砷是具有高度毒性的物質，且對人類健康產生廣泛危害。許多研究顯示癌症及其相關疾病與飲用受砷汙染之地下水具有相當程度之關聯。地下水中砷的來源尚無明確結論，但可能與該區域地底下之含水層有關。本研究分析之沉積物為中央地質調查所位於嘉義縣布袋之鑽井岩芯，樣本顯示該區沉積物主要由不同比例之砂、粉砂與泥所構成，可由沉積物顏色明顯區別。沉積物所含砷濃度範圍由1 mg/L至1677 mg/L，且濃度變化與深度並無系統性相關，其中砷濃度最高之樣本（1677 mg/L）位於深度189.8 m處。所有分析樣本之砷濃度均低於15 mg/kg，除七個樣本之砷含量高於20 mg/kg，這些「高砷樣本」砷濃度較受到嚴重砷汙染地區孟加拉與West Bengal沉積物所含之砷濃度高（20－30 mg/kg; Nickson et al., 2000）。在這些「高砷樣本」中，鋁與鐵濃度呈現正相關。而X光繞射分析，結果顯示高砷樣本中主要礦物相包括石英、長石、伊來石與綠泥石。
利用沉降法將這七個「高砷樣本」分為大、中、小三種粒徑群，並以Keon et al.（2001）連續萃取法找出寄主礦物。一般而言，砷主要富集於具吸附能力的相中，例如非晶質鐵氫氧化物、酸揮發硫化物、氧化錳與碳酸鹽等。七個高砷樣本中有六個樣本所含之砷主要透過吸附作用而富集，然而深度為136.5 m之樣本則主要透過與非晶質鐵氫氧化物共沉澱而富集。因此這些高砷樣本所含砷之寄主礦物推測主要為黏土礦物與非晶質鐵氫氧化物。「高砷樣本」皆採自於厚度小於10 cm且上下沉積物砷濃度低的地層，因此這些「高砷樣本」可能代表地下水中砷富集之處而非地下水砷的來源。而砷濃度與板岩屑含量之間缺乏相關性則指出板岩屑並非沉積物砷之來源。

Arsenic is highly toxic and can lead to a wide range of health problems in humans. Numerous studies showed some extents of connection between cancer-related illnesses and intakes of arsenic-contaminated ground water. The source of arsenic in groundwater is not ascertained definitely, but it might be related to the aquifer below this area. In this study, sediment samples collected from the core drilled by Central Geological Survey, MOEA at Budai, Chiayi were analyzed. These samples show variable admixtures of sand, silt and clay, characterized by distinct colors. Arsenic concentrations vary in the ranges of 1-1677 mg/L without a systematic correlation between arsenic concentration and depth. The highest arsenic concentration (1677 mg/L) occurs at the depth of 189.8 m. All the samples have arsenic concentrations lower than 15 mg/kg, except for seven samples with arsenic contents over 20 mg/kg, higher than that in the severely arsenic-polluted Bangladesh and West Bengal sediments (20-30 mg/kg; Nickson et al., 2000). There is a positive correlation between Al and Fe concentrations in the high-arsenic samples. XRD analyses indicate that these high-arsenic samples are consisted of quartz, feldspar, illite and chlorite.
Seven samples with arsenic content greater than 20 mg/L were analyzed by the arsenic sequential extraction procedure of Keon et al. (2001) to identify the arsenic-host minerals. The sediment samples were separated into fine, middle, and coarse grains by the precipitation method. In general, arsenic contents mainly concentrate at absorbable phases, such as amorphous iron oxyhydroxide, acid volatile sulfide, Mn oxides and carbonates. The majority of arsenic in six of seven of high-arsenic samples was concentrated by adsorption, while that in sample 136.5m were co-precipitated with amorphous Fe oxyhydroxides. The hosts of arsenic in the high-arsenic samples are inferred to be clay minerals and/or amorphous iron-oxyhydroxides. These high-arsenic samples were all collected from thin layers of < 10 cm thickness with adjacent samples having low arsenic concentration. Therefore, it is more likely that these high-arsenic samples represent sinks rather than sources of arsenic in ground water. The absence of a correlation between the abundance of detrital slates and arsenic concentration indicates that slate is not the source of arsenic in these sediments.

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