Dense Nonaqueous Phase Liquids (DNAPLs)

Halogenated Alkanes

1,1,1-Trichloroethane

Human Health Toxicity

In urban areas, the general population is exposed to 1,1,1-trichloroethane (1,1,1-TCA) via inhalation of ambient air. Concentrations of 1,1,1-TCA in indoor air are thought to be higher than those outdoors, due to outgassing of the compound from building materials. Ingestion of contaminated drinking water also can be a route of exposure for the population. Occupational exposure to the chemical during its manufacture and use is expected to be via inhalation and dermal contact.

1,1,1-TCA is rapidly absorbed from the lungs, skin, and intestinal tract of both humans and laboratory animals. Once absorbed, the chemical is distributed to all tissues, particularly fatty tissues, via the bloodstream. Most of this chemical is excreted unchanged in exhaled air irrespective of the route of administration, while little (<10 percent) is metabolized. The mechanisms by which it exerts toxicity are not well understood. It is thought that metabolites of 1,1,1-TCA might be responsible for the mild liver toxicity reported by some laboratory rodent studies but that the parent compound exerts the central nervous system (CNS) effects and associated respiratory depression seen in acute human exposure.

Acute human exposure to high concentrations of 1,1,1-TCA results in depression of the CNS, a drop in blood pressure, irregular heartbeat, and gastric distress. Death from 1,1,1-TCA poisoning arises from respiratory depression and cardiac arrhythmias resulting from CNS depression. 1,1,1-TCA produces anesthesia in humans and was once evaluated in human subjects as an inhalational anesthetic (ATSDR 2006).

Results from some long-term, chronic, and sub-chronic laboratory rodent studies suggest that 1,1,1-TCA is mildly toxic to the liver and that the kidney is not likely to be a target organ for toxicity (IRIS).

EPA's Integrated Risk Information System (IRIS) program's weight-of-evidence classification of 1,1,1-TCA states that the database for the compound provides inadequate information to assess carcinogenic potential.

An epidemiological study did not identify a relationship between adverse pregnancy outcomes (malformations, abortions) and exposure of male working spouses to 1,1,1-TCA. Neither did human epidemiological studies suggest a relationship between maternal exposure and adverse pregnancy outcomes (ATSDR 2006). A multigenerational study of the effects of 1,1,1-TCA on reproductive function of male and female mice did not report adverse effects (IRIS); however, evidence from other laboratory rodent investigations indicates that developmental milestones were delayed in the offspring of female mice exposed to high concentrations of 1,1,1-TCA late in gestation (ATSDR 2006).

In vitro genotoxicity studies using microorganisms, such as Salmonella and yeast, show 1,1,1-TCA to be weakly mutagenic. In addition, 1,1,1-TCA is positive in mammalian cell transformation assays that can be used as a preliminary screen for the carcinogenic potential of a chemical; however, 1,1,1-TCA does not show positive activity in a large number of other genotoxicity tests (ATSDR 2006).

References

1,1,1-Trichloroethane (CASRN 71-55-6)
U.S. EPA, Integrated Risk Information System (IRIS)

Toxicological Profile for 1,1,1-Trichloroethane
Agency for Toxic Substances and Disease Registry (ATSDR), 2023

For Further Information

1,1,1-Trichloroethane
IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. International Agency for Research on Cancer (IARC), Vol. 71, pt. 38, 23 pp, 1999

Ecological Toxicity

The Pesticide Action Network (PAN) Pesticides Database provides results of 1,1,1-TCA acute aquatic toxicity studies, as performed on a variety of organisms. The average acute toxicity of 1,1,1-TCA is summarized for each organism group. The compound is listed as "not acutely toxic" to the crustacean, the fairy shrimp, and to three species of zooplankton. Some groups of organisms are more sensitive to 1,1,1-TCA, and it is designated "slightly toxic" toward zooplankton, opossum shrimp, and five fish species. 1,1,1-TCA is not acutely toxic to fish such as the carp and medaka (Kegley et al. 2010).

Very little information is available regarding the toxicity of 1,1,1-TCA to terrestrial wildlife receptors. However, an ecological screening level (ESL) calculated to be protective of burrowing terrestrial animals is provided in Roy et al (2009).

References

1,1,1-Trichloroethane: Identification, Toxicity, Use, Water Pollution Potential, Ecological Toxicity and Regulatory Information
Kegley, S.E., B.R. Hill, S. Orme, and A.H. Choi.
PAN Pesticide Database. Pesticide Action Network, San Francisco, CA, 2009

Evaluating Vapor Risk Intrusion in Ecological Risk Assessment
Roy M., S. Smith, and B. Elkland.
2009 DoD Environmental Monitoring & Data Quality Workshop, San Antonio, Texas, March 30 - April 3, 2009

For Further Information

1,1,1-Trichloroethane
Irwin, R. et al.
Environmental Contaminants Encyclopedia, National Park Service, 1997