藥物化合物於河川水體自然降解之宿命與探討：吸附與生物轉化

Abstract

由於台灣健保體制健全，國人用藥習慣不佳，使得藥物代謝物或廢棄物量，皆可能比國外流佈調查來得高，又國內相關研究有限，因此，為了幫助了解這些可能潛在危害的藥物化合物之流佈與宿命，本研究調查四種在台灣自然水體，被檢測頻率或檢驗濃度高之藥物化合物（acetaminophen、 caffeine、propranolol及acebutolol），透過實場調查自然降解之潛勢，另利用清潭堰河水做為背景水樣進行批次實驗，以模擬目標化合物在自然水體中吸附與生物降解的行為，綜合評估探討該四種化合物，在河川水體自然降解的機制及宿命。 實場調查結果顯示，伴隨上游流經下游，其濃度有遞減之現象，代表目標化合物皆具有自然降解的潛力。於吸附與生物降解特性，生物降解為acetaminophen主要的自然降解機制（單純吸附之半衰期(t1/2)為4.4天；吸附加生物降解之t1/2為2.1天）；對caffeine來說，吸附與生物降解佔相等地位（單純吸附之t1/2為2.2天；吸附加生物降解之t1/2為0.6天）；而對propranolol與acebutolol而言，吸附則為主要降解機制（propranolol單純吸附跟綜合吸附與生物降解之t1/2皆約為2.2天；acebutolol為2.4天）。於脫附實驗結果發現，四種化合物皆不易脫附，表示該吸附行為在此實驗條件下（土壤為低有機含量，0.017 g/g），大部分為不可逆的，可能以化學吸附為主要的吸附機制。等溫吸附實驗結果得知，除了acetaminophen以外，皆能套用Freundlich等溫吸附模式，其R2皆大於0.94。取其線性部分計算Kd (Solid-Water Distribution Coefficient)值，發現除了acetaminophen以外（5.0 L/kg），caffeine、propranolol及acebutolol之Kd都偏高（245.0-1901.0 L/kg）的現象，意味該三種化合物，即便在一般有機質含量很低的底泥，大部分caffeine、propranolol與acebutolol仍能吸附於底泥中，此實驗結果與吸附及生物降解實驗結果（吸附為該三種化合物重要的自然降解機制）相符。另比較實驗結果及經驗模式所得之Kd值，發現其差異性大，推測可能為經驗模式較適用於疏水性反應的評估，無法有效運用於極性或離子性化合物的推估，此評估結果與前半部研究推論呼應（化學吸附可能以離子鍵鍵結為主）。 綜合批次實驗結果與實場調查，目標化合物均具自然降解潛力，但由於台灣河川坡陡流急，其自然降解程度有限，表示目標化合物將殘留於河水中，或進一步排至大海，因此，進一步說明提升廢水相關處理效率及進行環境風險評估的重要性。

This research used designed batch experiments to verify the fate (sorption and biotransformation, in particular) for four frequently used and detected pharmaceuticals (acetaminophen, caffeine, propranolol, and acebutolol) in aqueous environments. Acetaminophen, caffeine, propranolol, and acebutolol have all demonstrated significant potential to degrade in the natural aqueous system. For acetaminophen, biodegradation play a major role (the half-lives (t1/2) of biodegradation and sorption together was 2.1 days while sorption alone was 4.4 days); for caffeine, biodegradation and sorption are both important (t1/2 of biodegradation and sorption together was 0.6 days; the t1/2 of sorption was 2.2 days). However, in the case of propranolol and acebutolol, sorption seems to be the most significant removal mechanism (the t1/2 of sorption was approximately 2.2 days and biodegradation didn’t enhance this degradation rate). In desorption experiments, the results showed that sorption are mostly irreversible (small than 3% reversibility). Because of low organic sediment content (1.7%) and the properties of target compounds (acetaminophen, propranolol, and acebutolol) are alkaline, it was implied that the sorption mechanism in this condition likely belong to chemical sorption (ionic interaction). In Kd determination experiment, caffeine, propranolol, and acebutolol had high Kd values, ranging from 245.0 to 1901.0 L/kg. It means that there is high tendency of target compounds to be sorbed to the sediment even though in low organic carbon content system. The results of logKoc values were dissimilar between experimentally derived and calculated values based on correlation equations. It is probably owing to the fact that those approaches are well applied for hydrophobic interaction, but fail to predict sorption of polar and ionic compounds. Laboratory results were further combined with other studies and extrapolated to the field conditions, the information demonstrated that the degradation possibility of pharmaceuticals just by natural attenuation. However, the rivers in Taiwan have high flow rate and with steep slopes. It is implied that the residual pharmaceuticals may enter the ocean before significant attenuation during river transport. Filed occurrence data further supported this conclusion, and it is suggested that these pharmaceuticals are in need to be treated by advanced process before releasing to the aqueous environments.