International audience | With the large amount of attention being given to microplastics in the environment, several researchers have begun to consider the fragmentation of plastics down to lower scales (i.e., the sub-micrometer scale). The term “nanoplastics” is still under debate, and different studies have set the upper size limit at either 1000 nm or 100 nm. The aim of the present work is to propose a definition of nanoplastics, based on our recently published and unpublished research definition of nanoplastics. We define nanoplastics as particles unintentionally produced (i.e. from the degradation and the manufacturing of the plastic objects) and presenting a colloidal behavior, within the size range from 1 to 1000 nm.

International audience | The nanoscale size of plastic debris makes them potential efficient vectors of many pollutants and more especially of metals. In order to evaluate this ability, nanoplastics were produced from microplastics collected on a beach exposed to the North Atlantic Gyre. The nanoplastics were characterized using multi-dimensional methods: asymmetrical flow field flow fractionation and dynamic light scattering coupled to several detectors. Lead (II) adsorption kinetics, isotherm and pH-edge were then carried out. The sorption reached a steady state after around 200 min. The maximum sorption capacity varied between 97% and 78.5% for both tested Pb concentrations. Lead (II) adsorption kinetics is controlled by chemical reactions with the nanoplastics surface and to a lesser extent by intraparticle diffusion. Adsorption isotherm modeling using Freundlich model demonstrated that NPG are strong adsorbents equivalent to hydrous ferric oxides such as ferrihydrite (log against 11.76 for NPG and ferrihydrite, respectively). The adsorption is dependent upon pH, in response to the Pb(II) adsorption by the oxygenated binding sites developed on account of the surface UV oxidation under environmental conditions. They could be able to compete with Fe or humic colloids for Pb binding regards to their amount and specific areas. Nanoplastics could therefore be efficient vectors of Pb and probably of many other metals as well in the environment.

Increasing rates of commercialization and industrialization have led to the comprehensive evaluation of toxic effects of microplastics on crop plants. However, research on the impact of functionalized polystyrene nanoplastics on the toxicity of heavy metals remains limited. This study investigated the effects of polystyrene, carboxy-modified polystyrene, and amino-modified polystyrene on lead (Pb) toxicity in dandelion seedlings. The results showed that carboxy -modified polystyrene with a negative charge absorbed more Pb²⁺ than polystyrene and amino-modified polystyrene, and their maximum adsorption amounts were 5.328, 0.247, and 0.153 μg g⁻¹, respectively. The hydroponic experiment demonstrated that single amino-modified polystyrene was more toxic to dandelion seedlings than polystyrene and carboxy-modified polystyrene. The presence of Pb²⁺ was found to increase antioxidant enzymes (superoxide dismutase and catalase) and non-antioxidant enzymes (glutathione and ascorbic acid) activities in response to excessive reactive oxygen species in dandelion leaves and roots treated with polystyrene and carboxy-modified polystyrene, while it did not change much when amino-modified polystyrene was added. Interestingly, compared with single Pb²⁺, the addition of amino-modified polystyrene with positive charges induced an obvious decrease in the above parameters; however, they declined slightly in the treatments with polystyrene and carboxy-modified polystyrene despite a stronger adsorption capacity for Pb²⁺. Similarly, the bioactive compounds, including flavonoids, polyphenols, and polysaccharides in dandelion, showed a scavenging effect on O₂⁻ and H₂O₂, thereby inhibiting the accumulation and reducing medicinal properties. This study found that the effects of microplastics on the uptake, distribution, and toxicity of heavy metals depended on the nanoparticle surface charge.

Wastewater treatment plants (WWTPs) are almost the only place where plastic fragments are artificially removed, resulting in mass accumulation of nanoplastics (NPs). In this research, four different concentrations (0 mg/L, 0.1 mg/L, 1 mg/L, 10 mg/L) of polystyrene nanoplastics (PS-NPs) were used to investigate the cell damage and nitrogen inhibition of activated sludge, exposed in a self-assembled SBR reactor for 30 days. Intracellular reactive oxides (ROS) and extracellular lactate dehydrogenase (LDH) increased with the rise of exposure concentration, and morphological analysis disclosed the creases, collapse, and even rupture of cell membranes. However, exposure damage (PS-NPs ≤ 1 mg/L) appeared to be reversible, attributed to that extracellular polymeric substances (EPS) secretion can thicken the three protective layers outside the membrane. PS-NPs did not disrupt the EPS chemical structure, but increased humic acid content. Prolonged exposure time (from 15 to 30 days) was directly related to the nitrogen inhibition. Due to the habitat changes under PS-NPs exposure, abundance and diversity of microorganisms in the original activated sludge decreased significantly, and the dominant phylum was occupied by Patescibacteria (PS-NPs = 10 mg/L). Changes in enzyme activities of AMO, NR, NIR, and NOR with exposure concentration may explain the conversion of nitrogen in SBR. This research broadens our horizons to understand the response mechanism of activated sludge bacteria to PS-NPs exposure individually and collectively.

Multiple sources of microplastics (MPs) in farmland could result in the changing of microbial community and the plant growth. Most studies of MPs in agricultural system have focused on the effects of single types of MPs on growth of plants, while neglect interactions between multiple types of MPs. In this study a pot-experiment was conducted to investigate the effects of multiple types of MPs, including polystyrene beads: M1, 5 μm, M2, 70 nm and degradable mulching film (DMF) fragments on growth of wheat seedlings and associated rhizosphere microbial community. CKD (adding DMF) significantly reduced plant height and base diameter of wheat seedlings. DMF in combination with M2, significantly increased plant height and aboveground biomass, but decreased the base diameter. Actinobacteria was the dominant taxa in the rhizosphere bacterial community in various treatments. PCoA analysis showed that the bacterial composition in M2HD (100 mg kg⁻¹ M² with DMF) was significantly different from that of CKD and M2LD (10 mg kg⁻¹ M² with DMF). At the level of genera, the dominant fungi in CKD and M2LD were in the genus Fusarium, which is the cause of wheat fusarium blight and Alternaria, which results in decreased base diameter. In CK (control group) and M2HD, Blastobotrys exhibited the greatest abundance, which assisted wheat seedlings in resisting Verticillium disease. Cluster and PCoA analysis showed the fungal composition in CKD was significantly different from CK, M2LD and M2HD. These findings suggest MPs potentially have selective effects on pathogens that affect growth of plants and potentially safety of the food.

Wastewater treatment plants have been identified as an important gathering spot for nanoplastics, possibly having unintended impacts on important biological nutrient removal processes. The underlying effects of long-term exposure of activated sludge to nanoplastics on nutrient removal and the mechanisms involved remain unclear. This study investigated the effect of polystyrene nanoplastics (Nano-PS) on the treatment performance and microbial community structure, and network in activated sludge. The results indicate that 1000 μg/L Nano-PS had chronic negative effects on the treatment performance in a continuous test over 140 days. Nano-PS had no significant impact in the earlier stages (0–50 days). However, as exposure time increased, the removal efficiencies of chemical oxygen demand, total phosphorous, and total nitrogen (TN) decreased by 2.7, 33.2, and 23.5%, respectively, in the later stages (87–132 days). These adverse impacts further manifested as a change in the topological characteristics, forming a smaller scale, lower complexity, and weaker transfer efficiency of the microbial network. Moreover, the scale and complexity of subnetwork-nitrogen removal bacteria and subnetwork-nitrifier were inhibited, leading to an increase in the effluent TN and NH₄⁺-N. The decreased modules and connectors (keystone taxa) likely caused the deterioration of treatment performance and functional diversity, which was consistent with the change in PICRUSt results. Less competition, denser nodes, and more complex module structures were induced as a strategy to mediate the long-term stress of nano-PS. To our knowledge, this is the first attempt to explore the long-term effects of nano-PS on the microbial interaction network of activated sludge, laying an experimental foundation for reducing the risks associated with nanoplastics.

The interactions of plastics and soil organisms are complex and inconsistent observations on the effects of plastics on soil organisms have been made in published studies. In this study, we assessed the effects of plastic exposure on plants, fauna and microbial communities, with a meta-analysis. Using a total of 2936 observations from 140 publications, we analysed how responses in plants, soil fauna and microorganisms depended on the plastic concentration, size, type, species and exposure media. We found that overall plastics caused substantial detrimental effects to plants and fauna, but less so to microbial diversity and richness. Plastic concentration was one of the most important factors explaining variations in plant and faunal responses. Larger plastics (>1 μm) caused unfavourable changes to plant growth, germination and oxidative stress, while nanoplastics (NPs; ≤ 1 μm) only increased oxidative stress. On the contrary, there was a clear trend showing that small plastics adversely affected fauna reproduction, survival and locomotion than large plastics. Plant responses were indifferent to plastic type, with most studies conducted using polyethylene (PE) and polystyrene (PS) plastics, but soil fauna were frequently more sensitive to PS than to PE exposure. Plant species played a vital role in some parameters, with the effects of plastics being considerably greater on vegetable plants than on cereal plants.

The plastic debris that washes ashore and litters the shoreline often undergoes weathering under sunlight exposure, such that it fragments to form nanoplastics and microplastics, but the fragmentation rate for many thermoplastics is unknown. In this study, three major thermoplastics were exposed to simulated sunlight in an accelerated weathering chamber to evaluate the speed of photooxidation-induced fragmentation. The initiation of photooxidation-induced fragmentation extrapolated from the accelerated weathering chamber to real sunlight exposure in South Korea followed the order of PS (< 1 year) > PP (< 2 years) > LDPE (> 3 years). The surface cracks created by photooxidation were not directly reflected in the initiation of fragmentation of thermoplastics. The initiation of fragmentation was faster in PS than other polymers, but the total abundance of particles produced, and increasing ratio (exposure/non-exposure) were comparable or lower than those of PP. The increasing ratio pattern between nanoplastics and small microplastics of PP differed noticeably from other polymers. The initiation of nanoplastic and small-microplastic fragmentation determined in this study will be useful for the further estimation of secondary microplastic production by weathering and thus for decision-making regarding methods for the timely removal of plastic litter in the environment.

The adverse effects of plastic waste and nanoplastics on the water environment have become a focus of global attention in recent years. In the present study, using adult Chinese mitten crabs (Eriocheir sinensis) as an animal model, the bioaccumulation and the in vivo and in vitro toxicity of polystyrene nanoplastics (PS NPs), alone or in combination with the bacteria, were investigated. This study aimed to investigate the effects of PS NPs on apoptosis and glucose metabolism in Chinese mitten crabs, and whether PS NPs could synergistically affect the antibacterial immunity of crabs. We observed that NPs were endocytosed by hemocytes, which are immune cells in crustaceans and are involved in innate immunity. The RNA sequencing data showed that after hemocytes endocytosed NPs, apoptosis and glucose metabolism-related gene expression was significantly induced, resulting in abnormal cell apoptosis and a glucose metabolism disorder. In addition, exposure to NPs resulted in changes in the antimicrobial immunity of crabs, including changes in antimicrobial peptide expression, survival, and bacterial clearance. In summary, NPs could be endocytosed by crab hemocytes, which adversely affected the cell apoptosis, glucose metabolism, and antibacterial immunity of Eriocheir sinensis. This study revealed the effects of NPs on crab immunity and lays the foundation for further exploration of the synergistic effect of NPs and bacteria.

In response to the growing worldwide plastic pollution problem, the field of nanoplastics research is attempting to determine the risk of exposure to nanoparticles amidst their ever-increasing presence in the environment. Since little is known about the attributes of environmental nanoplastics (concentration, composition, morphology, and size) due to fundamental limitations in detection and quantification of smaller plastic particles, researchers often improvise by engineering nanoplastic particles with various surface modifications as models for laboratory toxicological testing. Polystyrene and other commercially available or easily synthesized polymer materials functionalized with surfactants or fluorophores are typically used for these studies. How surfactants, additives, fluorophores, the addition of surface functional groups for conjugation, or other changes to surface attributes alter toxicological profiles remains unclear. Additionally, the limited polymers used in laboratory models do not mimic the vast range of polymer types comprising environmental pollutants. Nanomaterials are tricky materials to investigate due to their high surface area, high surface energies, and their propensity to interact with molecules, proteins, and biological probes. These unique properties can often invalidate common laboratory assays. Extreme care must be taken to ensure that results are not artefactual. We have gathered zeta potential values for various polystyrene nanoparticles with different functionalization, in different solvents, from the reported literature. We also discuss the effects of surface engineering and solvent properties on interparticle interactions, agglomeration, particle-protein interactions, corona formation, nano-bio interfaces, and contemplate how these parameters might confound results. Various toxicological exemplars are critically reviewed, and the relevance and shortfalls of the most popular models used in nanoplastics toxicity studies published in the current literature are considered.