Characterization, Imaging and Degradation Studies of Quantum Dots in Aquatic Organisms

There are numerous potential environmental risks of engineered nanoparticles that are not yet well-characterized or understood. Nanoparticles may be introduced into aquatic environments during production processes and also as a result of release following their use in electronic and biological applications. The objectives of these studies were to characterize the behavior of quantum dots (QD) in water, and the accumulation of and toxicity to potential biological receptors in aquatic ecosystems. There are natural differences in environmental factors that may affect the degradation rates of QD’s as well as their toxicity, including temperature, salinity, and pH conditions. To assess the responses under different pH conditions, nonfunctionalized QD’s composed of a Cd/Se core surrounded by a ZnS shell (Evident Technologies) were added to distilled water, at pHs of 4, 6, and 8, and the changes in fluorescent emission spectra over time were determined. Likewise, to determine the effects of salinity on degradation rates, QD’s were added to 0.22 filtered seawater samples of different salinities (10, 20, and 30‰). The accumulation and potential toxicity of QD’s were evaluated using hepatopancreas cells of oysters, Crassostrea virginica.Fluorescent spectroscopy studies with water and cell samples indicated some degradation in low pH and high salinity waters, but did not indicate that there was increased degradation of QD’s accumulated in cells. Fluorescent confocal microscopy verified that QD’s were accumulated into the hepatopancreas cells. Transmission electron microscopy (TEM) studies verified cellular accumulation, and also indicated some limited degradation of the QD’s by the cells over the short time periods (e.g. hours) used in these preliminary studies. Using a lysosomal destabilization assay, there was some evidence of toxicity to hepatopancreatic cells. These kinds of basic studies are essential for characterizing potential cellular toxicity and addressing the potential impacts of nanoengineered particles on aquatic organisms and basic cellular responses.