Forever Chemicals then and Now: Comparative Toxicity Assessment of Emerging Versus Legacy PFAS on Synechocystis Growth

Per- and polyfluoroalkylated substances (PFAS), the “forever chemicals”, are a vast family of pollutant substances that can be divided into legacy and emerging PFAS. The former have been progressively phased out over environmental and health dangers and replaced with shorter-chain emerging PFAS, which are highly under-researched, comparatively unregulated and yet are found in many novel applications such as lithium-ion batteries. PFAS can cause growth inhibition, membrane peroxidation, cell signalling disruption and protein damage through production of excess reactive oxygen species and inducing oxidative stress. In this study, we compare the impact of high and low concentrations of legacy and emerging PFAS on model cyanobacterium Synechocystis after 21 days of exposure. We evaluate cell density as well as chlorophyll, carotenoid and allophycocyanin concentration. All growth parameters experienced toxicity from emerging PFAS, and there is no significant difference in the growth inhibition and photosystem oxidative damage caused by different PFAS types at the same concentration. Most parameters show significant inhibition occurs at high PFAS concentrations and stimulatory effects occur at low PFAS concentration for all types. This suggests both legacy and emerging PFAS cause environmental toxicity or at low concentrations trigger harmful algal blooms. We therefore bridge the gap in emerging PFAS toxicity research, concluding that emerging PFAS are not an improvement over legacy PFAS and stricter regulation is required for the former. Further research can differentiate the mechanisms of uptake and cellular damage of longer and shorter chains between legacy and emerging PFAS, allowing clearer understanding of their environmental impact.