溫泉地區砷汙染之地質化學程序及對水田與水稻之影響－台灣關渡平原為例

Geochemical Process of Arsenic-tained Site by Geothermal and Its Impact on Paddy Soils and Rice – A Case Study of Guandu Plain, Taiwan

林聖淇(Sheng-Chi Lin)

指導教授 ： 張尊國

國立臺灣大學/生物資源暨農學院/生物環境系統工程學研究所/博士(2014年)

https://doi.org/10.6342/NTU.2014.02466

摘要

西元2006年，研究調查發現北投關渡平原水田土壤有超過100公頃的農地，因引用含砷溫泉水灌溉長達百餘年而導致土壤遭受嚴重砷汙染。本研究目的希冀透過調查從溫泉水源頭(地熱谷)到水田中(關渡平原)砷在環境中流佈的現況，其中包含分析土壤溶液砷的物種來評估水稻在遭受砷汙染土壤的危害情形，同時並利用逐級萃取方法比較關渡平原土壤與磺港溪底泥砷的形態分布，藉以瞭解砷在該研究區域存在性態及對於環境所造成的危害潛勢。根據地熱谷中陰、陽離子組成的資料顯示，酸性溫泉水中的砷與鉛等重金屬會在河道中形成硫酸鹽的結晶顆粒。進一步研究發現在關渡平原土壤中的X光繞射分析結果顯示在黏土顆粒中有砷鉛鐵礬結晶存在。水稻植體與所對應根部土壤之砷濃度係利用原子吸收光譜儀(AAS)外掛自動化連續流動式氫化物產生裝置(HFS-3)分析；水稻根部土壤溶液砷種類檢測則是使用感應耦合電漿質譜儀(ICP-MS)外掛高效率液相層析儀(HPLC)。水稻植體砷含量多寡受灌溉水、土壤砷濃度與形式影響，然而水稻根部吸收土壤中砷的機轉尚無一致定論。研究結果得知水稻植體根部、莖葉與稻穀的含砷量平均值分別為98.7、3.49 與0.074 mg kg-1，顯示砷含量會隨著稻根-莖葉-稻穀而呈現遞減的現象；土壤總砷濃度平均值為135 mg kg-1 (67 mg kg-1至438 mg kg-1)；土壤溶液抽出液砷濃度(AsIII 與AsV)的平均值為30.1 μg L-1 (1.5 μg L-1至100.5 μg L-1)。水田在浸水條件下，砷在土壤溶液係以亞砷酸鹽(AsIII)的形式存在為主，平均約佔89%。土壤砷濃度與水稻根部砷含量成正比的線性相關；而莖葉和稻穀砷含量與土壤砷濃度則無顯著地的線性相關；土壤溶液的總砷濃度(AsIII 與AsV)值與水稻植體砷含量的關係也與上述現象一致。依據本研究逐級萃取結果分析得知水田土壤中的砷係以殘餘態(32-53 %)與無定形及弱結晶鐵鋁氧化物型態(33-53 %)所佔比率較高；底泥的砷型態分布大部分集中在無定形及弱結晶鐵鋁氧化物型態(32-38 %)、強結晶鐵鋁氧化物型態(12-37 %)與特定吸附型態(18-29 %)等三種。比較上述兩者的砷型態分布明顯得知，不管是考量砷濃度值或是逐級萃取中非特定吸附型態所佔百分比值，研究數據都顯示底泥中砷的移動性遠比水田土壤還高出許多。鑑於磺港溪上游的地熱谷至今都還持續地湧出大量含砷的溫泉水釋放於環境中，建議相關單位應持續且積極投入更多資源研究關渡平原地區砷的流佈以及對環境的影響，確保當地人民居住的安全與健康。

關鍵字

砷物種 ； 砷鉛鐵礬 ； 水稻田 ； 地熱溫泉 ； 逐級萃取

並列摘要

A study conducted in 2006 showed that over 100 hectares of rice paddies in Beitou, Taiwan, irrigated over the hundred years using water mixed with hot spring, was heavily polluted by arsenic. The objective of the present study was carried out to examine the intensively circulation of arsenic in the aqua system from geothermal (Thermal Valley) to paddy fields (Guandu Plain) and estimate the influence of arsenic-tained paddy soils on rice via analyzing arsenic-adsorbed forms in soil and arsenic species in soil solution. Meanwhile, the comparative analysis of arsenic fractionations by using sequential extraction procedure (SEP) between paddy soils in Guandu Plain and sediments in Huang Guang Creek (HGC) was executed in order to understand the existing arsenic behaviors and the potential hazards of arsenic in the surroundings. According to the analyzed datum of ion and anion in the Thermal Valley, supersaturated solution of lead (Pb2+) and arsenopyrite (H2AsO4-) leads to the process of beudantite precipitation via sulfide oxdation model. Furthermore, the XRD analysis of Guandu paddy soils indicated the beudantite particles are present in clay fractions. Soil samples and rice tissues were collected and analyzed separately, using Atomic Absorption Spectrophotometer (AAS) with automatic hydride generator (HFS-3); meanwhile, the SEPs of As-tainded paddy soils and sediments were also carried out and the arsenic speciation of soil solution in the rhizosphere was determined by the Inductively-Coupled Plasma Mass Spectrometer (ICP-MS) with high-pressure liquid chromatography system (HPLC). Arsenic contents of rice tissues depend on irrigation methods, quantity and speciation of arsenic in soils etc., however, the transformation mechanisms of arsenic from soils to rice don’t have the final conclusion until now. The studied results were showed that the mean arsenic contents in grains, straws and root were separately measured at 0.13 mg kg-1, 3.49 mg kg-1 and 98.7 mg kg-1, also indicated that rice tissues of arsenic has the decreasing trend following root-straw-grain. At the same time, the mean total arsenic concentration were estimated at 135 mg kg-1 (from 67 mg kg-1 to 438 mg kg-1) in paddy soils and 30.1 μg L-1 (from 1.5 μg L-1 to100.5 μg L-1) in paddy soil solution, respectively. The results of paddy soil solution indicated that the arsenite (AsIII) predominates (about 89%) under anaerobic conditions. Regression of soil arsenic levels with rice grains and straws were less significant compared to that with rice roots and so did soil solution arsenic content, including AsIII and AsV. Arsenic level in root strongly depended on arsenic concentration of soil suggesting that the high arsenic concentration may have the potential for translocation from root to grain which ultimately effects on the human health. The sequential extraction experiments resulted in the high portions of As remaining in the amorphous and poorly-crystalline hydrous oxides of Fe and Al (33-53 %), and residual (32-53 %) for paddy soils; mostly in the the amorphous and poorly-crystalline hydrous oxides of Fe and Al (32-38 %), well-crystalline hydrous oxides of Fe and Al (12-37 %), and specifically sorbed (18-29 %) for sediments. Comparing the distributions of arsenic fractionation between paddy soils and sediments, it was apparent that the percentages of amorphous or poorly crystalline Al and Fe hydrous oxides extracted and residual from paddy soils were greater than those removed from sediments, but the mobile of arsenic from the sediments in HGC was greater than from paddy soils in Guandu Plain, no matter what investigating total arsenic content or analyzing arsenic fractionation using SEP. The study suggests that more resources should be founded for the circulation of arsenic in Guandu Plain and its impact in the surroundings to make sure the safety and health of the local residents due to the going process of geochemical procedures that a large amount of arsenic is Continuously separated to surroundings from Thermal Valley in Beitou until now.

並列關鍵字

Arsenic speciation ； Beudantite ； rice field ； geothermal spring ； sequential extraction procedure

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