Introduction

TCE does not occur naturally; therefore, its presence indicates manufacture, use, or storage. Production of TCE has increased from just over 260,000 lbs in 1981 to 320 million lbs in 1991. The U.S. International Trade Commission (USITC) has not published more recent production statistics because there are only two U.S. manufacturers (Agency for Toxic Substances and Disease Registry 1997; HSDB April 2006).

Vapor degreasing of fabricated metal parts and some textiles accounts for 80% of its use. 5% is used as an intermediate in the production of organic chemicals and pharmaceuticals. Miscellaneous uses (5%) include solvents for dry cleaning, extraction and as a refrigerant/heat exchange liquid. An estimated 10% is exported.

Occupational Exposures

Occupational exposures may occur in chemical industries that manufacture:

• other polychlorinated aliphatic hydrocarbons, flame retardant chemicals, and insecticides where TCE is a chemical intermediate
• pentachloroethane
• polyvinyl chloride

Other potential exposures occur in the manufacturing processes of:

• disinfectants
• dyes
• perfumes
• pharmaceuticals
• soaps

The following occupations also have increased likelihood of exposure:

• dry cleaners
• mechanics
• oil processors
• printers
• resin workers
• rubber cementers
• shoemakers
• textile and fabric cleaners
• varnish workers
• workers reducing nicotine in tobacco

Although some dry cleaners used TCE in the past, most dry cleaners now use tetrachloroethylene (perchloroethylene) or 1,1,1-trichloroethane.

In the workplace, TCE is seldom present as a pure substance. Industrial grade TCE contains small amounts of stabilizers in the form of antioxidants or acid receptors; total chemical impurities usually do not exceed 0.1% by weight. Decomposition of TCE into dichloroacetylene (a neurotoxic compound) and phosgene (a serious pulmonary irritant) occurs in the presence of alkali at temperatures above 60C for the unstabilized compound and above 130C for the stabilized compound.

Environmental Exposures

Because of its widespread use, TCE has become a common environmental contaminant. Contamination results from:

• discharge to surface waters and groundwater by industry commerce, and individual consumers
• evaporative losses during use
• incidental addition of TCE during food production
• leaching from hazardous waste landfills leaching into groundwater

In the atmosphere, TCE is destroyed by photooxidation, with a half-life of 3-8 days during the summer months and approximately 2 weeks in cold climates during the winter. This relatively short half-life significantly limits the transport of TCE in air; however, the continual volatilization of TCE from emission sources or contaminated surface waters ensures its persistence in air.

The average TCE level detected in samples collected from ambient air in the Norwegian Arctic between 1982 and 1983 was 0.007 ppb. This compares to mean TCE concentrations of 0.03 ppb in rural or remote areas, 0.46 ppb in urban and suburban areas, and up to 1.2 ppb in areas near emission sources of TCE. Indoor air concentrations have ranged from 0.14 ppb in a school to 5 ppb in an office building (Agency for Toxic Substances and Disease Registry 1997).

TCE is now a common contaminant at Superfund sites and many Department of Defense facilities. TCE has been identified in at least 861 of the 1,428 sites proposed for inclusion on the U.S. EPA National Priorities List (Agency for Toxic Substances and Disease Registry 1997). According to U.S. EPA Toxic Release Inventory (Wu and Schaum 2000; U.S. EPA 2003). TCE releases into the environment have ranged from 55.6 million pounds in 1987 down to 7.2 million pounds in 2003.

TCE in drinking water is a result of its rapid leaching from landfills and its discharge from industrial wastewaters. TCE volatilizes quickly from water at a rate that depends on temperature, water movement, and aeration. The biodegradation of TCE under anaerobic conditions is slow, making TCE relatively persistent in subsurface waters. An EPA national groundwater survey (U.S Environmental Protection Agency 1985) detected TCE in approximately 10% of the wells tested. It is the most frequently detected organic solvent in groundwater supplies, and is estimated to be in up to 34% of the nation's drinking water supplies (Agency for Toxic Substances and Disease Registry 1997).

Because of TCE's volatility, household activities such as bathing, laundering, and cooking with contaminated water may produce TCE air concentrations above ambient levels.

Both natural and processed foods may contain TCE because of direct uptake through the environment, contamination of water used in food processing, and contamination by solvents used in cleaning food processing equipment. Most processed foods examined contain levels of a few parts per billion. Studies indicate that TCE has a low tendency to bioaccumulate in the food chain (Agency for Toxic Substances and Disease Registry 1997).

Exposures from Consumer Products

TCE is found as an ingredient in a number of consumer products such as

• adhesives
• cleaning fluids for rugs
• paint removers/strippers
• spot removers, spot removers
• typewriter correction fluids

Progress Check