| 摘要: | 台灣的地下水使用為水資源之三成，許多地區仍以地下水為飲用水源，而砷為地下水中常見的有害成份，瞭解台灣地下水中的砷濃度及其控因，實為一重要的工作。研究指出，地下水中砷濃度與氧化還原有極大之相關性，然而、台灣地下水的基本地化參數及氧化還原程度的數據仍相當缺乏。本研究之目的，藉由地下水觀測網610 口觀測井的水質採樣與分析，調查各區地下水之砷濃度、氧化還原程度，並探討此兩變項之關係。本研究以氧化還原離子對作為地下水之氧化還原指標。結果顯示，台灣九個地下水區中，以台中地區的地下水含溶氧比例最高，偏向氧化環境；而桃園、新苗、及台北已進入鐵錳還原環境；彰雲、嘉南、高雄、屏東、及蘭陽的部份地下水，可達甲烷生成環境，其中又以嘉南地區的還原程度最高。 地下水之砷濃度超過環保署飲用水源水質標準 0.05 mg/L 的井數，其多寡排列為：嘉南60%、高雄30%、彰雲20%、蘭陽18%及屏東8%；其餘之新苗、台北、桃園及台中皆低於此標準。超過環保署飲用水質標準0.01 mg/L 的井數，高雄85%、
嘉南82%、蘭陽55%、屏東40%、彰雲33%、新苗28%、台北24%、桃園23%及台中6%。本研究結果顯示，地下水區的氧化還原程度越高(碳酸氫根濃度大於400 mg/L或含有飽和甲烷氣)、其砷與鐵的濃度也都高，例如嘉南地區。因為地層深埋後，漸漸轉變為還原環境，鐵錳氧化物被還原後，其吸附的砷也被釋出，因此地下水中之砷濃度也增加。
Groundwater water makes up about 30 percent of total water supply in Taiwan and a lot population depends on groundwater for its drinking water supply. It is important to investigate arsenic concentration in groundwaters of Taiwan, which is a commonly occurring toxic substance in groundwater. Previous studies show that arsenic mobilization could be controlled by redox condition in aquifer. However, only few studies focus on the redox condition and arsenic concentration in groundwater of Taiwan. In this study, we take water samples from 610 monitoring wells of the Groundwater Monitoring Well Network in nine groundwater basins. The concentrations of arsenic and some redox couples in sampled groundwaters are determined for finding the correlation between the two variables. We use concentrations of redox couples as the index of redox condition in aquifers. The values and concentrations of pH, Eh, dissolved oxygen, nitrate, sulfate, iron, methane, sulfide, bicarbonate and ammonium in groundwaters were determined. More than 60% of wells in the T6 basin with a concentration of arsenic exceed 0.05 mg/L. The groundwaters in T6 basin also have the highest average arsenic concentration. The exceeding percent (>0.05 mg/L) of wells for T7, T5, T9 and T8 basins are 30%, 20%, 18% and 8%, respectively. All of arsenic concentrations in groundwaters of T1 to T4 basins are lower than 0.05 mg/L, but some samples are higher than 0.01 mg/L. The exceeding percent of samples for arsenic 0.01 mg/L in T3, T1, T2 and T4 basins are 28%, 24%, 23% and 6%, respectively. Our results suggest that the concentrations of arsenic as well as iron in groundwaters of Taiwan were elevated by the iron-reducing process in aquifers. Samples, especially those with higher concentration of bicarbonate (> 400 mg/L) and oversaturated methane, mostly in the T6 basin, show a trend of higher arsenic concentrations. |
