To summmarize: bromate can be ...

To summmarize: bromate can be present in purchased hypochlorite (not chlorine) and it can be produced during water treatment if bromide is present. Bromate is not produced in hypochlorite during storage like chlorate and perchlorate are. Ozone is very effective at producing bromate, but chlorination  is not, it only occurs in very low TOC water at warm temperatures and probably with copper catalysis. If TOC is present organobromine compounds like bromoform are produced. Bromate is regulated in in drinking water at 10 ppb, but that is not scientifically valid, because the body metabolizes bromate to bromide after ingestion. The animal studies at very high doses are not the appropriate basis for regulations and guidelines, because the animals were overdosed far beyond their ability to detoxify the bromate.