Toxicity of Oxidatively Degraded Quantum Dots

PIs: Joel A. Pedersen, Robert J. Hamers, Warren Heideman, Richard E. Peterson

Environmental conditions have the potential to alter nanoparticles (NPs) in a variety of ways (e.g., aggregation/agglomeration, dissolution, acquisition of coatings, redox transformations) making it unlikely that organisms will be exposed to NPs solely in their as-synthesized form. Few NP toxicity studies, however, have focused on environmentally altered NPs. We previously examined the oxidative stability of PEGylated CdSecore/ZnSshell quantum dots (QDs) under conditions representative of the extracellular environment of lignolytic fungi. Exposure of QDs to these conditions resulted in dissolution of the ZnS shell, release of Cd from the core, and production of amorphous Se-containing aggregates. We used embryonic zebrafish as a model to investigate changes in toxicity between as-synthesized and weathered QDs. Following 5-day exposure, weathered QDs were more potent (lower LC50) in causing mortality than as-synthesized QDs. Interestingly, both as-synthesized and weathered QDs were more potent in causing early life stage toxicity than equivalent concentrations of dissolved Cd. Although morphological endpoints of toxicity were the same for as-synthesized and weathered QDs (e.g., pericardial and yolk sac edema, curved spine, craniofacial malformations and tail malformation), weathered QDs had higher potency. Additionally, the severity of some morphological endpoints increased following exposure to weathered QDs. To simulate the Se-containing aggregates produced by the assay, we synthesized elemental selenium NPs (SeNPs). Zebrafish embryos/larvae exposed to SeNPs alone showed minimal mortality and no morphological endpoints of toxicity. However, embryos/larvae co-exposed to SeNPs and dissolved Cd recapitulated the profile of toxicity endpoints observed following exposures to weathered QDs. The Se-containing aggregates produced following assay exposure likely modulate the toxicity of the weathered QDs. Thus, environmental weathering is capable of increasing the potency of QD-induced developmental toxicity to an aquatic vertebrate.

Morphological endpoints of toxicity observed include pericardial edema (pe), ocular edema (oe), yolk sac malformations (ysm), tail malformations (tm) and craniofacial malformations. PEG350 and PEG5000 denote the molecular weight of the poly (ethylene glycol) coating on the QDs.