August 31, 2022

IARC Releases Monograph on 1,1,1-Trichloroethane, Other Industrial Chemicals

The International Agency for Research on Cancer (IARC) has classified the industrial chemical 1,1,1-trichloroethane as a Group 2A carcinogen, the agency’s designation for substances that are probably carcinogenic to humans. IARC’s evaluation of research on 1,1,1-trichloroethane concluded that positive associations exist between exposure and the blood cancer multiple myeloma. The findings appear in a new edition of the agency’s monographs series. A previous IARC monograph published in 1998 had designated 1,1,1-trichloroethane as Group 3, or not classifiable as to its carcinogenicity to humans.

Although EPA categorizes 1,1,1-trichloroethane as a high-production volume chemical, which means that at least one million pounds of the substance are manufactured or imported into the United States per year, IARC notes that production volumes have dropped dramatically since adoption of the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer and the 1990 Clean Air Act. 1,1,1-Trichloroethane was widely used as a degreasing solvent in the 1970s and 1980s, and it was an ingredient in many household products such as adhesives, lubricants, glues, and fabric finishes. By the early 2000s, the chemical was used almost exclusively as a precursor in the manufacture of hydrofluorocarbons.

The potential for occupational exposures to 1,1,1-trichloroethane occurred in its manufacture as well as in industries that used it for cleaning furniture, metal products, and electronic equipment, and in industries where the chemical was used in the manufacturing of paints, inks, and aerosol and adhesive products. In 2001, ACGIH set a Threshold Limit Value for 1,1,1-trichloroethane of 350 ppm as an 8-hour time-weighted average and a 15-minute short-term limit of 450 ppm.

The new monograph also assesses 1,2-diphenylhydrazine, previously used globally as a precursor in the production of dyes; diphenylamine, a component of lubricants, greases, metalworking fluids, and other products; n-methylolacrylamide, which is used in the manufacture of polymers with acrylic and vinylic monomers; and isophorone, a widely used solvent and chemical intermediate. IARC classifies all four of these substances as Group 2B, possibly carcinogenic to humans.

The new volume of the IARC monographs series is freely available on the agency’s website.