Environmental Factors Affecting the Mobility and Species Distribution of Arsenic in Rivers: A Case Study of Wuxi River

• Main Authors: Yun-Chia Hsu, 許允嘉
• Other Authors: 劉雨庭
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/cgi-bin/gs32/gsweb.cgi/login?o=dnclcdr&s=id=%22107NCHU5020008%22.&searchmode=basic

碩士 === 國立中興大學 === 土壤環境科學系所 === 107 === Arsenic (As) is carcinogenic to organisms, As pollution in soil and river has been a global problem recently. Studies have shown that under anaerobic conditions, the iron (hydrogen) oxidized minerals that adsorb or co-precipitate As in the soil will be reduced and dissolved, which will release arsenic into the liquid phase and cause harm to the ecology. Therefore, if the influence of environmental factors on the concentration, solubility and species transformation of As can be understood, it will help analyze and manage the movement and distribution of arsenic in river. This study focusing on Wuxi River in the Taichung area has two parts. The first part was the distribution of environmental factors in the Wuxi River Basin for the analysis and sampling of As, combined with principal components analysis (PCA), Pearson product-moment correlation coefficient (Pearson''s) analysis, and X-ray absorption spectroscopy (XAS) technique species identification showed that the accumulation of As in river sediment was mainly affected by amorphous Fe(III) hydroxide in sediment. As and Fe was highly positively correlated with the concentration distribution in the river, and the accumulation of arsenic in the sediment (W1-6) was higher than F1-6 as the riverbed is wide and the water flow is gentle downstream and the dry season with less water flow. At the sampling point S5, the distribution of the Taichung Science Park discharge port, and the downstream W5 analysis found that the As concentration in the sediment was higher than the lower quality index (11 mg kg-1). Additionally, the concentration of soluble As in the W1-6 water was also higher than F1-6. The results showed that although the iron (hydrogen) oxidized mineral in the sediment can fix As in the sediment, it accumulated in an unstable adsorption state and was easily released due to environmental changes. The second part was the incubation experiment which the dissolution of As was investigated by adjusting the environmental factors such as pH and carbon source concentration. The first incubation experiment is to adjust the pH (5.5, 7.5, 9.5) and the carbon source concentration (0 mM, 3 mM, 6 mM) as factors in order to observe the change of the dissolution concentration of Fe and As during the incubation period. The results showed that the higher carbon source was added under the acidic condition of pH 5.5 for the reduction of soil microorganisms, the higher the concentration of As and Fe dissolved in the sediment. Therefore, if the waste water discharged from the surrounding factories, it will influence the environmental balance and the amount of arsenic released to the river will increase. The second incubation experiment was to investigate the effect of different molar ratios of sulfate and amorphous iron in the environment (SO42-/Fe=0, 0.3, 1, 3) on the dissolution of As. Previous study showed that under higher concentration of sulfate, the iron-sulfur compound formed can reduce the release of arsenic into the liquid phase. However, the results of this study showed that under the incubation environment of SO42-/Fe=3, there was indeed a significant inhibition of As dissolution compared to the lower concentration of sulfate addition. However, there was no significant inhibitory effects on the control group. The results of SEP and XAS showed that after adding sulfate to the incubation experiment, Fe(III) minerals were reduced and recombined under anaerobic conditions and further indirectly caused an increase in arsenite species and increased the potential risk of As poisoning. This research aimd to understand the influence of environmental factors on the distribution and mobility of As in rivers in order to be used as a cornerstone for As remediation in rivers.