Nanoremediation Of Cytotoxicity From Cr（Ⅵ） By Mg（OH）₂Nanoflakes

Removal of Chromium ions (e.g. Cr(VI)) from environmental wastes and remediation of Chromium-induced toxicity are of utmost importance because of the high productivity of Chromium all over the world, large environmental release, and high carcinogenicity. Cr(VI) could be taken up through respiratory tract, gastrointestinal tract and skin, and cause systemic risks. The carcinogenic mode of Cr(VI) generally is "uptake-redution". Cr(VI) diffuses into cells, and induces oxdative stress, cell cycle arrest and apoptosis. Chromium wastes produced by industry are generally landfilled after reduction, which could cause secondary pollution after environmental oxidation. Owing to their small size, large surface area and high surface-adsorption affinity, nanomaterials (NMs) have been used as adsorbents for pollutants and have shown high treatment efficiency with a low cost. However, the gathering pollutant behaviors of NMs possibly change the transport, translocation or transformation of pollutants in the environment. The environmental behavior of pollutants-loaded NMs would be different from the pollutants or NMs alone. NMs have been found interaction effects with chemical mixtures on the ecosystem. After co-exposure, NMs enhanced the metal ion accumulation and their aquatic toxicity. However, the mechanism in cell level is not clear. And the bio-effects of pollutant-NM adducts were few investigated.As nanodisk was reported hardly to enter cells, we hypothesized that flake-like nanoparticles (NPs) could reduce cellular uptake of pollutants that adsorbed onto NPs. In this study, we demonstrated a nanotechnology approach for remediation of Cr(VI)-induced cytotoxicity. The Magnesium hydroxide nanoflake (Nano-Mg(OH)2) was synthesized by chemical precipitation method. The Nano-Mg(OH)2/Cr(VI) complex was prepared by CrO72-adsorbed onto Nano-Mg(OH)2. In the presene of Mg(OH)2nanoflakes, both HEK293and HepG2cell lines have shown to reduce cellular uptake of Cr(VI) due to little internalization of nanoflakes, which subsequently eliminated the generation of reactive oxygen species (ROS) and the corresponding cell cycle arrest and apoptosis. This cytotoxicity is only a fraction of toxicity from free Cr(Ⅵ) because nano-Mg(OH)2particles hold up2/3of Cr(Ⅵ) anions. Owing to the reduced internalization of Cr(Ⅵ) by Mg(OH)2nanoflakes, cytotoxicity of Cr(VI) was greatly reduced. Besides, with the anion carrier applied to block the free Cr(Ⅵ), Nano-Mg(OH)2/Cr(Ⅵ) complex was found little entering cells and generally nontoxic.Our study has testified that Mg(OH)2nanoflakes could be a promising absorbent for the environmental remediation of Cr(Ⅵ) or other heavy metal ions-induced toxicity. The nanoflake-adsorbent would be an ideal model for application. This study also encourages further in depth study of absorption-desorption behavior in vitro and remediation of toxicity in vivo.