The effect of single and composite additives on cd and pb mobility, speciation and accumulation in late rice (Oryza sativa l.) grown on contaminated soil

This field trial investigated the cadmium (Cd) and lead (Pb) immobilization in contaminated paddy soil. Five stabilizing agents including lime, biochar, phosphatic fertilizer (PF) and two composites (S1, S2) were investigated (1% w/w) for metals immobilization by growing late rice as a test crop. The results revealed the improved pH and decreased metal availability in lime, S1, biochar and S2 treated plots. The Cd and Pb speciation results depicted a decrease in exchangeable Cd content to less mobile forms (29 and 30%) with addition of biochar and S1 in harvest stage samples. The exchangeable fraction of Pb was significantly reduced to 29, 29 and 36% with S1, S2 and biochar, respectively. Moreover, Cd and Pb accumulation in rice grains was lowest in composite stabilizers and biochar treatments. Our results showed a significant increase in leaf photosynthetic rate, transpiration rate, biomass and grains yield in S1 amended plot. These lessening effects are owed to the conversion of available metal contents to the least mobile forms. Our results confirmed the effectiveness of organic additives alone and in mixture with inorganics in reducing metal mobility, improving immobilization, enhancing growth and decreasing accumulation in food parts and showed a great prospect in safer food production.