Chelates assisted phytoremediation of contaminated urban soils in large cities

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Chelates assisted phytoremediation of contaminated urban soils in large cities

 

Author: Zhang, Jianjun
Title: Chelates assisted phytoremediation of contaminated urban soils in large cities
Degree: M.Sc.
Year: 2013
Subject: Soil pollution.
Soil degradation.
Hong Kong Polytechnic University -- Dissertations
Department: Faculty of Construction and Environment
Pages: viii, 60 leaves : ill. ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2646936
URI: http://theses.lib.polyu.edu.hk/handle/200/7181
Abstract: Comparing with rural soils, urban soils receive lower dosis of pesticides and fertilizers generally, but they are normally more easily contaminated by waste disposal, traffic emissions, industrial activities and fuel combustion. The pollution of urban soils may have some negative impacts on the human who live in urban areas, and the surrounding ecosystems. There are many ways of categorizing available remediation technologies in recent years. From a practical viewpoint, the most obvious difference is whether this technology treats the contaminated soil in-place (the in situ technologies) or is based on the removal of soil to the surface for treatment (ex situ technologies). Biodegradable chelates induced phytoremediation is a rapidly developed treatment for dealing with heavy metal contaminated soils. In this research, not only the practicality of planting ryegrass as a phytoremediation approach for heavy metal contaminated soils with addition of three kinds of chelates (citric acid, EDDS and NTA) has been studied, but also the impacts of degradation of biodegradable chelates on soil nutrition and plant growth have been investigated. After 30 days growth of ryegrass, the chelates were introduced into soils. The first crop was collected at the 30th day, and the second crop and root of plants were collected at the 60th day. They were used for the laboratory analyses of the trace metals concentrations (like Cu, Zn, Cd, Pb, Ni) and some major elements (Ca, Al, Mg, Fe, N, P, K, etc.) in soil solution and plant tissue. The results showed that all the chelates application had positive effects on plant growth, while only the EDDS treatment decreased the biomass of roots. The EDDS also had the best efficiency in promoting the phytoextraction of Cu by ryegrass. The concentrations of Cu in the first, the second shoot and root of ryegrass reached about 135 mg kg⁻¹, 31.4 mg l⁻¹ and 239 mg kg⁻¹ respectively, which could be 5, 1.5 and 1.8 times higher than those of the control group. And the concentrations of Cu, Pb, Zn and Ni of the roots of the plants were higher than those in the shoots no matter with or without chelates, which indicated that the roots accumulated most of the metals. Nitrogen contents of ryegrass after the EDDS treatment were the highest among all the treatments due to the release of the nitrogen during the degradation of EDDS. The nitrogen contents in the first crop, the second crop and root were respectively 1.70, 1.30 and 1.44 times higher than those in control groups. Among the three kinds of chelates, EDDS have the strongest ability for complexing metals and releasing nitrogen during its degradation.

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