| In 2008, Yangzong Lake, one of nine big lakes in Yunnan Province, China, was polluted by arsenic (As) released from a nearby factory. Average concentration of As in the water was up to 0.117 mg L-1, suggesting that about 70 t As entered the lake. Phytoremediation technology has been widely advocated to treat polluted soil and water because it is cost-effective and environmental-friendly. It is important and urgent to screen out As hyperaccumulators in As contaminated water and use them efficiently in the control of As-contaminated water.In present study, firstly, the growth status and concentrations of heavy metals (As, Cd, Cu, Pb, and Zn) in 17 macrophytes naturally grown in south and north regions of Yangzong lake were evaluated by field survey and laboratory analysis. Concentrations of these five metals in water and sediments were also determined and compared with those in the plants, with the aim of finding suitable plant resources to phytoremediate As-contaminated water body such as Yangzong lake. Secondarily, plants with different As-hyperaccumulative characteristics, namely Hydrilla verticillata (Linn.f.) Royle, Ceratophyllum demersum L, Potamogeton malaianus Miq were used in two hydroponic experiments. One was conducted to investigate the effects of different As speciations[As(Ⅲ),As(Ⅴ),DMA] on As uptake of plants, distribution of arsenic at subcellular level and activities of antioxidative enzymes, including superoxide dismulase(SOD), peroxidase(POD) and catalase(CAT). The other was carried out to estimate the effects of different factors, including phosphate, iron, and pH, on As uptake by these tested plants growing in the same concentration of As. The results showed that:1. All these collected plants grew well, without any toxic symptoms. The water body was heavily and slightly polluted by As and Pb, respectively, while the concentrations of Zn, Cu and Cd were below their corresponding environmental quality standards. For 9 submerged species (Ceratophyllum demersum, Hydrilla verticillata, Blyxa octandra, Potamogeton pusillus, Potamogeton lucens, Potamogeton delavayi, Potamogeton pectinatus, Myriophyllum spicatum and Chara braunii), their bioconcentration factors (defined as the ratio of heavy metal concentration in whole plant to that in water) for As, Zn, Cu, Cd and Pb were all greater than 1, which showed a co-accumulative character for these five elements. Growing in water averagely containing 0.175 mg·As L-1, C. demersum, H. verticillata, P. pusillus and B. octandra showed a strong ability to accumulate As, with average As concentrations of (150±7.3), (179±35), (92±31) and (265±21) mg·kg-1(dry weight), respectively. For 8 hygrophyte and emerged species at north site, bioconcentration factors (the ratio of heavy metal concentration in aboveground part to that in sediment) were greater than 1 in Alternanthera philoxeroides, Echinochloa oryzicola, Ixeridium gracile and Echinochloa caudata for As, E. caudata, I. gracile, Paspalum orbiculare, Polygonum hydropiper and Cyperus alternifolius for Cd, Alocasia macrorrhiza and P. orbiculare for Zn. And translocation factors (the ratio of heavy metal concentration in aboveground part to that in root) were greater than 1 in P. orbiculare for Zn and Cd. The roots of A. philoxeroides, A. macrorrhiza, E. caudata and P. orbiculare accumulated high concentrations of As. Cluster analysis showed that C. demersum, H. verticillata, B. octandra, P. pusillus and M. spicatum could uptake and accumulate As, Zn, Cu, Cd and Pb simultaneously and had a great potential for phytoremediaiting water body contaminated with multiple metals. In general, accumulation of As, Zn, Cu, Cd and Pb in all tested submerged species were greater than that in hygrophyte and emerged species.2. The application of 3.0 or 5.0 mg·L-1 As(Ⅲ) and As(Ⅴ) significantly decreased the biomass of C. demersum, H. verticillata and P. malaianus, and this inhibitive effect was obvious in As(Ⅲ) treatment. In different As speciation treatments, As uptake by three tested plants decreased following the order As(Ⅲ)>As(Ⅴ)>DMA. The maximum Arsenic concentrations respectively reached 689.49±33.39,375.7±55.45 and 109.12±8.63 mg·kg-1 in As(Ⅲ), As(Ⅴ) and DMA treatments in H. verticillata, which significantly exceeded those of C. demersum and P. malaianus. Treated with 1.0 mg·L-1 As(Ⅲ) or DMA, H. verticillata and P. malaianus reached the maximum concentration of As after 6 days. Treated with 1.0 mg·L-1 As(Ⅴ), C. demersum reached the maximum concentration of As after 6 days. Additionally, the concentration of As in C. demersum reached the maximum after 2 days in 1.0 mg·L-1 As(Ⅲ) treatment,. Treated with 1.0 mg·L-1 As(Ⅴ), C. demersum reached the maximum concentration of As after 4 days. In different concentrations of As(Ⅲ) and As(Ⅴ) treatments, As mainly distributed in the cell wall and the cytoplasm of these three plants, but a few As were found in the chloroplast and mitochondria. In different concentrations of DMA treatments, As mainly distributed in the cell wall of these three plants, and a few As were found in the cytoplasm.3. The concentrations of As in H. verticillata and P. malaianus significantly increased when the pH of culture solution was adjusted to 5.0 in As(Ⅴ) treatment. The concentrations of As significantly decreased in H. verticillata when pH of As(Ⅲ)-containing solution was adjusted to 5.0 or 9.0. In As(Ⅲ) treatment, low level of Fe2+ significantly limited As uptake in P. malaianus. The application of 1.5 mg·L-1 Fe3+ significantly increased As concentrations in H. verticillata and C. demersum. In As(V) treatment, all levels of Fe2+ significantly increased As concentrations of tested plants. All levels of Fe3+ significantly increased As concentrations in C. demersum and P. malaianus. All levels of P significantly decreased As concentrations in three tested plants exposed to As(Ⅲ)-containing solution.4. The activities of SOD and POD in C. demersum were significantly higher than those in H. verticillata and P. malaianus in different As speciation trentments, but the activities of SOD were significantly inhibited by high concentrations of As. Different As concentrations significantly increased the activities of POD in C. demersum. The activities of CAT in H. verticillata and C. demersum were significantly higher than those of P. malaianus in different As(Ⅲ) and As(Ⅴ) trentments. High concentration of As could increase significantly the activities of CAT in H. verticillata and C. demersum. In different concentrations of DMA trentments, the activities of CAT in H. verticillata and P. malaianus were significantly higher than those of C. demersum. In a word, the antioxidant capacities of three plants followed as C. demersum> H. verticillata> P. malaianus. POD and CAT play a key role in plant antioxidative systems. |
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