Aquatic Biosafety Assessment Of Fe₃O₄ Nanoparticles In Sediments Using Zebrafish Embryos And Juveniles

With the large-scale production and wide application of ferroferric oxide nanoparticles Fe₃O₄ NPs in the market,a large amount of Fe₃O₄NPs are discharged into the aquatic ecosystem.Since Fe₃O₄ NPs are insoluble in water and have strong adsorption properties,they will settle into sediments and accumulate,and will have certain effects on aquatic organisms,and finally will be transmitted to humans through food chains and food networks.However,there is no research to evaluate the safety of Fe₃O₄ NPs in sediments.Therefore,it is very meaningful to give the safe concentration of Fe₃O₄ NPs in sediments,and it can also be used as a reference for the production and emission of Fe₃O₄ NPs.To study the toxic effects of Fe₃O₄ NPs on aquatic organisms in sediments,artificial pure sediments were prepared according to the protocol of OECD.233,and sediments with Fe₃O₄ NPs concentration of 0,0.2,0.4,0.8,1.6,3.2 mg/g(dry weight)were added.In order to better understand the water pollution situation,we collected five surface sediments from Xiangjiang River,and found Fe concentrations of 77.46,67.84,110.47,73.09,and 93.59?g/g(dry weight),respectively.The concentrations of Fe in the artificial pure sediments with 0,0.2,0.4,and0.8 mg/g Fe₃O₄ NPs were 0,68.94,97.08,and 151.78?g/g(dry weight),respectively.Since Fe in the sediments of Xiangjiang River exists mostly in other iron-containing chemicals,the content of Fe₃O₄ NPs in Xiangjiang sediments should be less than 0.8 mg/g.Subsequently,we evaluated the toxicity of Fe₃O₄ NPs in sediments using zebrafish embryos by sediment exposure experiments.With the increase of Fe₃O₄ NPs concentration in sediments,the mortality rate of zebrafish embryos and juveniles showed an increase trend,and the hatching rate showed a decrease trend,the significant difference was found in the concentration of 0.4 mg/g or above.The deformity is mainly edema of the pericardium,yolk cyst,skeletal deformity,and occasionally incomplete morphological development of the eye and the mouth and the tail deformity.In addition,the heartbeat,body length and autonomic activity of zebrafish juveniles also decreased significantly at high concentrations(1.6 and 3.2 mg/g).Oxidative stress in cells is the most important cause of the toxicity induced by Fe₃O₄ NPs.The concentration of malondialdehyde(MDA)increased significantly at the concentration of 0.8 mg/g Fe₃O₄ NPs(p<0.05),and very significantly at the highest concentration(3.2 mg/g)(p<0.01);The total antioxidant capacity(T-AOC)decreased significantly at the highest concentration(3.2 mg/g)(p<0.01);Superoxide dismutase(SOD)activity increased with increasing concentrations at concentrations of 0.2 mg/g and 0.4 mg/g,and it decreased to lower than the control group at the concentrations of 1.6 mg/g and 3.2 mg/g(p<0.05);Reactive oxygen species(ROS)levels showed a dose-dependent trend and a significant increase at 0.4 mg/g(p<0.05).The bioaccumulation of Fe₃O₄ NPs is reflected by the total iron content in zebrafish juveniles.The results showed that under the exposure of 0.4 mg/g Fe₃O₄ NPs,the total iron content in zebrafish juveniles increased significantly,which was 2.3 times higher than that of the control group(p<0.05).At the highest concentration(3.2 mg/g),it was extremely significant,which was 12.5 times higher than that of the control group(p<0.01).The results showed that the content of Fe₃O₄ NPs in artificial sediments was not higher than 0.2 mg/g,and had no significant effect on the development,oxidative stress and bioaccumulation of zebrafish embryos and juveniles.Therefore,the safe concentration of Fe₃O₄ NPs in sediments should be no higher than 0.2 mg/g.