Abstract
M.Sc. (Applied Chemistry)
Products that contain engineered nanomaterials (ENMs) are called nano-enabled products (NEPs) and they exhibit varying extent to emit ENMs into environment as nanopollutants. The ENMs are an emerging class of environmental contaminants of which their potential environmental risk is yet to be fully understood. Sunscreens can be incorporated with ENMs, commonly titanium dioxide (TiO2) ENMs in order to enhance UV absorption and protection against UV rays. Sunscreens are a dominant NEP type across international markets and exhibit high likelihood to release ENMs into the environment as the ENMs are suspended in liquid and cream, hence they are a priority source of nanopollutants specifically into waste and natural water systems. The current study examined the characteristics of ENMs incorporated in sunscreens as well as those released from sunscreen use. A sample of four sunscreens enabled with TiO2 ENMs (A–D) and one (E) containing TiO2 were selected. An extraction protocol infusing solvent and physical separation steps was adopted to extract the ENMs from the sunscreens. The extracts were examined by Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), Ultraviolet and Visible Spectrophotometry (UV/Vis), Inductively Coupled Plasma Mass Spectroscopy (ICP-MS), and the nanoparticle tracking analysis (NTA) in order to characterise and quantify the ENMs for size, shape, and concentration properties. The presence of TiO2 ENMs was confirmed in all the sunscreen samples.
The modal sizes of the TiO2 ENMs obtained from SEM analysis for sunscreen A, B, C, and E were 67.6, 69.8, 51.8, and 106.5 nm respectively and no TiO2 ENM was detected in sunscreen D with EDS. From analysis with TEM the modal sizes for sunscreen A, B, and C were 73.9, 81.5 and 44.7 nm respectively. Sunscreens D and E were not examined with TEM. The ENMs were predominantly of needle-like, plate, rod, and irregular shapes. The concentration of TiO2 ENMs in sunscreen A, B, C and E were 1.9, 0.6, 0.5 and 2.1 %w/w respectively, whereas it was below detection level in sunscreen D. Overall,..