| 摘要: | 生物有效性 (bioavailability)是毒理學的重要觀念，用以評估污染物經由不同途徑，於一段暴露時間後，目標污染物進入血液循環系統的劑量與總暴露劑量的比例，稱為絕對生物有效性係數 (absolute bioavailability factor, ABF)，若將該物質與某一標準物質兩者之ABF相除，即為該物質之相對生物有效性係數(relative bioavailability factor, RBF)，一般而言，當目標污染物在該物質的包封度(encapsulation)愈高時，RBF愈低，即相對於該標準物質，待測物質中的毒性污染物較不易被消化吸收進入血液循環系統。 鑒於廢棄物資源化為土壤改良劑時，並無明確的評估方法，本研究乃參考USEPA Region Ⅷ，研擬一種模擬腸胃環境的兩階段生物有效性體外試驗(in-vitro test)程序。第一階段模擬胃消化環境，加入0.15 M NaCl及1% porcine，於pH 1.8萃取1hr；第二階段模擬腸吸收環境，加入3.5 gm/L bile及0.35 gm/L pancreatin，但不使用吸收劑，於pH 5.5萃取1hr。本研究使用砷酸鈉 (Na2HAsO4?7H2O)及美國NIST 2710土壤為標準物質，以建立系統品管基準，並探討操作參數：氧化還原電位 (ORP)、蠕動強度、液固比、腸相萃取時間，期能將評估程序應用於玩具、牙材、中藥、食品等之健康風險評估。 本研究首先於1 L密閉容器下，以磁石進行攪拌，餵入樣品時不控制厭氧，進行胃腸相ORP監測，結果顯示兩種標準物質胃相ORP分別為220及265 mv，腸相分別為46及80 mv，說明若未進行厭氧控制，將高估人體腸胃相ORP(150及-50 mv)，唯推論應不會導致RBF之誤差。 進一步探討蠕動對生物有效性的影響，兩種標準物質均加入0.5 gm (1.0 gm/L)進行兩階段萃取，當液固比為1000 mL/gm時，於三種速度梯度 (G = 0, 470, 1006 sec-1)下，砷酸鈉胃及腸相ABF為95 ~ 102 %，標準土壤RBFG為39 ~ 58 %，RBFI為29 ~ 55 %，於信賴水準 (confidence level) 95%下，僅砷酸鈉胃相之ABF有顯著差異 (p=0.004)，但因砷酸鈉添加濃度遠低於其溶解度 (5.46 gm/100 mL at 0℃)，且並無包封度，故不易合理解釋試驗結果，大致而言，蠕動強度似乎不是一個重要的試驗條件，本研究仍建議G值暫訂為500 sec-1。 進一步探討於G為470 sec-1時，三種液固比(200, 1000, 5000 mL/gm)對生物有效性的影響，結果顯示胃及腸相砷酸鈉ABF為98 ~ 102 %，標準土壤RBFG為28 ~ 39 %，RBFI為27 ~ 32 %，標準土壤於腸相時有顯著性差異(p<0.001)，且液固比愈高RBF愈高 (R2 = 0.84)，但胃相時並無顯著性差異，推測在pH較低之胃相時，包封度降低，使液固比在胃相中似乎不是重要的試驗參數。綜合不同蠕動強度與不同液固比試驗結果，本研究RBFG較Hamel et al. (1998)之46~56%低，但因兩者之試驗參數不盡相同，不易釐清其原因，本研究仍建議在胃相時液固比暫定為1000 mL/gm。砷酸鈉與標準土壤腸相萃取1 hr總砷濃度分別為253 mg/L與0.19 mg/L，萃取2-10 hr平均濃度分別為259 mg/L與0.20 mg/L，與1 hr者僅分別相差2.3 %與4.7 %，說明胃腸相萃取時間定為1 hr是合宜的。 綜合本研究砷之生物有效性研究實證結果，初擬三種系統品管基準：試劑空白砷濃度低於方法偵測極限 (MDL)；標準砷酸鈉胃腸相之ABF平均值與標準偏差為100 ±10 %，NIST標準土壤之RBFG為40 ± 10%，RBFI為36 ± 10 %。以本研究及文獻中各種污染物質 (calcine、slag、soil) 之RBF估算砷之增加終身累積致癌風險 (excess lifetime cumulative risk, ELCR)，使用IRIS單位致癌風險係數為1.5 (mg/kg-d)-1，當攝入率(IR)為0.1 gm/day且平均體重(BW)為70 kg時，ELCR 為1.3 ~ 26.7×10-4，較一般可接受範圍 (10-6 ~ 10-4)高，顯示受污土壤及廢棄物資源化所引起的健康風險是一個值得注意的問題。; Bioavailability is an important concept in toxicology. The absolute bioavailability factor (ABF) is defined as the portion of a target toxicant entering the blood circulation system via a specific pathway in a certain period of time after exposure. To avoid inaccurate measurement, the relative bioavailability factor (RBF) is normally used in practice and is defined as the ratio of the ABF of the test material to the ABFof a surrogate reference material (SRM). Theoretically, a low level of RBF characterizes a high degree of encapsulation of the material being evaluated with a low level of the target toxicant being extracted in the gastrointestinal digestion environment. In reference of USEPA Region VIII’s method, this study proposed a two-step in-vitro bioavailability test for soil materials and the like. In the first step, 0.15 M NaCl and 1% porcine were used as the stomach liquid at a pH of 1.8 for 1 hour of extraction, while in the second step, 3.5gm/L bile and 0.35gm/L pancreatin were used as the intestinal liquid at a pH of 5.5 for 1 hr. Sodium arsenate (Na2HAsO4?7H2O) and NIST 2710 Montana soil were used as the SRM and matrix standard, respectively, for developing test criteria of oxidation reduction potential (ORP), peristalsis intensity, liquid to solid (L/S) ratio, and extraction period. The in-vitro test was first continuously monitored in a sealed vessel after feeding for ORP during the extraction. ORPs were obtained from the tests on the two standard materials were 220 and 265 mv for the stomach phase and 46 and 80 mv for the intestinal phase, respectively. Comparing with the ORP data (150 and -50 mv) reported for the human gastrointestinal system, the ORP values appeared to be overestimated for no control of oxygen from air in test preparation. The two-step procedure was evaluated at three levels of mixing intensity (G = 0, 470, 1006 sec-1) using a dosage of 0.5 gm (1.0 mg/L) and a L/S ratio of 1000 mL/gm for the two standard materials. The ABF obtained from both phases of the test ranged 95 ~ 102 % for the SRM; and the RBFG and RBFI ranged |
