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 The findings have not been peer reviewed and were not evaluated in accordance with the levels of evidence criteria established by NTP in March 2009.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/ozination 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.
The National Toxicology Program (NTP) requested that a dose range-finding study be performed in order to establish the potential effects of dichloroacetic acid (DCA) 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 DCA based on the concentration of the test article in the drinking water. Five DCA concentrations of 125, 250, 500, 1000 and 2000 mg/L for 28 days were utilized. The national average for DCA in finished drinking water is 12.4 µg/l. DCA solutions were prepared fresh every two weeks in tap water and stored refrigerated. The in-life phase of these studies was carried out between 10 April 1998 and 26 May 1998.
The baseline toxicology studies are summarized in Table ES-1. There were few notable changes among the standard toxicological parameters that were assessed with the exception of a dose-related increase in liver weight and decreases in reticulocytes counts.
The immunological studies are summarized in Table ES-2. In contrast to the toxicological effects observed, DCA, at the doses administered, had virtually no effect on the various immunological endpoints evaluated.
In summary, based on the results of this range-finding study, further investigation of the effect of DCA on the immune system appears unwarranted. As a disinfection by-product, human exposure to DCA can occur from the drinking water; however, the immune system does not appear to be a major target organ for DCA.