Per- and poly-fluorinated compounds (PFCs) are a large group of anthropogenic chemicals that holds unique surfactant properties. PFCs have been used in a wide range of domestic, commercial and industrial products, and have been released to the environment from various sources. The compounds are ubiquitous in the environment on a global scale, and have for instance been detected in arctic regions and in human serum samples from general populations. Due to PFCs chemical properties the compounds are toxic, persistent in the environment, bioaccumulating in organisms, biomagnifying in the food chain, and can be carcinogenic. Based on the adverse effects of PFCs in the environment perfluorooctosulfonic acid (PFOS), the compound that was considered of most concern, was recently prohibited in Norway (2007) and Canada (2008). PFOS was added to Annex B of the Stockholm convention on persistent organic pollutants in 2009.
Aqueous film forming foam (AFFF), a type of fire fighting agent used for extinguishing hydrocarbon fueled fires, contains PFCs. AFFF has been released to soil at airport fire fighting training stations, often through many years of fire fighting training activity. This Master thesis was initiated to obtain knowledge on the leaching behavior of PFCs from soil polluted by AFFF. Leaching of PFCs from soil is controlled by the individual compounds physicochemical properties, and the compounds chemical interaction. However, the soil characteristics also have a great influence on the leaching behavior of the compounds. The objectives were to use laboratory experiments for determining equilibrium partitioning coefficients (Kd) of PFCs between different soil types and porewater, study the influence of various soil charachteristics for sorption of PFCs, and describe the leaching of PFCs from different soil types.
Laboratory experiments were performed with soil samples from airport fire fighting training stations. Three Avinor airports were chosen where PFCs had been detected in the soil and groundwater at both older and active fire fighting training stations. Each airport has a distinct soil type which affects the transport of PFCs in the ground. In total seven different soil samples polluted by fire fighting activity were collected at these airports. Batch experiments in triplicate where performed for the seven soil samples, using a solid to liquid ratio of 10 for 10 days to reach equilibrium. PFC compounds with short carbon chain length (< 8C) was found to have a higher relative contribution to the ΣPFCs in the aqueous phase than in the soil. Compounds of longer carbon chain (≥ 8C) was found to have a higher relative contribution to the ΣPFCs in soil than in the aqueous phase. Kd for perfluorocarboxylic acids (PFCAs) were found to increase with increasing carbon chain length. Kd for perfluorosulfonic acids (PFSAs) was found to be higher than for PFCAs of similar carbon chain length. Leaching of three PFCA compounds with short carbon chain length (< C8) was dependent on the total concentration in soil. Leaching of four PFC compounds with long carbon chain length (≥ C8) was decreasing with increasing calcium concentration in the soil.
Leaching behavior of PFCs from soil was also studied using column experiments with the three soil types from the selected airports. Column experiments in parallel were performed using undisturbed soil columns from two sites, and for one site soil columns were repacked. Fresh water was infiltrated in the soil columns operated under saturated conditions, using a solid to liquid ratio of 10. The effluent water was sampled regularly during the 35 days experimental period to determine the leaching of PFCs from the soils. The relative contribution of shorter carbon chain compounds (< C8) decreased in leachate from the columns over time. Compounds with longer carbon chain length (≥ C8) had an increasing relative contribution in leachate over time. When comparing with the batch experiment, compounds with longer carbon chain length (≥ C8) had leached out more of the total amount from soil in the columns. The PFSA compounds were also in the column experiments higher retained in soil than the acidic compounds of similar carbon chain length.