Studies On The Transport And Enrichment Of Copper And Cadmium In Loess And Wheat

Heavy metal contamination in agricultural soil has become more and moreserious in China. Parts of soil which was polluted by heavy metals had endangered the safetyof food production. In order to know the specific chemical behaviors of heavy metals inenvironment comprehensively，we studied the regularity of migration and enrichment forheavy metals in the system of water, soil and plant. It provided a basis for risk assessment ofheavy metals. That had great significant in forecasting the pollution trends of heavy metals insoil. In this study, we chose copper (Cu) and cadmium (Cd) as the object of study, which isoutstanding in polluting soils to our country. We analyzed the regularity of heavy metaladsorption-desorption, and their chemical form transportation, migration and enrichmentprocess of copper and cadmium, by combining dynamic and static methods as laboratorysimulation and potted plants. We got the following conclusions from the experiments.1. Loess had a strong absorbing capacity of Cu (Ⅱ) and Cd (Ⅱ). The amount ofadsorption increased with a longer balance of time or bigger concentration of pollutants. Themaximum amount of adsorption was up to4020mg/kg and3550mg/kg of copper andcadmium in loess. Both of the adsorption isotherms fitted the Freundlish equation best. Thesorption distribution coefficient of Cu (Ⅱ) was bigger than Cd (Ⅱ). The acid extractablefractions and reducible fractions forms were the mainly existence of Cd, while the mainforms of Cu in loess were acid extraction and residual fractions.2. We studied desorption of copper and cadmium from losses by EDTA and sodiumdodecyl benzene sulfonate (SDBS). The highest resolution rates of copper and cadmium were52.01%and70.78%at optimum conditions, which referred to room temperature, and theratios between liquid and soil were60:1and80:1for Cu (Ⅱ) and Cd (Ⅱ), pH was6,standing and shocking time were2h and60min, with EDTA and SDBS mixed in certainproportions.35.14%acid extractable fractions and33.38%reducible fractions of copper wereremoved from the soil.65.24%acid extractable fractions and43.06%reducible fractions ofcadmium were removed from the soil.3. The biggest accumulation of copper and cadmium in losses was322.4mg/kg and 116.2mg/kg. The adsorption of Cu (Ⅱ) and Cd (Ⅱ) in soil column was divided into threestages, that was whole adsorption, part adsorption and saturated adsorption. The higher claycontent in soil, the greater amount of adsorption, the slower migration of pollutants.4. The germination rate of winter wheat decreased, and the germination time and heightwere inhibited when the content of copper and cadmium were exceeded in soil. Thegermination rate of wheat decreased by55%, and the germination time doubled delayednearly while copper and cadmium were stirred in the soil. The distribution order of Cu inwheat plant was root> leaves> ear> stems, and withering period heading> growing seedlingstage. The distribution order of Cd in the wheat plant was root> leaves≈stems> ear, andwithering period> seedling> growing> heading. The copper inhibited cadmium absorption,while the cadmium promoted copper absorption in wheat.