Effect of hydroxyapatite and straw biochar on reducing cadmium accumulation in vegetables
The contamination of farmland with heavy metals poses a significant threat to human health through the food chain,necessitating the enhancement of soil quality for safe agricultural practices and the assurance of the quality of agricultural products.Soil samples were obtained from Cd-contaminated farmland in northern Jiangsu for simulated incubation and greenhouse vegetable pot experiments.To investigate the passivation efficiency of various dosages of hydroxyapatite(HAP,1%,2%),rice straw biochar(BC,1%,2%),and their combined applications(0.5%HAP+0.5%BC,1%HAP+1%BC)were compared for their efficacy in immobilizing soil Cd and diminishing Cd absorption by vegetables.The study elucidated these effects through chemical speciation analysis and the plant physiological responses.Pot experiments with vegetables revealed that all immobilizing amendments increased the netphotosyntheticrateof leaves,resulting in a biomass increase ranging from 3.78%to 124%.Furthermore,the Cd accumulation in vegetables and the concentration of available Cd in the soil were reduced by 16.1%to 81.7%and 15.8%to 69.9%,respectively.Notably,Cd content in vegetables was decreased by 69.9%,66.4%and 18.7%under 2%HAP,1%HAP+1%BC and 2%BC amendments,respectively.In the 40-day soil incubation experiment,available Cd reductions varied from 28.9%to 87.6%among different amendments.The principal mechanisms included an increase in soil pH by 0.38 to 0.98 units,the residual content of Cd increasedby19.5%to37.0%,and the acid-soluble content of Cd decreased by 21.1%to 25.6%.Overall,all types of amendments effectively regulated the absorption and accumulation of Cd in vegetables by diminishing its chemical activity and phyto-availability in the soil.In acidic-polluted soils,at an equivalent dosage,inorganic amendment HAP proved to be the most effective in enhancing vegetable biomass and reducing Cd uptake,followed by the inorganic-organic composite amendment of HAP+BC.However,the organic amendment BC exhibited weaker and slower effects,necessitating co-application with HAP to improve immobilization efficiency.
Heavy metal pollutionamendmentschemical speciationphyto-availabilityfood safety of agricultural product
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