Pharmaceutical and cosmetic silica nanoparticles: towards an understanding of their structure, fate and behaviour in aquatic systems

Engineered oxide nanoparticles are widely used in cosmetics and personal care products (e.g. sunscreens, toothpastes, skin creams) and in topically-applied pharmaceutical formulations (e.g. creams for local and transdermal application) and are routinely released into wastewaters. This Small Grant examines the loadings of SiO2 nanoparticles to wastewaters from typical domestic use of cosmetic and pharmaceutical formulations, the efficiency of removal of SiO2 nanoparticles by wastewater chemical treatment (flocculation and sedimentation) and stability, structure and behaviour of SiO2 nanoparticles in natural waters. SiO2 nanoparticles were selected for this study as these types of oxide nanoparticles are widely used in the formulations under study. Previous research indicates that discrete nanoparticles and small aggregates are likely to be more bioavailable/toxic to aquatic organisms than larger aggregates and that flocculation and sedimentation of nanoparticles are likely to mitigate ecotoxicity and reduce dispersion of nanoparticles within aquatic systems. Therefore, this study provides a series of laboratory experiments to measure the dispersion-aggregation behaviour of SiO2 nanoparticles under a range of aquatic chemical conditions, thereby assessing whether SiO2 nanoparticles are likely to agglomerate and sediment out during chemical water treatment and when discharged into surface waters. Our hypotheses are: (1) Cosmetics (sunscreens, toothpaste) and pharmaceuticals (topically applied creams) provide a significant source of SiO2 nanoparticles to wastewaters. (2) Chemical water treatment (flocculation and sedimentation) is limited in its effectiveness in removing SiO2 nanoparticles. There is therefore potential for discharge of oxide nanoparticles via treated effluent into surface waters (3) The stability, transport and fate of SiO2 nanoparticles in aquatic environments (in relation to aggregate size, structure and rates of sedimentation), are influenced by: (a) aqueous matrix chemistry (pH, ionic strength and composition), (b) interactions with natural organic matter and (c) interactions with aquatic sediments.