Both monitoring and modeling data show benzene concentrations above the lower range of the health benchmark in the Twin Cities metropolitan area and in the state's smaller cities, including Duluth, Rochester, Mankato and St. Cloud. About two-thirds of benzene emissions can be attributed to mobile sources. In the metropolitan area, there has been a slight decrease in benzene concentrations since 1991, for which the reason is unclear. Given the magnitude of the measured concentrations, it would appear that benzene, a known human carcinogen, presents a potential health problem in both the Twin Cities metropolitan area and in smaller population centers. Minnesota's monitoring data do not show a decrease in concentrations since the ban.
Carbon tetrachloride is very persistent in the atmosphere and can take decades to degrade.
Carbon tetrachloride is a probable human carcinogen and also causes damage to the liver and kidneys. This location is in International Falls, adjacent to a U.S. paper mill and across the river from a Canadian paper mill, both of which are likely sources of the chloroform emissions. In addition to being classified as a probable carcinogen, chloroform may be involved in reproductive and developmental disorders. Target organs for chronic chloroform toxicity are the liver and the central nervous system. All rights reserved.