Dynamic probabilistic material flow analysis of engineered nanomaterials in European waste treatment systems

Knowledge on the material flows of engineered nanomaterials (ENMs) is crucial for assessing their environmental risks. Waste management processes constitute important parts of material flow analyses as they affect large fractions of the ENMs. Accordingly, their detailed representation could substantially improve the models. Our goal was to consider the temporal variations of wastewater and solid waste management in the dynamic probabilistic material flow analysis of carbon nanotubes (CNTs), nano-Ag, -TiO₂ and -ZnO in Europe from 2000 to 2020. New input parameters included wastewater and solid waste management rates for each year. The uncertainties associated with these data were assessed based on the type of consulted source, the geographical representativeness and temporal concordance. Results show modal values of 10-27% of ENMs going from sorting to reprocessing. Large shares of environmental releases of nano-Ag and nano-ZnO end in surface water (4.9 t and 1700 t respectively in 2020), while sludge-treated soil as environmental compartment is receiving most of nano-TiO₂ (22,000 t in 2020) and CNTs (8.8 t in 2020). Discharges from wastewater management to the subsurface soil make this compartment the largest environmental sink of nano-Ag and nano-ZnO (30 t and 3860 t accumulated in 2020, respectively). Landfills represent significant stocks of ENMs, with 105 t, 2077 t, 69,000 t and 1042 t of nano-Ag, nano-ZnO, nano-TiO₂ and CNTs. This model includes detailed descriptions of waste management and sources of ENMs released at the European scale. However, a better understanding of the behaviour, i.e. fate and potential transformations of ENMs in reprocessing systems, is needed to complete the full assessment.