These studies were supported in part by funds from the Comprehensive Environmental Response, Compensation, and Liability Act trust fund (Superfund) by an interagency agreement with the Agency for Toxic Substances and Disease Registry, U.S. Public Health Service.
Toxicity studies were performed with a chemically defined mixture of 25 groundwater contaminants, using dose levels considered to have environmental relevance. The mixture contained 19 organic compounds and six metals (shown below); the selection of these compounds was based primarily on the frequency of their occurrence in United States Environmental Protection Agency surveys of groundwater contamination in the vicinity of hazardous waste disposal sites. This report focuses primarily on 26-week drinking water toxicity studies with male and female F344/N rats and B6C3F1 mice. The endpoints evaluated included histopathology, clinical pathology, neurobehavioral studies, and reproductive toxicity. Additional studies using this same chemical mixture are briefly reviewed in this report and include an evaluation of spermatogenesis in B6C3F1 mice exposed to the chemical mixture for 13 weeks, a continuous breeding study with Sprague-Dawley rats and CD-1® Swiss mice, studies of myelotoxicity in B6C3F1 mice exposed to the chemical mixture for up to 31.5 weeks, studies of immunosuppression in B6C3F1 mice exposed for up to 13 weeks, in vitro mutagenicity assays in Salmonella typhimurium and Escherichia coli, and measures of genetic damage in bone marrow and peripheral blood of F344/N rats and B6C3F1 mice in 2-week drinking water studies.
In a 26-week drinking water study in which rats were administered the chemical mixture at composite contaminant concentrations of 0, 11, 38, 113, or 378 ppm, no deaths occurred and the body weight gain of high-dose males was slightly less than that of the controls. Water consumption decreased with dose and was 24% to 28% less than that of the controls at the highest concentration. Changes in organ weights occurred primarily in high-dose rats and included increased absolute and relative liver and kidney weights in females, increased relative kidney weight in males, and decreased absolute and relative thymus weights in males and females. Hematologic assessments indicated that rats receiving 378 ppm developed a microcytic anemia consistent with that accompanying iron depletion. Multiple foci of inflammation occurred in the liver of exposed rats. In high-dose females, these liver lesions were especially prominent and included bile duct and oval cell hyperplasia. Inflammation also occurred in the mesenteric lymph nodes, the adrenal gland, and the spleen. The amount of hemosiderin in the spleens of rats receiving the higher concentrations of the chemical mixture was less than normal.
In a 26-week study in which mice were exposed to the chemical mixture at concentrations of 0, 11, 38, 113, and 378 ppm in drinking water, there were no clear adverse effects noted in survival, weight gain, clinical pathology parameters, or histopathologic evaluations. Water consumption decreased with increasing dose, and water consumption by high-dose mice was approximately 40% less than that by the controls.
In neurobehavioral assessments, no clear treatment-related effects were observed in measures of forelimb and hindlimb grip strength, hindlimb footsplay, motor activity, response to a thermal stimulus, or startle response in rats or mice evaluated at 6-week intervals throughout the 26- week drinking water studies.
There were no effects on sperm morphology or motility or on estrous cycle length in rats or mice receiving the chemical mixture during the 26-week studies. Sperm concentration was decreased in F1 CD-1® Swiss mice during continuous breeding studies, although there were no clear adverse effects on the fertility of Sprague-Dawley rats or CD-1® Swiss mice in these studies. Pup weight, the number of live males, and the number of male pups per litter were slightly decreased in dosed rats in the continuous breeding study in rats; the number of live female mouse pups in litters born of the F0 and F1 generations was decreased in the 378 ppm group. The significance of these observations, if any, is not known. F1 mice receiving 378 ppm had increased incidences of hepatic inflammation compared to the controls.
In female B6C3F1 mice that received the chemical mixture in drinking water at concentrations as high as 756 ppm for 2 weeks or 378 ppm for 13 weeks, assessments of immune function showed suppression of hematopoietic stem cells and antigen-induced antibody-forming cells. This was manifested by impaired resistance to challenge with a nonlethal strain of mouse malaria, Plasmodium yoelii. Additional evidence of an adverse effect on hematopoietic stem cells was demonstrated by decreases in the in vitro colony-forming ability of granulocyte-macrophage progenitor cells and erythroid precursor cells isolated from female mice that had received the chemical mixture at a concentration of 378 or 756 ppm in 31.5 week studies. Potential genotoxic effects of the chemical mixture to the bone marrow of F344/N rats and B6C3F1 mice were assessed in 2-week drinking water studies with concentrations as high as 756 ppm. Small increases in sister chromatid exchanges and micronucleated polychromatic erythrocytes occurred in the bone marrow of dosed male mice, and micronucleated polychromatic erythrocytes were also increased in dosed female mice.
The chemical mixture did not induce mutations in Salmonella typhimurium strains TA98 and TA100 and did not induce DNA damage in Escherichia coli with or without metabolic activation.
In summary, rats receiving drinking water containing a mixture of 25 common groundwater contaminants at levels of potential environmental relevance developed inflammatory lesions in the liver, spleen, lymph nodes, and adrenal gland, as well as evidence of an iron deficiency anemia. The inflammatory lesions could not be predicted based on the known toxic effects of the individual components of the chemical mixture. Mice exposed to similar concentrations of the chemical mixture did not show adverse effects in a standard toxicity study but developed deficits in bone marrow function, evidence of genetic damage, hepatic inflammation, and immunosuppression in other studies that generally included exposures to higher concentrations or exposures of longer duration. A no-observed-adverse-effect level for histologic injury (granulomatous inflammation of the liver) was 11 ppm in rats; however, no clear evidence for histologic injury was seen in mice exposed to concentrations of the chemical mixture as high as 378 ppm in a standard 26-week study.