The ecotoxicity of α-Fe2O3 nanoparticles (NPs) and its interaction with a typical natural organic matter (NOM), fulvic acid (FA) on the physiological responses of Synechococcus sp. PCC7942 was studied. α-Fe2O3 NPs inhibited the algae growth at concentration higher than 10 mg L-1 and induced oxidative stress, indicated by enhanced antioxidant enzymes activities, elevated protein and sugar content. FA could efficiently recover cell growth and reduce antioxidant enzyme activities which induced by α-Fe2O3 NPs, indicating the toxicity of NPs was alleviated in the presence of FA. α-Fe2O3 NPs could form large aggregates coating on cell surface and inhibit cell growth. FTIR spectra verified FA interacted with α-Fe2O3 NPs through carboxyl groups, partly replaced the binding sites of α-Fe2O3 NPs on algal cell walls, thus reduced NPs aggregates coating on cell surface. This favors reducing the oxidative stress caused by direct contact and increasing light availability, thus mitigate NPs toxicity.
Keywords: Antioxidant enzymes; Fulvic acid; Nanoparticles; Surface coating; Synechococcus; α-Fe2O3.