Accumulation, isomeric fractionation, and cellular distribution of per- and polyfluoroalkyl substances (PFAS) in diverse marine diatoms

Per- and polyfluoroalkyl substances (PFAS) have garnered considerable attention over the last decade due to their persistence in the environment and potential negative health effects on living organisms, including humans. However, our understanding of their occurrence, transport, and fate in the marine environment remains limited. For example, the interaction of PFAS with marine phytoplankton, which serve as entry points for several contaminants into the marine food web, has not yet been thoroughly examined. In this study, we overcame the challenging issues related to PFAS sorption onto filter membranes and successfully investigated algal uptake of PFAS by various marine diatoms (i.e., Thalassiosira pseudonana, Thalassiosira weissflogii, Phaeodactylum tricornutum, and Chaetoceros muelleri) under environmentally realistic conditions. Volume concentration factors (VCFs) of PFAS by T. pseudonana showed a positive correlation with PFAS carbon chain length, and the presence of a sulfonic group enhanced uptake. For perfluorocarboxylic acids (PFCAs), logVCFs ranged from 0.17 (C4-PFCA) to 5.65 (C14-PFCA), and, on average, VCF increased by 4-fold per carbon added from C6 to C14. The uptake of PFAS isomers by algae was also examined. Linear PFAS showed a higher affinity for algal cells compared to branched PFAS (e.g., logVCFL-PFOS = 3.40, logVCFbr-PFOS = 3.20). Emerging PFAS such as HFPO-DA (GenX) exhibited very little accumulation in diatoms (logVCF = 0.39). We observed that temperature (18°C vs. 4°C) and light (light vs. dark) had no significant effect on PFAS uptake. Interestingly, reducing salinity appears to slightly increase algal PFAS uptake. Among the four diatom species tested in this study, T. weissflogii exhibited the lowest PFAS accumulation, and the degree of PFAS uptake was proportional to the surface-to-volume ratio of algal cells. The cellular distribution of PFAS in diatoms was also investigated. C8 to C10 PFCAs were primarily associated with the cytoplasmic fraction, whereas C11 to C14 PFCAs were mostly associated with the frustule. Our findings represent an important systematic study of PFAS uptake by marine phytoplankton and of algal PFAS accumulation in response to environmental factors, which will benefit modeling of emerging contaminants in the marine food web/environment.