| Arsenic(As) in paddy fields accumulates in rice tissues and move into human body through food chain so that the health of human beings is threatened. Understanding and evaluting the ecological effect of As pollution can be an effective way to control and predict its ecological risk. This research evaluates the ecological effect of As contamination soil and preliminarily studys the remediation of As in soil. The present research involves several aspects as follows:At present, the total As concentration was used as a indictor to evaluate the contamination sites, but the indicator could not good reflect their health risks. Here, rice roots, which could be easily and rapidly measured by using field portable X-ray fluorescence spectrometry(FP-XRF), were applied as an alternative indicator for evaluating the As pollution in paddy soil. The results showed that rice roots were superior to rhizosphere soils in generating FP-XRF signals, especially for the sites with As lower than the soil detection limits of FP-XRF(< 30.0 mg kg-1). Moreover, the linear relationship of As concentration in rice roots with corresponding leaves and grains provides better prediction of As in rice leaves and grains than soil As. The present work proposes that wetland plant roots with iron plaque could be considered as an efficient bio-indicator for FP-XRF to rapidly evaluate soil As contamination.As the heavy metal were co-excited with arsenic, there are heavy metal pollution in As contaminated sites. Heavy metal in paddy fields also can accumulate in rice grains and pose health risk for residents. The ecological effect of the combine exposion of As and heavy metals will be much more complicate, especially in the As polluted sites. The effect of As contamination on the transfer characterristics of other heavy metals was investigated. Results showed that As in paddy soil could stimulate the accumlation of light rare earth elements(LREEs) in rice grains. The sites with a high LREEs rice-soil transfer factor were found with a higher As concentration. While the tranfer and accumulation character of heavy rare earth elements in paddy soil is not effected by As pollution in soil., as well as the lead in the paddy soil. The reason may be the sampling sites are extensive and the mobility and bioavailability characteristics of REEs and lead in rice-soil system are closely related to the genotypes of rice as well as to other physicochemical soil properties. Results also suggests that REEs also can accumulated in the iron plaque on the surface of rice roots and the accumulation was not as strong as aresnic.Contaminated soil remediation can be an effictive way to avoid its ecological effect. As a hot research field for As pollution sites, bioremediation also brings some problems. Many microorganisms capable of As methylation could transfer the inorganic As into organic As which was much more mobilisation. Volatile As can move into atmophere and result in more extensive ecological threaten. Regulating the volatile As may be a key factor for the application of bioremediation. In this study, the biovolatiliation of As in paddy soil was regulated by introducing an bio-electrochemical system. It is found that As volatilization in experimental groups decreased 0.76 mg m-2 compared with the controls. Arsenic in pore water of paddy soil was also decresed 62.1 μg kg-1. Soil amended with biochar can release much more As in pore watre. When introducing an bio-electrochemical system, the As volatilization in experimental groups decreased 1.81 mg m-2. The bio-electrochemical system in paddy soil changes the soil enviroment conditions and thereby reduce the bio-availability of As. The results showed that the measure of introducing the bio-electrochemical system into paddy soil can be an effective way for controling As pollution ecological effect in paddy soil.The results of this research provide therotical basis for soil As remediation engineering and could be served as reference of the evaluation of soil As contamination. |
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