Despite the widespread occurrence of per- and polyfluoroalkyl substances (PFAS) contamination in bedrock formations, the fate and transport of these contaminants in fractured bedrock remains unexplored.
Fractured bedrock formations are complex, dominated by flow-through fractures and exhibit much different characteristics than soils and sediments. It is currently unclear whether distribution coefficients, retardation factors and sorption mechanisms of PFAS to soils and sediments are applicable to fractured bedrock formations.
To address this knowledge gap, a series of laboratory experiments was conducted to study the sorption of a suite of PFAS to rock. Crushed and re-wetted Lockport Dolostone was used to evaluate sorption kinetics, mechanisms, and competition for a suite of 13 PFAS (C4-C12) with varying functional head groups (carboxylates, sulfonates and sulfonamide). For long chain PFAS (C8-C12 for carboxylated or C6-C12 for sulfonated) sorption increased with increasing chain length, suggesting hydrophobic-like interactions to be the predominant sorption mechanism. For short chain PFAS (C4-C7 for carboxylated or C4-C5 for sulfonated) sorption was not correlated to chain length, potentially due to competition between short and long chain compounds for available sites. This phenomenon has not been observed in previous sorption studies conducted using soils and sediments, suggesting that PFAS fate and transport in fractured bedrock formations is likely different than in soils and sediments. Additionally, sorption of long chain length compounds exhibited two different behaviours depending on chain length, suggesting that long chain length compounds should be subdivided into intermediate chain length compounds and long chain length compounds (C10-C12). Sorption of sulfonated PFAS was found to be greater than sorption of carboxylate or sulfonamide analogs with the same carbon chain length, suggesting that electrostatic forces also play a role in sorption to these rock samples. This is the first data for sorption of PFAS to rock and thus represent the first step towards evaluating PFAS fate and transport in fractured bedrock aquifers.