Comparison of 6:2 chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFESA) and perfluorooctane sulfonate (PFOS) accumulation and toxicity in mung bean

Abstract

With the regulation of perfluorooctanesulfonate (PFOS), 6:2 chlorinated polyfluoroalkyl ether sulfonate (6:2 Cl-PFESA) has been used as a potential PFOS alternative in electroplating. In this study, the uptake, translocation and phytotoxicity of PFOS and 6:2 Cl-PFESA in mung bean (Vigna radiata (Linn.) Wilczek.) were investigated. The uptake kinetics of PFOS and 6:2 Cl-PFESA fit the Michaelis-Menten equation well, suggesting that the uptake is a carrier-mediated process. The root concentration factor (RCF) of 6:2 Cl-PFESA (34.55 mL g−1 dw) was 1.27 times that of PFOS (27.11 mL g−1 dw), and the translocation factor (TF) of 6:2 Cl-PFESA (0.177) was 1.07 times that of PFOS (0.165). Exposure to 6:2 Cl-PFESA and PFOS both resulted in the inhibition of mung bean seedling development. Treatment with 6:2 Cl-PFESA and PFOS led to the concentration-dependent elevation of malondialdehyde (MDA), carbonyl groups, and phosphorylated histone H2AX (γ-H2AX) levels in mung bean roots. The MDA and carbonyl group contents induced by 6:2 Cl-PFESA were 1.10–1.35 and 1.03–1.14 times, respectively, those of PFOS. The hydroxyl free radical (·OH) levels in mung bean roots after exposure to PFOS and 6:2 Cl-PFESA were elevated significantly, and the ·OH levels induced by 6:2 Cl-PFESA were higher than those induced by PFOS. Hydroxyl free radical levels were positively correlated with the MDA and carbonyl group contents in mung bean roots (p < 0.05). The dynamic changes in some antioxidative enzyme activities in mung bean seedlings were determined, including peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT). The results demonstrated the phytotoxicities of 6:2 Cl-PFESA and PFOS to mung bean in the early developmental stage. 6:2 Cl-PFESA is more harmful to mung beans than PFOS. The production of hydroxyl radical is the mechanism that causes the toxicity of PFOS and 6:2 Cl-PFESA toward plants.