| Summary: | 碩士 === 國立交通大學 === 環境工程系所 === 104 === 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.
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