隨著四、五十年來科技高速發展，糧食生產率大幅提高，酪農業養殖技術提升，以及人口急遽成長，人類與集中圈養的牲畜皆生活在高密度的環境中，而如此高密度的居住環境也成為傳染病傳播的溫床。為預防及治療傳染疾病，抗生素大量被研發及使用以利於感染發生時抑制體內病菌。抗生素廣泛用於預防性投藥防止開放性創傷導致進一步的感染，低劑量添加於動物飼料中以避免群居生活引起大範圍的感染，以及使用於非治療目的以增加牲畜的生長效率。目前歐美等國的年使用量已趨近於萬噸，著實為一龐大的潛在汙染源，早期開發出的廣效型抗生素-四環素，在目前西方先進國家的使用量約略佔整體使用量的三成。抗生素在動物體內的代謝率只有10-70 %，有30-90 %的抗生素以原型態排出生物體外乃至污水中，然而以目前的汙水處理設施卻無法完全去除水中的抗生素，這些溶於水中的抗生素隨水體進入環境中，可能導致環境中抗藥性病原菌的產生。此外養殖業為避免群聚感染而添加抗生素於飼料中致使牲畜體內長期維持低濃度的抗生素劑量，在這低濃度的抗生素環境下亦可能導致病原菌抗藥性的產生。更甚者，添加於飼料中的抗生素有部分屬於人畜共同使用，意味著當抗藥性的病原菌出現時，通過人畜共同傳染，人類也會因而受到此些抗藥性病原菌的感染。雖然目前瑞士、瑞典和英國已禁止使用抗生素作為生長促進劑，其餘歐美等國仍只限制部分抗生素的使用，因此，隨動物排泄物進入環境中的抗生素宿命便開始被廣泛地討論。本研究著重於氧四環素於田間土壤的吸附，氧四環素為一兩性離子，離子上的三個官能基在不同pH環境下經質子化或去質子化後可以表現四種不同的帶電情形。因為此兩性離子的特性，使得氧四環素在不同pH環境下主導的吸附機制有所不同。先前的研究已指出氧四環素在黏土及金屬氧化物上的各種吸附行為主要取決於pH值條件、吸附劑種類及特性、水中金屬離子的存在與種類以及水中有機物的溶解與否，以上吸附行為隨條件的不同而分別符合Freundlich isotherm 或是Langmuir isotherm 兩種等溫吸附曲線。文獻中所使用的吸附劑大多為乾淨的實驗室樣品，以環境樣本作為吸附劑的實驗仍鮮少被討論，本實驗以養豬場周遭三處不同地點的環境土壤作為吸附實驗的吸附劑，並以0.01 M CaCl2 作為背景離子。由於台灣的農地經長時間的淋洗及耕種，土壤的pH值多呈現中性偏酸，所以吸附實驗中pH環境控制在酸性及中性的條件下進行，此條件下的氧四環素帶電量為+1價及0價。本實驗及文獻皆指出帶電的氧四環素吸附效果優於不帶電的氧四環素，但較為不同的是其中兩處土壤在氧四環素超過一定濃度後不帶電氧四環素吸附效果超越帶電的氧四環素。另外背景離子中陽離子的存在顯著促進未帶電氧四環素的吸附效果，間接證明環境中的陽離子能導致氧四環素移動性下降。在溶解性有機物影響方面，雖然不同濃度的腐植酸(1, 5 and 10 ppm)無法明顯區分其對吸附效果的影響，但額外添加的腐植酸仍造成氧四環素的吸附效果下降。

Veterinary pharmaceuticals are widely used in livestock for treatment and prevention of disease. Following the increasing consumption, veterinary pharma-ceuticals nowadays are considered as emerging contaminants. Antibiotics in vet-erinary pharmaceuticals are physiologically highly active and widely used in live-stock to treat disease and trauma, and used as additive feeding to promote the meat growing. Most consumed livestock is applied with antibiotics, but animals have a low metabolism efficiency on these drugs. This situation leads to high antibiotics concentration in agricultural wastewater. In addition, long-term exposure of anti-biotics creates a high selection pressure for bacterial resistance. Although some countries have banned the antibiotics as feed additives, lots of countries still use antibiotics as feed additives to promote meat growing. Thus, the animal bodies content low concentration of antibiotic for long-term. Unfortunately, the sewage treatment plants cannot perfectly remove antibiotic from wastewater, implying lots of antibiotic could be released to the environment. In addition to sewage treatment plants, the compost amendments with manure on field means directly released an-tibiotics and antibiotics resistances into environment, and released antibiotics can increase selective pressure in human and animals. The resistance genes will result in bacterial resistance, suggesting antibiotics lose their effectiveness when break-ing out the zoonosis. Tetracyclines (TCs), a broad-spectrum antibiotics discovered in the 1940s, has 30-40 % consumption in western countries and 20 % in Taiwan. Oxytetracycline (OTC), one member of the tetracycline family, was chosen as the target compound in this study. OTC changes its charge at different pH levels and thus can exist as a cation (pH<3.27), a zwitterion (3.27<pH<7.32), or an anion (pH>7.32). The different charged OTC complicates the behavior of OTC in envi-ronment. Previous studies mainly focused on the pure adsorbent such as clay and metal oxides, and the behavior of OTC in the natural soils is rarely concerned. In this study, OTC adsorption on soils was investigated by varying sample location, particle size, pH, and presence of background ions and dissolved humic acid. The adsorption OTC onto soil could be fitted by either Langmuir isotherm or Freun-dlich isotherm. The adsorption capacity of OTC decreased with increasing pH value as the order: pH 3 > pH 6. The order inverted when exceeding specific con-centration for two sites soil, suggesting the adsorption of OTC involved in other mechanisms to promote adsorption of OTC at pH 6. Considering the influence of background ion at pH 6, the background ion promoted the OTC adsorption onto soil, suggesting the background ion may decrease its mobility in the environment. The presence of humic acid significantly decreased the adsorption capacity for OTC.

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