Medium-Dependent Phytotoxic Effects of Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS) on Early Development in Selected Monocot and Dicot Plant Species: A Comparative Assessment

Per- and polyfluoroalkyl substances (PFAS) are human-made organofluorine compounds that resist physical, chemical, and biological degradation. Used widely since the 1940s, they are now ubiquitous in the environment. Despite restrictions or bans in many countries, the extreme persistence, mobility, and bioaccumulation of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS)—the PFAS most commonly found in soils and waters—still pose major ecological risks. Phytotests use plants as bioindicators to assess the biological impact of the tested agent on various physiological end parameters, such as seed germination or root length. To our knowledge, the current literature lacks direct evidence regarding the toxic effects of PFOA on Sorghum bicolor germination and early seedling development, nor does it adequately characterize the individual effects of PFOA or PFOS on Lepidium sativum and Sinapis alba. To address this gap, this study examined how and to what extent the type of growth medium to which PFOA or PFOS is added affects their phytotoxicity. Empirical evidence shows that matrix type strongly affects plant physiological responses to PFOA and PFOS, as indicated by changes in root elongation. Root growth was most inhibited in the liquid phase. Specifically, the application of PFOS at a dose of 1 mg L−1 caused a 20.2% inhibition of Sorghum bicolor root growth. In contrast, Lepidium sativum and Sinapis alba exhibited 22.1% and 21.1% inhibition, respectively, but only at a higher dose of 10 mg L−1. Regarding PFOA, the strongest effect was observed at a dose of 10 mg L−1, which inhibited the root growth of Sorghum bicolor by 9.8%, Lepidium sativum by 14.9%, and Sinapis alba by 14.3%. In the reference soil, toxicity was lower, likely due to the high sorption capacity of kaolin clay for PFAS, while humus soil better reflects natural ecosystem conditions. Plant sensitivity depended on species and PFAS type: Sinapis alba was most sensitive to PFOS (27.2% root growth inhibition at 0.1 mg L−1 in humus soil) and least sensitive to PFOA (16.7% root growth induction at 1 mg L−1 in reference soil), and Sorghum bicolor and Lepidium sativum showed similar response patterns.