Distribution,Source And Interaction With Soluble Organic Matter Of Heavy Metals In Agricultural Soils Of Jianghan Plain

Soil heavy metal pollution has become a serious threat to ecosystem stability and human health because of its concealment,sustainability and ecological hazards.Its a key and basic work to studying the distribution characteristics and sources of heavy metals for prevent and control soil heavy metal pollution.On the other hand,the speciation and transformation of heavy metals in soils are largely controlled by soil soluble organic matter?DOM?,which will directly affect the adsorption and desorption behavior of heavy metals in soils,thus affecting the bioavailability and ecological hazards of soil heavy metals.Therefore,it is of great significance to study the distribution,pollution sources and the interaction with DOM of heavy metals in soil for the prevention and remediation of heavy metal pollution in soil.On the basis of previous studies,the pollution status and distribution characteristics of heavy metals in agricultural soils of Jianghan Plain?JHP,²2454 km²?were studied by measuring the concentrations,temporal trends and speciations of heavy metals in 234 samples.And the sources of heavy metals in JHP soils were analyzed by means of isotope analysis and multivariate statistical analysis comprehensively and quantitatively.Then,the effects of DOM from different sources on the adsorption and desorption of soil-heavy metals,and the migration and transformation of heavy metals in soil-plant system were studied to explore the interaction and mechanism between typical heavy metals?Hg and Cd?and DOM in agricultural soils of JHP.The results showed that:1.Concentrations of some metals in agricultural soils of JHP(0.48±0.2,48.2±15.9,0.12±0.23,48.8±16.4,36.5±9.8,and 96.8±42.2 mg kg^-1 for Cd,Cu,Hg,Ni,Pb,and Zn,respectively)were higher than background concentrations in Chinese soil.Compared with other areas in China and the world,the heavy metal pollution in JHP soils was relatively higher.Cd and Cu in agricultural soils of JHP exceed the background value in a wide range,Pb and Hg were obviously enriched in Jingzhou,while Ni elements was higher in Qianjiang,Tianmen,Xiantao,Hanchuan and Wuhan cities along the Han River.The concentration of Cd in soils increased significantly in the past 13 years,while the concentration of Cu decreased significantly.The proportions of the metals in the mobile fractions decreased in the order Pb?41.0%±10.6%?,Cd?39.5%±14.7%?,Zn(36.0%±14.7%,Cu?33.2%±11.4%?,Ni?14.6%±10.8%?,indicating that Pb,Cd,Zn,and Cu in JHP soils were mobile.2.The Cd isotope compositions for JHP soils(?^114/110Cd values-0.76‰to-0.25‰)were similar to Cd isotope compositions found for smelter dust and incinerator fly ash,indicating Cd was supplied to the JHP soils by ore smelting and/or refining processes.The Pb isotope compositions for the JHP soils(²⁰⁶Pb/²⁰⁷Pb 1.182¹.195 and ²⁰⁸Pb/²⁰⁶Pb2.078².124)were between the Pb isotope compositions found for Chinese coal and natural sources.The results of the two-terminal mixing model show that the average contribution rate of coal combustion to Pb in JHP soils was 52%,indicating that coal combustion was the main anthropogenic source of Pb in JHP soils.Multivariate statistical analysis indicated that the sources of heavy metals in JHP soils may consist of smelting and refining activities,coal combustion,agricultural activities,and natural sources?including Han River sediment and soil parent materials?.3.Adsorption and desorption experiments and pot simulation experiments show that the DOM from different sources and the differences of natures of heavy metals will affect the adsorption of heavy metals in soils.Compared with the straw DOM and farm manure DOM,the microbial DOM has higher aromaticity,and can increase the capacity and rate of heavy metals adsorption in soils,thus,reducing the bioavailability of heavy metals in soils.Hg and Cd combined with soil or DOM in different ways because of different natures,which resulting different speciations distributions and bioavailability between Hg and Cd in soils.