"EPA rejects Denka's request to weaken assessment of chloroprene," 17 Mar. 2022

The Environmental Protection Agency released a letter to Denka Performance Elastomer ... refusing the chemical company’s request to change its assessment of a chemical called chloroprene. Denka, which owns and operates a chloroprene-emitting plant in Louisiana’s St. John the Baptist Parish, had asked the EPA to revise its 2010 assessment of the chemical, arguing that the model used to estimate human cancer risk based on experiments in which mice were exposed to chloroprene wasn’t “sufficiently rigorous.”

... [T]he EPA wrote that it would not be changing its assessment, which found that chloroprene was “likely to be carcinogenic to humans” and set a safety threshold for inhalation based on the chemical’s effects on the nervous, immune, and respiratory systems.

... Denka did not respond to questions for this article.

... Denka has said that, since acquiring the plant in 2015, it has reduced its chloroprene emissions by 85 percent under a voluntary agreement with Louisiana’s Department of Environmental Quality.

... But Denka has not lowered its emissions all the way down to the level the EPA deemed safe. Instead, Denka hired scientists who painted a rosier picture of chloroprene, which is emitted during the production of the synthetic rubber neoprene.

... [T]he most recent data collected by air monitors installed near the Denka plant show that, in January 2022, levels of chloroprene were higher than at any other point over the last two years. ... the level of the chemical reached 30.1 micrograms per cubic meter on January 17, more than 150 times the EPA’s threshold of 0.2 micrograms per cubic meter.