Air is still contaminated 40 years after the Michigan Chemical plant disaster in St. Louis, Michigan.

The Michigan Chemical (also known as Velsicol Chemical) plant located in St. Louis, Michigan operated from 1936-1978. During this time, the plant manufactured polybrominated biphenyls (PBBs), hexabromobenzene (HBB), 1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane (DDT), and tris(2,3-dibromopropyl) phosphate (TDBPP), among other products. Due to widespread PBB contamination of Michigan, the plant eventually became a Superfund site, and despite years of cleanup activities, many of the compounds can still be found in the local ecosystem. To investigate the current atmospheric levels and to determine their spatial distributions, we collected tree bark samples from around Michigan and measured the concentrations of these pollutants. For comparison, other organic pollutants, such as polybrominated diphenyl ethers (PBDEs) and organophosphate esters (OPEs), which were not manufactured at the Michigan Chemical plant, were also measured in the same tree bark samples. Our results show levels of PBBs, DDT, and HBB in tree bark collected within 10 km of the Velsicol Superfund site (43, 477, and 108 ng/g lipid wgt., respectively) are 1-2 orders of magnitude higher than at sites located more than 10 km from the site (0.36, 28, and 0.36 ng/g lipid wgt., respectively). Levels of PBDEs and OPEs did not depend on distance from St. Louis. This is the first study on the atmospheric distribution of these chemicals around the Superfund site.