Closing the gap between small and smaller: towards a framework to analyse nano- and microplastics in aqueous environmental samples

Measuring concentrations and sizes of micro- and nanoplastics in the environment is essential to assess the risks plastic particles could pose. Microplastics have been detected globally in a variety of aquatic ecosystems. The determination of nanoplastics, however, is lagging behind due to higher methodological challenges. Here, we propose a framework that can consistently determine a broad spectrum of plastic particle sizes in aquatic environmental samples. Analytical evidence is provided as proof of principle. FTIR microscopy is applied to detect microplastics. Nanoplastics are studied using field-flow-fractionation and pyrolysis GC-MS that gives information on the particle sizes and polymer types. Pyrolysis GC-MS is shown to be promising for the detection of nanoplastics in environmental samples as a mass of approximately 100 ng is required to identify polystyrene. Pre-concentrating nanoplastics by crossflow ultrafiltration enables polystyrene to be identified when the original concentration in an aqueous sample is >20 g L-1. Finally, we present an approach to estimate polymer masses based on the two-dimensional microplastic shapes recorded during the analysis with FTIR microscopy. Our suite of techniques demonstrates that analysis of the entire size spectrum of plastic debris is feasible. Environmental significance Microplastics have been detected globally in various ecosystems. Recent experimental, modelling and field studies point towards nanoplastics also being present. With a decrease of particle sizes an increase of the particles' toxicity is widely assumed. To assess the risks that are related to plastic litter in the environment, effect and exposure concentrations need to be known and combined. Addressing the latter, we here present a framework that is able to sample and to consistently determine concentrations and sizes of plastics down to a size of 50 nm in an aqueous environmental sample.