The following abstract presents results of a study conducted by a contract laboratory for the National Toxicology Program. The findings have not been peer reviewed and were not evaluated in accordance with the levels of evidence criteria established by NTP in March 2009. The findings and conclusions for this study should not be construed to represent the views of the NTP or the U.S. Government.
Disinfection by-products (DBPs) are contaminants found in drinking water. DBPs are formed as by-products as a result of the chlorination/ozonization process used to purify water to acceptable drinking water standards. The potential effects of drinking water contaminants to affect adversely the immune system is a concern of both the Environmental Protection Agency (EPA) and the National Institute of Environmental Health Sciences (NIEHS). Several drinking water DBPs have been identified and selected for evaluation of their potential effects on the immune system in a joint project between the EPA and the NIEHS.
Chloramine has long been used to provide a disinfecting residual in distribution systems where it is difficult to maintain a free chlorine residual or where DBP formation is of concern. The reaction between chlorine and compounds containing a nitrogen atom with one or more hydrogen atoms attached to it will form chloramine.
The National Toxicology Program (NTP) requested that a dose range-finding study be performed in order to establish the potential effects of chloramine (CHL) on the Immune system and to determine doses that could be used in a full immunotoxicology study. These studies were conducted in female B6C3F1 mice. The animals were exposed to CHL based on the concentration of the test article in the drinking water. Five CHL concentrations of 2, 10, 20, 100, and 200 ppm for 28 days were utilized. CHL solutions were prepared fresh weekly and stored at ambient condition. The in-life phase of these studies was carried out between 28 February 2000 and 15 June 2000.
The baseline toxicology studies are summarized in Table ES-1. CHL was administered in the drinking water from water bottles for 28 days at 2, 10, 20, 100 and 200 ppm/day. There was no statistically significant difference in drinking water consumption between animals exposed to CHL and the deionized tap water controls. Exposure to CHL did not produce any signs of overt toxicity. There was no significant difference in body weight and body weight change between the exposed and control animals during the experimental period. No gross pathological lesions were observed in CHL-exposed animals; furthermore, there were no differences observed in the weights of thymus, liver, spleen, kidneys or lungs when the data were expressed as either an absolute or a percent value. The erythrocyte count, hemoglobin, hematocrit, MCV, MCH, MCHC, platelet count, the percentage of reticulocytes, total leukocyte count, and counts of leukocyte differentials were unaffected by CHL
The immunological studies are summarized in Table ES-2. As in the toxicological parameters, exposure to CHL produced no biologically significant effects in various immunological parameters. There were no changes in the percentage and number of total B cells, T cells, CD4+ T cells, CD8+ T cells, natural killer cells and macrophages. Exposure to CHL did not produce a significant effect on the IgM antibody-forming cell responses to sheep red blood cells or serum lgM antibody titer. The effect of CHL on the activity of spleen T cells and natural killers (NK) cells was evaluated using the one-way mixed leukocyte response (MLR) and cytotoxic assay of YAC-1 cells, respectively. There was no biologically meaningful alteration in MLR and NK activity after exposure to CHL. When the activity of peritoneal macrophages was evaluated using the cytotoxic/cytostatic assay of B16F10 tumor cells, minimal effects were observed.
In conclusion, CHL, when administered for 28 days in the drinking water at doses from 2 to 200 ppm, produced minimal toxicological and immunotoxic effects in female B6C3F1 mice. However, Abdel-Rahman et al.1 have reported that the glutathione content in rat blood was decreased significantly after 4 months of monochloramine treatment (0 - 100 mg/l). After 3 months, red blood cell counts and hematocrit were significantly decreased. Hemoglobin concentration and MCHC were also decreased at 10 months of treatment. Thus, exposure of mice to CHL for a longer period may be necessary to insure that CHL does not adversely affect the immune system.