Evidence That Nanoparticles
in Sunscreens Are Toxic
Scientists are reporting that particle size affects the toxicity of zinc oxide, a material widely used in sunscreens. Particles smaller than 100 nanometers are slightly more toxic to colon cells than conventional zinc oxide. Solid zinc oxide was more toxic than equivalent amounts of soluble zinc, and direct particle to cell contact was required to cause cell death. Their study is in ACS' Chemical Research in Toxicology, a monthly journal.
The Environmental Working Group who previously analyzed 15 studies on nanoparticles on sunscreen said that no investigations have ever assessed absorption through damaged skin. Such data is missing “for nearly all of the 17 sunscreen chemicals approved for use in the U.S.”
Philip Moos and colleagues note that there is ongoing concern about the potential toxicity of nanoparticles of various materials, which may have different physical and chemical properties than larger particles. Barely 1/50,000 the width of a human hair, nanoparticles are used in foods, cosmetics and other consumer products. Some sunscreens contain nanoparticles of zinc oxide. The scientists note that a concern is children accidentally ingesting nano-sized zinc oxide.
Their experiments with cell cultures of colon cells compared the effects of zinc oxide nanoparticles to zinc oxide sold as a conventional powder. They found that the nanoparticles were twice as toxic to the cells as the larger particles.
Amanda Barnard, of CSIRO's materials science and engineering division, found nanoparticles that provided the best transparency and sun protection were also the biggest producers of potentially-harmful free radicals.
With computer modelling, Dr Barnard studied man-made titanium dioxide nanoparticles found in some sunscreens and tested them in three areas: sun protection, transparency and potential free-radical production.
She found sunscreens with smaller nanoparticles had a higher surface-to-volume ratio, providing more scope for free radical production through photochemical reaction.
Although the nominal particle size was 1,000 times larger, the conventional zinc oxide contained a wide range of particle sizes and included material small enough to be considered as nanoparticles. The concentration of nanoparticles that was toxic to the colon cells was equivalent to eating 2 grams of sunscreen -- about 0.1 ounce. This study used isolated cells to study biochemical effects and did not consider the changes to particles during passage through the digestive tract. The scientists say that further research should be done to determine whether zinc nanoparticle toxicity occurs in laboratory animals and people.
April 8, 2010