蛇紋岩土壤之鉻、鎳含量及其來源查證

Chromium and nickel contents and their verification of source in serpentinitic soils

許文明(Hsu Wen-Ming)

指導教授 ： 許正一

國立屏東科技大學/工學院/環境工程與科學系所/博士(2013年)

https://doi.org/10.6346/NPUST.2013.00103

摘要

蛇紋岩是超基性火成岩經熱水蝕變而成，其所含的鐵鎂質原岩結晶構造以島狀矽酸鹽為主，故較易風化崩解，且鎂含量高於鈣，而鉻、鎳等重金屬含量偏高，其風化後之土壤特徵是Ca/Mg比值偏低，且含有大量鉻、鎳等重金屬。此類因地質因素所造成重金屬含量偏高之土壤，雖非人為污染所致，但一樣會影響生態環境與人體健康。本論文採集日本關西地區6個土壤剖面及台灣東部9個土壤剖面，共計95個化育層土壤，進行元素全量分析與鉻、鎳之DTPA萃取，研究結果指出，日本樣體Ca/Mg 比值較台灣低，風化程度較低，而所有樣體中鉻、鎳及鈷全量明顯高於非蛇紋石土壤，並且部分樣體已超過台灣的鉻、鎳土壤污染管制標準。在型態劃分中，鉻、鎳、鈷主要被固定在礦物晶格內，故集中在殘餘態，而鎳間移動性大於鉻。至於重金屬的DTPA萃取方面，鎳含量高於鉻，與序列萃取之型態分佈趨勢相符，表示蛇紋岩土壤中的鉻應不易被植物所攝取。土壤DTPA萃取之有效性鉻和鎳濃度遠低於總量，但有效性鉻和鎳分別與可交換鈣/鎂比值顯著地呈負相關，表示交換性鎂隨土壤化逐漸流失後，鉻與鎳的有效性濃度將因為氧化鐵固定作用而降低，這種現象是人為污染土壤不會有的，是驗證此類土壤鉻、鎳來源的重要證據。

關鍵字

關鍵字：土壤污染、鉻、鎳、蛇紋岩土壤

並列摘要

Serpentinites were derived from ultramafic igneous rocks through hydrothermal alteration, which original rocks are island silicate framework and high in Fe and Mg. Serpentinites are weakly resistant in weathering and characterized with high Mg and low Ca and abundant levels of Cr and Ni.The serpentinitic soils are characterized low Ca/Mg ratios and large amounts of Cr and Ni. These heavy metals are not produced from human activities in serpentine soils, but may have adverse effects on eco-environment and human health. This study collected nine soil profiles from Japan and six soil profiles from eastern Taiwan which totally are 95 horizon soil samples. Total and DTPA extraction were performed for chromium and nickel measurement.
Experimental results indicates that the Japanese pedons were low weathered compared to Taiwanese ones due to the low Ca/Mg ratios in the Japanese soil samples. However, total contents of Cr and Ni in all soils were much higher than non-serpentine soils, and the metal levels in some of them were over the control standards of Taiwan. Regarding the metal fractionation, Cr and Ni were mainly from the mineral lattices, and thus were concentrated in the residual fractions. The mobility sequence followed as Ni > Cr. With respect to DTPA extractable amount, Ni was higher than Cr. The difference in the DTPA extraction between metals was corresponding to the results of lability evalauted by sequential extraction; however, Cr is hardly absorbed by plant. The soil DTPA extraction effectiveness of Cr and Ni concentrations were much lower than the total contents. However, the effectiveness of chromium and nickel and exchangeable Ca//Mg ratio was negatively correlated significantly. This means that the gradual loss of exchangeable Mg with soil weathering. The effectiveness of the Cr and Ni concentrations will be reduced because of the fixation by iron oxides. This phenomenon can not be discerned in artificially contaminated soils to support the verification of Cr and Ni sources for serpentinitic soils.

並列關鍵字

Soil contamination, chromium, nickel, serpentinitic soils

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