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Environmental safety of nanomaterials has become a hot issue of global concern.Nano-TiO2 is one of the most common applications of nanomaterials.Since it is difficult recovery,TiO2 nanoparticles will inevitably enter the environment with wastewater discharge,and deposit in the sediment finally.To investigate the effects of nano-TiO2 on mercury release and activation in sediment,flooding simulation experiments were conducted.The impacts of nano-TiO2 on total mercury and methylmercury concentrations in overlying water were analyzed.And the influences of nano-TiO2 on migration and transformation of mercury were discussed based on changes of mercury speciation in sediment.The results indicated that nano-TiO2 promoted the release of mercury in sediment,leading to more mercury released into the water.Compared with the control,4 g/kg TiO2 nanoparticles cause the increase of total mercury by 91.32%,when the concentration of total mercury in overlying water were the highest.Release of mercury in soil increased by approximately 10%finally.The main reason may be the dissolution of oxidation state mercury improved by nano-TiO2.It indicated that the risk of mercury contamination in water may increase.Moreover,under the experimental conditions,nano-TiO2 may reduce the formation of methylmercury in sediment in the short term,but no significant effects in the long term.Generally,the effects of nano-TiO2 on release and transformation of mercury in sediment had the concentrate-dependence.Thus,with nano-TiO2 content increases in sediment or soil,its impact on the geochemical cycle of mercury may increase.