Environmental Microplastic Particles vs. Engineered Plastic Microparticles-A Comparative Review

Exploring the potential and challenges of developing physiologically-based toxicokinetic models to support human health risk assessment of microplastic and nanoplastic particles

Microplastics (MPs) and nanoplastics (NPs) pollution has emerged as a significant and widespread environmental issue. Humans are inevitably exposed to MPs and NPs via ingestion, inhalation, and dermal contacts from various sources. However, mechanistic knowledge of their distribution, interaction, and potency in the body is still lacking. To address this knowledge gap, we have undertaken the task of elucidating the toxicokinetic (TK) behaviors of MPs and NPs, aiming to provide mechanistic information for constructing a conceptual physiologically based toxicokinetic (PBTK) model to support in silico modeling approaches. Our effort involved a thorough examination of the existing literature and data collation on the presence of MPs in the human body and in vitro/ex vivo/in vivo biodistribution across various cells and tissues. By comprehending the absorption, distribution, metabolism, and excretion mechanisms of MPs and NPs in relation to their physicochemical attributes, we established a foundational understanding of the link between external exposure and internal tissue dosimetry. We observed that particle size and surface chemistry have been thoroughly explored in previous experimental studies. However, certain attributes, such as polymer type, shape, and biofilm/biocorona, warrant attention and further examination. We discussed the fundamental disparities in TK properties of MPs/NPs from those of engineered nanoparticles. We proposed a preliminary PBTK framework with several possible modeling approaches and discussed existing challenges for further investigation. Overall, this article provides a comprehensive compilation of existing TK data of MPs/NPs, a critical overview of TK processes and mechanisms, and proposes potential PBTK modeling approaches, particularly regarding their applicability to the human system, and outlines future perspectives for developing PBTK models and their integration into human health risk assessment of MPs and NPs.

Presence of microplastics in the groundwater of volcanic islands, El Hierro and La Palma (Canary Islands)

The increasing amount of plastic litter worldwide is a serious problem for the environment and its biodiversity, ecosystems, animal and human welfare and the economy. The degradation of these plastics leads to microplastics (MPs), which have been reported for the first time in groundwater in the Canary archipelago. This research investigates the presence of MPs at nine different points on La Palma and El Hierro, where samples were collected in galleries, wells and springs during the month of December 2022. Six different polymers were found with Fourier transform infrared spectroscopy (FTIR) - polypropylene (PP), polyethylene (PE), cellulose (CEL), polyethylene terephthalate (PET), polystyrene (PS) and polymethyl methacrylate (PMMA). The particle concentrations found ranged from 1 to 23 n/L, with a maximum particle size of 1900 μm, the smallest being 35 μm. PP and PE were the most common polymers found in the analysis, associated with the use of packaging, disposable products, textiles and water pipes, related to poorly maintained sewerage networks where leaks occur, allowing these MPs to escape into the environment and end up in groundwater. The detection of microplastic pollution in groundwater emphasises environmental hazards, including biodiversity disruption and water source contamination. Additionally, it presents potential risks to human health by transferring contaminants into the food chain and through respiratory exposure.

Preparation of synthetic micro- and nano plastics for method validation studies

Microplastic (MP) pollution is a persisting global problem. Accurate analysis is essential in quantifying the effects of microplastic pollution and develop novel technologies that reliably and reproducibly measure microplastic content in various samples. The most common methods for this are FTIR and Raman spectroscopy. Coloured, standardized beads are often used for method validation tests, which limits the conclusions to a very specific case rarely observed in the natural environment. This study focuses on the preparation of reference micro- and nanoplastics via cryogenic milling and shows their use for FTIR and Raman method validation studies. MPs can now be reproducibly milled from various plastics, offering the advantages of a better representation of MPs in real environment. Moreover, this study highlights issues with the current detection methods, up to now considered as the most reliable ones for MP detection and identification. Such issues, e.g. misidentification, will need to be addressed in the future. Additionally, milled MPs were used in experiments with commercial high-resolution imaging device, enabling a possible in-situ optical detection of microplastics. These experiments represent a step forward in understanding MPs in a water sample and provide a basis for a more accurate detection and identification directly from water, which would considerably reduce the time of analysis.

Interactive impacts of microplastics and arsenic on agricultural soil and plant traits

The ability of microplastics (MPs) to interact with environmental pollutants is currently of great concern due to the increasing use of plastic. Agricultural soils are sinks for multipollutants and the safety of biodegradable MPs in field conditions is questioned. However, still few studies have investigated the interactive effects between MPs and metals on the soil-plant system with agricultural soil and testing crops for human consumption. In this work, we tested the effect on soil and plant parameters of two common MPs, non-degradable plastic low-density polyethylene and biodegradable polymer polylactic acid at two different sizes (<250 μm and 250-300 μm) in association with arsenic (As). Lettuce (Lactuca sativa L.) was used as a model plant in a small-scale experiment lasting 60 days. Microplastics and As explained 12 % and 47 % of total variance, respectively, while their interaction explained 21 %, suggesting a higher toxic impact of As than MPs. Plant growth was promoted by MPs alone, especially when biodegradable MPs were added (+22 %). However, MPs did not affect nutrient concentrations in roots and leaves. The effect of MPs on enzyme activities was variable depending on the time of exposure (with larger effects immediately after exposure), the type and size of the MPs. On the contrary, the co-application of MP and As, although it did not change the amount of bioavailable As in soil in the short and medium term, it resulted in a significant decrease in lettuce biomass (-19 %) and root nutrient concentrations, especially when polylactic acid was applied. Generally, MPs in association with As determined the plant-soil toxicity. This work provides insights into the risk of copollution of MPs and As in agricultural soil and its phytotoxic effect for agricultural crops. However, the mechanisms of the joint effect of MP and As on plant toxicity need further investigation, especially under field conditions and in long-term experiments.

An Emerging Role of Micro- and Nanoplastics in Vascular Diseases

Vascular diseases are the leading causes of death worldwide, and they are attributable to multiple pathologies, such as atherosclerosis, diabetes, and chronic obstructive pulmonary disease. Exposure to various environmental contaminants is associated with the development of various diseases, including vascular diseases. Among environmental contaminants, micro- and nanoplastics have gained attention as global environmental risk factors that threaten human health. Recently, extensive research has been conducted on the effects of micro- and nanoplastics on various human diseases, including vascular diseases. In this review, we highlight the effects of micro- and nanoplastics on vascular diseases.

Responses of submerged macrophytes to different particle size microplastics and tetracycline co-pollutants at the community and population level

Microplastics (MPs) and antibiotics are ubiquitous in aquatic ecosystems, and their accumulation and combined effects are considered emerging threats that may affect biodiversity and ecosystem function. The particle size of microplastics plays an important role in their combined effects with antibiotics. Submerged macrophytes are crucial in maintaining the health and stability of freshwater ecosystems. However, little is known about the combined effects of different particle size of MPs and antibiotics on freshwater plants, particularly their effects on submerged macrophyte communities. Thus, there is an urgent need to study their effects on the macrophyte communities to provide essential information for freshwater ecosystem management. In the present study, a mesocosm experiment was conducted to explore the effects of three particle sizes (5 µm, 50 µm, and 500 µm) of polystyrene-microplastics (PSMPs) (75 mg/L), tetracycline (TC) (50 mg/L), and their co-pollutants on interactions between Hydrilla verticillata and Elodea nuttallii. Our results showed that the effects of MPs are size-dependent on macrophytes at the community level rather than at the population level, and that small and medium sized MPs can promote the growth of the two test macrophytes at the community level. In addition, macrophytes at the community level have a stronger resistance to pollutant stress than those at the population level. Combined exposure to MPs and TC co-pollutants induces species-specific responses and antagonistic toxic effects on the physio-biochemical traits of submerged macrophytes. Our study provides evidence that MPs and co-pollutants not only affect the morphology and physiology at the population level but also the interactions between macrophytes. Thus, there are promising indications on the potential consequences of MPs and co-pollutants on macrophyte community structure, which suggests that future studies should focus on the effects of microplastics and their co-pollutants on aquatic macrophytes at the community level rather than only at the population level. This will improve our understanding of the profound effects of co-pollutants in aquatic environments on the structure and behavior of aquatic communities and ecosystems.

Synthesis and characterization of novel thermoresponsive suspensions via physical adsorption of poly[di(ethylene glycol) methyl methacrylate] onto polystyrene microparticles

Thermoreversible colloidal suspensions/gels have attracted recent research attention in the field of biomedical applications. In this study, a novel thermoresponsive particle suspension with thermoreversible gelation properties has been prepared for biomedical application. First, polystyrene (PS) microspheres were synthesized by dispersion polymerization and poly diethyleneglycolmethylmethacrylate (PDEGMA) polymer were synthesized via free radical polymerisation. Then, the new developed thermoresponsive suspensions were prepared via physical adsorption of a thermoresponsive polymer, poly[di (ethylene glycol) methyl methacrylate] (PDEGMA), onto the surface of polystyrene microspheres. PDEGMA acts as a steric stabilizer and induces thermoreversible gelation via chain extending and collapsing below and above its lower critical solution temperature (LCST), respectively. Scanning electron microscopy (SEM), 1H NMR spectroscopy, Gel permeation chromatography (GPC), UV-vis spectroscopy, Rheometric measurement were conducted to characterize the prepared particles, polymers and suspensions. SEM images show that monodisperse microspheres with the sizes range 1.5-3.5 μm were prepared. UV-vis measurements demonstrate thermoresponsive properties of PDEGMA. 1H NMR and GPC analysis confirms structural properties of prepared PDEGMA. Tube inversion tests demonstrated that the aqueous suspensions of the particles and polymer exhibited thermoreversible fluid-to-gel transitions. Rheological characterization revealed that the viscoelastic properties of the prepared suspension/gels can be fine tuned. This enables applications of the prepared gels as scaffolds for three-dimensional (3D) cell cultures.

Microplastic contamination in commercial fish species in southern coastal region of India

Due to its potential impact on food safety and human health, commercial species that have been contaminated with microplastics (MPs) are drawing more attention on a global scale. This study investigated the possibility of MPs contamination in different marine fish species with substantial commercial value that was captured off the south coast of India, from Adyar and Ennore regions. Over the course of six months, from October 2019 to March 2020, 220 fish were examined. It was discovered that the gills and guts had accumulated more numbers of MPs (1115 MPs) of which 68% were fibres and fragments. The commercial fish samples contained an average of 3.2-7.6 MPs per fish. Greater MPs pollution is seen in the Ennore regions. The prevalence of MPs was observed in carnivorous and planktivorous fish collected from both the sites. Fish guts contained the most MPs, according to the data. Pelagic fish accounted for the least amount of MPs, followed by mid- and demersal fish. Four different types of polymers were also identified in the present study: polyethylene, polypropylene, polystyrene, and polyamide. These results clearly showed the degree of microplastic contamination in fish tissues from the south Indian coastal regions of Adyar and Ennore. These results we hope will create a baseline data for MPs contamination in commercial fish species. The presence of MPs in the fish could have detrimental effects both on the environment and human health and thus comprehensive steps are required to prevent plastic pollution of the environment in south India's coastal region.