Summary: | 碩士 === 國立臺灣大學 === 農業化學研究所 === 107 === Inorganic arsenic (As) is a highly toxic and carcinogenic metalloid which widely distributed in the environment. There is a fact that the serious health risk to human through the intake of rice grain grown in As-contaminated paddy soil, due to the high mobility and bioavailability of As in flooding conditions. In this study, we attempted to use oxygen releasing compound (ORC, calcium peroxide) to supply the oxygen in flooded soil, and further avoid iron (Fe) oxides reductive dissolution, arsenate reduction and dissolution. Therefore, the objectives of this study were to investigate the effects of ORC application and its application timing on As accumulation in rice grains. Two geogenic As-elevated soils including Gd [high organic carbon (OC) and iron (Fe) oxides contents] and Ms (relatively low OC and Fe oxides contents) were collected, and both soils have two distinct levels of As expressed as H (high) and L (low). Two ORC application timing [booting stage (B) and the two weeks after flowering stage (F)] were adopted in this study, and the dosage of ORC applications is 60g/kg soil. The results showed that the concentrations of As and Fe in pore water were obviously lessened after ORC application inferring that ORC might alleviate iron (oxy)hydroxide reductive dissolution through keeping soil environment oxygenated. The above phenomenon could be validated by observation of no significantly more iron plaque formation in ORC application treatments. In addition, results revealed that some ORC treatments contributed to increment of As concentration in pore water which might due to desorption of As in high pH range.
The results unveiled that the concentrations in brown rice of ORC applications at booting stage and the two weeks after flowering stage were significantly lower than control treatments in Gd-H and Gd-L soils. However, it was found that there were no significant differences in As concentration in brown rice between ORC and control treatments in Ms soils, predicting it mainly caused by the low contents of clay fraction, iron (oxy)hydroxides and organic matter in these soils leading to fewer chances of the oxidized-As being adsorbed by de novo soil iron (oxy)hydroxides. Therefore, it is crucial that there is not any soil types suitable for As remediation by ORC application. It must be considered thoroughly before applying ORC as soil As contamination renovation strategy especially for low contents of clay fraction, iron (oxy)hydroxides and organic matter soils.
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