Where Is Carbon Tetrachloride Found?
CCl4 does not occur naturally, but has been released into the environment by human activities. Because of past and present releases, CCl4 is still found in ambient air, water, and soil, but at very low background levels. The U.S. public can be exposed to CCl4 from ambient air. CCl4 is one of the priority pollutants regulated by the U.S. Environmental Protection Agency (EPA) [EPA 2014]. Workers involved in the manufacture or use of CCl4 are more likely to have significant CCl4 exposure than are members of the general public.
People can be exposed to small amounts of CCl4 through ambient air. The 2001-2002 National Health and Nutrition Examination Survey (NHANES) reported that for the U.S. population aged 20-59 years, the 95th percentile of blood CCl4 concentrations was 0.02 nanograms per milliliter (ng/mL). In the 2003-2008 survey, the 95th percentile of blood CCl4 concentration had fallen to less than 0.005 ng/mL [CDC 2017].
Using an analysis of 4,913 ambient air samples reported in the National Ambient Volatile Organic Compounds Database – including remote, rural, suburban, urban, and source dominated sites in the United States – the average carbon tetrachloride concentration was 0.168 parts per billion (ppb) (1.1 μg/m3) [Shah and Heyerdahl 1988]. More recent studies demonstrate a decrease in levels of CCl4 (0.072-0.09 ppb) in the ambient air, which could be a reflection of the current drop in production. Nevertheless, the resistance to atmospheric degradation allows for levels to remain somewhat constant [Mohamed et al. 2002].
Concentrations in indoor air are usually higher than in outdoor air. A review of 2,120 indoor air samples in the late 1980s in the United States showed that the average CCl4 concentration was 0.4 ppb (2.6 μg/m3) [Shah and Heyerdahl 1988]. Contemporary data suggest that this remains true today. A sampling of volatile organic compounds in day-care facilities in Washington, DC, found carbon tetrachloride air concentrations ranging from undetectable to 0.24 ppb (1.6 μg/m3) [Quirós-Alcalá 2016]. Household cleaning products containing bleach can produce volatile organic compounds, including chloroform and carbon tetrachloride [Odabasi 2008]. Use of these common agents might, in part, explain elevated indoor CCl4 concentrations.
Although overall ambient air concentrations are slowly declining, some regions might still have above-average concentrations. These include some National Priorities List (also known as Superfund) sites [EPA 2017] and the few industrial locations where CCl4 is still manufactured or used. A searchable database of current National Priorities List sites is available at: https://cumulis.epa.gov/supercpad/cursites/srchsites.cfm.
Water and Soil Contamination
CCl4 can contaminate water, air, and soil if it is not properly discarded. According to the 2015 Toxic Release Inventory,
- More than 5.9 million pounds of CCl4 were recycled,
- Approximately 12,600 pounds of CCl4 were transferred to landfills or waste management sites, and
- Approximately 140,000 pounds of CCl4 were discharged into air, water, and soil.
Persons living near hazardous waste sites where CCl4 is actively being released into the surrounding environment could be at higher risk for exposure to CCl4 in soil or water supplies.
Workers involved in the manufacture or use of carbon tetrachloride are more likely to have significantly higher exposure to CCl4 than are other persons. CCl4 is currently used to manufacture some of the following products:
- Brake cleaners,
- Electrical equipment and machinery cleaner’s
- Industrial-strength structural and plastic adhesives,
- Perchloroethylene (also known as PERC or tetrachloroethylene),
- Reference chemicals for laboratory applications, and
- Synthetic rubbers [EPA 2017].
- Sources of environmental contamination include industrial facilities and hazardous waste sites.
- Household cleaning products containing bleach can produce volatile organic compounds, including chloroform and carbon tetrachloride. Use of these common agents might, in part, explain elevated indoor CCl4 concentrations.
- Workers involved in the manufacture or use of CCl4 are more likely to have significant CCl4 exposure than are other persons.