Risk Assessment of Trichloroethylene
ExposuresDue to a long history of uses and wide applications of TCE in in-dustries, the chemical has been detected in various environmental matrices. It has been identified in majority of the hazardous waste sites in the United States . Potential human exposure occurs via
ingestion of drinking water, inhalation of indoor and outdoor air, and consumption of food. Biomonitoring results from the Third National Health and Nutrition Examination Survey (NHANES III, 1988-1994) showed whole-blood TCE levels below the detection limit (0.01 µg/L) in 90% of the surveyed population. The most recent NHANES IV study (2001-2002 survey data) further reported no TCE detec-tion (detection limit of 0.012 µg/L) in the whole blood of the entire surveyed population . The decline in TCE exposure to the general population is probably due to a combination of an increase in awareness of proper chemical disposal and continual efforts in environ-mental remediation. 22.214.171.124 AirWith a vapor pressure of 69 mm Hg at 25°C, TCE exists in vapor state once released to the atmosphere. The World Health Organization (WHO)  estimated that 60% to 90% of the annual world production of TCE is released into the atmosphere by evaporation, primarily from degreasing operations. Stack emissions from municipal and hazardous waste incineration further contribute to the atmospheric load . Once entering the atmosphere, TCE is photo-oxidized and decomposed to formic acid with half-lives approximated in days to weeks [2, 3, 6]. These relatively short half-lives of degradation suggests that TCE is not a persistent air pollutant . In 2006, the United States Environmental Protection Agency (USEPA) reported ambient air TCE levels of 0.03 to 7.73 µg/m3 (an average of 0.23 µg/m3) from 258 monitors located in 37 states . Although exposure to TCE in the ambient air is negligible for the general population, data from monitoring surveys suggested that workers may be exposed to approximately 1 to 100 ppm TCE in the air . 126.96.36.199 WaterTCE, at micrograms per liter, has been reportedly detected in rainwater and seawater samples collected in the United States and United Kingdom [2, 6]. Discharges and accidental releases from the industries led to a wide distribution of TCE in water bodies . In addition to the industrial releases, leachate of TCE from contaminated soils and landfills, as well as river water infiltration to groundwater can contribute to the groundwater contamination .