CHAPTER 2-154: TRICHLOROETHANE, TRICHLOROETHYLENE, AND TETRACHLOROETHYLENE

INTRODUCTION

Trichloroethane and trichloroethylene are organic solvents that have historically been used as ingredients in many products, including typewriter correction fluid ("Wite-Out"), color film cleaners, insecticides, spot removers, fabric-cleaning solutions, adhesives, and paint removers. They have also been used extensively in industry as degreasers. Trichloroethane is available in two isomeric forms, 1,1,2-trichloroethane and 1,1,1-trichloroethane, with the latter (also known as methyl chloroform) being the more common. Tetrachloroethylene (perchloroethylene) is another related solvent that is widely used in the dry cleaning industry, although some regulatory agencies, such as the California Air Resources Board, have mandated its gradual phase-out for this application. Similarly, recognition of the stratospheric ozone depletion potential of 1,1,1-trichloroethane has resulted in the substitution of other chemicals for most applications.

MECHANISM OF TOXICITY

1. These solvents act as respiratory and CNS depressants and skin and mucous membrane irritants. As a result of their high lipid solubility and CNS penetration, they have rapid anesthetic action, and both trichloroethylene and trichloroethane were used for this purpose medically until the advent of safer agents. Peak blood levels occur within minutes of inhalation exposure or 1–2 hours after ingestion. Their proposed mechanism of action includes neuronal calcium channel blockade and gamma-aminobutyric acid (GABA) stimulation.

2. Trichloroethane, trichloroethylene, their metabolite trichloroethanol, and tetrachloroethylene may sensitize the myocardium to the arrhythmogenic effects of catecholamines.

3. Trichloroethylene or a metabolite may act to inhibit acetaldehyde dehydrogenase, blocking the metabolism of ethanol and causing "degreaser's flush."

4. Carcinogenicity.

   1. In 2014, the International Agency for Research on Cancer (IARC) upgraded its classification of trichloroethylene from probable human carcinogen (Group 2A) to carcinogenic in humans (Group 1), based on sufficient evidence for kidney cancer and suggestive evidence for non-Hodgkin lymphoma and liver cancer. IARC continues to classify tetrachloroethylene as having limited evidence as a human bladder carcinogen, but showing sufficient evidence in animals (Group 2A). The US National Toxicology Program (NTP) classifies both trichloroethylene and tetrachloroethylene as "Reasonably Anticipated to be Human Carcinogens."

   2. Both 1,1,1- and 1,1,2-trichloroethane are listed by IARC as "not classifiable as to carcinogenicity in humans" (Group 3), and neither has been systematically evaluated by the NTP.

TOXIC DOSE

1. Trichloroethane. The acute lethal oral dose to humans is reportedly between 0.5 and 5 mL/kg. The recommended workplace limits (ACGIH TLV-TWA) in air for the 1,1,1-trichloroethane and 1,1,2-trichloroethane isomers are 350 and 10 ppm, respectively, and the air levels considered immediately dangerous to life or health (IDLH) are 700 and 100 ppm, respectively. Anesthetic levels are in the range of 10,000–26,000 ppm. The odor is detectable by a majority of people at 500 ppm, but olfactory fatigue commonly occurs.

2. Trichloroethylene. The acute lethal oral dose is reported to be approximately 3–5 mL/kg. The recommended workplace limit (ACGIH TLV-TWA) is 10 ppm (269 mg/m³), and the air level considered immediately dangerous to life or health (IDLH) is 1,000 ppm.

3. Tetrachloroethylene. The recommended workplace limit (ACGIH TLV-TWA) ...