飼料中戴奧辛之健康風險評估

Abstract

戴奧辛為多種化合物之總稱，包含75種多氯二聯苯戴奧辛（Polychlorinated Dibenzo-p-Dioxins, PCDDs）以及135種多氯二聯苯呋喃（Polychlorinated Dibenzofurans, PCDFs），其中7種PCDDs以及10種PCDFs具有較高毒性會對健康造成危害，因此受到許多研究關注，而本研究所稱之戴奧辛為此17種PCDD/Fs。 人類暴露到戴奧辛的主要途徑為飲食，其中又以攝入動物源性食品貢獻最大。而動物暴露到戴奧辛的主要途徑是飼料，家禽家畜攝入受污染之飼料後，戴奧辛會累積於動物組織中，民眾再經由飲食暴露到戴奧辛。因此，了解飼料中戴奧辛轉移至動物組織中的濃度是相當重要的，過去研究使用轉移因子以及以生理學為基礎的藥物動力學作為估計飼料中戴奧辛轉移累積至動物組織中的方法，但這些方法具有侷限性以及不確定性，並且主要針對牛奶、雞蛋或雞、豬、牛的肉類進行評估。 考量台灣人的飲食習慣，本研究基於藥物動力學，建立不同情境下評估飼料中戴奧辛轉移至家禽家畜組織中濃度的模型，使用貝氏統計以描述群體的分佈，模擬台灣現行飼料中戴奧辛最大限量下五種畜禽組織濃度，包含牛、豬、羊、雞以及鴨。由於戴奧辛為非基因毒性致癌物質，藉由蒙地卡羅模擬，估計民眾經由攝入畜禽食品的戴奧辛平均每日暴露劑量以及危害指數，用以評估目前飼料標準是否可保護民眾免於暴露過高之風險。 基於藥物動力學進行推導，建構飼料轉移模型，推導結果顯示當半衰期小於五分之一飼養期時，有害物質於動物體內可達穩定狀態；當半衰期大於3.5倍飼養期，有害物質於動物體內累積濃度隨時間呈線性增加。依照五種物種各自符合之模型，模擬飼料濃度為0.75 ng TEQ/kg下，組織中殘留濃度，除雞以外，其餘四種物種之組織濃度高低順序皆為，脂肪、肝臟、肉、腎臟或其他器官。根據此濃度估算民眾經由飼料間接暴露戴奧辛的平均每日暴露劑量以及危害指數，結果顯示，所有年齡層之危害指數皆大於1，民眾面臨較高之風險，其中孩童相較於其他年齡層所面臨的風險更高，表示現行飼料標準並不足以保護民眾之健康。本研究針對飼料中不同戴奧辛濃度進行模擬，建議飼料中戴奧辛最大限量為2.0×10-3 ng TEQ/kg時，危害指數將低於1，可保護民眾之健康。 本研究建立多種情境的飼料中戴奧辛轉移評估方法，此方法可應用於評估其他有害物質在不同物種之轉移濃度，評估結果可作為未來訂定飼料中戴奧辛最大限量之參考。

Dioxins are a class of structurally and chemically related polychlorinated aromatic hydrocarbons, including 75 polychlorinated dibenzo-p-Dioxins (PCDDs) and 135 polychlorinated dibenzofurans (PCDFs). Among these analogs, 7 PCDDs and 10 PCDFs are considered toxic and lead to adverse health effects. In this study, the term “dioxin” refers to these 17 toxic PCDD/Fs. More than 90% of human dioxin exposures were reported through dietary intakes, mainly via animal products. Animals are mainly exposed to dioxins through contaminated feed, accumulating dioxins in their tissues. Therefore, it is essential to estimate the concentration of dioxin transfer from feed to animal tissues. Previous studies have used transfer factors and physiologically based pharmacokinetic (PBPK) models to estimate the transfer of dioxin from feed to animal tissues. However, these methods have some limitations and uncertainties and primarily focus on milk, eggs, or meat from chickens, pigs, or cows. Considering Taiwanese eating habits, this study established a model based on pharmacokinetics to evaluate the concentration of dioxin transferred from feed to poultry and livestock tissues under different scenarios. Bayesian statistics were used to describe population distribution, simulating the dioxin concentration in tissues of five species under the current maximum limit of dioxin in feed in Taiwan. These five species included cows, pigs, sheep, chickens, and ducks. Since Dioxin is a non-genotoxic carcinogen, Monte Carlo simulation was used to estimate the average daily dose and hazard index of dioxin from animal products to assess whether the current feed standards can protect the public from excessive risk. Based on pharmacokinetic model, the derived results showed that when the half-life of compound is less than one-fifth of the feeding period, the compound can reach a steady state in the animal. When the half-life is more than 3.5 times feeding period, the concentration of the compound in the animal increases linearly over time. According to the models for the five species, concentration simulations were conducted for the feed concentration of 0.75 ng TEQ/kg. Except for chickens, the tissue concentrations in the other four species, in descending order, are fat, liver, meat, and kidney or other organs. Based on these concentrations, the average daily dose and hazard index of dioxin indirectly exposed through feed were estimated. The results show that the hazard index of all age groups is greater than 1, and children face higher risks than other age groups. This indicates that current feed standards are not sufficient to protect public health. This study simulated different dioxin concentrations in feed and suggests that when the maximum limit of dioxin in feed is 2.0×10-3 ng TEQ/kg, the hazard index would be below 1, ensuring the protection of public health. This study established methods for assessing the transfer of dioxin in feed under various scenarios. The method can be applied to assess the transfer of other hazard in different species. These results lay the foundation for setting the maximum residue limits of dioxins in animal feeds.