Preliminary Data on the Fate of Bromate Ion in Simulated Gastric Juices

Ozone is a drinking water disinfectant that quickly and efficiently kills many types of pathogens. However, the ozonation of bromide ion containing waters can form the disinfection byproduct, bromate ion. Bromate ion is a possible human carcinogen that is regulated by the US EPA at a Maximum Contaminant Level (MCL) of 10 micrograms per liter (μg/L). The lifetime risk at the MCL was calculated from studies where laboratory animals received large doses of bromate ion that would produce effects in their lifetimes. The data from these large doses was fitted to a low-dose linear extrapolation (also called a linearized dose-response) model. The model assumes there is a finite, albeit small, risk at any dose above zero of a genotoxic carcinogen. The validity of the linearized dose-response model projection at low doses is being questioned (i.e., the actual shape and slope of the dose/response as the dose approaches zero). The test system is bromate ion in synthetic and real gastric juices. The results reported here show that the bromate ion half-life, in the presence of typical H⁺, Cl^?, and H₂S concentrations found in the stomach, is 1.5–2 minutes. Thus, as much as 99% of the ingested bromate ion should be decomposed, while it is retained in the stomach. The results of these experiments will be used in the development of a more scientifically rigorous methodology for determining low level effects of bromate ion.