Screening Research On Cr Hyperaccumulators

Chromium is an impotant environmental element, with its compounds widely used as the basic row materials in such industries as metallurgy, metal processing, electroplating, tanning, painting and so on. Cr-containing wastewater and solid waste generated in those production processes were put into soil through many kinds of ways. At present, traditional remediation technologies of heavy metal pollution are very expensive and disturbing the soils configuration, with potential decrease of soil activity and fertility. So it is impossible to be used at large scale, especially in the developing countries. In addition there are short of experience of application and the effect of dealing with the polluted soils is lack of stabilization. As a kind of newly invented bio-environmental technology, bioremediation is much more available than the traditional technology of physical and chemical remediation as its advantages of low cost, high efficiency and no secondary pollution. As a matter of fact, it has attracted attentions from countries all over the world, and played an increasing role in the treatment of soil pollution.In this paper the heavy metal pollution is investigated and assessed in one tanning zone of Wenzhou, Zhejiang province of East China. Then the filtration of hyperaccumulators was carried out based on the content of Cr in plants. Plant growth and Cr accumulation of accumulating ecotypes of the plants were studied with field experiments. The main results obtained are summarized as follows:The research focused on heavy metal concentrations of soil and plants in Wenzhou's tanning zone and relationship with soil pollution. According to the Soil Environmental quality standardâ…¡, the soil was seriously polluted by Cr. The available plant germplasm resources for Cr contaminated soil restoration were initially definited. Twenty-five species belonging to 13 families were found in the polluted area, including 8 dominant species: Cynodon dactylon(L.), henopodium glaucum Linn., gerarum houstonianum, Malachium aquaticum(L.)ries(Stellaria aquatica(L.)Scop.) , Eleusine indica (Linn.) Gaertn., Rorippa montana (Wall.) Small, Amaranthus retroflexus L. and Sinobambusa tootsik(Sieb.)Makino.. The investigation showed that Cynodon dactylon(L.), Chenopodium glaucum Linn., Eleusine indica (Linn.) Gaertn., Rorippa montana (Wall.) Small, Amaranthus retroflexus L. were the adaptive pioneer species for soil ecological restoration. Cr concentrations in the aboveground were 110.26⁷74.05mg·kg^-1, and the average value was 280.95mg·kg^-1;Cncentrations in roots were 774.05²334.56mg·kg^-1, the average value was 1229.75mg·kg^-1. Cr concentrations in the aerial and root of Cynodon dactylon(L.) were the highest, 774.05 mg·kg^-1 and 2334.56mg·kg^-1, respectively, but still not reached the standard of Cr hyperaccumulator(the Cr concentrantions of aerial parts is 1000 mg·kg^-1). According to correlation analysis, the heavy metal content in aboveground plants and the roots had weak correlation with the content in soil. The result of regressive analysis indicated that the root bioaccmulation coefficients of Pb and Cr was closely associated with the aboveground plants. The root bioaccmulation coefficients were enhanced with the increased aboveground plants.The soil experience's results showed that Cr content in soil inhabited growth of microorganisms, the number of bacteria, actinomycetes and fungi reduced, respectively. The activities of urease and catalase was remarkably reduced by the introduction of Cr into soil, and the relationships between them were up to the significant negative correlation level(r=-0.862 and r=-0.650, respectively) so that urease and catalase activities could be used as indicators for soil Cr pollution; In the 16 testing plants , there were no Cr hyperaccumulators, but we found that Cupressus funebris and Ligustrum lucidum were most suitable for remediation of Cr-contaminated soil, which were evergreen trees, growing rapidly. Cr concentrations in the aerial parts of the plants were the highest, 223.81mg·kg^-1 and 227.06mg·kg^-1, respectively, and the average bioaccumulation coefficient and translation coefficient of aerial parts were also very high. Platycladus orientails(Linn.)Franco and Cinnamomum Camphora(L.)Presl. were good plant germplasm resources, Gramineae could be taken into account as the potential plant.