Study Of The Accumulation And Toxic Effects Of ZIF-8 In Corbicula Fluminea

Metal-organic frameworks（MOFs）have been widely studied and possibly applied to many fields their unique properties such as high specific surface area and high porosity.A rational and comprehensive evaluation of the ecotoxic effects of MOFs materials is essential to achieve safe production applications of the materials in practice.The toxic effects of MOFs nanoparticles on aquatic organisms should be of concern as benthic bivalves live for a long time at the water-sediment interface and are prone to come into contact with and enrich these nanomaterials into the organism.However,the studies so far have focused on the potential applications of MOFs and to a lesser extent on their toxicity in animal cells and plants in vitro,and there is a dearth of studies on their toxic effects on benthic organisms in the water.Therefore,in this study,the zeolitic imidazolate frameworks-8（ZIF-8）was selected as a typical MOFs material,and the benthic bivalve Corbicula fluminea was used as a test biological model,combined with the stability performance of ZIF-8 in the aquatic environment,to comprehensively assess the toxic effects toxic mechanisms of ZIF-8 on benthic organisms in aquatic media.The results showed that ZIF-8 nanoparticles were subject to dissolution behavior in complex aqueous environments due to environmental factors such as environmental p H,ionic type,and ionic strength,which consequently affected the risk of contact with benthic organisms.With exposure doses ranging from 0～50 mg·L^-1,Zn accumulation in the Corbicula fluminea tissues and shells showed a concentration-and time-dependent pattern.In the experimental concentration range,the ZIF-8nanoparticles induced an antioxidant defense mechanism similar to the hormesis effect in organisms.ZIF-8 suspensions significantly increased the levels of oxidative stress,including superoxide dismutase activity（SOD）,catalase activity（CAT）,and malondialdehyde content（MDA）in all ZIF-8 suspension-treated Corbicula fluminea’s tissues.Besides,we also found that ZIF-8 particles and dissolved Zn²⁺may result in different mechanisms of toxicity and accumulation depending on the dosages.When ZIF-8 nanoparticles were at low concentrations(5 mg·L^-1),a high proportion of Zn²⁺was released from ZIF-8.The continuous release of Zn²⁺would be preferentially taken up by the Corbicula fluminea and might directly induce antioxidant defense mechanisms within the tissues,resulting in oxidative damage to the Corbicula fluminea cells.Conversely,at higher concentrations(50 mg·L^-1),ZIF-8 was mostly taken up by Corbicula fluminea in the form of particles carrying more Zn²⁺.Then,the ZIF-8 particles that enter the body of the Corbicula fluminea were transferred and accumulated in various tissues and gradually internalized by the cells,resulting in a persistently high level of biotoxicity and leading to higher mortality and persistent cell damage.These results have important implications for understanding the fate and toxic effects of ZIF-8 nanoparticles in the natural aquatic environment.