Study On The Relationship Between The Water-Soluble Fraction And Wheat Bioavailability Of Cd And Pb In Soil Under Stabilizing Amendments

Cadmium(Cd)and lead(Pb)are highly toxic to humans,and dietary exposure is the main exposure pathway for Cd and Pb.Due to Cd and Pb contamination in agricultural soils,the problem of excessive Cd and Pb contents in cereals frequently happens and poses a serious threat to human health.In order to reduce the accumulation of soil Cd and Pb in crops and the risk of dietary exposure,accurate assessment and reduction of the bioavailability of soil heavy metals is the key to reduce the accumulation in crops.Currently,chemical extraction methods,such as BCR extraction,exchangeable fraction extraction,and water extraction,are commonly used to assess the mobility,lability,and bioavailability of soil heavy metals.However,it requires further evaluation on which assessment methods are more suitable for assessing the bioavailability of Cd and Pb.Our previous work found that the water-soluble fraction can be used to accurately assess the bioavailability of Cd in acidic soils and indicate Cd accumulation in rice.However,it still needs further research on whether the water-soluble fraction is suitable for the bioavailability assessment of different metals and different types of soil.To reduce the accumulation of heavy metals in cereals,soil stabilization remediation techniques are commonly used for the remediation of large areas of agricultural soils.Therefore,in this study,soil incubation experiments and wheat pot experiments were designed 1)to investigate the stabilization and aging effects of different soil stabilizing amendments on newly introduced and existing Cd and Pb using enriched isotope tracing techniques,water extraction,BCR extraction and extraction of the exchangeable fraction,2)to investigate the accumulation,transport and distribution of soil Cd and Pb in soil-wheat systems under different soil stabilizing amendments,and 3)to assess the relationship between various chemical extraction methods(particularly water extraction)and the bioavailability of Cd and Pb.In this paper,various chemical extraction methods were used to investigate the stabilization and aging processes of Cd and Pb in soil under different soil stabilizing amendments.For this tested soil,different soil stabilizing amendments had little impact on the four fractions by BCR extraction and isotope exchangeable concentrations(E values),but the concentrations of water-soluble Cd and Pb significant changed.Among them,slaked lime and magnesium hydroxide had the most obvious stabilization effect on water-soluble Cd and Pb,followed by biochar,while calcium dihydrogen phosphate activated Cd and Pb.These results indicated that the water-soluble fraction can more sensitively reflect the stabilization and aging processes of heavy metals under stabilization amendments,and may be more suitable for the evaluation of heavy metal bioavailability in soil.In addition,research has found that the aging process of newly introduced Cd and Pb is more significant,and the proportion of the acid-soluble fraction,water-soluble fraction,and E value were higher than that of the original metal,indicating that the newly introduced metal may have stronger mobility and bioavailability.Besides,different chemical evaluation methods were used to investigate the accumulation,transport,and distribution characteristics of Cd and Pb in the soil-wheat system under different stabilization amendments.This study found that there was a good correlation between soil water-soluble Cd concentrations at heading and ripening stages and Cd accumulation in the whole wheat plant and grain,indicating the water-soluble Cd in soil can well reflect the accumulation of Cd in wheat(whole plant: r=0.777-0.898,P<0.001;grain: r=0.640-0.779,P<0.01 or P<0.001).However,the water-soluble fraction cannot reflect the accumulation of Pb in wheat,and the acid-soluble fraction and E value of soil cannot reflect the accumulation of Cd and Pb in wheat tissue.It was also found that wheat had a stronger ability to accumulate and transport Cd.The accumulation and transport coefficients of different Cd were similar,but there were significant differences between the original and newly introduced Pb,with newly introduced Pb accumulated more in wheat roots.In addition,slaked lime,magnesium hydroxide,biochar,and calcium dihydrogen phosphate can reduce the accumulation of Cd and Pb in wheat grains,providing data for in situ soil stabilization remediation.