抗生素對水體生態食物鏈之混合毒性效應及風險評估

Abstract

抗生素不只在人類或畜牧業廣泛被使用，在水產養殖和農業中亦是。然而在真實水體環境中，並非只有單一種抗生素的存在，通常是多種抗生素存在於水體而產生交互作用，可能造成水生生態具潛在的危害，因此有必要進行抗生素的風險評估。 為了瞭解不同機制抗生素混合毒性效應，以及不同物種之間的敏感度，本研究選用了三種抗生素，分別是Ciprofloxacin、 Sulfamethoxazole、Tetracycline進行月芽藻、水蚤、羅漢魚的毒性評估。 單一毒性試驗上，抗生素對於月芽藻的毒性由高到低為Tetracycline > Ciprofloxacin > Sulfamethoxazole，水蚤則是Ciprofloxacin> Sulfamethoxazole > Tetracycline，而羅漢魚毒性評估上僅有Tetracycline產生毒性影響。混合毒性研究部分，本研究選用水蚤進行抗生素兩兩混合毒性試驗，結果顯示Sulfamethoxazole 和 Tetracycline混合產生簡單相加作用；Ciprofloxacin和Sulfamethoxazole 以及 Ciprofloxacin 和 Tetracycline 兩組則為拮抗作用；另外將三種抗生素以環境水體濃度混合，分別以月芽藻、水蚤、羅漢魚進行試驗，在水蚤及羅漢魚方面則沒有生物死亡或抑制的現象，而當以月芽藻試驗終點最敏感之final yield發現試驗結果與control相比有顯著影響且有抑制月芽藻生長的現象，對於植物性浮游生物有立即的危害，造成環境水體嚴重威脅，需進一步深入探討。 敏感度結果顯示，月芽藻對於Tetracycline最敏感，其半致死影響濃度(EC50)為0.056 mg/L，無顯著影響的最高濃度(NOEC)為0.008 mg/L；水蚤對Ciprofloxacin最敏感，其EC50為31.3 mg/L，但NOEC則是對Tetracycline最敏感，其值為0.26 mg/L；羅漢魚對於三種抗生素敏感度皆小於上述的兩種生物。 在毒性評估上，研究中使用最敏感試驗物種月芽藻去計算風險評估，分別求得急、慢毒之風險商數(RQ)。結果顯示不論在急性及慢性毒性中Sulfamethoxazole 和 Tetracycline所求的風險商數皆大於1，若經食物鏈傳遞將會對生物及環境產生更大危害，對於此兩種抗生素，必須限制及減少其用量，確保生物達到保護。

Antibiotics are one of the most widely used pharmaceuticals, not only for human and veterinary medication but also for aquaculture and livestock. However, It found in the aquatic environment usually occur as mixtures, not as a single substance. They might be potential micropollutants in aquatic ecosystems that negative impact. Therefore, it is necessary to evaluate the risk of antibiotics. In order to evaluate the combined toxic effect of antibiotics on aquatic organisms of different trophic levels, this study choose three antibiotics of different mode of actions i.e., Ciprofloxacin(CIP), Sulfamethoxazole(SMX) and Tetracycline(TC) for conducting the toxicity assessment on Pseudokirchneriella subcapitata (Alga), Daphnia magna (water flea) and Pseudorasbora parva (fish). In the single-compound toxicity test, the toxicity for P. subcapitata in degreasing order is: Tetracycline > Ciprofloxacin > Sulfamethoxazole. For D. magna is Ciprofloxacin> Sulfamethoxazole > Tetracycline. However, only Tetracycline has toxic effect for P. parva. Binary mixture toxicity was investigated by using D. magna.The results shows simple addition effect was observed with the combination of Sulfamethoxazole + Tetracycline, while the others show antagonism. Combination of antibiotics with D. magna and P. parva are no mortality or inhibit the biological, when the most sensitive endpoint of final yield of P. subcapitata have significant effect as compared with control and inhibit the growth of P. subcapitata, causing harm to the ecological environment. On the other hand, the results from species sensitivity test show that among different trophic levels of P. subcapitata has the highest sensitivity to Tetracycline in which the 50 % effective effect concentration(EC50) is 0.056 mg/L, respectively, and the no observed effect concentrations(NOEC) value is 0.008 mg/L.For D. magna, it is most sensitive to the Ciprofloxacin with an EC50 of 31.3 mg/L, but NOEC is most sensitive by Tetracycline, it value is 0.26 mg/L. The sensitivity of these three antibiotics on P. parva were found to be lower than the above two organisms. For the toxicity assessments, using the most sensitive species of P. subcapitata, which is among different trophic level, calculate the risk quotient (RQ). RQ values of Sulfamethoxazole and Tetracycline are larger than 1 for both acute and chronic toxicity, which means that it has a significant effect to environment. Future, the usage of the two antibiotics would be limited.