Cadmium Selenide quantum dots release toxic ions in soil

Cadmium Selenide quantum dots release toxic ions in soil

4:39 PM, 19th July 2011
Cadmium Selenide quantum dots release toxic ions in soil
It's important for scientists to learn more about how quantum dots and other nanomaterials interact with the environment after disposal, said Diana Aga, Chemistry Professor.

BUFFALO, US: Quantum dots made from cadmium and selenium degrade in soil, unleashing toxic cadmium and selenium ions into their surroundings, a University at Buffalo study has found.

The research, accepted for publication in the journal Environmental Science and Technology, demonstrates the importance of learning more about how quantum dots - and other nanomaterials - interact with the environment after disposal, said Diana Aga, the Chemistry Professor who led the study.

Quantum dots are semiconductor nanocrystals with diametre of about 2 to 100 nanometre. Though quantum dots are not yet commonly used in consumer products, scientists are exploring the particles’ applications in technologies ranging from solar panels to biomedical imaging.

“Quantum dots are not yet used widely. But they have a lot of potential and we can anticipate that the use of this nanomaterial to increase,” said Aga, who presented the findings in late June at a National Science Foundation-funded workshop on nanomaterials in the environment.

Aga’s research into the afterlife of quantum dots is funded by a $400,000 Environmental Protection Agency grant to investigate the environmental transport, biodegradation and bioaccumulation of quantum dots and oxide nanoparticles.

Her collaborators on the new study in Environmental Science and Technology include PhD student Divina Navarro, Assistant Professor Sarbajit Banerjee and Associate Professor David Watson, all of the UB Department of Chemistry.

Working in the laboratory, the team tested two kinds of quantum dots: Cadmium selenide quantum dots and cadmium-selenide quantum dots with a protective, zinc-sulfide shell. Aga’s team found that both varieties of quantum dot leaked toxic elements within 15 days of entering soil.

The researchers also used calcium chloride solution to mimic rain. What they observed: Almost all the cadmium and selenium detected in each of the two columns - more than 90 per cent of that in the column holding unshelled quantum dots and more than 70 per cent of that in the column holding shelled quantum dots - remained in the top 1.5 centimetre of the soil.

But how the nanomaterials moved depended on what else was in the soil. Aga said that even if the quantum dots remain in top soil, without contaminating underground aquifers, the particles’ degradation still poses a risk to the environment.

In a separate study submitted for publication in a different journal, she and her colleagues tested the reaction of Arabidopsis plants to quantum dots with zinc sulfide shells. The team found that while the plants did not absorb the nanocrystals into their root systems, the plants still displayed a typical phytotoxic reaction upon coming into contact with the foreign matter; in other words, the plants treated the quantum dots as a poison.

(C) 2011 University at Buffalo News




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