不同粒徑底泥顆粒中重金屬分佈特性之研究

Abstract

河川底泥同時扮演著重金屬的儲存與排放兩種角色，重金屬以游離態進入河川，並藉由物理化學作用，化學錯合、化學沈澱、離子交換及吸附的作用而沈降於河川底部形成底泥。底泥環境因子的改變可促使已沈降於底泥的重金屬物種分解並進入水體，因此，底泥中的重金屬具有潛在的危害性。 底泥中重金屬再釋出的機率取決於重金屬形成的物種，底泥中金屬可分為可交換態、碳酸鹽結合態、鐵錳氧化物結合態、硫化物/有機結合態及殘存相等。本研究探討河川底泥不同粒徑中重金屬的分佈行為，並進一步評估底泥重金屬的危害潛勢。 本研究結果顯示底泥五種重金屬的穩定度依序為 Cr > Cu ~ Pb > Ni ~ Zn，不同粒徑之底泥顆粒中重金屬含量受鐵錳氧化物與有機物多寡的影響。底泥中Cr 與Ni 的相態分佈受到粒徑大小影響的機率最高，Pb 受影響的潛能次之，而 Cu 及 Zn 幾乎不受粒徑大小的影響。底泥中重金屬的離子交換相與碳酸鹽相釋出至水體的潛能受粒徑大小的影響，細小粒徑上的離子交換相與碳酸鹽釋出的潛能最高，其次為較大粒徑之底泥，介於兩者之間中尺寸底泥之離子交換相與碳酸鹽相的金屬物種釋出的潛能最低，底泥中細小粒徑上的可移動相，對於水體危害性最大。

River sediment plays an important role of source and sink in heavy metal pollution. Heavy metal ion forms deposit by physical and chemical processes, such as sedimentation-resuspension, sorption- desorption and complexation-decomplexation. The heavy metal deposits can be decomposed and released into liquid phase by dramatic changes on environmental conditions. However, the metal deposits have a potential of causing changes of nature water system, especially for aquatic living. The releasing probability of heavy metal in sediments depends on metal speciation. Metal speciation in sediments can be listed five classifications, such as Exchange, Carbonate, Fe/Mn oxides, sulfide/organic and matrix. This study focuses on the characteristics of heavy metals in sieve fraction of river sediments and assesses the damage potential of heavy metal deposits. The results show the heavy metal in order of stability is Cr > Cu ~ Pb > Ni ~ Zn. The content of metal in sediment depends on Fe/Mn oxides and Organic matters. The speciation of Cr and Ni could be affected by "particle size effect". One of Pb has a little affection and ones of Zn and Cu have not been affected by "particle size effect". The fine sediment has a high potential of Exchange metal speciation and Carbonate than medium or coarse ones. The order of risk is Fine > coarse > medium and the fine sediments may be a highest mobile potential.