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An assessment of the fate, behaviour and environmental risk associated with sunscreen TiO₂ nanoparticles in UK field scenarios

Johnson, Andrew C., Bowes, Michael J., Crossley, Alison, Jarvie, Helen P., Jurkschat, Kerstin, Jürgens, Monika D., Lawlor, Alan J., Park, Barry, Rowland, Phillip, Spurgeon, David, Svendsen, Claus, Thompson, Ian P., Barnes, Robert J., Williams, Richard J., Xu, Nan
The Science of the total environment 2011 v.409 no.13 pp. 2503-2510
activated sludge, application rate, bacteria, direct contact, earthworms, effluents, fertilizers, industrial applications, nanoparticles, prediction, risk, river water, rivers, sewage, sewage sludge, sewage treatment, titanium dioxide, toxicology, ultraviolet radiation, viability, England
The fate of Ti was examined in an activated sludge plant serving over 200,000 people. These studies revealed a decrease of 30 to 3.2μg/L of Ti<0.45μm from influent to effluent and a calculated Ti presence of 305mg/kg DW in wasted sludge. Thus, using sludge as a fertiliser would result in a predicted deposition of up to 250mg/m² of Ti to soil surfaces using a recommended maximal agricultural application rate. Given the major use of TiO₂ in many industrial and domestic applications where loss to the sewer is possible, this measured Ti was presumed to have been largely TiO₂, a proportion of which will be nanoparticle sized. To assess the behaviour of engineered nanoparticle (ENP) TiO₂ in sewage and toxicology studies, Optisol (Oxonica Materials Ltd) and P25 (Evonik Industries AG), which are representative of forms used in sunscreen and cosmetic products, were used. These revealed a close association of TiO₂ ENPs with activated sludge. Using commercial information on consumption, and removal rates for sewage treatment, predictions were made for river water concentrations for sunscreen TiO₂ ENPs for the Anglian and Thames regions in Southern England. The highest predicted value from these exercises was 8.8μg/L for the Thames region in which it was assumed that one in four people used the recommended application of sunscreen during a low flow (Q95) period. Ecotoxicological studies using potentially vulnerable species indicated that 1000μg/L TiO₂ ENP did not affect the viability of a mixed community of river bacteria in the presence of UV light. Direct exposure to TiO₂ ENPs did not impair the immuno-effectiveness of earthworm coelomocyte cells at concentrations greatly above those predicted for sewage sludge.