January 28, 2009 -- Researchers in Texas are reporting that quantum dots (QDs) — a product of the revolution in nanotechnology increasingly used in electronics, solar cells, and medical imaging devices — may be toxic to cells under acidic or alkaline conditions. Their study, the first to report on how different pH levels may affect the safety of QDs, appears in the Jan.15 issue of ACS’Environmental Science & Technology, a semi-monthly journal.
In the new study, Pedro Alvarez, Shaily Mahendra, and colleagues note
that QDs are semiconductor nanocrystals composed of a metal core surrounded by a shell composed of zinc or cadmium sulfide. Scientists are increasingly concerned that these submicroscopic dots, about 1/50,000th the width of a human hair, could decompose during normal use or after disposal. That decomposition could release toxic metals into the environment, posing a health risk to humans and animals.
To explore this concern, the scientists exposed two common types of
bacteria that serve as models of cell toxicity and indicators of
environmental health to QDs under different conditions of acidity and
alkalinity. At near neutral pH levels, bacteria exposed to
QDs experienced decreased rates of growth, but did not die. However, at
moderately acidic or alkaline conditions, many of the QD-exposed
bacteria died as QDs shells decomposed, releasing their content of
toxic metals. However, proteins and natural organic matter
may be able to mitigate toxicity by complexing metal ions or coating
particles. The study cautions, “the release of toxic inorganic
constituents during their weathering under acidic or alkaline
conditions in the human body or the environment may cause unintended harm that might be difficult to predict with short-term toxicity tests.”
-- News release courtesy of American Chemical Society