity and cytochrome P-450 level in liver were studied in nonpretreated and in phenobarbital + beta-naphtoflavone-pretreated mice. In the suspension test, both isomers exhibited dose dependent toxicity, and survival was lower with metabolic activation than without. In this test also, both isomers exhibited genetic activity as measured by increases in recombinants at the ade 2 locus in experiments with metabolic activation. In the host-mediated assay, only the cis isomer showed evidence of mutagenic activity with significant increases in convertants at the trp locus and revertants at the ilv locus. Such mutagenic activity was found both after acute and chronic doses and in liver, kidney, and lung tissue. The two isomers exhibited different effects with respect to aminopyrine N-demethylase activity and cytochrome P-450 level. In general, the trans isomer appeared to emphasize induction of enzyme activity or level while the cis isomer more frequently tended to inhibit activity or destroy the enzyme.

Inhibition of mixed function oxidases in rat liver by trans- and cis-1,2-dichloroethylene

A single 8-h exposure to trans-1,2-dichloroethylene (t-DCE) or cis-1,2-dichloroethylene (c-DCE) at 200 ppm (hygienic standard in workplaces) resulted in a significant increase in the hexobarbital sleeping time, the zoxazolamine paralysis time, and the metabolic formation of 4-aminoantipyrine from aminopyrine in adult female Wistar rats. Higher DCE concentrations caused a dose-dependent and substantial enhancement of these effects, the effects of c-DCE being stronger than that of t-DCE. In the course of enzyme-kinetic measurements in isolated rat liver microsomes, t-DCE proved to be a competitive inhibitor of the oxidative N-demethylation of aminopyrine and of the O-demethylation of p-nitroanisole. It is concluded from the results that the inhibition of hepatic drug metabolism is caused by a competitive and reversible interaction of the 2 DCE isomers with the mixed-function oxidase system, the interaction possibly operating at the type I binding site.

Haloethylene-related compounds of industrial, environmental, and medical significance

A broad-based literature survey was made for chemicals that contain either a haloethylene or a related substructure. Two hundred and sixty-two compounds, including synthetic intermediates, pesticides, solvents, drugs, food components, natural products, and metabolites, are grouped by their structures. Some are in current use or are bioavailable while little exposure is expected from others. As more biologic-response information is reported for small compounds of these types, it should become possible to select others for research on additional questions of structure-activity relationships. Some of the compounds are widespread while others are not. Some are used or found in large amounts while others may be trace contaminants, minor or more major by-products of synthesis or isolation. The pesticides and solvents, for example, are knowingly and often deliberately released to the environment, sometimes in very large quantities. Inadvertent release also occurs, sometimes referred to as fugitive emission. Food contaminants and drugs are directly accessible to humans. Sparsely distributed natural products could be accessible to humans, for example, via the food chain. Some of the compounds in food may be formed during preparation, storage or metabolically. Last, the haloethylene function has often been synthesized into compounds in order to achieve desired biologic activities. There are many types and degrees of relatedness of structure, depending upon atomic dimensions and stereochemical, polar, resonance, and other factors. Furthermore, for some chemical series, biologic responses are continuously variable while, in other cases, it is not uncommon that qualitatively different types of response occur with apparently very close homologs. Genetic, metabolic, and behavioral factors affecting response must also be considered. Thus, safety or hazard cannot yet be predicted conclusively by apparent relatedness of structure alone. Also, since the tables are noncomprehensive, some relevant compounds have likely been omitted. The haloalkanes, for example, are not here because of their large number, despite the knowledge that some are either metabolized or nonbiologically converted to haloalkenes.