A 1981 study of more than 2,000 Mallinckrodt uranium division workers showed an increase in three different cancers, including a 24 percent above-normal rise in the rate of leukemia . In addition, a controversial a series of cancer cases has plagued one block of Nyflot Avenue, a residential street in North County, a dump route where radioactive waste was spilled. In 1993, the Missouri Department of Health (MDOH) ruled the cancers on Nyflot were probably not related to radioactive exposure. But some environmentalist doubt MDOH’s conclusion.