nC60於天然有機物與黏土礦物水溶液中之聚集行為及其對斑馬魚胚胎發育之影響

Abstract

富勒烯(fullerene, C60)具親電、導電、導熱和吸附能力等優異的物化特性使得其廣泛應用於半導體奈米元件、藥物載體以及藥妝和能源產業，但隨著商業化量產的同時，C60暴露至環境的機率亦跟著上升，並能在水中形成穩定分散的膠體團粒(C60 aggregates, nC60)。天然水體組成複雜，nC60之形成性質受水質參數所改變，並間接影響其生物毒性，因此探討nC60毒性時若將環境因子一併納入實驗將更具說服力。本研究採用溶劑置換法製備nC60，探討四種水質參數，如pH、離子強度、天然有機物與黏土礦物，對nC60自由懸浮濃度及其粒徑與界達電位之影響，並利用斑馬魚(Danio rerio)胚胎評估nC60之毒性。 結果顯示隨pH值降低或是離子強度增高，nC60的聚集會越顯著。nC60於強酸性(pH < 3)以及離子強度大於10 mM之環境下均不易形成，但若水中同時存在天然有機物則有助於nC60生成並穩定懸浮於水中；天然有機物含量越高，自由懸浮狀態之nC60越多，其中腐植酸對nC60的分散效果大於黃酸。nC60與黏土礦物間的作用以靜電吸引力為主，因此當高嶺土濁度大於100 NTU時，nC60易吸附於高嶺土而非自由懸浮狀態。在班馬魚胚胎發育毒性方面，胚胎具絨毛膜保護時，20至35 mg/L的nC60會短暫性地延遲胚胎的孵化，但不會使其死亡或是畸形，毒性甚低。進一步將斑馬魚胚胎絨毛膜(chorion)提早脫去以提高其靈敏度後發現，nC60的致畸胎率會隨著水中腐植酸含量增加而小幅上升，且畸形型態以心包膜水腫(pericardial edema, PE)為主。綜觀上述，相較於水中無機物顆粒，天然有機物之存在除了會造成nC60物化性質上的改變，亦可能影響其對斑馬魚胚胎之毒性。

The increasing amount of fullerene (C60) released in aqueous environments as the result of its growing use has arisen concerns over its environmental fate. In the water, C60 can form stable, nanoscale and suspended aggregates (nC60) which might possess altered toxicity after its interaction with environmental components, such as ubiquitous natural organic matter (NOM) and clay minerals. Consequently, careful characterization of nC60 physicochemical properties in the natural aqueous environment is required in evaluating its toxicity. This study investigated the effects of humic acid (HA), fulvic acid (FA) and kaolin with various pH values and ionic strengths on the formation of nC60 — produced by solvent exchange (Tol/nC60) — in terms of suspended concentration, aggregate size, and zeta potential. Zebrafish (Danio rerio) embryo was used to study the developmental toxicity of nC60 with disparate physicochemical properties. The results have indicated that increased nC60 aggregation with decreasing pH value or increasing ionic strength, which is attributed to decreased electrostatic repulsion, consistent with the classical DLVO theory. NOM sterically has stabilized the nC60 suspension therefore it is easily formed and stable even at pH 3 or low ionic strength (10 mM NaCl). Besides, HA is more effective than FA in suppressing nC60 aggregation. Interactions between nC60 and clay minerals are primarily dominated by available surface area and electrostatic interaction at charged surfaces. As a result, more nC60 is suspended in the presence of clay minerals under low turbidity (2 ~ 100 NTU) than high turbidity (> 100 NTU). In addition, 20 to 35 mg/L of nC60 may cause hatching delay in zebrafish embryos but no mortality and malformation have been observed. With increasing humic acid concentrations, malformation rate has been found to slightly increase in dechorionated embryos. The major development abnormality caused by nC60 is pericardial edema. In conclusion, in the presence of NOM, the physicochemical properties of nC60 play a significant role in their reactions and subsequent zebrafish embryonic toxicity.