以土柱試驗模擬砷在農業土壤之動態

台灣地下水含砷的現象來自於地層的還原環境，且含砷地下水長期被當作灌溉水源之一。宜蘭冬山河岸測站之地下水檢測出含砷量約為0.2 mg/L，且有87.8% 為三價砷，施用於農地會有累積或溶出之虞，因此本研究針對重金屬砷利用序列萃取方式，了解重金屬於土壤中之相態變化，並利用動態模式模擬含砷地下水施用於土壤之後的型態變化及移動，最後估計出最大的施用容許量。本研究所採樣地點之農地表土與附近背景土壤含砷量分別為 64.98 mg/Kg及17.37 mg/Kg，含砷量超過台灣食用作物農地的管制標準(砷為60ppm)，推測長期灌溉含砷地下水可能造成土壤砷的累積。根據土壤序列萃取結果，發現在農地土壤中，砷主要與無定型和結晶型鐵鋁鍵結，總共佔了約80%。實驗室土壤管柱淋洗試驗結果顯示，外添加的砷首先轉換成非特異性吸附與特異性吸附相態，且明顯地累積於表土2 公分以內，表土中的砷有約51% - 65%是與無定型和結晶型鐵鋁鍵結；亦會隨著灌溉水及入滲水的移動而離開土壤系統。比較旱地條件與水田條件下的土壤管柱試驗則可發現旱地條件下表土的砷累積更為明顯。

關鍵字

砷；土壤；地下水；重金屬型態；序列萃取；管柱試驗

並列摘要

Arsenic (As) in groundwater in Taiwan comes from the natural materials in the aquifers under reducing conditions. As-contaminated groundwater has long been one of the irrigation sources. Arsenic concentration of groundwater close to Dong Shan River is 0.2 mg/L, 87.8% of which is in the form of As(III). In this study, the fractionation of arsenic in soils from Dong Shan River basin was performed to shed light on the movement and transformation of arsenic species, and the allowable rate of application of As-contaminated groundwater was estimated. The arsenic level of the soils from the sampled farmland (LT) and background soil (BG) are 65.0 mg/Kg and 17.4 mg/Kg, respectively. It implies that arsenic accumulation in soil under long-term irrigation of As-contaminated groundwater. The result of sequential extraction showed that 80% of total arsenic in the soil from farmland is associated with amorphous (F3) or crystalline hydrous Fe/Al oxides (F4). There are dynamic changes of different fractions in laboratory-scale soil columns with time, and the accumulation of arsenic in topsoil within 2 cm is obvious. Arsenic added to soil through irrigation was firstly converted to non-specific bound fraction (F1) and specific bound fraction (F2), but the net change of amorphous Fe/Al hydrous oxides-bound As (F3) or crystalline Fe/Al hydrous oxides-bound As (F4) was little. Arsenic was also found being removed from soil by leaching.

並列關鍵字

Arsenic ； soil ； groundwater ； fractionation ； sequential extraction ； leaching

參考文獻

Aggett, J. and G. A. O’Brlen (1985). "Detailed model for the mobility of arsenic in lacustrine sediments based on measurements in Lake Ohakuri." Environ. Sci. Technol., 19: 231-238.

Aggett, J. and L. S. Roberts (1986). "Insight into the mechanism of accumulation of arsenate and phosphate in hydro lake sediments by measuring the rate of dissolution with ethylenediaminetetraacetic acid." Environ. Sci. Technol. , 20: 183-186.

Appelo, C. A. J., M. J. J. Van Der Weiden, C. Tournassat and L. Charlet (2002). "Surface complexation of ferrous iron and carbonate on ferrihydrite and the mobilization of arsenic." Environ. Sci. Technol., 36: 3096-3103.

Bauer, M. and C. Blodau (2006). "Mobilization of arsenic by dissolved organic matter from iron oxides, soils and sediments." Sci Total Environ, 354(2-3): 179-190.

Bennett, B. and M. J. Dudas (2003) "Release of arsenic and molybdenum by reductive dissolution of iron oxides in a soil with enriched levels of native arsenic." Journal of Environmental Engineering and Science 2, 265-272.

國際替代計量

以土柱試驗模擬砷在農業土壤之動態

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