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.

La datation des eaux souterraines par analyse des CFC : un outil de gestion durable de la ressource en eau

“…La production de ces gaz a commencé au cours des années 50 dans un premier temps pour remplacer les gaz réfrigérants habituels plutôt dangereux et toxiques (ammoniaque, isobutane…). Ils ont eu depuis de nombreuses autres applications comme gaz propulseur des aérosols, solvants, matière première dans la synthèse de composés synthétiques, agent d'expansion de mousse… [HÖHENER et al, 2003]. Il n'existe non pas un mais des CFC suivant les combinaisons des atomes de chlore et de fluor dont ils sont composés.…”

Residence time, mineralization processes and groundwater origin within a carbonate coastal aquifer with a thick unsaturated zone

“…Lag times may be observed and are mostly dependant on gas solubility, diffusion coefficients and soil water content (Cook and Herczeg, 2000;Heaton and Vogel, 1981) and geology (Cook et al, 1995;Cook et al, 2006). In addition, contamination problems may occur in presence of individual sewage treatment plants and tips (Archbold et al, 2012;Hohener et al, 2003) or gardening activities (Busenberg and Plummer, 2000;Spurlock et al, 2000). Within the Bonifacio aquifer, the presence of a thick UZ (with variable thickness, see Table 1) as well as the presence of some individual sewage treatment plants and gardening activities may probably modify groundwater residence time in some places.…”

Using environmental tracers to assess the extent of river–groundwater interaction in a quarried area of the English Chalk

“…Decay of CFCs during infiltration has been observed for some rivers (Höhener et al, 2003), but Chalk stream hyporheic zones, where so far measured, do not achieve the low-oxygen status necessary for CFC reduction (Pretty et al, 2006;Allen et al, in press). Alternatively, it is possible that the relatively shallow depth of the river promotes rapid atmospheric equilibration and attenuation of any CFC signal, even if the discharging groundwater is at ~10 times the modern background.…”

“…Providing there is no subsurface addition, groundwater concentrations can then be directly related to the year of recharge. However, the CFCs in particular are prone to augmentation under certain circumstances (Höhener et al, 2003). In such an event they may still be useable as flowpath tracers.…”