Heavy metal pollution risk of desulfurized steel slag as a soil amendment in cycling use of solid wastes

The by-product of wet flue gas desulfurization,desulfurized steel slag(DS),had chemical characteristics like natural gypsum that can be used to improve saline-sodic soil.However,contamination risk of heavy metals for cycling utilization of DS in agriculturewas concerned mostly.Both pot and field experiments were conducted for evaluating the potential pollution risk of DS as the amendment of saline-sodic soil.Results showed that application of DS decreased the contents of Cd,Cu,Zn,and Pb,while significantly increasing chromium(Cr)content in DS-amended soils.The field experiment demonstrated that the migration of heavy metals(Cd,Zn,Cu,and Pb)in the soil profile was negligible.The application of DS at the dosage of 22.5–225 tons/ha significantly increased the Cr content in alfalfa(Medicago sativa L.)but lower than the national standard for feed in China(GB 13078-2017).DS altered the chemical fraction of heavy metals(Zn,Cu,and Pb),transferred exchangeable,reducible into oxidizable and residual forms in DS-amended soil.Application of DS combined with fulvic acid(FA)could effectively reduce the movement of heavy metals in soil and the accumulation of Cr in alfalfa.Based on our results,DS was a safe and feasible material for agricultural use and presented relatively little pollution risk of heavy metals.However,the results also showed that DS to a certain extent had a potential environmental risk of Cr if larger dosages of DS were used.

Soil inorganic amendments produce safe rice by reducing the transfer of Cd and increasing key amino acids in brown rice

The digestibility of cadmium(Cd)in brown rice is directly related to amino acid metabolism in rice and human health.In our field study,three kinds of alkaline calcium-rich soil inorganic amendments(SIAs)at three dosages were applied to produce safe rice and improve the quality of rice in Cd-contaminated paddy.With the increased application of SIA,Cd content in iron plaque on rice root significantly increased,the transfer of Cd from rice root to grain significantly decreased,and then Cd content in brown rice decreased synchronously.The vitro digestibility of Cd in brown rice was estimated by a physiologically based extraction test.Results showed that more than 70%of Cd in brown rice could be digested by simulated gastrointestinal juice.Based on the total and digestible Cd contents in brown rice to evaluate the health risk,the application of 2.25 ton SIA/ha could produce safe rice in acidic slightly Cd-contaminated paddy soils.The amino acids(AAs)in brown rice were determined by high-performance liquid chromatography.The contents of 5 key AAs(KAAs)that actively respond to environmental changes increased significantly with the increased application of SIA.The structural equation model indicated that KAAs could be affected by the Cd translocation capacity from rice root to grain,and consequently altered the ratio of indigestible Cd in brown rice.The formation of indigestible KAAs-Cd complexes by combining KAAs(phenylalanine,leucine,histidine,glutamine,and asparagine)with Cd in brown rice could be considered a potential mechanism for reducing the digestibility of Cd.