Recent advances in toxicological research of nanoplastics in the environment: A review

Metro station free drinking water fountain- A potential "microplastics hotspot" for human consumption

Microplastics have become an inevitable component of our environment. Worldwide, free public fountains are common and one of the best sources of drinking water which are being installed with one of the viewpoints of reducing single-use plastics bottle consumption. However, the state of knowledge on how microplastics might be affecting in those free public drinking fountains is unknown. In this study, free drinking water fountains from 42 metro stations in Mexico City were being looked into for the occurrence of microplastics and investigated their shape type, size, abundance, distribution, polymer composition and surface morphology. Microplastics were detected in all the samples analyzed. The results revealed the significant abundance of microplastics ranging from 5 ± 2 to 91 ± 14 L^-1 in drinking water with an overall average of 18 ± 7 microplastics L^-1. Transparent fibers (69%) were predominant in the identified microplastics followed by blue (24%) and red colored (7%) fibers. The most frequent microplastics dimensions ranged between 0.1 and 1 mm which is approximately 75% of the total microplastics. Micro-Raman spectroscopy analysis indicated that microplastics contained in drinking water were mainly polyesters (poly (trimethylene terephthalate)) and epoxy resin suggesting the possible contribution of wastewater discharges for microplastics contamination. Thus, this study findings show that free public drinking water fountains are potential microplastics hotspot for human consumption and provide useful references for mitigation measures.

Two sigma and two mu class genes of glutathione S-transferase in the waterflea Daphnia pulex: Molecular characterization and transcriptional response to nanoplastic exposure

Two isoforms of Glutathione S-Transferase (GST) genes, belonging to mu (Dp-GSTm1 and Dp-GSTm2) and sigma (Dp-GSTs1 and Dp-GSTs2) classes, were cloned and characterised in the freshwater Daphnia pulex. No signal peptide was found in any of the four GST proteins, indicating that they were cytosolic GST. A highly conserved glutathione (GSH) binding site (G-site) occurred in the N-terminal sequence, and a substrate binding site (H-site), interacting non-specifically with the second hydrophobic substrate, was present in the C-terminal. A Tyr residue, for the stabilization of GSH, was found to be conserved in the analysed sequences. The secondary and tertiary structures indicated that these genes possess the typical cytosolic GST structure, including a conserved N-terminal domain with a βαβαββα motif. The μ loop (NVGPAPDYDR and NFIGAEWDR in Dp-GSTm1 and Dp-GSTm2, respectively) was identified between the βαβ (β1α1β2) and αββα motifs (α2β3β4α3) in the N-terminal domain. The expressions of Dp-GSTs1, Dp-GSTs2, and Dp-GSTm1 were higher in other age groups compared to the newly-born neonates (1 d); however, the expression of Dp-GSTm2 first increased and then decreased with age. Gene expression was significantly reduced by high concentration (1 and 2 mg/L) of 75 nm polystyrene nanoplastic. However, nanoplastic exposure at the predicted environmental concentration (1 μg/L) had a low effect. Exposure of mothers to nanoplastic (1 μg/L) elevated the Dp-GSTs2 level in their neonates. These results improve our understanding on the response of different types of Daphnid GST to environmental contaminants, especially nanoplastic.

The Complex Toxicity of Tetracycline with Polystyrene Spheres on Gastric Cancer Cells

Nowadays, microplastics (MPs) exist widely in the marine. The surface has strong adsorption capacity for antibiotics in natural environments, and the cytotoxicity of complex are poorly understood. In the study, 500 nm polystyrene (PS-MPs) and 60 nm nanoplastics (PS-NPs) were synthesized. The adsorption of PS to tetracycline (TC) was studied and their toxicity to gastric cancer cells (AGS) was researched. The adsorption experimental results show that PS absorbing capacity increased with increasing TC concentrations. The defense mechanism results show that 60 nm PS-NPs, 500 nm PS-MPs and their complex induce different damage to AGS cells. Furthermore, 600 mg/L PS-NPs and PS-MPs decline cell viability, induce oxidation stress and cause apoptosis. There is more serious damage of 60 nm PS-NPs than 500 nm PS-MPs in cell viability and intracellular reactive oxygen species (ROS). DNA are also damaged by 60 nm PS-NPs and PS-TC NPs, 500 nm PS-MPs and PS-TC MPs, and 60 nm PS-NPs damage DNA more serious than 500 nm PS-MPs. Moreover, 60 nm PS-NPs and PS-TC NPs seem to promote bcl-2 associated X protein (Bax) overexpression. All treatments provided us with evidence on how PS-NPs, PS-MPs and their compounds damaged AGS cells.

Effect of weathering on environmental behavior of microplastics: Properties, sorption and potential risks

Microplastic (MP) pollution is a raising global concern in recent years due to its wide distribution. Additionally, most of the MPs have undergone extensive weathering in the environment, and weathered MPs may exhibit different physicochemical properties from pristine ones. The review reveals the change in physicochemical properties (e.g. size, color, crystallinity, mechanical property and oxygen-containing groups) and the release of additives and MP-derived intermediates (i.e. oligomers and oxygenated compounds) during weathering processes. Weathering further affects the sorption behavior of MPs for environmental pollutants because of the changed crystallinity, specific surface area and oxygen functional groups. The interaction mechanisms of pristine and weathered MPs with pollutants are summarized, and how weathering processes affect sorption behavior is critically revealed. Because of the changed size, color and surface charges, weathered MPs might be ingested by aquatic organisms in different ways from the pristine ones. The detailed effects of weathering on the ingestion of MPs are discussed, and the potential toxicity of leachates from weathering processes is evaluated. In addition, the environmental components (e.g. natural organic matter and salinity) and biofilm correlated to the sorption behavior of MPs are reviewed. As for the knowledge gap, further studies should focus on the long-term weathering of MPs and the relationships between weathering properties and sorption capacities toward pollutants. The potential risks of weathered MPs and leachates on organisms should be explored.

How climate change and eutrophication interact with microplastic pollution and sediment resuspension in shallow lakes: A review

Climate change and eutrophication are both critical environmental issues currently. Climate change induces more critical microplastic pollution and sediment resuspension in eutrophic lakes, and conversely the presence of microplastics and resuspension events would intensify these two environmental effects. Via evaluating the impacts of microplastics and sediment resuspension on climate change and eutrophication, it is favorable to provide recommendations for ecological protection and policy formulation in regard to the nutrient input as well as the production and utilization of plastic. In this review, we explore how climate change and eutrophication interact with microplastic pollution and sediment resuspension in shallow lakes, highlighting that both of the latter two play a significant role in the former two. Furthermore, future prospects are put forward on the further and deeper research on the global warming and eutrophication in shallow lakes with microplastic pollution.

Effect of nanoplastics on fish health and performance: A review

Small plastic particles are considered emerging pollutants, and this has motivated a considerable number of studies to establish their environmental consequences. At present, the study of the effects of nanoplastics (NPs) on aquatic organisms is still scarce, especially in organisms from higher trophic levels such as fish. This review describes the effects reported in different fish species after exposure to plastic particles smaller than 100 nm. Studies show that NPs can adversely affect fish at different stages of development, with reported accumulation in tissues, decreased locomotor and foraging activities, effects on growth and the immune system and alterations on lipid metabolism and neurotoxicity. However, mortality, effects on hatching success or malformations related to NPs have not been reported to this date.

Challenges with Verifying Microbial Degradation of Polyethylene

Polyethylene (PE) is the most abundant synthetic, petroleum-based plastic materials produced globally, and one of the most resistant to biodegradation, resulting in massive accumulation in the environment. Although the microbial degradation of polyethylene has been reported, complete biodegradation of polyethylene has not been achieved, and rapid degradation of polyethylene under ambient conditions in the environment is still not feasible. Experiments reported in the literature suffer from a number of limitations, and conclusive evidence for the complete biodegradation of polyethylene by microorganisms has been elusive. These limitations include the lack of a working definition for the biodegradation of polyethylene that can lead to testable hypotheses, a non-uniform description of experimental conditions used, and variations in the type(s) of polyethylene used, leading to a profound limitation in our understanding of the processes and mechanisms involved in the microbial degradation of polyethylene. The objective of this review is to outline the challenges in polyethylene degradation experiments and clarify the parameters required to achieve polyethylene biodegradation. This review emphasizes the necessity of developing a biochemically-based definition for the biodegradation of polyethylene (and other synthetic plastics) to simplify the comparison of results of experiments focused for the microbial degradation of polyethylene.

Can microplastics pose a threat to ocean carbon sequestration?

Global climate change has attracted worldwide attention. The ocean is the largest active carbon pool on the planet and plays an important role in global climate change. However, marine plastic pollution is getting increasingly serious due to the large consumption and mismanagement of global plastics. The impact of marine plastics on ecosystem responsible for the gas exchange and circulation of marine CO₂ may cause more greenhouse gas emissions. Consequently, in this paper, threats of marine microplastics to ocean carbon sequestration are discussed. Marine microplastics can 1) affect phytoplankton photosynthesis and growth; 2) have toxic effects on zooplankton and affect their development and reproduction; 3) affect marine biological pump; and 4) affect ocean carbon stock. Phytoplankton and zooplankton are the most important producer and consumer of the ocean. As such, clearly, further research should be needed to explore the potential scale and scope of this impact, and its underlying mechanisms.

Can biotechnology strategies effectively manage environmental (micro)plastics?

With the convenience of plastic products to daily life, the negative sides of the plastic-age have gradually emerged. Like other pollutants, complex environmental factors result in the ubiquitous presence of (micro)plastics worldwide, raising potential risks to the ecological systems. However, due to the limitation of traditional technologies in treating these materials, new strategies should be developed. More recently, researchers have showed that biotechnology strategies could be promising approaches to effectively manage and control (micro)plastics in the environment, because some microorganisms have been confirmed to be successfully capable of degrading (micro)plastics. Nevertheless, the biotechnology is still in its infancy, and most studies are carried out under laboratory conditions. The biodegradation process is affected by many factors: microorganism species, carbon sources, material types and sizes. Problematically, (micro)plastics are highly stable in the environment, which are difficult to be used as carbon sources for microorganisms. Biodegradation of (micro)plastics requires appropriate conditions, which are not always feasible in field conditions. As such, although biotechnology strategies might be a promising approach to remove environmental (micro)plastics, we believe it is not now at least.

Toxicological considerations of nano-sized plastics

Undoubtedly, plastics have changed human existence. These pervasive products are used in nearly every field to include technological, biomedical, and domestic applications. Post-consumer plastic waste disposal leading to plastic pollution in landfills, waterways, and oceans represents a worldwide environmental challenge. Accumulation and continued material fragmentation from micro- to nanoplastics has identified concerns pertaining to environmental and human exposures and toxicity. While many studies have focused on particle fate and identification, the toxicological considerations must focus on the biological relevance of particle deposition within a particular organism, compartment, organ, and tissue. Further, concerns exist regarding the physical and chemical properties of the plastic particles during their production and/or degradation. In this mini-review we will discuss (1) particle characterization and assessment, (2) environmental concerns, and (3) human toxicity.