水體環境中二氧化錳氧化降解頭孢子類抗生素之研究

Abstract

民眾錯誤的用藥觀念及任意拋棄藥物的習慣，導致藥物進入環境中造成生態系統的衝擊，進而對人類健康產生潛在的風險。其中抗生素是許多研究關注的議題，尤其台灣民眾廣泛地使用以及在自然水體中檢測出較高濃度。本研究目的為探討三種頭孢子類抗生素 (cephalexin (CFX), cefazolin (CFZ), cephapirin (CFP))於不同環境因子下(二氧化錳濃度、目標污染物初始濃度、pH、水體溶氧量、水中陽離子及溶解性有機物(HA))，經由兩種不同型態的二氧化錳(δ-MnO2和c-MnO2)之化學氧化反應及轉換作用的宿命研究。批次實驗結果顯示，CFZ (100 μg/L)於合成水樣中不會被兩種二氧化錳氧化降解。反之CFX (100 μg/L)與CFP (100 μg/L)於酸性環境(pH = 5)下，經過48小時後分別被4 mg/L δ-MnO2氧化降解30 ± 2%、90 ± 1%，其CFP的半生期為13.9小時；中性環境(pH = 7)下則無任何的降解情況(≤5%)；鹼性環境(pH = 9)下，CFP有明顯的水解現象。另外，水中二氧化錳濃度上升會加速CFX與CFP反應速率。若CFP的初始濃度提高 (500 μg/L)，其反應速率則呈現減緩的情形。再者，水體中存在二價(Mn2+. Ca2+, Mg2+)，三價(Fe3+)陽離子和HA會抑制反應，其陽離子抑制能力的權重為Mn2+ > Fe3+> Ca2+ > Mg2+，伴隨二、三價陽離子與HA的濃度提高，其氧化反應抑制的情形也會隨之上升。本研究亦發現水中溶氧不會造成反應速率的改變。於CFP降解機制中遵循擬一階模式(R2 = 0.929-0.994)。環境水體批次實驗中，發現二氧化錳對於目標污染物之氧化反應並不顯著，推測由於水體pH、水體二價陽離子和溶解性有機碳所造成之抑制情形。綜合以上結果，證實水中pH及基質對於二氧化錳之氧化反應具有影響性，由於環境水體的差異性甚大，二氧化錳氧化頭孢子類抗生素仍可能為自然淨化的一環，未來其降解機制亦可應用於廢污水處理程序。

Incorrect practices of disposing residual medicine cause potential risk for ecosystem and human health. Antibiotics, in particular, are of significant concern. This study used batch experiments to investigate the transformation of three cephalosporin antibiotics (cephalexin (CFX), cefazolin (CFZ), cephapirin (CFP)) by manganese dioxides (δ-MnO2 and c-MnO2) in aquatic environments and to study the effect of different environmental factors such as MnO2 loading, initial cephalosporin concentration, pH, presence of dissolved oxygen, humic acid (HA) and cations on the transformation rates. In the synthetic water experiments, CFZ (100 μg/L) cannot be degraded by MnO2 while CFX (100 μg/L) and CFP (100 μg/L) can be dagraded by 4 mg/L δ-MnO2 to 30 ± 2% and 90 ± 1% respectively after 48 hours reaction at pH 5. The half life of CFP is 13.9 hours. Higher MnO2 concentration increased the reaction rate of CFX and CFP. On the other hand, the reaction rate decreased as initial concentration of CFP increased to 500 μg/L. The reaction rate increases with decreasing pH from 7 to 5. The presence of dissolved cations and HA could cause inhibitive effects, and the inhibitive capacity is Mn2+ >Fe3+ > Ca2+ > Mg2+. Dissolved oxygen has no significant effect in this reaction. In the river water system, MnO2 doesn’t play a major role to degrade selected cephalosporins due to the inhibitory effects from dissolved cations and humic acid. These results demonstrated that the degradation of cephalosporins by MnO2 could be affected by pH and matrix in the aqueous environment; therefore, according to the differences of natural water, MnO2 may facilitate, to various degrees, transformation of cephalosporin antibiotics in the natural environment.