| Summary: | 碩士 === 國立臺灣大學 === 農業化學研究所 === 97 === The distribution of As species in soils is influenced by redox potential, pH, and microbial activity. Arsenite is more toxic and mobile than arsenate. Therefore, to understand the As species distribution is very important to evaluate the mobility and phytotoxicity in As-contaminated soils. In this study, the As speciation in soil solutions of flooded As-contaminated soils were determined and the relationship between the As speciation and toxicity to rice plants was investigated.
Three Guandu soils containing different levels of As and three soils spiked with various levels of As(V) were used in this study to determine the As speciation of soil solutions under flooded incubation condition for 42 days. The soil solutions were taken and preserved in 0.01 M H3PO4 immediately and then the concentrations of As(Ⅲ), DMA, MMA and As(V) were determined using HPLC/ICP/MS. The results showed that in all studied soils As(Ⅲ) concentrations increased with flooding time and the extent of increase was higher in Guandu soils than that in other studied soils. In addition, the change of As concentration had the same pattern with that of Fe. It may result from that As release in soil solution due to Fe reduction or As precipitation with Fe. Moreover, total As concentration in soil solutions also increased with flooding time and the extent of increase was higher in Guandu soils than three As(V)-spiked soils. It may be due to that spiked-As(V) was adsorbed by soil solids during the flooding incubation period. Among the studied soils, As(Ⅲ) percentages of total As in solutions of acid soils were higher that As(V). On the contrary, As(V) percentages of total As in solutions in alkaline soils were higher that As(Ⅲ). For the relationship between As species concentration in soil solutions with rice seedling growth, As(Ⅲ) concentration before flooding was significantly and better correlated with plant height of rice seedlings than other As species. The effective toxicity concentrations of decreasing 20% of rice plant height were 0.02 mg As(Ⅲ) L-1. The results also showed that there was a significant relationship between the plant height of rice seedlings and soil arsenic extracted by NaH2PO4, and the effective toxicity concentrations of decreasing 20% of rice plant height were 78.7 mg As(Ⅲ) kg-1. Therefore, soil solutions As(Ⅲ) and NaH2PO4 extracted As could be used for the assessment of availability and phytotoxicity of arsenic in soils.
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