Using Sequential Extraction Procedure to Analyze the Arsenic Form in the Contaminated Paddy Soils at Guandu
Date Issued
2009
Date
2009
Author(s)
Shyu, Wei-Jhan
Abstract
About 128 hectares of paddy soil was heavily contaminated at Guandu and exceeded the national standard of 60 mg As kg-1, due to irrigated with arsenic-rich hot spring water in the past 20-250 years. The purpose of this study is to analyze the form and the concentrations of arsenic and other heavy metals, including lead, silicon, iron, manganese and aluminum, of the horizontal and vertical contaminated paddy soil samples by using the sequential extraction procedure(SEP). The SEP could obtain five chemical fractionations: the non-specifically sorbed, specifically-sorbed, amorphous and poorly-crystalline hydrous oxides of Fe and Al, well-crystallized hydrous oxides of Fe and Al, and residual phases. These results showed that the amorphous and poorly-crystalline hydrous oxides of Fe and Al and residual phases dominated the arsenic fractionations of paddy soils. Only 5% non-specifically sorbed and specifically-sorbed were in the top-soils. The mean arsenic concentrations in the non-specifically sorbed phase and the specifically sorbed phase were 0.19 mg kg-1 (0.03-0.41 mg kg-1) and 4.9 mg kg-1 (0.6-10 mg kg-1). Notably, the arsenic value in the deep soils (60-120 cm) was higher than that in the top-soils (0-30 cm). Top-soil arsenic concentration decreases due to long-term of paddy cultivation, such as the crop absorption, adsorption of rhizosphere and leaching. Arsenic the demonstration of this case study, performing a SEP can target all potential primary chemical forms of arsenic in the soil solid phase, provide useful information to explain the agricultural land and soil heavy metal contamination, and then propose countermeasures.
Subjects
Arsenic, Sequential extraction procedure
Chemical fractionation
Guandu Plain
Type
thesis
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