小球藻胞內外有機物促進光降解藥物之動力學與機制研究

Abstract

藻類可以有效去除水中的新興污染物，且陽光照射可加速污染物的降解速度。本研究目的在研究小球藻 (Chlorella vulgaris) 及其藻類物質對乙醯氨酚 (acetaminophen)、可待因 (codeine) 和頭孢拉定 (cephradine) 的光降解效果與機制探討。與直接光解相比，自然光照下藻類對乙醯氨酚的降解率相對於直接光解提升78％。在實驗期間污染物的生物吸附和水解作用不明顯。因此，降解速率提升可歸因於光照藻類溶液中的物質，包含藻類、胞外有機物 (EOM) 和胞內有機物 (IOM)。為了瞭解藻類成分對乙醯氨酚光降解之影響，本研究探討胞內及胞外有機物濃度 (5–20 mg C L–1) 和pH值4–10的變化對降解速率的影響。結果顯示，隨著pH值或有機物濃度的升高，乙醯氨酚之自然光降解效率提高。 此外，本研究透過自由基抑制劑實驗 (添加異丙醇、山梨酸及曝氮、曝氧)，來探討可能生成於此系統的反應物種，包括羥基自由基 (･OH)、單支態氧 (1O2) 和三重激發態之溶解性有機物 (3DOM*) 以了解胞內及胞外有機物對乙醯氨酚的光降解機制。當抑制羥基自由基或三重激發態有機物時，乙醯氨酚的光降解速率降低，而氧氣的缺乏反而使其降解速率增加。此結果代表羥基自由基或三重激發態有機物是系統中可能的自由基，而水中溶氧可能與三重激發態有機物競爭，影響三重激發態有機物的生成。此外，本研究透過添加自由基之探針在胞內有機物溶液之光降解濃度變化，進一步確定系統中存在的反應物種。在胞內有機物溶液中，最具貢獻的自由基為三重激發態有機物，佔整體的93.52％，亦計算出三重激發態有機物與乙醯氨酚之擬一階反應速率為 1.56 × 10–4 s–1。 然而，藻類在自然光下降解不同污染物可能有不同機制。小球藻可有效促進光降解頭孢拉定和可待因，但是此兩種汙染物之光降解行為機制則需要進一步研究。本研究不僅證明了藻類成分可在自然光下有效去除乙醯氨酚、可待因和頭孢拉定，且深入探討過程中各反應物質對於藥物的光降解機制。

Algae is able to effectively remove emerging contaminants from water bodies, and has been shown to accelerate the photodegradation rate of contaminants under sunlight irradiation. This study aimed to investigate the photodegradation efficiencies and mechanisms of three pharmaceutical contaminants, acetaminophen, codeine and cephradine, by microalgae Chlorella vulgaris and its algal substances. Microalgae enhanced the photodegradation rates of acetaminophen by 78% compared with that of direct sunlight photolysis. Furthermore, there was no significant biosorption or hydrolysis of the contaminants in the experimental period. Thus, the improved degradation rates could be attributed to photodegradation of the substances in the algal solution, namely, the algae, extracellular organic matter (EOM) and intracellular organic matter (IOM). To determine the influence of algal substances on the photodegradation of acetaminophen, various EOM and IOM concentrations (5–20 mg C L–1) and pH values (pH 4–10) were investigated. As the pH values or organic matter concentrations increased, the photodegradation efficiency of acetaminophen improved. In addition, the photodegradation mechanisms of acetaminophen in the EOM and IOM were explored by scavenger experiments (the addition of isopropanol and sorbic acid and purging with N2 and O2) for specific reactive species, including hydroxyl radicals (･OH), singlet oxygen (1O2) and the triplet excited state of dissolved organic matter (3DOM*). The degradation rates decreased when ･OH or 3DOM* were suppressed, but the rate increased with a low oxygen saturation. The scavenging results implied that ･OH and 3DOM* were potentially dominant radicals, while oxygen might compete with 3DOM*, thus affecting the formation of 3DOM*. Furthermore, the reactive species were determined by probes in the IOM photodegradation process. The dominant reactive species was triplet excited state of IOM (3IOM*), with a 93.52% contribution, and the estimated pseudo-first-order rate constant for the 3IOM* with acetaminophen was 1.56 × 10–4 s–1. However, an algae-involved photodegradation of different compounds under sunlight irradiation may operate with different mechanisms. Chlorella vulgaris were found to be effectively enhancing the photodegradation of codeine and cephradine, but the photodegradation mechanisms of the two pharmaceuticals require further investigation. This study proves that acetaminophen, codeine and cephradine can be effectively degraded under sunlight irradiation in separate algal substances, and provides a thorough investigation into the photodegradation mechanisms of the pharmaceuticals by the reactive species produced from the algal substances.