The objective of this study was to compare the cytotoxicity of monomeric and aggregated cadmium telluride quantum dots (CdTe QD) in human hepatoma (HepG2) and rainbow trout hepatocytes (RTH). Hepatocytes were exposed to concentrations of monomeric CdTe QDs (4 nm diameter) and isolates of different size aggregates for 48 h. The results revealed that the added Cd concentration in the cell culture media increased with the additions of both the monomeric and aggregated QDs where most (72%) of the total Cd was between 100 and 450 nm diameter size range as determined by ultrafiltration. CdTe QDs were cytotoxic to both cell types with an estimated 48 h-EC50 of 3.6 and 7.3 mg/L Cd for monomeric CdTe QDs for the HEPG2 and trout hepatocytes respectively. For the aggregated QDs, analysis of the concentration-response slopes revealed that HepG2 cells were able to significantly discriminate between 2 size ranges: nanoparticles < 4.6 nm and aggregates between 4.6 and 450 nm with the < 4.6 nm group being more toxic than the latter. The RTH model discriminated between 3 distinct size ranges in decreasing order of toxicity: 6.8 nm and smaller > 6.9-50 nm > 50-450 nm. In all cases, the toxicity of QD aggregates decreased with increasing size of the aggregates.
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