Immunotoxicologic evaluation of chlorine-based drinking water disinfectants, sodium hypochlorite and monochloramine

Male Sprague-Dawley rats were exposed to chlorine-based disinfectants in the drinking water from weaning to 12 weeks of age, at which time they were terminated and assessed for immune competence. Chlorine-based drinking water disinfectants used were sodium hypochlorite (5, 15 and 30 ppm) and monochloramine (9, 19 and 38 ppm). Parameters of immunity measured were spleen and thymus weights, antibody production, delayed-type hypersensitivity (DTH) reactions, natural killer cell (NKC) cytotoxicity, oxidative metabolism response (i.e chemiluminescence-CL) and phagocytosis by macrophages, and production of 2 immunoregulatory cytokines, interleukin 2 (IL2) and prostaglandin E2 (PGE2). Significant (P less than or equal to 0.05) reductions of spleen weight, DTH reactions, and oxidative metabolism by macrophages were observed only in groups of rats exposed to high levels (30 ppm) of sodium hypochlorite, while PGE2 production was elevated. Rats exposed to the higher doses of monochloramine had reduced spleen weights (38 ppm), decreased antibody synthesis (9 and 19 ppm) and augmented PGE2 production (19 and 38 ppm). These results extend the earlier observations of others that macrophage function of laboratory rodents may be impaired by exposure to high concentrations of chlorinated drinking water. Furthermore, the function of other major populations of immunocytes and types of immune responses may also be altered following subchronic exposure to high concentrations of chlorinated drinking water. These types of effects on the immune system are a previously unrecognized potential side-effect of the ubiquitous practice of disinfection of water with chlorine compounds. Alteration of immune function of chlorine-based disinfectant-exposed rats in this study was only evident at relatively high doses, and only selected immune responses were altered. It appears, therefore, that these chlorine-based disinfectants are not particularly strong immunodepressants. However, further studies in different species may be warranted in order to better extrapolate to implications to human health following chronic low-level exposure.