鉛同位素示蹤法鑑識關渡農地砷、鉛濃度異常之成因

Abstract

關渡農地含砷量超過土壤管制標準值（60 mg kg-1）之土壤面積達 128公頃，此乃導因於早期農民引用地熱谷含砷的水源作為灌溉農地之用所致。在天然環境和人為汙染的物質其鉛同位素組成具有極大差異，因此可用鉛同位素鑑別環境中鉛的來源。本研究利用「多偵測器感應耦合電漿質譜儀」偵測鉛同位素比例變化（206Pb/207Pb和208Pb/207Pb）以鑑識不同鉛源的汙染。由群集分析結果指出，關渡農地位處磺港溪沖積範圍內，受大屯火山母岩影響甚深；農地含鉛量之異常則是長期引用地熱谷溫泉水所造成，此外，本區含鉛量異常處亦有人為汙染的情況。因此，鉛同位素比例變化可被視為有效鑑識關渡農地相異鉛源的方法，尤以辨別天然和人為鉛量最是顯著。

In Guandu Plain, 128 hectares of paddy soils with the high arsenic content, exceeding soil pollution control standards (over 60 mg kg-1), were determined due to the irrigation with the water mixed hot spring with arsenic in the early periods. The isotopic compositions of lead exhibits wide variations in natural and anthropogenic materials that often can be used as a diagnostic“signature.”Lead isotopic compositions, analyzed on multi-collector inductively coupled plasma mass spectroscopy was used to distinguish pollution sources. The results of cluster analysis clearly indicate that the paddy soils of Guandu Plain have been primarily influenced by the parent rock of Tatun Volcano Group because those were located within the basin of Huang Gang Creek and the soil of the polluted extremely polluted lead was from the long-term irrigated with the water mixed hot spring in the Thermal Valley. Furthermore, the anthropogenic pollution was also verified in the paddy soils with the exceptional lead content. The results suggest that lead isotope ratios can be used effectively to constrain the sources of lead in Guandu Plain, especially for natural versus anthropogenic influence can be identified.