以不同低分子量有機酸組合萃取土壤重金屬之生物有效性濃度

Bioavailability of heavy metals in soils extracted by assembling different low molecular weight organic acids

蕭凱勛(Kai-Hsun Hsiao)

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(2009年)

https://doi.org/10.6346/NPUST.2009.00079

摘要

土壤重金屬的全量並不能全然為植物所吸收，而目前常用以評估重金屬生物有效性的各種測定方法，均有其適用範圍及限制條件，故無一適用各種土壤之理想化學萃取方法。因此，本論文以縮蘋果酸、琥珀酸、檸檬酸、蟻酸及醋酸等小白菜根圈較常分泌之5種低分子量有機酸（low molecular weight organic acids, LMWOAs）萃取台灣22種代表性土壤中的重金屬（Cd、Cr、Cu、Ni、Pb、Zn、Fe及Mn），並考量這些LMWOAs之種類與特性，以主成份分析方法調整最適比例之組合酸，其莫耳比為縮蘋果酸：琥珀酸：檸檬酸：蟻酸：醋酸＝3：3：2：1：1，以小白菜盆栽根圈新鮮根圈土壤萃取重金屬，與0.1 M NaNO3、0.01 M CaCl2、0.05 M EDTA（pH = 7.0）、0.005 M DTPA（pH = 7.3）、0.1 N HCl及去離子水等6種常見之傳統單一化學試劑萃取做比較。結果發現，5種LMWOAs中以縮蘋果酸、琥珀酸及檸檬酸所能萃取Cd、Cu及Ni之濃度較高，而蟻酸及醋酸則較低。除重金屬本身特性外，影響LMWOAs萃取之能力與其COOH官能基多寡有關。整體而言，LMWOAs萃取土壤重金屬能力大小，由高而低依序為縮蘋果酸＞檸檬酸＞琥珀酸＞蟻酸＞醋酸。本論文所有萃取法之重金屬萃取能力由高而低依序為HCl＞EDTA＞DTPA＞HOAc＞H2O＞combined acid＞CaCl2＞NaNO3。盆栽試驗結果指出，各種土壤萃取法濃度與植物地上部Cd、Cu、Ni、Pb及Mn等含量之相關性明顯（p < 0.05），甚至在Cd其r值可以達0.999（p < 0.001）。由根圈土壤與植物地上部重金屬含量之線性迴歸結果顯示，組合酸萃取Cd、Cu、Ni、Pb及Mn之濃度可有效代表其生物有效性多寡（p < 0.001），非根圈土壤與植物地上部重金屬之相關性以Cd、Cu、Ni及Pb為佳（p < 0.001）。土壤溶液與根圈土壤之相關性亦是以Cd、Cu、Ni及Pb效果較為顯著，可用來合理解釋為何目前常以土壤溶液來代表土壤重金屬之生物有效性。

關鍵字

重金屬 ； 低分子量有機酸 ； 組合酸 ； 根圈土壤 ； 生物有效性

並列摘要

Soil total heavy metals are not completely available for plant absorption. However, any current methodology in evaluating the bioavailability of heavy metals exists some limits. Therefore, low molecular weight organic acids (LMWOAs) such as malonic acid, succinic acid, citric acid, formic acid and acetic acid commonly produced in the rhizosphere of Chinese cabbage were applied to extract heavy metals (Cd, Cr, Cu, Ni, Pb, Zn, Fe and Mn) from 22 representative arable soils in Taiwan. Based on the result of principal component analysis the proportions of a set of optimal combination of LMWOAs are adjusted and determined with the molar ratio of malonic acid: succinic acid: citric acid: formic acid: acetic acid was determined as = 3:3:2:1:1 for extraction. Moreover, six traditional single extractions including 0.1 M NaNO3, 0.01 M CaCl2, 0.05 M EDTA (pH = 7.0), 0.005 M DTPA (pH = 7.3), 0.1 N HCl and deionized water, were used to compare the extraction results by the LMWOAs. By single LMWOA showed higher concentration than formic acid and acetic acid due to the number of carboxyl functional group. Overall, the extractability of single LMWOA was malonic acid > citric acid > succinic acid > formic acid > acetic acid, respectively. In this study, the order of extractability was HCl > EDTA > DTPA > HOAc > H2O > combined LMWOAs > CaCl2 > NaNO3. Clear correlation (p < 0.05) was found between the extractable amount in the soils and plant shoot uptake Cd, Cu, Ni, Pb and Mn, particularly in Cd up to 0.999 in r value (p < 0.001). According to the positively significant correlation (p < 0.001) between the extractable amount of rhizospheric soil and plant shoot uptake, the combined LMWOAs extractable amount of Cd, Cu, Ni, Pb and Mn can reveal the bioavailability of metals. Furthermore, the extraction by LMWOAs in non-rhizospheric soil also showed significant correlation Cd, Cu, Ni and Pb. The correlation between in situ soil solution and rhizospheric soil extraction showed positively significant in Cd, Cu, Ni and Pb, so that is why in situ soil solution extraction is the current methodology to evaluating the bioavailability of heavy metals in soils. The results identified that the combined LMWOAs extraction with non-rhizospheric soil in place of rhizospheric soil was feasible and can be solved the problem of rhizospheric soil with hard obtaining.

並列關鍵字

heavy metals ； low molecular weight organic acids ； combined LMWOAs ； rhizospheric soil ； bioavailability

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