Catching nano: Evaluating the fate and behaviour of nano-TiO₂ in swimming pools through dynamic simulation modelling

Engineered titanium dioxide nanoparticles (nano-TiO₂) in consumer products such as sunscreens widely used by swimmers in aquatic settings have raised concerns about their potential adverse impact on ecosystems and human health due to their small size and unique physicochemical properties. Therefore, this research paper aims to investigate the fate and behaviour of nano-TiO₂ from sunscreens in swimming pools using System Dynamics Modelling. The study developed a dynamic simulation model that considers various factors, including weather conditions, sunscreen and pool usage behaviour, filtration efficacy, pool maintenance, water chemistry, pool chemicals, and TiO₂ concentration levels, which can affect exposure levels for different scenarios. The study considered non-linear interdependent relationships, feedback structures, and temporal changes and dealt with parameter uncertainties through Monte Carlo analyses. The results reveal that the regular use of sunscreen leads to nano-TiO₂ concentrations ranging from 0.001 to 0.05 mg/L within a year, reflecting seasonal and pool usage variations. The study also found that changes in the weight percentage of TiO₂ in the sunscreen formulation and the filtration duration per day are the most sensitive factors affecting TiO₂ concentrations. Scenario analyses exploring different nano-TiO₂ removal strategies suggested that one daily turnover is necessary for sufficient removal. Regular manual pool maintenance and monthly use of a pool clarifier are recommended for enhanced and accelerated removal without substantial additional costs. The study is novel in its integrated approach, combining empirical work with dynamic simulations, resulting in a novel approach to model the environmental fate and behaviour of nano-TiO₂. The study makes important methodological contributions to the field and has initiated an interdisciplinary collaboration to create more accurate models. This study is of great significance as it presents a pioneering analysis of the impact of sunscreen properties, user behaviour, and environmental stressors on the fate and behaviour of nano-TiO₂ in swimming pools.