TiO2 and SiO2 Nanoparticles Combined with Surfactants Mitigate the Toxicity of Cd2+ to Wheat Seedlings

Abstract

Engineered nanoparticles (NPs) could be coated by surfactants and modify the bioavailability and toxicity of heavy metals. In this study, the single and combined effect of sodium dodecyl benzene sulfonate (SDBS) and NPs on the toxicities of Cd2+ to wheat seedlings was investigated by a root elongation, and the underlying influence mechanism was further discussed. The results showed that the presence of SDBS improved the Cd2+ adsorption capacity of TiO2 and SiO2 NPs. The reaction of SDBS and TiO2 and SiO2NPs could increase TiO2 and SiO2 NPs dispersion stability and produced more available adsorption sites. The adsorption coefficients of Cd2+ on TiO2 and SiO2 NPs were enhanced from 3.84 to 4.52 mg/g and from 4.51 to 7.16 mg/g after SDBS coating. Both SDBS-coated TiO2 and SDBS-coated SiO2 NPs reduced Cd2+ phytotoxicity. The presence of bare TiO2 and SiO2 NPs at 1000 mg/L promoted root length of the wheat seedlings by 31.2% and 39.3%; however, SDBS-coated TiO2 and SiO2 NPs increased the root length by 41.2% and 51.4%, which demonstrated that SDBS-coated NPs had a much better effect on reducing the toxicity of Cd2+ than bare NPs. The results indicated the mitigation of Cd2+ toxicity was due to a decrease in bioavailable soluble Cd2+ which was adsorbed by NPs through electrostatic attraction.