PFAS uptake by lettuce: Roles of PFAS properties, co-present organic acids, and nanoplastics

The accumulation of per- and polyfluoroalkyl substances (PFAS) in food crops poses a significant food safety and human health risk, yet studies on the accumulation of PFAS in food crops in conditions that more realistically represent a growth environment with various co-occurring chemicals are still lacking. This study investigated the accumulation of perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), and perfluorobutane sulfonic acid (PFBS) by lettuce in a hydroponic system in the co-presence of polystyrene nanoplastics (NPs, 300 nm) and/or three prevalent organic acids [humic acid (HA), fulvic acid (FA), and oxalic acid (OA)]. Results showed that NPs decreased the concentration of all three PFAS compounds in lettuce shoots after seven days of exposure compared with plants exposed to PFAS alone. However, the three organic acids all increased PFAS concentrations in lettuce shoots, regardless of the presence of NPs. Three interesting trends were observed: (1) long-chain PFAS (PFOA, PFOS) appeared to depend more heavily on the active transport pathway than short ones; (2) the properties of organic acids play a major role in their impact on PFAS accumulation in lettuce; and (3) organic acids showed greater impact on the accumulation of short-chain PFAS (PFBS) in lettuce shoots than the long ones. Overall, the co-presence of organic acids increased PFAS accumulation in lettuce, suggesting that interactions with organic acids and nanoplastics can materially alter PFAS uptake. These findings highlight the need for additional mechanistic and soil-based studies to better understand PFAS food-safety risks under realistic field conditions.