Study On Cd And Pb Accumulation In Aquatic And Wetland Plants

In recent years, cadmium and lead have significant accumulation in the soil of the West Lake scenic spot, which makes its heavy metal pollution become an acute problem. Phytoremediation technology has gradually become one of the most effective methods for heavy metal contaminated soil repair because of its low cost and environmentally-friendly. The research of adopting garden plants to repair the heavy metal contaminated soil has just risen, but the potential is tremendous. While repairing the contaminated soil could also bring huge economic and ecological benefits at the same time. The identification of high Cd and Pb accumulating aquatic and wetland plants and related research which are special for the West Lake scenic spot has not been reported till now. This paper aims to study on the distributional characteristics of heavy metals in the soil and native plants, as well as Cd and Pb accumulation characteristics in some aquatic and wetland plants, and then apply the results to repair the heavy metal contaminated soil in the West Lake scenic spot, which would be of great significance for the protection of the West Lake’s ecological environment, the rational planning of urban development and human health.According to the heavy metal pollution condition of the wetland ecological system in the West Lake scenic spot and the existing species resources of aquatic and wetland garden plants, Thalia dealbata, Iris pseudacorus L., Canna glauca L., Water Iris, Cyperus microiria, Ngmphaea tetragona, Typha angustifolia L. and Nelumbo nucifera were used as research objects to study the accumulation characteristics of Cd and Pb in their aboveground and underground parts through the pot experiment with artificial contaminated soil. Meanwhile,24 sampling points in the West Lake scenic area were settled, and the Cd and Pb contents of their soil samples were measured and analyzed in order to know the Pb and Cd accumulation in the soil of West Lake scenic spot. In addition, field samples of Thalia dealbata, Iris pseudacorus L., Ngmphaea tetragona and Typha angustifolia L. were also collected from the West Lake scenic, and the Pb and Cd accumulation of their aboveground and underground parts were detected and analyzed to understand their abilities to accumulate Cd and Pb from the polluted soil. The main research results were as follows:1. The Cd and Pb contents in the soil of CK were 0.34±0.09 mg/kg and 58.76±3.51 mg/kg respectively. The Cd contents for Cdl and Cd2 were 1.57±0.16 mg/kg and 5.45±0.45 mg/kg respectively, while their Pb contents did not show significant difference compared to CK. The Pb contents of Pbl and Pb2 were 113.49±9.82 mg/kg and 161.55±10.98 mg/kg respectively, and their Cd content did not show significant difference compared to CK.2. Under Cd treatments, the Cd content in aboveground part of Cyperus microiria was highest among all tested plants. Ngmphaea tetragona mainly accumulated Cd in its aboveground part, which showed that it could transfer Cd from underground to aboveground part, while both Canna glauca L. and Nelumbo nucifera mainly accumulate Cd in their underground parts.3. Under Pb treatments, the Pb content in aboveground parts of all tested plants were very low, with the highest number was 2.90±0.35 mg/kg, but it was even lower than the Pb content of general plants (5.00 mg/kg). However, their Pb contents in underground parts were 10～20 times more than the aboveground ones, which meaned that all tested plants mainly accumulated Pb in their roots.4. The transfer coefficients of Water Iris, Cyperus microiria and Ngmphaea tetragona to Cd could be higher than 1, which meaned that these plants might be able to transfer Cd from their roots to aboveground parts effectively. While the transfer coefficients of all tested plants to Pb were lower than 1, indicated that their abilities to transfer Pb from underground to aboveground parts were not high enough.5. The bioconcentration factors of all tested plants to Cd and Pb were all less than 1, suggested that these plants might have very low ability to enrich Cd and Pb from soil.6. By using Duncan, the aboveground biomass of Typha angustifolia L., Thalia dealbata and Cyperus microiria had no obvious difference, so are Iris pseudacorus L., Water Iris and Ngmphaea tetragona. When Cd and Pb additive concentration increased, the biomass of Water Iris and Nelumbo nucifera did not show obvious reduction, while some plants’aboveground biomass reduced with the rise of the content of Cd and Pb. The order of average biomass of all tested plants was Typha angustifolia L.> Thalia dealbata> Cyperus microiria> Canna glauca L.> Nelumbo nucifera> Water Iris> Iris pseudacorus L.> Ngmphaea tetragona.7. The survey of 24 soil samples from the West Lake scenic area found that the average Cd content was 0.44 mg/kg, while for Pb was 62.90 mg/kg, and both values were above the geological background value of Cd and Pb in Hangzhou. In addition, about 70% of the samples had different degree of Cd pollution,4.2% belong to heavy-degree pollution; while about 87.5% of the samples had different degree of Pb pollution, and most of them belong to minor or mild pollution.8. The survey of 42 native plant samples from the West Lake scenic area found that the Cd enrichment capacity of the aboveground parts of Iris pseudacorus L. and Ngmphaea tetragona were obviously better than Thalia dealbata, while the underground part of Thalia dealbata could accumulate more Cd. Besides, all the samples did not show excess accumulation of Pb.9. When the Cd and Pb content of artificial polluted soil and natural polluted soil in West Lake scenic area were the same, the Cd and Pb accumulation capacity of the same kind of plant did not show significant difference in pot experiment and under natural conditions.