Ozone can react with bromide ion to form bromate. Currently, the USEPA has a limit of 10 micro grams per liter for ozone in drinking water. This level has been extended to other water treatment applications, for example, ground water remediation. The USEPA is considering lowering the allowable limit for bromate to 5 micro grams per liter. The concern about bromate is that it might be a possible carcinigen.
While there are countermeasures for minimizing the formation of bromate where ozone is applied, in applications with high doses of ozone and high levels of bromide bromate formation can be a problem.
Recent studies sponsored by the International Ozone Association and the American Water Works Association Research Foundation have indicated that bromate might not be as serious a concern as previous thought. Dr. Joseph Cotruvo presented an update on this research at the recent IOA conference in Milwaukee.
It appears that when bromate enters the digestive track it is broken down by processes in the stomach and intestines such that it does not reach target organs of concern. The research suggests that the bromate levels may in fact be increased to as high as 20 micro grams per liter.
A final decision on the matter is not expected for another 6-8 years.