Environmental Fate

Environmental modelling of PFOA and its salts cannot be conducted using widely accepted models, such as the Level III fugacity model, as they cannot be applied to ionic surfactants. The high water solubility of PFOA, coupled with the negligible volatility of ionized species, suggests that all PFOA species will partition primarily to the aquatic environment. Based upon experimental results, PFOA may have some ability to re-enter the gas phase from water (US EPA 2002). However, studies have shown that if this process occurs, then it occurs to a negligible extent around pH 8.5 (Oakes et al. 2004). Once in the aqueous phase, PFOA may partition to sediments, as is evident by its measurement in this medium (Giesy and Newsted 2001; Stock et al. 2007). However, a comparison of concentrations observed in the aqueous phase and in sediments suggests that sediments are unlikely to be a major sink for PFOA. This is supported by observations made by Oakes et al. (2004) and Masunaga and Odaka (2005). The adsorption and desorption properties of APFO were investigated in one activated sludge sample and four soil samples (Dekleva 2003). Dekleva (2003) found that the average adsorption of APFO ranged from 40.8% to 81.8%. Adsorption coefficient (K_d) values ranged from 0.41 to 36.8 mL/g. Organic carbon adsorption coefficient (K_oc) values ranged from 48.8 to 229 mL/g, and organic matter adsorption coefficient (K_om) values ranged from 28.4 to 133 mL/g. These values indicate that PFOA is more likely to sorb to organic carbon in soils than to other soil solids. Moodyand Field (1999) suggested that since PFOA could be measured in groundwater in areas where PFOA is no longer used, a fraction of the compound must be bound to soil and slowly released to water. However, it is recognized that the presence in groundwater may simply reflect the slow migration of PFOA rather than soil binding. It is unlikely that terrestrially deposited PFOA will undergo any long-range transport (Franklin 2002).