鉛同位素特徵在土壤與水稻鑑識上的應用

Abstract

鉛同位素特徵指紋鑑識為環境法醫學之分析利器，於臺灣環境研究之應用尚屬起步階段。借助鍶離子交換樹酯分離術與多頻感應耦合電漿質譜儀，本研究建立適用於環境介質與相關樣本之高解析鉛同位素特徵指紋鑑識技術，除昔日國際文獻常見之鉛206、207、208同位素比值外，更提供了具備更優異的實質解釋力之鉛204同位素測量比值，並將之實際應用於臺灣環境系統調查，同時彙整文獻報告，以建立臺灣土本鉛同位素特徵資料庫。本論文所發現之土壤作物系統間的同位素變異現象為首次提出，呈現於盆栽試驗及現地試驗之中。在水稻各生育階段，經作物攝取之化學元素鉛於植株內轉置時，伴隨有鉛同位素比值變異，但生育於嚴重人為污染農地之水稻，其植株各部位則一致地呈現出污染質鉛同位素特徵，同位素變異作用較不明顯。綜整4縣市場址調查案例，得知臺灣農田土壤鉛同位素特徵背景比值為~2.472（208Pb/207Pb）、~1.170（206Pb/207Pb）、~18.47（206Pb/204Pb）、~15.66（207Pb/207Pb）以及~38.7（208Pb/204Pb），且受人為污染者與自然背景呈顯著差異，其鉛同位素特徵比（208Pb/207Pb與206Pb/207Pb）的數值隨污染程度而降低。鉛同位素技術於環境研究上可應用於污染源鑑識，但相較傳統之檢測分析，其檢測技術培訓與設置之初始與維護成本仍極昂貴。

Lead (Pb) isotopic fingerprinting is a robust means in environmental forensic and new to Taiwan. In this study, the analytical procedure of high-precision Pb isotopic characterization in environmental materials through chromatographic separation with Sr-Spec resin and MC-ICP-MS was developed and applied to agro-environmental system in Taiwan. Besides, other reported values from literatures were also collected for built-up the database of Taiwan’s Pb isotopic ratios. The phenomenon of isotopic anomaly in soil-rice system was first found and raised. The above isotopic variation occurred within rice plants during uptake and translocation in each growing periods for both pot and field experiments. Whereas, crops grown in Pb-tainted farms exhibit Pb isotopic characteristics of the pollutant. That anomaly was interrupted at the paddy fields suffering from seriously anthropogenic heavy metal contamination. Observation from varios study sites around Taiwan suggest that the Pb isotopic ratios of Taiwan’s non-polluted soils are ~2.472 for 208Pb/207Pb, ~1.170 for 206Pb/207Pb, ~18.47 for 206Pb/204Pb, ~15.66 for 207Pb/207Pb and ~38.7 for 208Pb/204Pb; while those values of soils collected at anthropogenic contaminated sites show distinctive lower in 208Pb/207Pb and 206Pb/207Pb ratios. Lead isotopic characterization helps precise evaluation and identification of contamination sources, then, the liability of the contaminated site could be revealed, but is expensive for set-up and maintaining costs of the novel instrument and the high technology training.