Effect of hydrochemical conditions on transport of HFPO-DA in saturated quartz sand and limestone porous media.

Hexafluoropropylene oxide dimer acid (HFPO-DA, tradename Gen-X) is used as a substitute to perfluorooctanoic acid (PFOA). Its widespread presence in the environment and potential health risks on humans. Nevertheless, the research on transport of HFPO-DA in saturated porous media remains limited. This study investigates the effects of hydrochemical conditions on the transport behavior of HFPO-DA and PFOA in quartz sand and limestone porous media, such as ionic type (Na⁺, Ca²⁺), ionic strength (1 mM, 10 mM, 50 mM) and initial solution pH (pH = 4, 7, 10). Findings indicate that both HFPO-DA and PFOA have high mobility in saturated media. The transport of HFPO-DA through quartz sand and limestone porous media is not notably influenced by different ionic types and strengths, with recoveries all over 98.94% and R_f all below 1.02. Similarly, PFOA showed high mobility under different ionic conditions, with recoveries exceeding 101.68% and Rf less than 1.02.The influence of initial pH on the transport of HFPO-DA showed that HFPO-DA is pH-sensitive in quartz sand, with retention enhanced and significant trailing of the BTC at pH = 4; however, the pH-buffering capacity of limestone media reduced the impact of pH on HFPO-DA transportation. Compared with PFOA, HFPO-DA transported faster at pH = 4 with an R_f value of 0.97, lower than that of PFOA at 1.21, due to its smaller molecular weight and shorter carbon chain. Overall, the research reveals the potent mobility of HFPO-DA and PFOA in the environment, highlighting their groundwater pollution potential and environmental risks.