Research progress on passivation technologies and their mechanism of reducing soil cadmium uptake by tobacco

Tobacco is an important economic crop which is readily to uptake cadmium (Cd) from soils, rendering it to be one of the main source of Cd to human bodies. Therefore, reducing Cd content in tobacco leaves through regulation and control measures is important to ensure tobacco quality, safety and human health. The soil Cd passivation technologies to reduce Cd content in tobacco were summarized, and the passivation mechanism of passivators, including adsorption, ion exchange, precipitation, complexation and ion antagonism, was expounded. The factors affecting Cd content in tobacco were also analyzed, including soil Cd concentration and chemical forms, soil pH, redox potential, organic matter concentration, cation exchange capacity, and competitive metal ions. The passivation efficiencies of normal passivators and the parameter conditions in the applications were illustrated, including lime, hydroxyapatite, metal oxides, biochar, organic fertilizer, sepiolite, zeolite and bentonite. Some suggestions were proposed to provide basic data and technical reference for the reduction of Cd content in tobacco, including clarifying the standard system of tobacco Cd content, developing new passivation materials and using molecular biology technologies, etc.