Biodistribution of Cadmium Selenide/Zinc Sulfide Quantum Dots in Aquatic Organisms

This thesis investigates the biodistribution and toxicological effects of amphiphilic polymer coated CdSe/ZnS quantum dots (QDs) in two aquatic species, Daphnia magna (daphnia) and Danio rerio (zebrafish). The use of QDs in the life sciences has become common practice over the past decade. In addition QDs are being incorporated in commercially available light emitting diodes and photovoltaic solar cells. As the widespread commercial use of QDs increases, environmental release is inevitable, and water will contain the highest environmental concentrations based on life cycle assessments. Despite increased attention to the aquatic toxicology of nanomaterials in recent years, little information exists on the biological fate of QDs in aquatic organisms. Quantitative data on the uptake and excretion of QDs from daphnia and zebrafish were collected using fluorescence imaging paired with metal analysis. First, daphnia were examined after aqueous and dietary exposure to amphiphilic polymer coated CdSe/ZnS QDs. Surface coating influenced QD acute toxicity and high particle aggregation correlated with daphnia mortality. QDs were readily ingested by daphnia and accumulated in the intestines. High body burdens of 150-200 μg/g were found in the daphnia, with intestinal QD concentrations significantly elevated above the exposure media concentration. The slow elimination observed in daphnia suggested that trophic transfer of QDs to higher organisms may occur. Using daphnia and zebrafish as a model food chain revealed that QDs can transfer to zebrafish through dietary exposure with body burdens of 8-9.5 μg/g found. However, no biomagnification between daphnia and zebrafish was observed and the biomagnification factor (BMF = 0.04) was significantly less than one. This work demonstrates that aqueous and dietary exposures to QDs can result in high total body concentrations in aquatic organisms with little to no gross toxicity. The low acute toxicity observed for some surface coated QDs encourages further design optimization to improve the biocompatibility and reduce the environmental impact of QDs