Dermal absorption and short-term biological impact in hairless mice from sunscreens containing zinc oxide nano- or larger particles

Abstract

Previous studies have shown no, or very limited, skin penetration of metal oxide nanoparticles following topical application of sunscreens, yet concerns remain about their safety compared to larger particles. Here, we assessed the comparative dermal absorption of a traceable form of Zn (68Zn) from 68ZnO nano-sized and larger particles in sunscreens. Sunscreens were applied to the backs of virgin or pregnant hairless mice over four days. Control groups received topical applications of the sunscreen formulation containing no ZnO particles, or no treatment. Major organs were assessed for changes in 68Zn/64Zn ratios, 68Zn tracer and total Zn concentrations. Short-term biological impact was assessed by measuring levels of serum amyloid A in blood, and by performing whole-genome transcriptional profiling on livers from each group. Increased concentrations of 68Zn tracer were detected in internal organs of mice receiving topical applications of 68ZnO (nano-sized and larger particles), as well as in fetal livers from treated dams, compared with controls. Furthermore, concentrations of 68Zn in organs of virgin mice treated with sunscreen containing 68ZnO nanoparticles were found to be significantly higher than in mice treated with sunscreen containing larger 68ZnO particles. However, no ZnO-mediated change in total Zn concentration in any of the major organs was observed. Thus, despite 68Zn absorption, which may have been in the form of soluble 68Zn species or 68ZnO particles (not known), Zn homeostasis was largely maintained, and the presence of ZnO particles in sunscreen did not elicit an adverse biological response in the mice following short-term topical applications.

Release of engineered nanomaterials from personal care products throughout their life cycle

“…Some studies indicate ZnO is a better UV blocker because it is more transparent and covers a broader UVA spectrum than TiO 2 (Morabito et al 2011). However, others question its effectiveness as a photoblocker (Lewicka et al 2013), and there are also some health concerns (Osmond-McLeod et al 2013). Nevertheless, there has been a steady and significant increase in the use of ZnO in sunscreens since its approval in 1997 (Wang et al 2013).…”

Nanomaterial translocation–the biokinetics, tissue accumulation, toxicity and fate of materials in secondary organs–a review

“…As an example, amorphous silica seems to dissolve in tissues over time . Additionally, dissolution of ZnO NMs might be important for their rapid distribution from the lung (Konduru et al 2014) and slow uptake on the skin (Osmond-McLeod et al 2014). Cadmium-based QDs and Ag are examples of NMs that are likely to be oxidised in physiological environments ).…”

Bridging the divide between human and environmental nanotoxicology

“…OsmonMcLeod et al 47 faced a similar challenge while assess ing dermal adsorption of ZnO nanoparticles. Their solution was to use isotopically enriched nanoparticles, and this approach could also be applied in algal toxicity testing.…”