Environ. Sci. Technol. doi:10.1021/es201010f (2011)

Quantum dots have applications in biomedical imaging, solar panels and various lighting technologies, and these semiconductor nanocrystals may eventually enter environmental compartments such as the soil column. Although the polymer coating around certain quantum dots is thought to be stable, Diana Aga and colleagues from the State University of New York in Buffalo now show that the integrity of quantum dots in soil will compromise over time depending on their formulation.

Aga and co-workers packed soil into a polypropylene column and saturated it with calcium chloride, which represents artificial rain. CdSe, CdSe/ZnS and polymer-coated quantum dots were applied to the top of the soil column and different leaching solutions that represent rain or chelating agents in the environment were introduced. Fractions of the eluate were collected and analysed for cadmium and selenium ion species. In the presence of calcium chloride, more than 70% of the total cadmium and selenium species from the quantum dots remained on top of the soil column, suggesting that quantum dots will not move even when rained upon. Introducing EDTA (a common chelating agent used in various household products), however, resulted in mobilization of cadmium and selenium species. Polymer-coated quantum dots that were incubated in the soil for up to 15 days before being subjected to leaching solutions showed degradation and reduced mobility, suggesting that aging in soil can affect the mobility of the quantum dots.

Although the mechanisms for how the quantum dots are transformed in the soil are unknown, it is clear that they are susceptible to changing environmental conditions.