US Agency for Toxic Substances and Disease Registry Establishes Minimum Risk Levels for 1 1 1-Trichloroethane

The U.S. Agency for Toxic Substances and Disease Registry (ATSDR) has established minimum risk levels (MRLs) for 1,1,1-trichloroethane. Although the use of these substances has decreased significantly in recent years, there is still some potential for human exposure. According to the ATSDR toxicological profile released on March 29, some production of 1,1,1-trichloroethane persists.

U.S. facilities have reported quantities of this substance to databases of the Environmental Protection Agency (EPA) such as the Toxics Release Inventory and Chemical Data Reporting. These facilities primarily handle or dispose of hazardous waste, including substantial amounts of 1,1,1-trichloroethane.

Introduction:

1,1,1-trichloroethane, a synthetic compound, does not occur naturally but is released into the environment as a result of human activities. Heating it or using it in welding can produce the toxic gas phosgene. It's commonly found in soil and water, especially at hazardous waste sites, with its vapor form being prevalent due to its high volatility. Historically, it has been widely used in both industrial and domestic settings as a solvent for dissolving substances such as glues and paints, as well as for degreasing manufactured parts and in various household products such as spot cleaners, glues, and aerosol sprays.

History:

After January 1, 2002, the U.S. Environmental Protection Agency (EPA) banned domestic use of 1,1,1-trichloroethane due to its impact on the ozone layer. Limited production for essential uses continued until 2005, with export production permitted until 2012. The phase-out of U.S. production was mandated by Section 604 of the Clean Air Act and the Montreal Protocol. Although not completely halted, production of 1,1,1-trichloroethane was scheduled to cease by 2012 under the Montreal Protocol agreements, contributing to a decline in ambient levels despite ongoing production.

Side Effects of Exposure:

Health effects observed in controlled human exposure studies include impaired cognitive skills, manual dexterity, balance and coordination. Animals show signs of central nervous system depression, such as impaired performance, ataxia, and unconsciousness, similar to humans. Neurochemical, behavioral, and physiological changes have also been observed. Case reports suggest that high concentrations of 1,1,1-trichloroethane may cause hepatic effects in humans, including changes in liver enzymes and progressive liver disease. Consistent findings in animal studies indicate hepatic effects after inhalation exposure, including increased liver weight, fatty changes, and hepatocyte swelling.

ATSDR Established Minimal Risk Levels (MRLs) for 1,1,1-Trichloroethane:

The purpose of MRLs is to serve as screening thresholds used by ATSDR health assessors and other responders. Their aim is to identify contaminants and potential health effects that may be of concern at hazardous waste sites.