New studies advance scientific knowledge of drinking water disinfection byproducts

Studies published in International Journal of Toxicology

In its September/October issue, the International Journal of Toxicology is pleased to publish the last in a series of four studies examining possible reproductive and developmental health effects from two byproducts of drinking water chlorination. These studies fill significant data gaps identified by a Federal Advisory Committee formed by the U.S. Environmental Protection Agency (EPA) on drinking water regulations.

Small amounts of disinfection byproducts, including bromodichloromethane (BDCM) and dibromoacetic acid (DBA), are formed in drinking water when chlorine disinfectants combine with naturally occurring organic matter. Several epidemiology studies have reported a possible association between these byproducts and adverse reproductive outcomes, including spontaneous abortion. Because the existing toxicology data was very limited, the Federal Advisory Committee recommended that BDCM, in particular, should be thoroughly studied for a potential causal relationship to reproductive and developmental toxicity.

To address these data gaps, researchers at Argus Research Laboratories examined laboratory animals exposed to BDCM and DBA through drinking water. Each study found no adverse effects at dose levels thousands of times higher than those to which humans are exposed. Based on the results of these studies, the researchers concluded that BDCM and DBA are unlikely to pose a reproductive or developmental health risk to humans. EPA will review this research as it develops new regulations on disinfection byproducts.

The studies were designed to comply with the EPA’s Federal Insecticide Fungicide and Rodenticide Act (FIFRA) Guidelines and with the EPA’s Guidelines for Good Laboratory Practices. Each study was independently monitored. In addition, an independent panel of experts reviewed the study designs and interpretation of data. The studies were sponsored by the Research Foundation for Health and Environmental Effectsâ, a tax-exempt foundation established by the Chlorine Chemistry Council.

Following are brief summaries of each study:

Biodisposition of DBA and BDCM in Rats and Rabbits

Christian, et al. 2001. Biodisposition of Dibromoacetic acid (DBA) and Bromodichloromethane (BDCM) Administered to Rats and Rabbits in Drinking Water During Range-Finding Reproduction and Developmental Toxicity Studies. International Journal of Toxicology, 20:239-253.

The study evaluated whether detectable concentrations of DBA or BDCM were absorbed from the drinking water provided to rats and rabbits and whether there were detectable levels of either DBA or BDCM present in the maternal blood, placentas, fetuses, pups, or maternal milk. No quantifiable concentrations of BDCM were found, suggesting that BDCM is rapidly degraded or metabolized in the body. DBA produced quantifiable concentrations in the maternal blood, placentas, fetuses, pups, and maternal milk. No reproductive and developmental effects were observed in these preliminary studies, suggesting that neither DBA nor BDCM are reproductive or developmental risks for humans.

Developmental Toxicity Studies of BDCM

Christian et al. 2001. Oral (Drinking Water) Developmental Toxicity Studies of Bromodichloromethane (BDCM) in Rats and Rabbits. International Journal of Toxicology, 20:225-237.

Two studies, one using rats and one using rabbits, evaluated pregnant animals exposed to BDCM concentrations of 0, 15(rats), 50 (rabbits), 150, 450, and 900 parts per million (ppm) in drinking water. By comparison, drinking water concentrations of BDCM rarely exceed 0.025 parts per million. Researchers observed no adverse developmental effects at concentrations up to 450 ppm in rats and 900 ppm in rabbits. Based on the results of these studies, the authors concluded, “BCDM should not be identified as a risk to [human] development.”

Reproductive Toxicity Study of BDCM

Christian et al. 2002. Oral (Drinking Water) Two-Generation Reproductive Toxicity Study of Bromodichloromethane (BDCM) in Rats. International Journal of Toxicology, 21:115-146.

The study evaluated rats exposed to BDCM concentrations of 0, 50, 150 and 450 ppm in drinking water. In this study, the researchers observed no adverse reproductive or developmental effects at any of these concentrations. Based on the results of this study, the authors concluded, “BCDM should not be identified as a risk to human reproductive performance or development.”

Reproductive Toxicity Study of DBA

Christian et al. 2002. Oral (Drinking Water) Two-Generation Reproductive Toxicity Study of Dibromoacetic Acid (DBA) in Rats. International Journal of Toxicology, 21:237-276.

The study evaluated rats exposed to DBA concentrations of 0, 50, 250 and 650 ppm in drinking water. Researchers observed no adverse effects at 50 ppm, an estimated 45,000 – 116,000 times the human adult exposure level. Based on the high multiples of human exposure required to produce effects, the study authors concluded, “DBA should not be identified as a human reproductive or developmental risk.”