| With the mineral resource mining, selecting and smelting, heavy metal pollution in cultivated soil is getting serious and endangers food security and human health. It is a realistic way to explore plant species or varieties with low metal uptake which can be planted at metal-contaminated sites, because of long period and high difficulties in control of metal-contaminated soil.In this research, firstly, a filed survey was conducted to investigate the present situation of crop food safety in Jijie, Gejiu City, Yunnan province. Heavy metal pollution in soil was assessed and plant species or varieties with different metal uptake abilities were selected. Secondly, mechanisms of metal exclusion and uptake in species with low absorption [the broad bean (Vicia faba L.), the pea(Pisum sativum L.)] and high absorption [the lettuce (Lactuca sativa L.), the peppermint (Mentha arvensis L.)] were researched by using orthogonal design under pot trial conditions. Thirdly, a series of remediation measures [adjusting soil pH value (8,8.5,9), increasing humic acid (2,5,10 g·kg-1), increasing sulfide (2,5,10 g·kg-1) and increasing Ca2+-contained compound (2,5,10·g kg-1)] were adopted to reduce metal uptake in the high absorption species (lettuce, peppermint) and to achieve the goal of food safe. In addition, the effects of remediation measures to physiological and biochemical parameters of high absorption species (lettuce and peppermint), such as plant height, photosynthetic pigments, catalase (CAT), peroxide enzyme (POD), superoxide mutase (SOD), soluble sugar, root system vigor etc., were evaluated. The soil qualities after adopting remediation measures were also researched. The results indicated as follows.1. Average concentrations of lead (Pb), zinc(Zn), copper(Cu) and cadmium(Cd) at study site were 1185.48±490.72,628.87±175.58,453.50±129.11 and 7.50±5.40 mg·kg-1, surpassing " Environment Quality Standard for Soils" (GB 15618-1995) (GradeⅡ). There was a significantly positive correlation between diethylenetriaminepentaacetic acid (DTPA) and total concentrations of soil Pb, Cu, Cd (p< 0.01) and Zn (p< 0.05), respectively. The soil fertility situation at study site was good.2. Concentrations of Pb in all crops sampled at the study site surpassed the limit standard for food safety. Concentrations of Zn in other crops surpassed this standard except the pea, broad bean, rice(Oryza.sativa L.) and corn (Zea mays L.). Concentrations of Cu in Lettuce, leaf mustard(Brassica juncea (L.) Czern. et Coss.), peppermint, and cabbage (Brassica rapa L. glabra Regel) also surpassed this standard. Concentrations of Cd in other crops surpassed this standard except the pea, broad bean and sea cabbage(Brassica oleracea L. var. capitata L.). Comparatively speaking, the lettuce, peppermint and leaf mustard were not suited for planting at the metal-contaminated site. Sugar cane (Saccharum officinarum Linn.) and rice (paddy rice) were more suitable to plant, and pea, fragrant-flowered garlic (A. schoenoprasum L.), blue cauliflower (B. oleracea L.var italica Plench), cauliflower(Brassica oleracea L. var. botrytis L.), sea cabbage, broad bean, carrot (Raphanus sativus L.), onion(A. fistulosum L.), pod pepper(Capsicum annuum L.), potato (Solarium tuberosum L.) and corn were reluctantly suited for planting. The chard(Beta vulgaris L. var. cicla Koach), cabbage and green vegetables were hardly suitable to plant.3. Under orthogonal design conditions, differences of metal subcellular distribution were observed in peppermint (high absorption species) and broad bean (low absorption species). Lead (Pb), Zn and Cu in broad bean were mainly concentrated in the cell wall and unbroken residual (F1) except for Cd. However, differences were appeared in subcellular distribution of Pb, Zn, Cu, Cd in peppermint along with the different group of orthogonal design. As for peppermint, leaf concentrations of Pb, Cu and Cd were significantly affected by soil Pb, but Zn concentrations in leaf were not significantly affected. Leaf concentrations of Pb, Zn, Cu and Cd were significantly affected by soil Zn and Cu. Leaf concentrations of Cd, Pb and Zn were significantly affected by soil Cd, but Cu concentrations of leaf were not significantly affected. As for broad bean, leaf concentrations of Cd, Pb and Zn were significantly affected by soil Pb, but Cu concentrations in leaf were not significantly affected.Leaf concentrations of Pb, Cu, Cd and Zn were significantly affected by soil Zn. Leaf concentrations of Pb and Zn were significantly affected by soil Cu, but Cu and Cd concentrations in leaf were not significantly affected. Leaf concentrations of Zn and Cd were significantly affected by soil Cd, but Pb and Cu concentrations in leaf were not significantly affected.4. As for peppermint (high absorption species), the heavy metal constitutes resulting in a minimum concentration of Zn, Cu and Cd was group 2 [control Pb (not added), low concentrations of Zn (200 mg·kg-1), low concentration of Cu (100 mg·kg-1), low concentration of Cd (5 mg·kg-1)]. The heavy metal constitutes resulting in a minimum concentration of Pb was group 10 [middle concentration of Pb (800 mg·kg-1), low concentration of Zn (200 mg·kg-1), high concentration of Cu (800 mg·kg-1), middle concentration of Cd (10 mg·kg-1)]. As for broad bean (low absorption variety), the heavy metal constitutes resulting in a minimum concentration of Cu and Cd was group 6 [low concentration of Pb (400 mg·kg-1), low concentration of Zn (200 mg·kg-1), control Cu (not added), high concentration of Cd (20 mg·kg-1)]. The heavy metal constitutes resulting in a minimum concentration of Pb was group 4 [control Pb (not added), high concentration of Zn (1000 mg·kg-1), high concentration of Cu (800 mg·kg-1), high concentration of Cd (20 mg·kg-1)], group 8 [low concentration of Pb (400 mg·kg-1), high concentration of Zn (1000 mg·kg-1), middle concentration of Cu (400 mg·kg-1), low concentration of Cd (5 mg·kg-1)] and group 9 [middle concentration of Pb (800 mg·kg-1), control Zn (not added), middle concentration of Cu (400 mg·kg-1), high concentration of Cd (20 mg·kg-1)]. Group 2 could lead to a minimum of Zn in leaves of this plant.5. Under metal compounded pollution conditions, as for lettuce and peppermint (high absorption species), POD and SOD activities in their leaves were significantly affected by soil Pb and Cd. Chlorophyll content, POD and SOD activities in leaves were significantly affected by soil Zn, and plant heights by soil Cu. As for pea and broad bean (low absorption species), plant heights, chlorophyll content and SOD activities were significantly affected by soil Pb, and SOD activities by soil Zn. Root activities were significantly affected by Pb, Zn, Cu and Cd in peppermint, as well as Cu and Cd in broad bean, respectively.6. As for peppermint and lettuce (high absorption species), leaf Cu was mainly concentrated in the parts containing cell nucleus and the chloroplast (F2) under remediation conditions. However, leaf Pb, Zn and Cu were mainly concentrated in the cell wall and unbroken residual (F1). Compared with other treatments, concentrations of Pb, Zn, Cu and Cd were significantly decreased in leaves of peppermint and lettuce under pH 9 or 5 g·kg-1 humic acid treatments. Concentrations of Pb, Cd and Zn, Cu were significantly decreased in leaves of these two plants by adding 10 and 5 g·kg-1 Ca2+, respectively. Concentrations of Pb, Zn and Cd were significantly decreased in leaves of these two plants by adding 5 g·kg-1 sulfide.7. Under remediation conditions, chlorophyll contents in leaves of peppermint and lettuce were significantly higher than those of controls when soil pH was adjusted to 8.5. Root activities were also higher than control when soil pH was adjusted to 8. Chlorophyll contents in leaves of the two plants significantly increase by adding 5 or 10 g·kg-1 humic acid. SOD activities were also significantly higher than other treatments by adding 5 g kg-1 humic acid. Root activities were higher than the controls when 10 g kg-1 humic acid was added. Contents of chlorophylls and carotenoids were significantly higher than the controls under 10 g·kg-1 Ca2+ treatments, and POD and root activities were significantly higher than other treatments. Soluble sugar contents were significantly higher than the controls under 5 g·kg-1 Ca2+ treatment. CAT, SOD and POD activities, soluble sugar contents and root activities were significantly higher than other treatments.8. Difference was observed in Pb, Zn, Cu and Cd speciation of soils after adopting remediation measures. Ferro-maganese oxidation and residuals were the major speciation of Pb, Cd, and Zn, Cu, respectively. Concentrations of DTPA-extractable Pb were significantly lower than the controls by adding humic acid and Ca2+. Concentrations of DTPA-extractable Zn were significantly lower than the controls by adding 10 g·kg-1 Ca2+. Soil pH was significant higher than the controls by adding 2, humic acid or 10 g·kg-1 sulfide. Concentrations of soil total nitrogen were also significantly higher than the controls by adjusting pH to 9 or adding 2 g·kg-1 Ca2+. |
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