Worldwide Occurrence and Fate of Chlorofluorocarbons in Groundwater

Abstract

Chlorofluorocarbons (CFCs) are synthetic halogenated volatile organic compounds that have been manufactured since 1930 and can be detected analytically in water in pg L−1 concentrations. The use as tracers for age dating of pristine groundwater has been summarized by previous review articles, where occasional failure of the CFC age-dating technique caused by local CFC contamination in excess of the equilibrium with modern air was reported. This article summarizes the worldwide occurrence of CFCs in groundwater with a focus on contaminated aquifers. CFC data from 24 aquifers and two regions on four continents are compiled. In 10 aquifers, contamination in more than 20% of samples with either CFC-11, CFC-12, or CFC-113 is reported. Pathways of CFC input to groundwater such as local atmospheric pollution, river water infiltration, landfills, and industrial solvent spills are discussed. The aerobic and anaerobic biotransformation reactions and natural attenuation processes of CFCs in aquifers are also reviewed. Microbially catalyzed reductive dechlorination of CFCs occurs in anaerobic aquifers. Little is known about the presence of other CFCs and degradation products of CFCs, among which some are known to be toxic (HCFC-21) or carcinogenic (HCFC-31). Risk assessment for groundwater resources should include HCFC measurements to better identify transformation reactions.