The vast amount of plastic waste emitted into the environment and the increasing concern of potential harm to wildlife has made microplastic and nanoplastic pollution a growing environmental concern. Plastic pollution has the potential to cause both physical and chemical harm to wildlife directly or via sorption, concentration, and transfer of other environmental contaminants to the wildlife that ingest plastic. Small particles of plastic pollution, termed microplastics (>100 nm and <5 mm) or nanoplastics (<100 nm), can form through fragmentation of larger pieces of plastic. These small particles are especially concerning because of their high specific surface area for sorption of contaminants as well as their potential to translocate in the bodies of organisms. These same small particles are challenging to separate and identify in environmental samples because their size makes handling and observation difficult. As a result, our understanding of the environmental prevalence of nanoplastics and microplastics is limited. Generally, the smaller the size of the plastic particle, the more difficult it is to separate from environmental samples. Currently employed passive density and size separation techniques to isolate plastics from environmental samples are not well suited to separate microplastics and nanoplastics. Passive flotation is hindered by the low buoyancy of small particles as well as the difficulty of handling small particles on the surface of flotation media. Here we suggest exploring alternative techniques borrowed from other fields of research to improve separation of the smallest plastic particles. These techniques include adapting active density separation (centrifugation) from cell biology and taking advantage of surface-interaction-based separations from analytical chemistry. Furthermore, plastic pollution is often challenging to quantify in complex matrices such as biological tissues and wastewater. Biological and wastewater samples are important matrices that represent key points in the fate and sources of plastic pollution, respectively. In both kinds of samples, protocols need to be optimized to increase throughput, reduce contamination potential, and avoid destruction of plastics during sample processing. To this end, we recommend adapting digestion protocols to match the expected composition of the nonplastic material as well as taking measures to reduce and account for contamination. Once separated, plastics in an environmental sample should ideally be characterized both visually and chemically. With existing techniques, microplastics and nanoplastics are difficult to characterize or even detect. Their low mass and small size provide limited signal for visual, vibrational spectroscopic, and mass spectrometric analyses. Each of these techniques involves trade-offs in throughput, spatial resolution, and sensitivity. To accurately identify and completely quantify microplastics and nanoplastics in environmental samples, multiple analytical techniques applied in tandem are likely to be required.

The efficacy of plastic particle removal by municipal water treatment plants is currently uncertain, and the mechanisms involved in microplastic (MP) coagulation and flocculation have only been superficially investigated. The removal of pristine versus weathered plastic debris and the impact of plastic particle size on removal remain largely unexplored. In this study, coagulation, flocculation, and settling performances were investigated using pristine and weathered MPs (polyethylene (PE) and polystyrene (PS) microspheres, and polyester (PEST) fibers). Weathering processes that changed the surface chemistry and roughness of MPs impacted MP affinity for coagulants and flocculants. A quartz crystal microbalance with dissipation monitoring was used to identify the mechanisms involved during MP coagulation and flocculation. Measured deposition rates confirmed the relatively low affinity between plastic surfaces and aluminum-based coagulants compared to cationic polyacrylamide (PAM). In every case examined, coagulant efficiency increased when the plastic surface was weathered. Removals of 97 and 99% were measured for PEST and weathered PE, respectively. Larger pristine PE MPs were the most resistant to coagulation and flocculation, with 82% removal observed even under enhanced coagulation conditions. By understanding the interaction mechanisms, the removal of weathered MPs was optimized. Finally, this study explored the use of settled water turbidity as a possible indicator of MP removal.

Wet, cold or freeze-thaw conditions enhanced the release of TiO2 nanoparticles from outdoor painted surfaces.

With growing applications of TiO 2 nanoparticles (NPs) in outdoor surface coatings, notably in paints and stains, their release into the environment is inevitable. While NP release has potential ecotoxicological risk, reliable risk assessments are often complicated by the near absence of analytical data on release rates under natural weathering scenarios, and the lack of a chemical characterization of the NPs following their release. This work measured NPs released from painted and stained surfaces and characterized them by size and composition using magnetic sector single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) and SP-ICP-time-of-flight-MS (SP-ICP-TOF-MS). Two in situ experimental plans were examined in which natural precipitation interacted with nano-enhanced surfaces to varying degrees during the fall and winter. Weathering data showed that longer contact times of the precipitation (snow and rain) resulted in greater NP release. Although the stained surfaces had far fewer NPs per unit area, they lost a much higher fraction of their NP load (max 6% leached, as opposed to <10 −4% in paints), over similar exposure times. NP release was particularly enhanced for conditions of frequent rainfall and spring snow melt (i.e., slushy snow). SP-ICP-TOF-MS measurements on the Ti NPs indicated that they were often associated with a secondary metal in both the liquid paint (Al was detected in ∼20% of the Ti NPs; Zr in about ∼1% of the NP) and the liquid stain (Fe was detected in ∼7%, Si in ∼8% and Al in ∼3% of the Ti NPs). In contrast, for the vast majority of Ti NPs being leached out of the painted/stained surfaces, only Ti was detected. Metal interactions in the paint were explained by binding of the TiO 2 within a complex paint matrix; while in the stain, TiO 2 NPs were hypothesized to be found in heteroagglomerates, potentially with aluminosilicates (Fe, Si, and Al). In rain and snow, Ti was the only element detected in about half of the Ti NPs; in the other half, Ti often co-occurred with Fe, Si and Al. The results indicate that single element, likely anthropogenic, Ti NPs are already prevalent in the natural precipitation and that NP release from surface coatings will further increase their presence in the environment.

Nanoparticle (NP) emissions to the environment are increasing as a result of anthropogenic activities, prompting concerns for ecosystems and human health. In order to evaluate the risk of NPs, it is necessary to know their concentrations in various environmental compartments on regional and global scales; however, these data have remained largely elusive due to the analytical difficulties of measuring NPs in complex natural matrices. Here, we measure NP concentrations and sizes for Ti-, Ce-, and Ag-containing NPs in numerous global surface waters and precipitation samples, and we provide insights into their compositions and origins (natural or anthropogenic). The results link NP occurrences and distributions to particle type, origin, and sampling location. Based on measurements from 46 sites across 13 countries, total Ti-and Ce-NP concentrations (regardless of origin) were often found to be within 10 4 to 10 7 NP mL −1 , whereas Ag NPs exhibited sporadic occurrences with low concentrations generally up to 10 5 NP mL −1 . This generally corresponded to mass concentrations of <1 ng L −1 for Ag-NPs, <100 ng L −1 for Ce-NPs, and <10 μg L −1 for Ti-NPs, given that measured sizes were often below 15 nm for Ce-and Ag-NPs and above 30 nm for Ti-NPs. In view of current toxicological data, the observed NP levels do not yet appear to exceed toxicity thresholds for the environment or human health; however, NPs of likely anthropogenic origins appear to be already substantial in certain areas, such as urban centers. This work lays the foundation for broader experimental NP surveys, which will be critical for reliable NP risk assessments and the regulation of nano-enabled products.