Fate of volatile fluorinated compounds in the subsurface

Since their discovery around 1930, the synthetic compounds of the class of chlorofluorocarbons (CFCs) have been produced and used worldwide at very large scale. Their physico-chemical properties (non-flammability, chemical inertia, miscibility with water and oil, compatibility with many metals and plastics, solvent capacity) have made them ideal candidates for several applications, such as refrigerant fluids, aerosol propellants, foam blowing agents, or as solvents or intermediates of chemical synthesis. In the 70', it was demonstrated that following their release in the atmosphere, they are implicated in the process leading to the commonly called stratospheric ozone hole. The governments of several industrialised country have thus signed a protocol with the objective to stop the production and use of CFCs. CFCs have been increasingly replaced by compounds with similar structure, the hydrochlorofluorocarbons (HCFCs), but whose reactivity in the lower layers of the atmosphere is quite different from that of CFCs. Due to their chemical inertia, CFCs has been used as tracers for surface and groundwater datation. During such investigations, the biodegradability of these compounds and the existence of punctual pollution sources in soil and groundwater have been evidenced. It has been demonstrated that some of these compounds can be dechlorinated under anoxic conditions producing other compounds with sometimes higher toxicity and higher water solubility, and resulting in a risk linked to the consumption of natural groundwater. The goal of this thesis was to get indications about reductive transformations of CFCs and especially HCFCs in Swiss aquifers and landfills, on the potential of different microbial communities to reductively dechlorinate certain compounds, and under which redox conditions the transformations occur in aquifer systems. Data concerning the production, use, emission, regulation, as well as the biodegradability and toxicity of these compounds are presented in chapter 1 and in the appendix. The analytical methods developed and used during this work are presented in chapter 2. Particularly, a versatile analytical system allowing the measure of trace but also higher concentrations in different media, solid or aqueous, has been set up and used during this work. CFCs and HCFCs were analyzed at 3 sites in Switzerland. Samples were collected from a natural groundwater in which a chloroethene plume had been observed, from an old landfill closed in 1980, and from a more recent bioactive landfill constructed in horizontal layers. In addition, the behaviour of different CFCs and HCFCs was studied in microcosms inoculated with sludge originating from several sewage treatment plants in the canton of Vaud, and with a sediment originating from a contaminated aquifer in Holland. The studied CFCs and HCFCs were furthermore injected at the inlet of a 1.2 m height column filled with the aquifer sediment from Holland. In this quasi natural aquifer, the o