The Life and Times of Sunscreen

Abstract

Chemistry![Figure][1] CREDIT: [PHOTOS.COM][2] Nanomaterials boast a multitude of current and projected commercial uses that take advantage of their unique and beneficial properties, but the health and environmental risks they present are relatively unknown. Screening and eventual regulation are problematic because even materials of the same chemical composition have such a wide range of morphologies (including size, shape, coating, aggregation state, and crystalline phase variations) that affect their reactivity. In a demonstration of the complexity of such systems, Labille et al. examined the aging of composites of titanium dioxide (TiO2) nanoparticles commonly used in sunscreen and cosmetics. The composites—composed of several nanoparticles surrounded by a thin Al(OH)3 shell and bound in a hydrophobic polymer matrix—dispersed in water over time because of the degradation of the polymer. When aged in the presence of light, the polymer degradation rate increased, possibly due to photocatalysis by TiO2. In either case, once the polymer degraded, the remaining Al(OH)3 shell determined the stability of the composites. Stability was also sensitive to the concentration of natural organic matter; at low levels characteristic of groundwater, the composites aggregated, but higher levels characteristic of surface waters kept the composites suspended. These and similar studies raise the question of whether the nanomaterials studied and characterized in laboratory settings look or behave as they do in the environment. Environ. Pollut. 158 , 10.1016/j.envpol.2010.02.012 (2010). [1]: pending:yes [2]: http://PHOTOS.COM