Uptake of nanoparticles from sunscreen physical filters into cells arising from increased environmental microwave radiation: increased potential risk of the use of sunscreens to human health.

This study examines the microwave chemical risks posed by photocatalysts present in sunscreens (physical filters) against the increasing use of microwaves (radio waves) in the environment, sometimes referred to as electronic smog. Specifically, the study assesses the damage caused by silica-coated physical filters (photocatalysts, TiO2⋅ and/or ZnO) contained in commercially available sunscreens and fresh silica-coated ZnO for sunscreens to mouse skin fibroblasts cells (NIH/3T3) evaluated in vitro by the life/death of cells using two types of electromagnetic waves: UV light and microwave radiation, and under simultaneous irradiation with both UV light and microwaves. Conditions of the electromagnetic waves were such as to be of lower light irradiance than that of UVA/UVB radiation from incident sunlight, and with microwaves near the threshold power levels that affect human health. The photocatalytic activity of the physical filters was investigated by examining the degradation of the rhodamine B (RhB) dye in aqueous media and by the damage caused to DNA plasmids from E. coli. Compared to the photocatalytic activity of ZnO and TiO2 when irradiated with UV light alone, a clear enhanced photocatalytic activity was confirmed upon irradiating these physical filters concurrently with UV and microwaves. Moreover, the uptake of these metal oxides into the NIH/3T3 cells led to the death of these cells as a result of the enhanced photocatalytic activity of the metal oxides on exposure to microwave radiation.