富砷土壤作物砷含量及降低地下水砷方法之研究

環保署調查顯示，目前國內農地砷污染主要成因大多數都是因長期引用富砷的地下水進行灌溉所致。污染範圍主要分布在蘭陽平原、濁水溪沖積扇、嘉南平原及屏東平原四個區域，涵蓋面積相當的廣。面對這麼多因地質因素所造成的富砷農地，若要整治，所需費用相當龐大。若屬地質因素不進行改善，對於富砷土壤種植食用蔬菜之安全性，有待評估。生物炭具有改變土壤特性及碳封存的功用，為目前在農業與環保方面相當積極推廣的農藝資材。本研究以農業廢棄物稻殼製備生物炭，依重量比0%、5%、10%、15%的方式施用生物炭，探討施用生物炭對蔬菜作物吸收砷濃度之影響。另外降低灌溉水砷濃度，才能減緩農地土壤砷濃度累積速度。本研究選擇十二種資材進行富砷水溶液吸附試驗，探討不同資材對於砷的吸附能力，藉此開發降低灌溉水砷的處理技術。研究結果顯示，除了水耕水蕹菜外，其它五種試驗蔬菜作物施用生物炭皆可提升產量，且五種蔬菜作物可食用部位砷含量均低於衛福部公告之白米無機砷食用限量標準0.2 mg/kg，顯示富砷農地土壤種植蔬菜作物，可食用部位對砷之累積濃度不高。水蕹菜砷含量遠高於其它五種蔬菜植物，建議富砷農地盡量不要種植水生食用作物。施用生物炭有提升作物根部及地上部砷濃度的趨勢，若以植生復育改善砷污染土壤，施用生物炭具有加速砷移除速率的潛力。台灣製造之超深燒陶粒，不論是塊狀或粉狀時，對砷具有非常高的吸附能力，對於0.25~1.0 ppm的砷水溶液，砷去除效率皆可達99%以上。本研究自行製備之氯化鈣改質生物炭，對砷之去除能力也可達60%以上，未來可再繼續探討其做為灌溉水移除砷技術之可行性。

關鍵字

地下水；重金屬砷；生物炭

並列摘要

According to the EPA survey, most of the main causes of arsenic pollution in agricultural land in China are caused by long-term arsenic-based groundwater irrigation. The pollution range is mainly distributed in the Lanyang Plain, the Zhuoshuixi Alluvial Fan, the Jianan Plain and the Pingtung Plain, covering a wide area. In the face of so many arsenic-rich agricultural land caused by geological factors, the cost of rectification is quite large. If the geological factors are not improved, the safety of planting edible vegetables in arsenic-rich soils needs to be evaluated. Biochar has the function of changing soil properties and carbon sequestration, and is agronomic material that is currently actively promoted in agriculture and environmental protection. In this study, biochar was prepared from agricultural waste rice husks, and biochar was applied at a weight ratio of 0%, 5%, 10%, and 15% to investigate the effect of biochar application on the absorption of arsenic in vegetable crops. In addition, reducing the arsenic concentration of irrigation water can slow down the accumulation rate of arsenic concentration in agricultural land. In this study, twelve kinds of materials were selected for the adsorption test of arsenic-rich aqueous solution, and the adsorption capacity of different materials for arsenic was explored, thereby developing a treatment technology for reducing arsenic in irrigation water. The results showed that in addition to hydroponic water, the application of biochar in the other five experimental vegetable crops could increase the yield, and the arsenic content of the edible parts of the five vegetable crops was lower than the white rice inorganic arsenic consumption limit published by the Ministry of Health and Welfare. Mg/kg, showing that arsenic-rich agricultural soils are planted with vegetable crops, and the cumulative concentration of arsenic in edible parts is not high. The arsenic content of water amaranth is much higher than that of the other five vegetable plants. It is recommended that arsenic-rich agricultural land should not plant aquatic food crops as much as possible. The application of biochar has a tendency to increase the arsenic concentration in the roots and shoots of crops. If phyto-contaminated soil is improved by phytoremediation, the application of biochar has the potential to accelerate the rate of arsenic removal. The ultra-deep-burning ceramsite made in Taiwan has a very high adsorption capacity for arsenic in both bulk and powder form. For 0.25-1.0 ppm arsenic aqueous solution, the arsenic removal efficiency can reach more than 99%. The self-prepared calcium chloride modified biochar can also remove more than 60% of arsenic. In the future, it can continue to explore its feasibility as an arsenic removal technology for irrigation water.