Field Scale Phytoremediation Experiments On A Cd And Zn Contaminated Site By Ricinus Communis L. And Helianthus Annuus L.

As the research object in this paper, castor(Ricinus communis L.) and sunflower(Helianthus annuus L.) are typical economic crops. The Cd and Zn accumulation characteristics of experiment plants in different growth periods were tested by in situ field experiment. The potential phytoremediation capabilities of three economic crops were also studied to provide some scientific suggestion for phytoremediation application. The results we acquired were summarized as follows:(1) The heavy metals concentration of study field as follow: The average concentration of Zn was 548.32 mg/kg(146.59~1618.66 mg/kg); Cu was 46.36 mg/kg(26.74~66.36 mg/kg); Cr was 116.47 mg/kg(85.31~239.02 mg/kg); Cd was 1.04 mg/kg(0.50~2.19 mg/kg).(2) Taking Evaluation Standards of Soil Environmental Quality for Exhibition(provisional)(HJ350-2007) as reference, the expertiment field was mainly polluted by Cd and Zn. Zn pollution was more serious with wider coverage.(3) The order of Hakanson potential ecological risk index was: Cd>Cu>Zn>Cr. While the ecological risk caused by Cu, Zn and Cr was slight, the ecological risk caused by Cd was strong. The potential ecological risk of the study field was medium. Thus, Cd and Zn were choosed as polluted heavy metals to study the phytoremediation effectiveness and efficiency of economic crops.(4) The distribution of heavy metals in contaminated site was uneven. In order to eliminate the influence of heavy metal heterogeneity, significant difference analysid was conducted to divide samples into different groups according to the concentration of heavy metal in soils. Thus, the effect of soil heavy metal concentration on plant biomass, heavy metal concentration and contents in plant tissues was analyzed.The Cd and Zn co-contaminant restrained the growth of R. communis. The biomass and Cd concentration in roots and stems of R. communis increased first and then started to drop along with the increase of Cd concentration in soil. The order of caster organs accumulating Cd was: root>stem>leaf>fruit. Zn concentrations in roots and stems of R. communis continued to decline during the growing period. Cd and Zn contents in all organs of R. communis keep rising with the increasing growth time. The contents of Cd and Zn in aboveground tissues were always higher than roots at all experiment field.(5) When Cd and Zn concentrations in soil increased, Cd and Zn concentrations in organs of Russian sunflower(Helianthus annuus var. Russian) increased initially and decreased afterwards at the growth period of 30 day and 120 day. So, the capacity of Russian sunflower to absorb heavy metal from soil was restrained by high heavy metal concentration in soils. The contents and concentrations of Cd and Zn in aboveground tissues were always higher than roots at all experiment field, indicating that the Russian sunflower was suitable for phytoremediation.(6) During the regular sunflower(Helianthus annuus var. Chinese) growing period, the concentrations of Cd and Zn in all organs of plant increased firstly and then declined along with the increasing Cd and Zn concentrations in soils, suggesting that the regular sunflower’s heavy metal uptake ability was restrained by high heavy metal concentration in soils.The root and aboveground heavy metal contents of regular sunflower had a sustainable growth, and the contents of Cd and Zn in aboveground tissues were always higher than roots at all experiment field during the growth period.(7) The potential Cd and Zn phytoremediation capacity, effectiveness and benefits of Russian sunflower were stongest among three experimental plants. About 2.03 g of Cd can be removed per hectare of land where Russian sunflower were grown for 120 days; in addition, biomass energy of 50.34 GJ can be produced. The amount of Zn that Russian sunflower can remove per year is estimated as 305.08 g/ha at the growth period of 60 days, and using harvested plants as fuel can produce a heat value of 49.6 GJ/ha. Thus, using sunflower is feasible for the phytoremediation, which can be supported by revenues derived from the crops in heavy metal contaminated site.