有機砷動物用藥品洛克沙生之使用效益與對環境之衝擊

The Effect on Animal Growth and the Impact on the Environment by Roxarsone, an Organic Arsenic Veterinary Drug

王家琪(Chia-Chi Wang) ； 吳欣穎(Hsin-Ying Wu) ； 詹東榮(Tong-Rong Jan)

《臺灣獸醫學雜誌》 36卷2期 (2010/06) Pp. 115-123

https://doi.org/10.7009/TVJ.201006.0115

摘要

洛克沙生(roxarsone; 3-nitro-4-hydroxyphenylarsonic acid)為一種有機砷化合物，做為禽畜飼料添加劑，以促進生長和提高飼料換肉率；在治療用途上可用於控制雞球蟲症(coccidiosis)及治療豬赤痢(dysentery)。家禽飼料中常見同時添加攜帶離子型抗生素(ionophores)、洛克沙生及其他抗生素以增加飼料換肉率及降低死亡率。然而近年報告指出，在現今的飼養環境中，添加洛克沙生並無顯著的增重效益。洛克沙生於美國的使用相當普遍，有近七成的家禽業者使用建議的最高劑量(50 ppm)，其他國家如加拿大、台灣、中國、日本、紐澳、拉丁美洲、南非等國都核准該藥的上市，歐盟從1999年開始，已經全面禁用洛克沙生。洛克沙生較無機砷安全，並無報告指出在活體中會轉變成無機砷，口服高劑量洛克沙生會引起神經症狀、腸胃道疾病及肝臟的病變。口服洛克沙生大部分以原型排出體外伴隨少量的三氨四氫苯砷酸(3-amino-4-hydroxyphenylarsonic acid)，停藥後於組織殘留量低，且肌肉含量低於肝腎。餵食洛克沙生的禽畜場，偵測其家禽排泄物的砷濃度可達12-30ppm，於豬排泄物中也可達0.1-6.7ppm。排泄物中殘留的砷種類以原型的洛克沙生及砷酸鹽(arsenate; As (V))為主，其他包含少量的亞砷酸鹽(arsenite; As (Ⅲ))、單甲基砷酸(monomethylarsonic acid; MMA)、雙甲基砷酸(dimethylarsinic acid; DMA)及3-氨基－4氫基苯砷酸(3-amino-4-hydroxyphenylarsonic acid; 3-HPPA)等。研究指出殘留在禽畜排泄物中的洛克沙生可能會經由生物分解而產生具有毒性的無機砷，而環境因子包括溫度、濕度、存放時間、含氧量及微生物等均會影響排泄物中洛克沙生的轉換。例如在厭氧環境下，洛克沙生會經由梭狀桿菌進行生物轉換成無機砷，進而汙染土壤、地下水、地表水及作物，增加人類和禽畜暴露於毒性高且具有致癌性無機砷的風險。本文主旨在探討洛克沙生在禽畜之生長效益及評估對環境之可能影響。洛克沙生在一定劑量下具有促進禽畜生長的效益，但禽畜排泄物所含的洛克沙生部分經由生物轉換為無機砷而有汙染環境、進入生物鏈之虞，其應用為飼料添加劑之環境風險應予重新審慎評估。

關鍵字

洛克沙生 ； 效益作用 ； 殘留 ； 環境衝擊 ； 文獻探討

並列摘要

Roxarsone, 3-nitro-4-hydroxyphenylarsonic acid, is an organic arsenic compound used as a feed additive to promote animal growth and feed efficiency. It is also employed as a therapeutic agent to treat coccidiosis in chicken and dysentery in pigs. Roxarsone is commonly added into feeds in combination with ionophores and antibiotics to increase feed efficiency and reduce mortality. However, some reports indicate that roxarsone is not beneficial for animal growth under a good husbandry practice. It has been reported that roxarsone is used in approximately 70% of the broiler industry operations in the United States. Roxarsone is also approved for use in food-producing animals in Canada, Taiwan, China and many other countries. In contrast, the European Union banned the use of arsenical drugs in 1999. The toxicity of roxarsone is less than that of inorganic arsenic. Neurological disturbances, hemorrhagic gastroenteritis and liver damage are the major adverse affects after oral exposure to high doses of roxarsone. Results from pharmacokinetic studies indicate that roxarsone is stable in vivo. Following ingestion by animals, roxarsone is primarily eliminated without being metabolized, and the tissue residue is low. The level in the muscle is lower than that in the liver and kidney. The content of arsenicals in poultry litter, collected from poultry farms where roxarsone was used, could reach the level of 12-30 ppm, and the total As amount in pig feces is ranging from 0.1-6.7 ppm. The major As compounds in poultry litter include roxarsone and arsenate, whereas arsenite, monomethylarsonic acid, dimethylarsonic acid and 3-amino-5-hydroxy-phenylarsonic acid are minor derivatives. It has been shown that the residual roxarsone in poultry litter can be converted into inorganic As via biotransformation. Environmental factors, including temperature, humidity, time, oxygen concentrations and microbes may affect the biotransformation. For example, the biotransformation of roxarsone under anaerobic conditions is mediated by Clostridium spp, potentially resulting in As environmental pollution that subsequently increases the exposure risk of human and animals to As. The objective of this article is to review the literature evidence pertaining to the beneficial effect on animal growth and the potential environmental impact associated with the use of roxarsone in food-producing animals. Scientific evidence indicates that roxarsone exhibits a growth-promoting effect under certain conditions. However, it was also reported that the inorganic As released from the biotransformation of roxarsone in poultry litter may lead to environmental pollution and food chain contamination. The environmental risk of using roxarsone as a feed additive deserves a further cautious evaluation.

並列關鍵字

roxarsone ； beneficial effect ； residue ； environmental impact ； review