U.S. EPA Contaminated Site Cleanup Information (CLU-IN)

U.S. Environmental Protection Agency
U.S. EPA Technology Innovation and Field Services Division

Dense Nonaqueous Phase Liquids (DNAPLs)

Chemistry and Behavior

Halogenated Alkanes



1,1,1-Trichloroethane1,1,1-Trichloroethane (1,1,1-TCA, CAS # 71-55-6) has a vapor pressure of 124 mmHg at 20oC (ATSDR 2006) and is a combustible liquid that burns with difficulty (NIOSH 2005). The log Koc of 1,1,1-TCA is 2.03, the log Kow is 2.49, and the Henry's constant is 6.3 e-3 atm at 20oC (ATSDR 2006). The solubility of 1,1,1-TCA is about 1,500 mg/L at 20oC (ATSDR 2006), and its specific gravity is about 1.34. The Agency for Toxic Substances and Disease Registry's toxicological profile for 1,1,1-TCA contains a useful summary tableAdobe PDF Logo of the compound's physical properties. The relatively low calculated Koc value for 1,1,1-TCA in soil indicates that 1,1,1-TCA is likely to move quickly through soil and sediment (ATSDR 2006).

Based on a Henry's law constant of 6.3x10-3 atm-m3/mol at 20oC, 1,1,1-TCA is expected to volatilize rapidly from water surfaces (ATSDR 2006). Modeling information for this compound in the Hazardous Substances Data Bank (HSDB) suggests that the half life of 1,1,1-TCA in a model river is about one hour, and about four and a half days in a model lake.

Because of the low Kow of 1,1,1-TCA, bioaccumulation is not expected to occur to any significant extent (ATSDR 2006). Microbial degradation of 1,1,1-TCA can occur under aerobic or anaerobic conditions, but it is slow (ATSDR 2006). Chang et al. (2002) demonstrated that 1,1,1-TCA can be degraded anaerobically to dichloroethane and chloroethane. The anaerobic process can stall at chloroethane, which generally degrades aerobically (ATSDR 2006).

1,1,1-TCA can undergo abiotic degradation in soil or water very slowly by elimination of hydrochloric acid (HCl) to form 1,1-dichloroethene, or it can undergo hydrolysis to form acetic acid. Direct photochemical degradation is not expected to be an important fate process (ATSDR 2006).

When released to the atmosphere, hydroxyl radicals are expected to degrade 1,1,1-TCA with a half life of about 6 years. Direct photolysis is not expected to occur (ATSDR 2006). Due to its long atmospheric lifetime, the compound will gradually diffuse into the stratosphere above the ozone layer, where it will slowly degrade due to direct photolysis from UV-C radiation and contribute to the catalytic removal of stratospheric ozone (HSDB).


Hazardous Substances Data Bank (HSDB)
TOXNET, National Library of Medicine Web site.

Degradation of 1,1,1-Trichloroethane in Groundwater by Indigenous Microorganisms under Anaerobic Conditions
Chang, P.R., E. Edwards, S. Dworatzek, D. Major, and P. Zeeb.
The 18th Annual International Conference on Contaminated Soils, Sediments and Water, 21-24 October 2002, University of Massachusetts at Amherst. CD-ROM, 2002
View abstract Adobe PDF Logo

Methyl Chloroform
NIOSH Pocket Guide to Chemical Hazards.
National Institute of Occupational Safety and Health, NIOSH Publication Number 2005-149, 2005

Toxicological Profile for 1,1,1-Trichloroethane
Agency for Toxic Substances and Disease Registry (ATSDR), 371 pp, 2006

For Further Information

DNAPL Site EvaluationAdobe PDF Logo
Cohen, R. and J. Mercer.
EPA 600-R-93-022, 369 pp, 1993

This document has a broad discussion of DNAPL site evaluation and contains a comprehensive table of physical properties of selected DNAPL chemicals, including 1,1,1-TCA, in its Appendix A.