釩在臺灣不同類型土壤的分佈與有效性評估

Abstract

2001到2017年間，全球工業中釩的需求量增加超過一倍，如此迅速成長的釩需求也成為環境品質以及人類健康的潛在威脅。然而，關於釩的地質化學方面的知識仍十分薄弱。因此，本研究欲利用17個採集自臺灣不同母質 (板岩、砂頁岩互層、安山岩、玄武岩以及蛇紋岩) 之土壤剖面進行釩全面性的探討，包含其來源、潛在移動性、剖面中的分佈以及生物有效性。結果顯示，由ICP-AES測定氫氟酸消化後之供試土樣中總釩濃度為35.4-475 mg/kg其平均值為182 mg/kg，其中，玄武岩母質的土樣中總釩濃度遠高於其餘土樣。此外，風化程度並未對總釩濃度有顯著影響。攜帶式X射線螢光光譜儀之測定結果顯示其在土樣中釩的快速檢測具有高度實用性。BCR序列萃取結果指出，供試土樣中的釩主要固定於礦物晶格中，然而鐵錳氧化物結合態的釩也佔有可觀的比例。利用DCB萃取法以及電子探針顯微分析儀，本研究更進一步證實釩在母質以及風化後的土壤中皆具有高度親鐵性。釩的X射線吸收近邊緣結構圖譜顯示在供試土樣中釩的主要化學物種V(IV) (VO2+) 和V(V) (H2VO4-)，此兩者皆可有效地被NaHCO3所萃取。以小白菜 (Brassica rapa var. chinensis) 進行之盆栽試驗顯示NaHCO3土壤釩萃取量和植物地上部之釩吸收量呈顯著正相關，此結果同時證明，釩潛在的生物有效性可由包含土壤總釩濃度以及土壤酸鹼值之多變因回歸等式計算而出。

The global vanadium (V) demand in industry increased over 100% from 2001 to 2017, thus the burgeoning V demand leads to potential risks to environment quality and human health. However, there is still a knowledge gap in pedogeochemical aspect of V. This study attempted to explore the sources, fractionation, profile distribution, and bioavailability of V from 17 soil pedons with 94 horizon samples in Taiwan. These pedons were derived from different parent materials including slate, sandstone interstratified with shale, andesite, basalt, and serpentine. The total V content was measured by using ICP-AES followed with HF-digestion and portable x-ray fluorescence (pXRF). The total V content by ICP-AES in the soils ranged from 35.4 to 475 mg/kg with an average level of 182 mg/kg. Moreover, the total V content in the basalt-derived soils was much higher than those of other parent materials. Nevertheless, the weathering degree of soil did not clearly affect the V level among soils. Furthermore, the pXRF showed high practicality in rapid V determination. The Commission of the European Communities Bureau of Reference (BCR) selective sequential extraction (SSE) method indicated V was primarily fixed in the mineral lattices. However, the Fe/Mn-oxide-bound fraction was remarkably observed. The siderophilic affinity of V in parent materials and derived soils was further confirmed by the dithionite-citrate-bicarbonate (DCB)-extractable Fe and element mapping conducted with electron probe X-ray microanalyzer (EPMA). V(IV) (VO2+) and V(V) (H2VO4-) were the dominant species of V in the soils demonstrated by the V K-edge X-ray absorption near edge structure (XANES) spectra, while both can be efficiently extracted by NaHCO3 extraction to predict a better bioavailability of V than CaCl2, HCl, and EDTA. The plant assay conducted with Chinese cabbage (Brassica rapa var. chinensis) revealed the soil NaHCO3 extractable V positively and significantly correlated with the plant shoot uptake of V, supporting the potentially bioavailable V can be computed by using multivariate regression equation considering the soil total V and pH.