| 摘要: | 由質量平衡的觀點，排入河中重金屬不是吸附在懸浮固體及底泥中就是存在水相（溶解態）中，底泥顆粒中重金屬受水中鹽度增加，重金屬釋出到水體中也跟著增加，本研究於實驗室控制條件下，探討鹽度影響二仁溪感潮河段河水中溶解態重金屬及吸附在底泥中重金屬的關係。鎘主要由易交換態及與碳酸鹽鍵結態釋出為主；鈷由與碳酸鹽鍵結態；鉻由與鐵錳氧化物鍵結態；銅由與碳酸鹽鍵結態；鎳由與鐵錳氧化物及與有機物鍵結態；鉛由與鐵錳氧化物及與有機物鍵結態；鋅由與碳酸鹽及與鐵錳氧化物鍵結態為主。當底泥流經鹽度漸增之河口水域，各種粒徑底泥釋出到水中之重金屬（鎘、鈷、鉻、銅、鎳、鉛及鋅）量，有隨著鹽度濃度增加而增加之趨勢。至於受鹽度影響重金屬自不同粒徑底泥中的釋出結果，為顆粒愈小釋出量愈少。
鹽度影響底泥中五種鍵結型態重金屬與水中溶解態重金屬量之分佈係數（KDSP）。底泥顆粒中與水相中重金屬濃度達濃度平衡時，鹽度愈大，分佈係數（KDSP）愈小，代表重金屬自該鍵結型態中愈易釋出，其中（1）鎘為KF1DSP及KF2DSP（2）鈷：KF2DSP、KF3DSP及KF4DSP（3）鉻：KF3DSP（4）銅：KF2DSP、KF4DSP（5）鎳：KF3DSP、KF4DSP（6）鉛：KF2DSP、KF3DSP及KF4DSP（7）鋅：KF3DSP、KF2DSP，這樣的結果可以看到鎘從易交換態的釋出能力最強，鈷、銅及鉛是於碳酸鹽鍵結態時的釋出能力較強，鉻、鎳及鋅則是自鐵錳氧化物鍵結態中釋出的能力較強。另外顆粒粒徑對重金屬自底泥中各個鍵結型態釋出能力（分佈係數）的影響，顆粒越小釋出能力越弱、分佈係數越大，鎘為KF1DSP、鈷是KF2DSP、鉻為KF3DSP、銅是KF2DSP、鎳是KF3DSP、鉛為KF2DSP而鋅為KF3DSP這樣的結果，其各個鍵結型態的分佈係數與受鹽度影響的結果相似。
另外本實驗所得結論，當重金屬存在的底泥流經高鹽度水域且底泥顆粒粒徑較大時，其重金屬釋出能力較強，而不同金屬有其差異如：此時對生物體的危害會大於低鹽度而底泥顆粒粒徑較小的環境，此外本實驗的其他結論希望可以對重金屬在底泥及水體中的流佈及宿命之研究有進一步的幫助。
With the laboratory control, the aim of this study is to realize the effect of salinity on the distribution of heavy metal between dissolved and five heavy-metal binding fractions in river sediment as well as on the remobilization of metals from different size of particles.
Heavy metals could be adsorbed onto suspended particulate and sediments with different particle sizes when they were discharged into the river. When sediment flowed through estuary and mixed with overlying water containing different salinity, the remobilized metals (Cd, Co, Cr, Cu, Ni, Pb, and Zn) concentration from different size of particles increased with the increase of salinity. The smaller the particle size was, the lower concentration of metals remobilized.
Cd was remobilized from fractions of exchangeable and carbonates with the action of salinity. Similarly, Co and Cu was remobilized from carbonates fractions; Cr from Fe and Mn oxides fractions; Ni and Pb from Fe and Mn oxides and organic matters fractions; Zn from carbonates and Fe and Mn oxides fractions. The partitioning coefficients (KF1DSP, KF2DSP, KF3DSP, KF4DSP, and KF5DSP) of heavy metals between dissolved phase and five heavy-metal binding fractions were affected by salinity in sediment particles. The increase of salinity induced the decrease of KDSP, when the equilibrium of metals existed between particle and dissolved phases. The significant variation of one KDSP value with salinity means the easier release of heavy metals from one binding fraction to the dissolved phase. From the results the more significant variations of KDSP value were from KF1DSP and KF2DSP for Cd; from KF2DSP, KF3DSP, and KF4DSP for Co and Pb; from KF3DSP for Cr; from KF2DSP, and KF4DSP for Cu; from KF3DSP, and KF4DSP for Ni; and from KF2DSP,and KF3DSP for Zn.
The amounts of heavy metals remobilized from sediment with larger particle sizes and higher salinity were larger than these from sediment with smaller particle sizes and lower salinity environment. |
