| Behavioural process and ecological risk of heavy metal in soil-plant system play a dominantrole in hindering heavy metals passing into food chain and threatening human health. The study willnot only accelerate the land protection and sustainable development but also will providetechnological support for soil management and remediation of soils contaminated by heavy metals.Field-survey method, Field-leaching experiments, pot-culture experiments, laboratory-leachingexperiments and laboratory analysis were carried to study the chemical behavior and ecological riskon soil-plant system for representative soils in the arid area, which was taking the oasis in the Hexicorridor for an example. The main results show as follows:(1) The average content of Zn, Ni, Cu, Pb, Cd in surface soils all surpassed background value insoil from GanSu province. Moreover the average content of Ni surpassed theⅡgrade standard of soilenvironmental quality and the average content of Cu surpassed theⅢgrade standard of soilenvironmental quality. Zn content between different land use was as follows:woodland＞farmland＞residential areas＞highway green belt＞desert; Ni content was as follows:woodland＞residential areas＞highway green belt＞farmland＞desert; Pb content was as follows:farmland＞residential areas＞highway green belt＞woodland＞desert; Cu content was as follows:woodland＞highway green belt＞farmland＞desert; Cd content was as follows: woodland＞residentialareas＞highway green belt＞farmland＞desert. Different land use had effect on heavy metal content insoils, and the degree was as follows: Pb＞Zn＞Cd＞Cu＞Ni.(3) Single factor index showed that Ni in all sites was in heavy polluted; Cu in soil from highwaygreen belt, residential areas and woodland was in heavy polluted; while other heavy metals were notpolluted states. Nemerow multi-factors index of heavy metals was as follows: Ni＞Cu＞ed＞Zn＞Pb. Thegeoaccumulation index indicated Zn and Pb were in unpolluted states, Cd was in light-middle polluted,Ni was in middle polluted and Cu was in middle-heavy polluted. There was some sites from farmlandand woodland, the Zn and Cd content of which were in heavy polluted. The content of Cu followingan order were highway green belt＞residential aeras＞woodland＞farmland＞Desert. While the content ofNi was as follows: residential aeras＞woodland＞highway green belt＞farmland＞desert.(4) The activity index of Cu was higher than other heavy metals and the second of activityindex was Cd. These showed Cu and Cd had great potential harm to surroundings. While Zn activityindex and Pb activity index were relatively lower and they had less harm to surroundings. The totalcontent of Ni increased harm to biology although its activity index was lower. The results from factoranalysis suggested that Cu and Ni in top soil were mainly originated from industrial and miningactivities, while Zn, Pb and Cd were mainly originated from agricultural activities. The potentialecological risk assessment showed that the risk of about half sites were in middle-heavy level. Thesingle potential ecologicao risk index of heavy metal following an order was Cd＞Cu＞Ni＞Pb＞Zn.Moreover Cd, Cu, Ni existed different degrees of risk and the risk of Pb, Zn were in a low level. There were highest available concentrations of heavy metals neighbourhood BaiJiaZui and MaJiaYaZi.The Cu and Ni content extracted by EDTA was high neighbourhood DongWan. The Cdconcentrations extracted by EDTA was high neighbourhood ZhongPai.(5) Profile distribution of heavy metals are similar in soil through field-leaching experimentsand laboratory-leaching experiments. The result indicated that the maximum values of total Cu, Zn, Pband Cd were in the superficial horizons (0-10cm) in soil columns. The result indicated distance ofheavy metals downward movement were short in soil columns of leaching experiments during theperiod of test. Filed-survey result showed that action of distribution and transfer for total contents ofCu, Ni were similar in soil column from field-survey. Cu ,Ni were enriched in the upper layer andconcentrations decreased with increasing soil depth firstly and reached a steady level. The transferdepth of Cu and Ni down profiles reached 45centimeters. Moreover Cu content in top layer, inferiorlayer and Ni content in top layer, inferior layer, subsoil layer all surpass theⅡgrade standard of soilenvironmental quality. The results showed that although additive heavy metals were enriched in soilcolumn, the horizon depth which additive heavy metals reached was limited, heavy metals did not acthigh pollution risk to shallow groundwater.(6) Cu and Ni were riched in the roots, while Zn was riched in the seeds. Thetransfer capacity of Cu, Zn, Ni was as follows:Zn＞Cu＞Ni. The average concentrations ofCu in seeds was 9.37mg/kg, and the max concentrations was 11.64mg/kg. Cu contentabout 18.18% of sites exceeded the national hygienic limits for food in China. The averageconcents of Zn in seeds was 31.39mg/kg ,the max concents was 43.25mg/kg. The Zn content of allsites were below the national hygienic limits for food in China. The average content of Ni in seedswas 3.57mg/kg, the max content was 3.57mg/kg. The Ni content of all sites exceeded the referencevalue.(7) The percent of Cu in carbonate fraction, Zn in carbonate fraction, Zn in Fe-Mn oxidefraction, Pb in carbonate fraction in soil horizon (0-10cm) of leaching experiments column werehigher than they in original soil column, while percent of Cd in exchange fraction in all layer werehigher . Although total content distribution of heavy metals in soil column were not impactedseriously by additive heavy metals content and the pH of irrigation water, distribution of forms forheavy metals were impacted. Distribution of forms for Cd and Zn were influenced by the pH ofirrigation water, while Cu and Ni were influenced by additive heavy metals content. Field-surveyresult showed that Copper was distributed mainly in the organic fraction and the residual fraction, Zndistributed mainly in the residual fraction, Ni was distributed mainly in the Fe-Mn oxide fraction andthe residual fraction. The percent of Cu, Zn, Ni in the exchange fraction waslower than one percent..From 0 to 45 centimeters, Cu was distributed as follow: organic fraction＞residual fraction＞Fe-Mnoxide fraction,carbonate fraction＞exchangeable fraction, The content of Ni was Fe-Mn oxidefraction＞organic fraction,residual fraction,carbonate fraction＞exchangeable fraction., while Cu andNi were mainly in the residual fraction after 45 centimeter horizon. Zn was distributed in the residual fraction in all layer. Cd,Pb content in shoot and root of rape were more than other organs. Zn contentin organs of rape was not very different. Cd,Zn,Pb content in shoot of Celery was more. Cd contentin shoot of carrot was more than that of in the root slightly. The distribution of Zn, Pbin shoot and in root was different with additive heavy metals content increasing.Comparative analysis revealed that the accumulation level of Cd, Zn, Pb by carrot wasthe worst, while the accumulation level of Cd, Zn, Pb by the root of Celery and the shootof rape were the most. Distribution of forms for heavy metals were different. Cd was mainlydistributed in the residual fraction and carbonate fraction in original soil planted rape, while Cd wasmainly distributed in the Fe-Mn oxide fraction in polluted soil. Cd distributed mainly in Fe-Mn oxidefraction and carbonate fraction in original soil while Cd distributed mainly in the carbonate fractionand exchange fraction in polluted soil with planting Celery. For carrot, Cd was mainly distributed inthe residual fraction in original soil, while distribution of Cd in polluted was different with additiveheavy metal content increasing. Zn was mainly distributed in the residual fraction in original soilplanted rape, while Zn was mainly distributed in the Fe-Mn oxide fraction and carbonate fraction inpolluted soil. Zn distributed mainly in the residual fraction in original soil while Zn distributed mainlyin the Fe-Mn oxide fraction and carbonate fraction in polluted soil with planting Celery. For carrot, Znwas mainly distributed in the residual fraction in original soil. while distribution of Zn in polluted soilwas mainly in the Fe-Mn oxide fraction and residual fraction.Pb was mainly distributed in the residualfraction in original soil planted rape, while Pb was mainly distributed in the Fe-Mn oxide fraction andcarbonate fraction in polluted soil. Pb distributed mainly in the residual fraction and Fe-Mn oxidefraction in original soil while Pb distributed mainly in the Fe-Mn oxide fraction and carbonate fractionin polluted soil with planting Celery. For carrot, Pb was mainly distributed in the residual fraction inoriginal soil. while distribution of Pb in polluted soil was mainly in the Fe-Mn oxide fraction andcarbonate fraction.Correlation analysis showed that Cd in the exchange fraction was more available to rape, celeryand carrot. Zn in the exchange fraction and carbonate fraction was more available to rape, celery;while Zn in the carbonate fraction and Fe-Mn oxide fraction was more available to carrot. Pb in theexchange fraction and carbonate fraction was was more available to rape. Pb in the exchange fractionwas more available to celery. Pb in the carbonate fraction was more available to carrot.The BCF of celery for Cd, Zn, Pb was highest while BCF of carrot for Cd, Zn was lowest. ForPb, the accumulation level of carrot was worst. The transfer level of celery for Cd, Zn, Pb was worst.Under different content, transfer level of carrot and rape for Cd, Zn were different. The TF of carrotfor Pb was highest.
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