A Meta‐analysis of Ecotoxicological Hazard Data for Nanoplastics in Marine and Freshwater Systems

Abstract

There is emerging concern about the potential health and environmental impacts of nanoplastics in the environment. Information on exposure has been lacking, but a growing amount of ecotoxicological hazard data is now available, allowing a hazard assessment to be conducted for nanoplastics in freshwater and marine systems. Based on a critical evaluation of published studies and the construction of probabilistic species sensitivity distributions (PSSDs), we present a comprehensive, state-of-the-art understanding of nanoplastic ecotoxicity. Different freshwater and marine datasets were constructed based on different data quality levels, and for each of the datasets, PSSDs were built for both mass-and particle number-based concentrations. Predicted no-effect concentrations (PNECs) were then extracted from the PSSDs. We report PNECs at 99 and 72 μg L-1 , respectively, for the freshwater and marine dataset after the removal of data measured in the presence of sodium azide (NaN 3), which is considered to be a major interfering factor in the ecotoxicity testing of nanoplastics. By comparing the PNECs, we found that nanoplastics are less toxic than microplastics and many engineered nanomaterials. In addition, the effects of size and polymer type on toxicity were also statistically tested. We observed no significant difference in ecotoxicity for nanoplastics of different sizes, whereas polystyrene nanoplastics were significantly more toxic than all other tested nanoplastics. In conclusion, the results we present provide a comprehensive description of nanoplastic ecotoxicity based on current knowledge. The results constitute a fundamental step toward an environmental risk assessment for nanoplastics in freshwater and marine systems.

Illustrating a Species Sensitivity Distribution for Nano‐ and Microplastic Particles Using Bayesian Hierarchical Modeling

“…For chemicals, on average, such systematic differences in effect concentrations between freshwater and saltwater species were not observed (see de Zwart, 2002; Wheeler et al, 2002, 2014). According to a previous study that derived SSDs for nanoplastics (Yang & Nowack, 2020), the HC5 value estimated based on the full data set obtained in marine media (1.3 μg/L) was lower than that obtained in freshwater media (71 μg/L), but values were comparable after removing data measured in the presence of NaN 3 . It is not possible to identify the underlying reasons because of the limited availability of data.…”

“…We incorporated the reference‐level random effects (parameter r ) in the HSSD modeling to describe the variations in effect concentrations due to reference‐specific unmodeled factors. These unmodeled factors include differences in physicochemical conditions (e.g., the presence or absence of NMP particle preprocessing including removal of sodium azide stabilizer (Besseling et al, 2019; Yang & Nowack, 2020) and biological conditions (e.g., developmental stage and origin of organisms) in tests. Without incorporating random effects in the estimation of HC5, the posterior medians of HC5 were 166.0 and 17.6 μg/L for plastic particles with a size of 0.1 μm in freshwater and marine environments, respectively.…”

“…Furthermore, to consider the influence of polymer type of NMP particles, we categorized them as (1) polystyrene and mixtures of polystyrene and polyethyleneimine ( n = 18 and 4, respectively; hereafter, PS) or (2) other polymer types (polyethylene, n = 3; polyvinyl chloride, n = 1). This is because the numbers of individual polymer types, excluding polystyrene, were very limited and because the difference in effect concentrations between polystyrene and non‐polystyrene was detected (Yang & Nowack, 2020). We used a binary dummy variable corresponding to the two polymer types (polymer types other than PS, 0; PS, 1) as a predictor variable.…”

“…Some reference (or test)–specific unmodeled factors may also influence the effect concentrations. For example, previous studies noted the variations in effect concentrations due to other properties of NMP particles, including origin (pristine particles or particles collected in the field) and removal of sodium azide (NaN 3 ) stabilizer for nanoplastic particles (Besseling et al, 2019; Yang & Nowack, 2020). Thus, we included the reference‐level random effects ( r j ) in the HSSD models to consider such influences that could not be captured by the three predictor variables of particle size, polymer type, and type of medium.…”

How Relevant Are Direct Emissions of Microplastics into Freshwater from an LCA Perspective?

“…When including HONEC (Highest Observed No Effect Concentration) values, there was a trend that particles larger than 100 µm had a larger NOEC, i.e., were less toxic. A meta-analysis of nanoplastics ecotoxicity data [55] revealed that the nanoplastic predicted no-effect concentration (PNEC) was much larger than the microplastics PNEC, suggesting that smaller plastic particles are not necessarily more toxic as often suggested. Hence, the use of one effect factor for all sizes of microplastics is, therefore, a suitable approach given the current state of knowledge.…”