A Multilevel Risk Assessment Framework for Nanoplastics in Aquatic Ecosystems

To date, the assessment of risks related to nanoplastics (NPLs) has been incipient. Attempts to establish safety levels to support decisions regarding restrictions on the use or reuse of materials derived from petrochemicals are critical, but the complexity of datasets makes it difficult to communicate potential NPLs-related environmental risks. Therefore, it seems essential to reduce the relevant data to a factor/number that makes it easier to clarify whether there is a risk and, above all, easily report relevant information to legislators so that prohibition, reductions, and/or readjustments to monitoring programs can be implemented accordingly. Accordingly, this study aimed to propose an improved and tiered risk assessment for NPLs following the NORMAN network, which may be outlined as follows: (i) conducting screenings to assess the risk level through deterministic methodologies (involving the collection of effective concentrations or, in their absence, the no-effect or lowest-effect concentrations, also known as NOEC and LOEC, respectively); (ii) comparing exceedance levels of risk values obtained previously in relation to predicted non-environmental effective concentrations (PNECs); and (iii) ranking the different NPL types based on prioritization indeces to facilitate future decision-making. Of a total of six polymers for which data are available, it was only possible to deliver prioritization indices for three (two freshwater and one saltwater) due to the lack of PNEC or predicted environmental concentrations (PECs). The majority of the research on this topic is focused on PS. PS is classified as a high-priority polymer, since its estimated prioritization index was >= 65 (the base value is 1). Furthermore, in freshwater, PE was also indicated to be a priority polymer (with a prioritization index exceeding 1000). It should be noted that for other widely used polymers (such as PMMA or PVC), there is insufficient data. It is therefore clear that current management and control measures for products containing PS and PE must be reconsidered to reduce NPLs' environmental impacts.