Detection, Measurement and Toxicology of Semiconductor Nanocrystals in Ceriodapnia dubia

We have begun assessing the toxicology of commercially available fluorescent semiconductor nanocrystals that contain toxic metals. We have found that: 1) Fluorescence of the aquatic invertebrate Cerodaphnia dubia increased significantly after a 4 hr exposure to 200 ppt nanocrystals. Changes in fluorescence were time and dose dependent. 2) 48-h acute toxicology endpoint assessment of these nanocrystals (using US EPA standard protocol) found no measurable toxicity at concentrations as high as 100 ppb ([Cd] in 100 ppb nanocrystals was >7000 ppb). Measured Cd LC50 in 48-h laboratory exposures was 28.55 ppb. 3) Inductively coupled plasma mass spectrometry (ICPMS) can be used to detect and measure Cd and Se in organisms exposed to these nanocrystals. These results suggest that coatings present on nanocrystals provide a protective measure from toxic metals during acute exposures.