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Nano-TiO2 is one of the most common applications of nanomaterials.Since it is difficult recovery,TiO2 nanoparticles will inevitably enter the environment.Its environmental safety has become a hot issue of global concern.To investigate the effects of nano-TiO2 on migration and transformation of heavy metals in soil,flooding simulation experiments were conducted in the outdoors.The results showed that,after flooding months,high concentrations of rutile and anatase particles led to the release of 20.08%and 18.11%oxidizable chromium and 60.55%and 68.78%residual chromium,respectively.Thus nano-TiO2 promoted the activation of chromium and improved the mobility of chromium in soil.High concentration of rutile particles resulted in the decreased of acid exchangeable lead by 25.92%and oxidizable lead by 33.09%,also enhanced mobility of lead.However,anatase particles caused the increase of oxidizable zinc by 30%in soil,which facilitated fixing of zinc.In addition,two types of nano-TiO2 particles were no significant effect on the speciation changes of Cu and Cd.Therefore,there is a big difference in the impact of nano-TiO2 with different structures on different heavy metals in soil.It must be treated differently when used nano-TiO2 to remedy heavy metals contaminated soil and assessed its environmental risk.