Aging of microplastics increases their adsorption affinity towards organic contaminants

Are volatile methylsiloxanes in downcycled tire microplastics? Levels and human exposure estimation in synthetic turf football fields

Downcycled rubber, derived from end-of-life tires (ELTs), is frequently applied as crumb rubber (CR) as infill of synthetic turf in sports facilities. This practice has been questioned in recent years as numerous studies have reported the presence of potentially hazardous chemicals in this material. CR particles fall into the category of microplastics (MPs), making them possible vectors for emerging micropollutants. A preliminary study where volatile methylsiloxanes (VMSs) were found in CR originated the hypothesis that VMSs are present in this material worldwide. Consequently, the present work evaluates for the first time the levels and trends of seven VMSs in CR from synthetic turf football fields, while attempting to identify the main sources and impacts of these chemicals. A total of 135 CR samples and 12 other of alternative materials were analyzed, employing an ultrasound-assisted dispersive solid-phase extraction followed by gas chromatography-mass spectrometry (GC-MS), and the presence of VMSs was confirmed in all samples, in total concentrations ranging from 1.60 to 5089 ng.g-1. The levels were higher in commercial CR (before field application), a reflection of the use of VMS-containing additives in tire production and/or the degradation of silicone polymers employed in vehicles. The VMSs generally decreased over time on the turf, as expected given their volatile nature and the wearing of the material. Finally, the human exposure doses to VMSs in CR (by dermal absorption and ingestion) for people in contact with synthetic turf in football fields were negligible (maximum total exposure of 20.5 ng.kgBW-1.year-1) in comparison with the European Chemicals Agency (ECHA) reference doses: 1.35 × 109 ng.kgBW-1.year-1 for D4 and 1.83 × 109 ng.kgBW-1.year-1 for D5. Nevertheless, more knowledge on exposure through inhalation and the combined effects of all substances is necessary to provide further corroboration. This work proved the presence of VMSs in CR from ELTs, another family of chemical of concern to take into account when studying MPs as vectors of other contaminants.

Organ-specific distribution and size-dependent toxicity of polystyrene nanoplastics in Australian bass (Macquaria novemaculeata)

Micro- and nano-plastics (MNPs) are emerging contaminants found in air, water, and food. Ageing and weathering processes convert aquatic plastics into MNPs which, due to their small size, can be assimilated by organisms. The accumulation of MNPs in aquatic life (e.g., fish, oysters, and crabs) will, in turn, pose risks to the health of ecosystems and human. This study focuses on the uptake, biodistribution, and size-dependent toxicity of polystyrene nano-plastics (PS-NPs) in a commercially important food web, the Australian Bass (Macquaria novemaculeata). Fish were fed artemia containing PS-NPs of various sizes (ranging from 50 nm to 1 μm) for durations of 5 and 7 days. The findings revealed that smaller NPs (50 nm) accumulated in the brain and muscle tissues at higher concentrations, whereas larger NPs (1 μm) were primarily found in the gills and intestines. In addition, an inverse correlation was observed between the size of NPs and the rate of trophic transfer, with smaller PS-NPs resulting in a higher transfer rate from artemia to fish. Polystyrene NPs caused both activation of the enzyme superoxide dismutase and damage to the DNA of fish tissues. These effects were size dependent. Metabolomic analysis revealed that indirect exposure to different-sized PS-NPs resulted in altered metabolic profiles within fish intestines, potentially impacting lipid and energy metabolism. These results offer novel perspectives on the size-specific toxic impacts of NPs on fish and the transfer of plastics through the food chain.

Exposure to phagolysosomal simulated fluid altered the cytotoxicity of PET micro(nano)plastics to human lung epithelial cells

The occurrence of micro(nano)plastics into various environmental and biological settings influences their physicochemical and toxic behavior. Simulated body fluids are appropriate media for understanding the degradation, stability, and interaction with other substances of any material in the human body. When the particles enter the human body via inhalation, which is one of the avenues for micro(nano)plastics, they first come into contact with the lung lining fluid under neutral conditions and then are phagocytosed under acidic conditions to be removed. Therefore, it is important to examine the physicochemical transformation and toxicity characteristics after interaction with phagolysosomal simulant fluid (PSF). Here, we focused on exploring how the physicochemical differences (e.g. surface chemistry, elemental distribution, and surface charge) of micro(nano)plastics under pH 4.5 phagolysosome conditions impact cytotoxicity and the oxidative characteristics of lung epithelia cells. The cytotoxicity of lung epithelia cells to those treated with PSF and non-treated micro(nano)plastics was tested by various viability indicators including cell counting kit-8 (CCK-8), MTT, and LDH. Furthermore, the cytotoxicity background was examined through the oxidative processes (e.g. reactive oxygen species, antioxidant, superoxide dismutase (SOD), catalase, and reduced glutathione). The results showed that all tested surface physicochemical characteristics were significantly influenced by the phagolysosome conditions. The staged responses were observed with the treatment duration, and significant changes were calculated in carbonyl, carbon-nitrogen, and sulfonyl groups. Moreover, the negativity of the zeta potentials declined between exposure of 2-40 h and then increased at 80 h compared to control owing to the chemical functional groups and elemental distribution of the plastic particles. The tested viability indicators showed that the micro(nano)plastics treated with PSF were cytotoxic to the lung epithelia cells compared to non-treated micro(nano)plastics, and SOD was the dominant enzyme triggering cytotoxicity due to the particle degradation and instability.

Nano- and micro-plastic transport in soil and groundwater environments: Sources, behaviors, theories, and models

With the increasing use of plastics, nano- and micro-plastic (NMP) pollution has become a hot topic in the scientific community. Ubiquitous NMPs, as emerging contaminants, are becoming a global issue owing to their persistence and potential toxicity. Compared with studies of marine and freshwater environments, investigations into the sources, transport properties, and fate of NMPs in soil and groundwater environments remain at a primary stage. Hence, the promotion of such research is critically important. Here, we integrate existing information and recent advancements to compile a comprehensive evaluation of the sources and transport properties of NMPs in soil and groundwater environments. We first provide a systematic description of the various sources and transport behaviors of NMPs. We then discuss the theories (e.g., clean-bed filtration and Derjaguin-Landau-Verwey-Overbeek theories) and models (e.g., single-site and dual-site kinetic retention and transport models) of NMP transport through saturated porous media. Finally, we outline the potential limitations of current research and suggest directions for future research. Overall, this review intends to assimilate and outline current knowledge and provide a useful reference frame to determine the sources and transport properties of NMPs in soil and groundwater environments.

Surface functional groups and biofilm formation on microplastics: Environmental implications

Microplastics (MPs) contamination is becoming a significant environmental issue, as the widespread omnipresence of MPs can cause many adverse consequences for both ecological systems and humans. Contrary to what is commonly thought, the toxicity-inducing MPs are not the original pristine plastics; rather, they are completely transformed through various surface functional groups and aggressive biofilm formation on MPs via aging or weathering processes. Therefore, understanding the impacts of MPs' surface functional groups and biofilm formation on biogeochemical processes, such as environmental fate, transport, and toxicity, is crucial. In this review, we present a comprehensive summary of the distinctive impact that surface functional groups and biofilm formation of MPs have on their significant biogeochemical behavior in various environmental media, as well as their toxicity and biological effects. We place emphasis on the role of surface functional groups and biofilm formation as a means of influencing the biogeochemical processes of MPs. This includes their effects on pollutant fate and element cycling, which in turn impacts the aggregation, transport, and toxicity of MPs. Ultimately, future research studies and tactics are needed to improve our understanding of the biogeochemical processes that are influenced by the surface functional groups and biofilm formation of MPs.

Recent progress of microplastic toxicity on human exposure base on in vitro and in vivo studies

Microplastics are widely distributed in the environment, including the atmosphere, soil and water bodies. They have been found to have toxic effects on organisms. The impact on human health is also receiving considerable attention. Microplastics can be found in drinking water, food, air and plastic products, and they can enter human body through the pathways such as ingestion, inhalation, and skin contact. After exposure to microplastics, they can induce cellular toxicity and produce toxic effects on multiple organs and systems, including the digestive, respiratory, nervous, reproductive and cardiovascular systems. This paper presents a comprehensive review and analysis on the recent progress of human exposure studies, in vitro experiments, rodent experiments, and other model experiments in microplastic human toxicity research. It comprehensively analyzes the potential human toxic effects of microplastics, providing a theoretical basis for further research on microplastic human toxicity and its mechanisms. Furthermore, this paper highlights the knowledge gaps and provides the recommendations for future research on human toxicity of microplastics.

Long-range atmospheric transport of microplastics across the southern hemisphere

Airborne microplastics (MPs) can undergo long range transport to remote regions. Yet there is a large knowledge gap regarding the occurrence and burden of MPs in the marine boundary layer, which hampers comprehensive modelling of their global atmospheric transport. In particular, the transport efficiency of MPs with different sizes and morphologies remains uncertain. Here we show a hemispheric-scale analysis of airborne MPs along a cruise path from the mid-Northern Hemisphere to Antarctica. We present the inaugural measurements of MPs concentrations over the Southern Ocean and interior Antarctica and find that MPs fibers are transported more efficiently than MPs fragments along the transect, with the transport dynamics of MPs generally similar to those of non-plastic particles. Morphology is found to be the dominant factor influencing the hemispheric transport of MPs to remote Antarctic regions. This study underlines the importance of long-range atmospheric transport in MPs cycling dynamics in the environment.

Aging characteristics of degradable and non-biodegradable microplastics and their adsorption mechanism for sulfonamides

As emerging pollutants, microplastics (MPs) and antibiotics (ATs) became a research hotspot in recent years. To evaluate the carrier effect of degradable and non-biodegradable MPs in the aquatic environment, the adsorption behaviors of polyamide (PA) and polylactic acid (PLA) towards two sulfonamide antibiotics (SAs) were investigated. Both chemical and photo-aging were used to handle the virgin MPs. Compared with PA, PLA was aged more drastically, showing the obvious grooves, notches and folds. However, due to the higher temperature during chemical aging, the tiny KPLA (PLA aged by K2S2O8) particles were agglomerated and the specific surface area was reduced to nearly 95 %. For PA, the oxidation of chemical aging was stronger than photo-aging. After aging, the hydrophilicity and polarity of MPs increased. In the adsorption experiments, the adsorption capacity of PA towards SAs was 1.7 times higher than that of PLA. Aging process enabled the adsorption capacity of PLA increased 1.22-3.18 times. Overall, the adsorption capacity of sulfamethoxazole (SMX) by both MPs was superior to sulfamerazine (SMR). These results would help to understand the carrier effects and potential ecological risks of MPs towards co-existing contaminants.

Adsorption/desorption of mercury (II) by artificially weathered microplastics: Kinetics, isotherms, and influencing factors

While both mercury (Hg) and microplastics (MPs) are well-studied global pollutants, comparatively little is known about the interactions between them and the mobilization of Hg from MPs into organisms. We examined the affinity of Hg(II) to artificially weathered MPs, including polyamide (w-PA), polyethylene (w-PE), polyethylene terephthalate (w-PET), polyester fibers (w-PEST), polyvinyl chloride (w-PVC), and polylactic acid (w-PLA), along with crumb rubber (CR) and PE collected from a wastewater treatment plant (WWTP-PE). WWTP-PE, CR, and w-PEST had particularly high Hg(II) affinities, which can be attributed to electrostatic interaction and pore filling. The adsorption followed a pseudo-second-order kinetic process and fitted the Freundlich model, suggesting multi-step (mass transfer and intraparticle diffusion) and heterogeneous adsorptions. Hydrochemical conditions (pH, dissolved organic matter (DOM), salinity and co-existent metal ions) all impacted Hg-MP behavior. Changes in Hg speciation and MP surface properties contributed to the different Hg(II) adsorption capacities for the MPs. Weathering of MPs generally increased the adsorption of Hg(II) onto MPs, but CR, PET and PEST did not follow this trend. Less than 3% of adsorbed Hg(II) was mobilized from the MPs in freshwater, but that increased up to 73% under simulated avian digestive conditions, suggesting increased bioavailability of Hg(II) from ingested MPs. Overall, weathered MPs adsorb and retain Hg(II) under environmentally relevant conditions but desorb much of it in simulated avian digestion fluid, suggesting that birds that ingest MPs may have increased Hg(II) exposure.

Size-selective microplastic uptake by freshwater organisms: Fish, mussel, and zooplankton

Microplastics, as an emergent pollutant, have garnered substantial attention within aquatic environments, yet a significant knowledge gap persists regarding the interplay of organism size and pollution impacts on microplastic uptake in freshwater ecosystems. The main aim of the current study is to assess the microplastic ingestion by aquatic organisms across diverse trophic levels. To achieve this objective, zooplankton, mussels (Anodonta anatina), and fish (Carassius gibelio) were collected from the highly polluted Susurluk River Basin in Türkiye. The size distribution encompassed 160.8 ± 56.9 μm for the prevailing zooplankton, 6.9 ± 2.2 cm for mussel, and 20.4 ± 3.1 cm for fish, respectively. While no microplastic ingestion was observed among zooplankton, the finding highlights the influence of body-size and pollution on microplastic ingestion. In contrast, A. anatina and C. gibelio contained 617 and 792 microplastic particles, respectively. Predominantly, fibers emerged as the most prevalent microplastic type across trophic levels (except zooplankton) followed by films. Notably, only fish exhibited fragments within their gastrointestinal tract. A substantial correlation emerged between microplastic abundance and mussel size and weight, but no such correlation manifested for fish. The study also revealed a positive link between microplastic count and turbidity (phosphate and high Chl a level), impacting mussel ingestion capacity due to the variability in the food availability and potential shifts in feeding preferences. Conversely, no distinct pattern emerged for fish concerning water quality parameters and ingested microplastics. Consequently, our study underscores diverse microplastic uptake patterns in freshwater ecosystems, with a predominant frequency of microplastics falling with the 0.3 mm-3.0 mm range, emphasizing the significance of size-selective uptake by organisms.

Adsorption-desorption behaviors of ciprofloxacin onto aged polystyrene fragments in aquatic environments

As two emerging pollutants of great concern, microplastics (MPs) and antibiotics inevitably cooccur in various aquatic environments and interact with each other, impacting the fate and ecological risks. Aging obviously complicates their interaction and deserves further study. Therefore, the adsorption-desorption behaviors of ciprofloxacin (CIP) onto polystyrene (PS) fragments with various aging extent were investigated, and the key physiochemical properties influencing the interaction and the interaction mechanisms were clarified by redundancy analysis, FTIR and XPS spectra. The physicochemical properties of PS MPs were significantly changed with aging time, and the morphological and chemical changes seemed to occur asynchronously. The adsorption of CIP onto the pristine PS MPs relied on physisorption, especially the ion-involving electrostatic and cation-π interaction. Due to the hydrogen bonding formed by the C-OH, CO, and O-CO groups of PS and CIP, the adsorption capacities of the aged PS MPs were greatly increased. The desorption efficiency of CIP from MPs in the gastric fluid was closely related to the solution ionic strengths, C-OH and CO groups of MPs, while that in the intestinal fluid was associated with O-CO groups of MPs. The different impact factors could be well described by the differences in the chemical components and pHs of the simulated gastric and intestinal fluids. This study gives a comprehensive understanding of the adsorption-desorption behaviors of antibiotics onto MPs at a molecular level and indicates that MPs could act as Trojan horses to transport antibiotics into aquatic organisms.

Removal efficiencies of microplastics of the three largest drinking water treatment plants in Bangladesh

Drinking water treatment plants (DWTPs) are intended to provide safe water to the municipality, typically by treating surface waters from rivers, lakes, and streams. Regrettably, all of these water sources for DWTPs have been reported to be contaminated by microplastics (MPs). Hence, there is an urgent need to investigate the removal efficiencies of MPs from raw waters in the conventional DWTPs anticipating public health concerns. In this experiment, MPs in the raw and treated waters of the three major DWTPs of Bangladesh, having different water treatment processes, were evaluated. The concentrations of MPs in the inlet points of Saidabad Water Treatment Plant phase-1 and 2 (SWTP-1 and SWTP-2), which share a similar water source of the Shitalakshya River, were 25.7 ± 9.8 and 26.01 ± 9.8 items L-1. The third plant, Padma Water Treatment Plant (PWTP) utilizes water from the Padma River and had an initial MP concentration of 6.2 ± 1.6 items L-1. The studied DWTPs, with their existing treatment processes, were found to reduce the MP loads substantially. The final MP concentrations in treated waters of SWTP-1, SWTP-2, and PWTP were 0.3 ± 0.03, 0.4 ± 0.01, and 0.05 ± 0.02 items L-1 with the removal efficiencies of 98.8, 98.5, and 99.2 %, respectively. The considered size range of MP was 20 μm to <5000. Fragments and fibers were the two predominant MP shapes. In terms of polymer, the MPs were polypropylene (PP, 48 %), polyethylene (PE, 35 %), polyethylene terephthalate (PET, 11 %), and polystyrene (PS, 6 %). The field emission scanning electron microscopy-energy dispersive X-ray spectroscopy (FESEM-EDX) revealed the fractured and rough surfaces of the remaining MPs, which were also found to be contaminated with heavy metals, like lead (Pb), cadmium (Cd), chromium (Cr), arsenic (As), copper (Cu), and zinc (Zn). Hence, additional initiatives are required to remove the residual MPs from the treated waters to safeguard the city dwellers from potential hazards.

Adsorption behaviors and bioavailability of tetrabromobisphenol A in the presence of polystyrene microplastic in soil: Effect of microplastics aging

Microplastics, a kind of emerging pollutant, have become a global environmental research hotspot in recent years due to its wide distribution in soil and its impact on soil ecosystems. However, little information is available on the interactions between microplastics and organic contaminants in soil, especially after microplastic aging. The impact of polystyrene (PS) microplastic aging on the sorption of tetrabromobisphenol A (TBBPA) in soil and the desorption characteristics of TBBPA-loaded microplastics in different environments were studied. The results showed a significant increase of 76.3% in adsorption capacity of TBBPA onto PS microplastics after aging for 96 h. Based on the results of characterization analysis and density functional theory (DFT) calculation, the mechanisms of TBBPA adsorption changed mainly from hydrophobic and π-π interactions on pristine PS microplastics to hydrogen bond and π-π interactions on aged PS microplastics. The presence of PS microplastics increased the TBBPA sorption capacity onto soil-PS microplastics system and significantly altered the distribution of TBBPA on soil particles and PS microplastics. The high TBBPA desorption over 50% from aged PS microplastics in simulated earthworm gut environment suggested that TBBPA contamination combined with PS microplastics might pose a higher risk to macroinvertebrates in soil. Overall, these findings contribute to the understanding of impact of PS microplastic aging in soil on the environmental behaviors of TBBPA, and provide valuable reference for evaluating the potential risk posed by the co-existence of microplastics with organic contaminants in soil ecosystems.

Aging behavior of biodegradable polylactic acid microplastics accelerated by UV/H2O2 processes

The usage of biodegradable plastics is expanding annually due to worldwide plastic limits, resulting in a substantial number of microplastics (MPs) particles formed from biodegradable plastic products entering the aquatic environment. Until now, the environmental behaviors of these plastic product-derived MPs (PPDMPs) have remained unclear. In this work, commercially available polylactic acid (PLA) straws and PLA food bags were used to evaluate the dynamic aging process and environmental behavior of PLA PPDMPs under UV/H2O2 conditions. By combining scanning electron microscopy, two-dimensional (2D) Fourier transform infrared correlation spectroscopy (COS) and X-ray photoelectron spectroscopy, it was determined that the aging process of the PLA PPDMPs was slower than that of pure MPs. The 2D-COS analysis revealed that the response orders for the functional groups on the PLA MPs differed during the aging process. The results demonstrated that the oxygen-containing functional groups of the PLA PPDMPs were the first to react. Subsequently, the -C-H and -C-C- structural responses began, and the polymer backbone was ruptured by the aging process. However, the aging of the pure-PLA MPs started with a brief oxidation process and then breakage of the polymer backbones, followed by continuous oxidation. Moreover, compared to the PLA PPDMPs, the pure-PLA MPs exhibited a greater adsorption capacity, which was increased by 88% after aging, whereas those of the two PPDMPs only increased by 64% and 56%, respectively. This work provides new insights into the behaviors of biodegradable PLA MPs in aquatic environments, which is critical for assessing the environmental risks and management policies for degradable MPs.

Study of the ageing and the sorption of polyaromatic hydrocarbons as influencing factors on the effects of microplastics on blue mussel

The mussels are species with high socio-economic weights and are often used as bioindicators of biological and chemical contamination. In the field and aquaculture, they can intake microplastics during filter-feeding, and the microplastics can have a negative impact on their health, even at low concentrations. The effects of microplastics have yet to be fully examined on the blue mussel (Mytilus edulis), considering the factors of ageing and sorption of some polyaromatic hydrocarbons (PAHs), ubiquitous environmental contaminants. In this work, 5 different exposure conditions were studied: pristine microplastics, microplastics aged for 1000 days under UV radiation, microplastics sorbing PAHs, as well as microplastics both aged and sorbing PAHs, in parallel to controls. The microplastic changes after ageing were studied with spectroscopic and chromatographic methods. Then, 8-day laboratory exposures of mussels at 10 µg/L of microplastics were performed. The oxidative stress, as well as neurotoxic and immunological responses of M. edulis, were measured using a battery of biomarkers (catalase/CAT, superoxide dismutase/SOD, glutathione S-transferases/GST, acetylcholinesterase/AChE) in 3 different organs (digestive gland, gills and mantle), and acid phosphatase in hemolymph. Then, a study of lipid impairments on the digestive gland was performed through the use of lipidomic tools. No significant difference of oxidative stress activity was observed for all the tissues of mussels exposed to pristine microplastics at 10 µg/L, compared to controls. The ageing and the PAH soption onto microplastics were influencing factors of the oxydative stress in mussels with increased CAT activities in the digestive glands and decreased SOD activities in the mantles. The neurotoxicity was highlighted by higher AChE activities measured in the mantle of mussels exposed to all the microplastic treatments, compared to controls. Concerning lipidomics, no compound was determined as a biomarker of microplastic exposure. The study demonstrated a low toxicity of microplastics at environmental relevant concentration with a 8-day exposure and using the chosen biomarkers. However, some microplastic changes seemed to lead to specific effects on mussels.

Fluorescence Correlation Spectroscopy Studies of Dye Diffusion on Fresh and Aged Polyethylene Terephthalate

Microplastics accumulate a wide variety of organic pollutants and thus may serve as efficient vectors for the transport of toxic substances. Much remains to be learned about how organic molecules interact with the surfaces of plastics and how these properties evolve as the microplastics are weathered. In this Letter, we report, for the first time, the application of confocal fluorescence correlation spectroscopy (FCS) to studies of organic molecules adsorbed from aqueous solution onto the surfaces of synthetic secondary microplastics. Both fresh and artificially aged poly(ethylene terephthalate) (PET) plastics are employed. The plastics are artificially aged in a UV-ozone chamber. Raman and infrared spectra confirm the composition of the PET microplastics. Water contact angle and surface roughness measurements reveal, respectively, an increase in wettability and a change in the nature of roughness with aging, consistent with surface oxidation. Rhodamine B (RhB) dye is used as a fluorescent probe in FCS studies and serves as an analogue for organic pollutants commonly found on microplastics. The FCS results reveal the accumulation of dye on the PET surfaces as they age. Dye motion is significantly slower on the plastics than in bulk aqueous solution and occurs by anomalous subdiffusion. The rate of diffusion becomes dramatically slower and more anomalous as the plastics are aged. Surface diffusion is likely slowed by either ionic interactions or hydrogen bonding between the dye and plastic. These results provide new insights critical to the understanding of how microplastics accumulate and transport organic pollutants as they weather in the environment.

Size-dependent long-term weathering converting floating polypropylene macro- and microplastics into nanoplastics in coastal seawater environments

In this study, we systematically developed the long-term photoaging behavior of different-sized polypropylene (PP) floating plastic wastes in a coastal seawater environment. After 68 d of laboratory accelerated UV irradiation, the PP plastic particle size decreased by 99.3 ± 0.15%, and nanoplastics (average size: 435 ± 250 nm) were produced with a maximum yield of 57.9%, evidencing that natural sunlight irradiation-induced long-term photoaging ultimately converts floating plastic waste in marine environments into micro- and nanoplastics. Subsequently, when comparing the photoaging rate of different sized PP plastics in coastal seawater, we discovered that large sized PP plastics (1000-2000 and 5000-7000 μm) showed a lower photoaging rate than that of small sized PP plastic debris (0-150 and 300-500 μm), with the decrease rate of plastic crystallinity as follow: 0-150 μm (2.01 d-1) > 300-500 μm (1.25 d-1) > 1000-2000 μm (0.780 d-1) and 5000-7000 μm (0.900 d-1). This result can be attributed to the small size PP plastics producing more reactive oxygen species (ROS) species, with the formation capacity of hydroxyl radical •OH as follows: 0-150 μm (6.46 × 10-15 M) > 300-500 μm (4.87 × 10-15 M) > 500-1000 (3.61 × 10-15 M) and 5000-7000 μm (3.73 × 10-15 M). The findings obtained in this study offer a new perspective on the formation and ecological risks of PP nanoplastics in current coastal seawater environments.

Aging behavior of microplastics accelerated by mechanical fragmentation: alteration of intrinsic and extrinsic properties

Microplastics (MPs) inevitably undergo multiple aging processes during their life cycle in the environment. However, the information regarding the mechanical fragmentation behavior of MPs remained unclear, including the changes in the intrinsic properties of aged MPs, the measurement of aging degree, the underlying mechanism, and the interaction with heavy metals. Here, MPs (PS, PP, PET) were aged by crushing (-CR) and ball-milling (-BM) to simulate mild and severe mechanical fragmentation, respectively. Our results indicated that mechanical fragmentation significantly affected the morphology of MPs. The aging degree of MP-BM was deeper compared to MP-CR owing to smaller particle size, larger specific surface area, poorer heat resistance, better hydrophilicity, and richer oxygen-containing functional groups. The carbonyl index (CI) and O/C ratio were used to measure the aging degree of the two mechanical aging treatments. Besides, the mechanism was proposed and the discrepancy between the two treatments was elaborated from three aspects including the excitation energy source, reaction interface, and reaction dynamics. Furthermore, the extrinsic properties of MPs altered with the increase of aging degree; specifically, the adsorption capacities of heavy metals were enhanced. Meanwhile, it was unveiled that the CI value and O/C ratio played a vital role in estimating the adsorption ability of heavy metals. The findings not only reveal the mechanical fragmentation behavior of MPs but also provide new insights into the assessment of the potential risks of the aged MPs via chemical indexes.

Microplastics and nanoplastics toxicity assays: A revision towards to environmental-relevance in water environment

Plastic pollution poses a serious risk to the oceans, freshwater ecosystems, and land-based agricultural production. Most plastic waste enters rivers and then reaches the oceans, where its fragmentation process begins and the forming of microplastics (MPs) and nanoplastics (NPs). These particles increase their toxicity by the exposition to external factors and binding environmental pollutants, including toxins, heavy metals, persistent organic pollutants (POPs), halogenated hydrocarbons (HHCs), and other chemicals, which further and cumulatively increase the toxicity of these particles. A major disadvantage of many MNPs in vitro studies is that they do not use environmentally relevant microorganisms, which play a vital role in geobiochemical cycles. In addition, factors such as the polymer type, shapes, and sizes of the MPs and NPs, their exposure times and concentrations must be taken into account in in vitro experiments. Last but not least, it is important to ask whether to use aged particles with bound pollutants. All these factors affect the predicted effects of these particles on living systems, which may not be realistic if they are insufficiently considered. In this article, we summarize the latest findings on MNPs in the environment and propose some recommendations for future in vitro experiments on bacteria, cyanobacteria, and microalgae in water ecosystems.

Microcystins-Loaded Aged Nanoplastics Provoke a Metabolic Shift in Human Liver Cells

Studies concerning the toxicity of pollutant-loaded nanoplastics (NPs) toward humans are still in their infancy. Here, we evaluated the adsorption of microcystins (MCs) by pristine and aged polystyrene nanoplastics (PSNPs), prepared MCs-loaded aged PSNPS (1, 5, 10, 15, and 19 μg/mg), and systematically mapped the key molecular changes induced by aged and MCs-loaded PSNPs to human hepatoblastoma (HepG2) cells. According to the results, MC-LR adsorption is increased 2.64-fold by aging, and PSNP accumulation is detected in HepG2 cells. The cytotoxicity of the MC-LR-loaded aged PSNPs showed a positive relationship with the MC-LR amount, as the cell viability in the 19 μg/mg loading treatment (aPS-MC19) was 10.84% lower than aged PSNPs; meanwhile, more severe oxidative damage was observed. Primary approaches involved stressing the endoplasmic reticulum and reducing protein synthesis that the aged PSNPs posed for HepG2 cells, while the aggravated cytotoxicity in aPS-MC19 treatment was a combined result of the metabolic energy disorder, oxidative damage, endoplasmic reticulum stress, and downregulation of the MC-LR target protein. Our results confirm that the aged PSNPs could bring more MC-LR into the HepG2 cells, significantly interfere with biological processes, and provide new insight into deciphering the risk of NPs to humans.

The combined effects of polyethylene microplastics and benzoanthracene on Manila clam Ruditapes philippinarum

Microplastic (MP) toxicity has recently been explored in various marine species. Along with the toxicity of plastics polymer itself, additional substances or pollutants that are absorbed onto it may also be harmful. In the present study, we investigated the combined impacts of polyethylene microplastics (PE MPs) and an organic pollutant (Benzo(a)anthracene, BaA) on Manila clam Ruditapes philippinarum during a one-week exposure. Two PE MPs concentrations (26 μg L^-1 and 260 μg L^-1) and one BaA concentration (3 μg L^-1) were tested. The clams were exposed to BaA and PE MPs either alone or in combination. BaA and PE MPs were incubated before the combined exposure. The biological effects of PE MPs and BaA on the clams were evaluated by considering several assays such as feeding rate, anti-oxidant enzyme activities, and the expression levels of stress-related genes. The feeding rate significantly decreased in individual PE MPs and individual BaA groups while it remained unchanged in combined groups. Superoxide dismutase (SOD) was the most affected among the biochemical parameters. Malondialdehyde (MDA), and glutathione peroxidase (GPx) activities were slightly affected, whereas no changes were observed in glutathione s-transferase (GST) activities. CYP1A1, CYP3A4, and HSP70 gene expressions displayed slightly significant changes. Considering all stressor groups, high PE MPs exposure (260 μg L^-1 PE MPs) more effectively altered the biological parameters in the clams compared to individual low PE MPs and BaA exposure, and their combination. The results also indicated the negligible vector role of PE MPs to transport BaA into the clam tissues.

Impact of aged and virgin microplastics on sedimentary nitrogen cycling and microbial ecosystems in estuaries

Microplastics (MPs) entering the environment undergo complex weathering (aging) processes, however, the impacts of aged MPs on estuarine nitrogen cycling and microbial ecosystems remain largely unknown. In this study, a 50 days microcosm experiment was conducted to investigate the response of sedimentary nitrogen (N) transformation processes, N2O emission and microbial communities to virgin and aged MPs (PE and PS) exposure. We found that aged MPs influenced sediment nitrogen turnover more rapidly and profoundly than virgin MPs and showed type and dose-response effect. During the first 10 days, higher concentration (3 % by weight of sediment) aged MPs (both PS and PE) treatments significantly promoted denitrification (ANOVA, P < 0.05), while virgin MPs treatments had weak effect on denitrification, compared with the control (P > 0.05). Moreover, higher concentration aged PS-MPs remarkably enhanced N2O emission on the 10th day, while N2O was consumed in the control. After 50 days incubation, there was an overall increase in nirK gene abundance exposed to MPs, and nosZ gene copies in aged PS treatments were around twice that in the control based on qPCR (P < 0.05). The function prediction also showed significant elevation of relative abundance of denitrification and DNRA relevant genes in bacterial community. In addition, aged PS treatment (3 %) recruited specific bacterial and archaeal assemblies, with Sedimenticolaceae, Lentimicrobiaceae, SCGC_AAA011-D5, SG8-5, Lokiarchaeia, and Odinarchaeia selectively enriched in the treatment. Our study highlighted that virgin and aged MPs had different impact on sediment nitrogen cycling, and the ecological risks of aged MPs should be concerned since all MPs eventually get weathered when they enter the environment.

Probing the aging process and mechanism of microplastics under reduction conditions

Microplastics (MPs) are becoming a class of pollutants with high global concerns. Research on the aging of MPs has focused on oxidative environments, it is of great interest to study the aging of MPs under reduction conditions. In this study, a reduction environment was constructed by purging nitrogen and adding reducing agents (NaBH₄, VC, Na₂S, C₂Na₂O₄) to understand the aging behavior and mechanism of MPs. The results proved that PVC occurred aging under four reduction conditions, and the aging degree was the strongest under NaBH₄ reduction condition. The aged PVC became broken, particle size decreased, and dechlorination phenomenon was observed. These phenomena were more obvious under the reduction condition in light, which was the superposition of photo-aging and reduction aging. The functional group components of PVC changed (C-C/CC increased, and oxygen-containing functional groups decreased) under reduction conditions, but photo-aging was dominant in the light system. Electron transfer occurred during the reduction process, and the EDC of PVC aged increased and EAC decreased. This study may shed light on a highly efficient aging pathway of MPs that is often overlooked in nature, contributing to understanding the aging behavior of MPs in complex environments.

New sight of microplastics aging: Reducing agents promote rapid aging of microplastics under anoxic conditions

The aging of microplastics (MPs) occurs extensively in the environment, and understanding the aging mechanisms of MPs is essential to study the properties, fate and environmental impact of MPs. We proposed a creative hypothesis that polyethylene terephthalate (PET) can be aged by reducing reactions with reducing agents. Simulation experiments based on the principle of reduction of carbonyl by NaBH₄ were conducted to test the correctness of this hypothesis. The results showed that after 7 days of experiments, physical damage and chemical transformation occurred in the PET-MPs. The particle size of MPs was reduced by 34.95-55.93 %, and the C/O ratio was increased by 2.97-24.14 %. The changing order of surface functional groups (CO > C-O > C-H > C-C) was obtained. The occurrence of reductive aging and electron transfer of MPs was further supported by electrochemical characterization experiments. These results together reveal the reductive aging mechanism of PET-MPs: CO is firstly reduced to C-O by BH₄^- attack, and then further reduced to ·R. The resulting ·R recombines to form new C-H and C-C. This study is beneficial to deepen the understanding of the chemical aging of MPs, and can provide a theoretical basis for further research on the reactivity of oxygenated MPs with reducing agents.

The adverse impact of microplastics and their attached pathogen on hemocyte function and antioxidative response in the mussel Mytilus galloprovincialis

Microplastics (MPs) are widely distributed in marine environments, and they are easily attached by various microorganisms, including pathogenic bacteria. When bivalves mistakenly eat MPs, pathogenic bacteria attached to MPs enter their bodies through the Trojan horse effect, causing adverse effects. In this study, the mussel Mytilus galloprovincialis was exposed to aged polymethylmethacrylate MPs (PMMA-MPs, 20 μm) and Vibrio parahaemolyticus attached to PMMA-MPs to explore the effect of synergistic exposure by measuring lysosomal membrane stability, ROS content, phagocytosis, apoptosis in hemocytes, antioxidative enzyme activities and apoptosis-related gene expression in gills and digestive glands. The results showed that MP exposure alone did not cause significant oxidative stress in mussels, but after long-term coexposure to MPs and V. parahaemolyticus, the activities of antioxidant enzymes were significantly inhibited in the gills of mussels. Both single MP exposure and coexposure will affect hemocyte function. Coexposure can induce hemocytes to produce higher ROS, improve phagocytosis, significantly reduce the stability of the lysosome membrane, and induce the expression of apoptosis-related genes, causing apoptosis of hemocytes compared with single MP exposure. Our results demonstrate that MPs attached to pathogenic bacteria have stronger toxic effects on mussels, which also suggests that MPs with pathogenic bacteria might have an influence on the immune system and cause disease in mollusks. Thus, MPs may mediate the transmission of pathogens in marine environments, posing a threat to marine animals and human health. This study provides a scientific basis for the ecological risk assessment of MP pollution in marine environments.

Additive effects of microplastics on accumulation and toxicity of cadmium in male zebrafish

Microplastics (MPs) have emerged as contaminants of concern because of their ubiquitous presence in almost all aquatic environments. The ecological effects of MPs are complex and depend on multiple factors including their age, size and the ecological matrix. There is an urgent need for multifactorial studies to elucidate their impacts. We measured the effects of virgin and naturally aged MPs, alone, pretreated with cadmium (Cd), or in combination with ionic Cd, on the bioaccumulation of Cd, metallothionein expression, behavior, and histopathology of adult zebrafish (Danio rerio). Zebrafish were exposed to virgin or aged polyethylene MPs (0.1% MPs enriched diets, w/w) or waterborne Cd (50 μg/L) or a combination of the two for 21 days. There was an additive interaction between water-borne Cd and MPs on bioaccumulation in males but not in females, Cd accumulation increased by twofold when water-borne Cd and MPs were combined. Water-borne Cd significantly induced higher levels of metallothionein compared to MPs pre-exposed to Cd. However, Cd-treated MPs caused greater damage to the intestine and liver compared to untreated MPs suggesting that bound Cd could be released or modulate MPs toxicity. We also showed that co-exposure to water-borne Cd and MPs increased anxiety in the zebrafish, compared with water-borne Cd alone, suggesting using microplastics as a vector may increase toxicity. This study demonstrates that MPs can enhance the toxicity of Cd, but further study is needed to elucidate the mechanism.

Systematic Review of Nano- and Microplastics' (NMP) Influence on the Bioaccumulation of Environmental Contaminants: Part II-Freshwater Organisms

Nano- and microplastic fragments (NMPs) exist ubiquitously in all environmental compartments. The literature-based evidence suggests that NMPs interact with other environmental contaminants in freshwater ecosystems through sorption mechanisms, thereby playing a vector role. Chemically bound NMPs can translocate throughout the environment, reaching long distances from the contaminant discharge site. In addition, they can be ab/adsorbed by freshwater organisms. Although many studies show that NMPs can increase toxicity towards freshwater biota through the carrier role, little is known regarding their potential to influence the bioaccumulation of environmental contaminants (EC) in freshwater species. This review is part II of a systematic literature review regarding the influence of NMPs on bioaccumulation. Part I deals with terrestrial organisms and part II is devoted to freshwater organisms. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews (PRISMA ScR) was used for the literature search and selection. Only studies that assessed the bioaccumulation of EC in the presence of NMPs and compared this with the bioaccumulation of the isolated EC were considered. Here, we discuss the outcome of 46 papers, considering NMPs that induced an increase, induced a decrease, or caused no effect on bioaccumulation. Lastly, knowledge gaps are identified, and future directives for this area of research are discussed.

Revealing the sorption mechanisms of carbamazepine on pristine and aged microplastics with extended DLVO theory

The co-occurrence of microplastics (MPs) and organic contaminants in aquatic environment can complexify their environmental fate via sorption interactions, especially when the properties of MPs can even vary due to the aging effect. Thus, quantitatively clarifying the sorption mechanisms is required to understand their environmental impacts. This study selected popularly occurring carbamazepine (CBZ) and four types of MPs as model systems, including polyethylene, polyvinyl chloride, polyethylene terephthalate and polystyrene in their pristine and aged forms, to investigate the sorption isotherms, kinetics, and desorption. The variation of MPs during the aging process were analyzed with scanning electron microscopy, contact angle, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. It was found that the aging process elevated the sorption capacity and intensified the desorption hysteresis of CBZ on MPs via increasing the surface roughness, decreasing the particle size, and altering the surficial chemistry of all MPs. The extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory was innovatively applied hereby to calculate the interfacial free energies and revealed that the hydrophobic interaction was significantly lessened after aging for all MPs with the slightly enhanced van der Waals interaction. Then the total interfacial free energies were dropped down for all MPs, which resulted in their declined specific sorption capacity. This work reveals the sorption mechanisms of CBZ on pristine and aged MPs with XDLVO and provides a useful reference to study the sorption of other neutral organics onto MPs.

A new point to correlate the multi-dimensional assessment for the aging process of microfibers

Fiber, the most prevalent plastic type, can be weathered and eroded easily in the natural environment. Although a variety of techniques have been applied to characterize the aging characteristics of plastics, a comprehensive understanding was critically essential to correlate the multi-dimensional assessment of the weathering process of microfibers and their environmental behavior. Therefore, in this study, microfibers were prepared from the face masks and Pb²⁺ was selected as a typical metal pollutant. The weathering process was simulated by xenon aging and chemical aging, and then subjected to Pb²⁺adsorption to examine the effect of weathering processes. The changes in fiber property and structure were detected by using various characterization techniques, with the development of several aging indices to quantify the changes. The two-dimensional Fourier transform infrared correlation spectroscopy analysis (2D-FTIR-COS) and Raman mapping were also performed to understand the order of changes in the surface functional groups of the fiber. The results showed that both aging processes altered the surface morphology, physicochemical properties, and polypropylene chain conformations of the microfibers, with stronger effect after chemical aging. The aging process also enhanced the affinity of microfiber to Pb²⁺. Moreover, the changes and correlation of the aging indices were analyzed, showing that the maximum adsorption capacity (Q_max) was positively related to carbonyl index (CI), oxygen-to-carbon atom (O/C) ratio and intensity ratio of the Raman peaks (I_841/808), but negatively related to contact angle and the temperature at the maximum weight loss rate (T_m). The O/C ratio was more suitable to quantify the surface changes with lower aging degree while the CI value explained the chemical aging process better. Overall, this study discussed the weathering processes of microfibers based on a multi-dimensional investigation, and attempted to correlate the aging characteristics of the microfibers and their environmental behavior.

Adsorption and desorption characteristics of heavy metals onto conventional and biodegradable plastics

Biodegradable plastics have been widely used to replace conventional plastics to minimize environmental impacts of plastic packaging. However, before biodegradable plastics decompose in the environment, they could pose a threat to terrestrial and aquatic creatures by acting as vectors of contaminants in the food chain. In this study, conventional plastic bags (CPBs) made of polyethylene and biodegradable plastic bags (BPBs) made of polylactic acid were examined for their heavy metal adsorption. Effects of solution pHs and temperatures on adsorption reactions were investigated. Because of a larger BET surface area, presence of oxygen-containing function groups, and smaller crystallinity, the heavy metal adsorption capacities of BPBs are significantly larger than those of CPBs. Among Cu (up to 791.48 mg⋅kg^-1), Ni (up to 60.88 mg⋅kg^-1), Pb (up to 1414.58 mg⋅kg^-1), and Zn (up to 295.17 mg⋅kg^-1), Pb and Ni show the largest and the lowest extents of adsorption onto the plastic bags, respectively. In the different waterbodies in nature, Pb adsorption on the CPBs and the BPBs were 318.08-379.91 and 528.41-764.22 mg⋅kg^-1, respectively. Consequently, Pb was selected as the target contaminant in the desorption experiments. After Pb was adsorbed onto the CPBs and the BPBs, Pb could be completely desorbed and released into simulated digestive systems in 10 h. In conclusion, BPBs could be potential vectors of heavy metals, and their suitability as a substitute for CPBs must be thoroughly investigated and confirmed.

Adsorption behaviors of chlorpyrifos on UV aged microplastics

Both non-degradable and biodegradable plastics can act as vectors of diverse organic pollutants. In this study, two types of biodegradable microplastics [poly (butylene adipate-co-terephthalate) (PBAT) and polylactic acid (PLA)] and one type of non-degradable microplastics [polypropylene (PP)] were selected to investigate the impacts of ultraviolet (UV) irradiation for one month on microplastics surface modification and their adsorption behaviors for chlorpyrifos (CPF). The study revealed that PBAT held the largest adsorption capacity, and PLA held the fastest adsorption rate. The UV irradiation diminished the adsorption capacities on PLA and PP but enhanced the adsorption capacities on PBAT. The adsorption capacity normalized by specific surface area revealed that specific surface area was the dominant factor for affecting the adsorption capacities on PP and PLA after UV irradiation. These findings further clarify the interaction between CPF and microplastics, and provide a theoretical basis for assessing the ecological risk of microplastics in water.

Characterizing the binding interactions between virgin/aged microplastics and catalase in vitro

Microplastics (MPs) undergo physical, chemical, and biological aging in the environment, leading to changes in their physicochemical properties, affecting migration characteristics and toxicity. Oxidative stress effects induced by MPs in vivo have been extensively studied, but the toxicity difference between virgin and aged MPs and the interactions between antioxidant enzymes and MPs in vitro have not been reported yet. This study investigated the structural and functional changes of catalase (CAT) induced by virgin and aged PVC-MPs. It was shown that light irradiation aged the PVC-MPs, and the aging mechanism was photooxidation, resulting in a rough surface and appearing holes and pits. Because of the changes in physicochemical properties, aged MPs had more binding sites than virgin MPs. Fluorescence and synchronous fluorescence spectra results suggested that MPs quenched the endogenous fluorescence of CAT and interacted with tryptophane and tyrosine residues. The virgin MPs had no significant effect on the skeleton of CAT, while the skeleton and the polypeptide chains of CAT became loosened and unfolded after binding with the aged MPs. Moreover, the interactions of CAT with virgin/aged MPs increased the α-helix and decreased the β-sheet contents, destroyed the solvent shell, and resulted in a dispersion of CAT. Due to the large size, MPs cannot enter the interior of CAT and have no effects on the heme groups and activity of CAT. The interaction mechanism between MPs and CAT may be that MPs adsorb CAT to form the protein corona, and aged MPs had more binding sites. This study is the first comprehensive investigation of the effect of aging on the interaction between MPs and biomacromolecules and highlights the potential negative effects of MPs on antioxidant enzymes.

Microplastics in Sewage Sludge: A review

Microplastics (MPs) represent a serious problem for the environment and for this reason they have been studied in many articles, especially their presence in aquatic environments and soils. MPs have been found in wastewater and sewage sludge from municipal wastewater treatment plants (WWTPs). Most part of the published works have focused on the detection and elimination of MPs in the water line and several reviews have been published in the last years. In addition, the application of sewage sludge produced from WWTPs for agricultural use is known to be a primary source of MPs in soils. However, in the scientific literature less attention has been paid to the sludge and little is known about MPs fate when it is applied in agriculture. This work aims to give a global revision on the most used techniques to identify and detect MPs in sludges, their characteristics and incidence, their effect on sludge treatments and their impact on the environment. As far as we know, there are no standardized protocols for MPs extraction from soil and the possible repercussions on the cultivation of plants are not known. This review evidences that more studies are necessary to stablished standardized protocols and decipher the main mechanisms and the effects of MPs from sewage sludge in the environment.

Aging process does not necessarily enhance the toxicity of polystyrene microplastics to Microcystis aeruginosa

Microplastic (MP) pollution in aquatic systems has attracted increasing attention in recent years. MPs will inevitably encounter aging process in the environment. However, research on the effects of aged MPs on freshwater ecosystems remains limited. This study compared the properties of pristine and aged polystyrene (PS) MPs of different sizes (20 nm, 200 nm, 2000 nm) and determined the effects of aging on the toxicity of PS MPs to typical freshwater cyanobacteria, Microcystis aeruginosa. Aging process induced significant changes to the properties of the MPs, especially their microstructures and surface functional groups. Aging process also influenced zeta potential, which could further affect stability and toxicity of PS MPs. After 96 h exposure, increase of algal growth and photosynthetic activity was observed in the treatment of pristine 200 nm, aged 20 nm and aged 200 nm PS MPs. In addition, pristine 20 nm, pristine 200 nm, pristine 2000 nm, aged 20 nm and aged 200 nm PS MPs were adsorbed on algal cell surface, which could influence the cell permeability. Pristine PS MPs promoted microcystin synthesis and release, which could do harm to drinking water safety and freshwater ecosystems. However, there was no significant increase in aged PS MPs treatments. Furthermore, the increased ¹³C content of algal cells in all pristine PS MPs treatments indicated that M. aeruginosa assimilated more CO₂ and generate more energy to resist the stress of pristine PS MPs when compared with aged PS MPs. These results indicate that aging process did not necessarily enhance the toxicity and biological risk of PS MPs to freshwater ecosystems. Findings of this study fill the knowledge gap in understanding the effects and risks of aged MPs on freshwater ecosystems.

Multispectroscopic Characterization of Surface Interaction between Antibiotics and Micro(nano)-sized Plastics from Surgical Masks and Plastic Bottles

Recent studies have shown that plastic particles can sorb antibiotics, and these sorption properties have been examined in various studies; however, the possible mechanism responsible for the interactions requires a deeper investigation in terms of further interaction with living systems. Moreover, the usage of disposable surgical masks and plastic bottles has increased the plastic pollution risk for living systems like humans. Therefore, this study aimed to examine the sorption characteristics between antibiotics (amoxicillin and spiramycin) and plastic particles from surgical masks and plastic bottles through batch sorption experiments. In the study, their surface interactions were characterized using multispectroscopic approaches including FTIR, Raman spectrometry, and SEM-EDX, and various surface indicators (e.g., surface oxidation, deformation, and biological potential) were examined. The sorption results showed that adsorption kinetics and the isotherm of amoxicillin and spiramycin on micro(nano)plastics from surgical masks and plastic bottles closely fit the pseudo-second-order kinetic model and Langmiur isotherm. These results indicated that the evidence for the antibiotic interaction with particles was changes in the surface functional group intensities and up-shifting, and this correlated with the sorption of antibiotics on micro(nano)-sized plastics. The C/N ratio of the plastic particles before and after antibiotic treatment was used as an indicator for the surface biological interaction, and the results showed that C/N ratios of surgical mask particles increased with both types of antibiotic sorption. However, the C/N of the particles from plastic bottles showed antibiotic type-dependence. The surface deformation indicators (e.g., O/C, C=O, C=C, and O-H indices) showed that the O/C ratios of micro(nano)plastics from surgical masks were higher with the amoxicillin and spiramycin sorption, and the C=O indices were positively linked with the amoxicillin sorption stages, whereas the C=C and O-H had a negative correlation with the amoxicillin sorption stages. Moreover, amoxicillin sorption influenced the O/C ratio and indices of O-H and C=C of micro(nano)plastics from plastic bottles in a limited manner. The C=O groups of the micro(nano)plastics from plastic bottles were positively influenced by the spiramycin sorption stages, whereas it was negatively linked with amoxicillin sorption stages. Overall, the findings from surface indicators indicated that the micro(nano)plastics from surgical masks can be more influenced with antibiotic sorption compared to plastic bottles.

Effect of aging on polyethylene microfiber surface properties and its consequence on adsorption characteristics of 17alpha-ethynylestradiol

This study assessed the interactive changes to the endocrine disruptor 17 alpha-ethynylestradiol (EE2) triggered by photoaging onto fibrous microplastics frequently found in the environment. The physicochemical property change of the polyethylene (PE) microfiber according to irradiation (i.e. 14 d UV-C (254 nm)) was studied through Fourier transform infrared spectroscopy, scanning electron microscope, and contact angle analysis. Additionally, the EE2 adsorption kinetics experiment was performed for the PE microfiber before and after UV irradiation to assess the change in adsorption characteristics. After UV irradiation, the PE microfiber surface roughness increased, the oxygen-containing functional group (e.g. carbonyl group) increased, and the contact angle (virgin PE: 80.02°, aged PE: 65.13°) decreased. A decrease in the surface hydrophobicity led to a decrease in the adsorption rate of EE2 (virgin PE: k = 0.0105 h-1, aged PE: not calculated). The hydrophobic interaction significantly affects the adsorption behavior of hydrophobic organic pollutants such as EE2 onto MPs, and continuous photo-aging of MPs may cause a new pattern of ecological risk. Therefore, there is a greater necessity for additional research relevant to this issue.

UV-induced microplastics (MPs) aging leads to comprehensive toxicity

Herein, the toxicity of 4 MPs and additives released from MPs during UV-aging was quantitatively evaluated by the transcriptional effect level index (TELI) based on E. coli whole-cell microarray assay, and MPs-antibiotics complex pollutants. Results showed that MPs and these additives had high toxicity potential, the maximum TELI was 5.68/6.85 for polystyrene (PS)/bis(2-ethylhexyl) phthalate (DEHP). There were many similar toxic pathways between MPs and additives, indicating that part of the toxicity risk of MPs was caused by the release of additives. MPs were compounded with antibiotics, the toxicity value changed significantly. The TELI values of amoxicillin (AMX) + polyvinyl chloride (PVC) and ciprofloxacin (CIP) + PVC were as high as 12.30 and 14.58 (P < 0.05). Three antibiotics all decreased the toxicity of PS and had little effect on polypropylene (PP) and polyethylene (PE). The combined toxicity mechanism of MPs and antibiotics was very complicated, and the results could be divided into four types: MPs (PVC/PE + CIP), antibiotics (PVC + TC, PS + AMX/ tetracycline (TC)/CIP, PE + TC), both (PP + AMX/TC/CIP), or brand-new mechanisms (PVC + AMX).

Biological responses of Chironomus sancticaroli to exposure to naturally aged PP microplastics under realistic concentrations

Microplastic (MP) is yet another form of chronic anthropogenic contribution to the environment. MPs are plastic particles (<5 mm) that have been widely found in the most diverse natural environments, but their real impacts on ecosystems are still under investigation. Here, we studied the toxicity of naturally aged secondary polypropylene (PP) MPs after constant exposure to ultraviolet radiation (26 µm) to the third instar larvae of Chironomus sancticaroli, a dipteran species. The concentrations tested were 13.5; 67.5; and 135 items g^-1 of dry sediment. C. sancticaroli organisms were investigated for fragment ingestion, mortality and changes in enzymatic biomarkers after 144 h of exposure. The organisms were able to ingest MPs from the first 48 h, and the amount of items internalized was dose-dependent and time-dependent. Overall, the results show that mortality was low, being significant at the lowest and highest concentrations (13.5 and 135 items g^-1). Regarding changes in biochemical markers, after 144 h MDA and CAT activities were both significantly altered (increased and reduced, respectively), while SOD and GST levels were unchanged. In the present study, naturally aged polypropylene MPs induced biochemical toxicity in C. sancticaroli larvae, with toxicity being higher according to exposure time and particle concentration.

Physiological Toxicity and Antioxidant Mechanism of Photoaging Microplastics on Pisum sativum L. Seedlings

Recent studies have confirmed that changes in the physical properties of microplastics (MPs) trigger toxicological effects and ecological risks. To explore the toxicity of different types of MPs on plants, and the influence of MP photoaging, this study investigated the toxicity mechanisms of pristine, 7 and 14 d photoaged polystyrene (PS), polyamide (PA), polyethylene (PE), and polyethylene terephthalate (PET) MPs on seed germination, root growth, nutrient fraction, oxidative stress, and antioxidant systems of Pisum sativum L. (pea) seedlings. The results showed that pristine PS and 14 d photoaged PET inhibited seed germination. Compared to the pristine MPs, photoaged MPs had negative effects on root elongation. Moreover, photoaged PA and PE impeded the nutrient transport of soluble sugars from roots to stems. Notably, the production of superoxide anion radicals (•O₂^-) and hydroxyl radicals (•OH) through the photoaging of MPs exacerbated oxidative stress and reactive oxygen species formation in roots. Antioxidant enzyme data revealed that the activities of superoxide dismutase and catalase were significantly activated in photoaged PS and PE, respectively, in order to scavenge •O₂^- and hydrogen peroxide (H₂O₂) accumulation and alleviate lipid peroxidation levels in cells. These findings provide a new research perspective on the phytotoxicity and ecological risk of photoaged MPs.

Modified linear solvation energy relationships for adsorption of perfluorocarboxylic acids by polystyrene microplastics

Microplastics (MPs) could act as vectors of organic pollutants such as per- and polyfluoroalkyl substances (PFAS). Therefore, understanding adsorptive interactions are essential steps towards unraveling the fate of PFAS in the natural waters where MPs are ubiquitous. Linear solvation energy relationships (LSER)-based predictive models are utilitarian tools to delineate the complexity of adsorption interactions. However, commonly studied PFAS are in their ionic forms at environmentally relevant conditions and LSER modeling parameters do not account for their ionization. This study aims to develop the first LSER model for the adsorption of PFAS by MPs using a subset of ionizable perfluoroalkyl carboxylic acids (PFCA). The adsorption of twelve PFCAs by polystyrene (PS) MPs was used for model training. The study provided mechanistic insights regarding the impacts of PFCA chain length, PS oxidation state, and water chemistry. Results show that the polarizability and hydrophobicity of anionic PFCA are the most significant contributors to their adsorption by MPs. In contrast, van der Waals interactions between PFCA and water significantly decrease PFCA binding affinity. Overall, LSER is demonstrated as a promising approach for predicting the adsorption of ionizable PFAS by MPs after the correction of Abraham's solute descriptors to account for their ionization.

Fourier Transform Infrared Spectroscopy to Assess the Degree of Alteration of Artificially Aged and Environmentally Weathered Microplastics

Fourier transform infrared (FTIR) is a spectroscopy technique widely used to identify organic materials. It has recently gained popularity in microplastic (MP) pollution research to determine the chemical composition of unknown plastic fragments. However, it could also be used to evaluate the degree of ageing of MPs collected from the environment. In this context, the principal aim of our research has been to qualitatively evaluate the natural weathering of environmental MPs collected in an Italian freshwater body (the Ofanto River) using ATR-FTIR technology. Furthermore, we compared environmental particles to weathered artificial MPs under controlled light and temperature conditions and to unaltered pristine materials to assess the results. FTIR spectra were acquired using a Nicolet Summit FTIR (ThermoFisher Scientific) equipped with an Everest ATR with a diamond Crystal plate and a DTGS KBr detector (wavenumber range 4000-500 cm^-1, 32 scans per spectrum, spectral resolution of 4 cm^-1). The degree of ageing was assessed using three different indexes known to be related to changes in MPs: Carbonyl Index (CI), Hydroxyl Index (HI), and Carbon-Oxygen Index (COI). The overall results showed that the regions reflecting changes (hydroxyl groups, peaks from 3100 to 3700 cm^-1, alkenes or carbon double bonds, 1600 and 1680 cm^-1, and carbonyl groups, 1690 and 1810 cm^-1) appeared significantly modified in artificial and natural weathered particles compared to the pristine materials. The indexes calculated for polymers degraded under the artificial photo and thermo ageing conditions displayed a general tendency to increase with the time in contact with irradiation time. Particular enhancements of CI of PS fragment and PE pellet, HI of PE and PS fragments and PE pellet, and COI of PS fragment were observed. Otherwise, the following incubation of the same particles at a constant temperature of 45 °C did not further affect the chemical composition of the particles. Moreover, new unique peaks were also observed in the freshwater particles, almost all in the fingerprint region (1500-500 cm^-1). Differences in CI, HI, and COI were evidenced among the different morphological MP shapes. On the one hand, the CI calculated for the environmental PE pellets showed values ranging from 0.05 to 0.26 with a mean value of 0.17 ± 0.10. Most samples (57%) presented a CI with values between 0.16 and 0.30. On the other hand, fragments presented slicer modifications in the carbonyl region with CI values lower than pellets (0.05 ± 0.05). This index helps evaluate the degradation of PE MPs by UV light, increasing with enhancing residence time in the environment. Conversely, fragments showed greater values of HI (5.90 ± 2.57) and COI (1.04 ± 0.48) than pellets, as well as lines, which presented the maximum value of HI (11.51). HI is attributed to the bond vibrations of hydroxyl, carboxyl, or phenol groups. In contrast, COI is frequently attributed to the vibrations of C_O bonds found in carbohydrates, alkanes, secondary alcohols, and ketones. In conclusion, our results showed characteristics spectra acquired from environmental particles compared to pristine and artificial aged ones. The interpretation of our main results emphasizes the need to conduct ecotoxicological experimental studies using naturally weathered particles due to the unicity of their properties, which are more helpful for understanding microplastic pollution effects.

Assessment of relationship between aging and contaminant-carryover for different filter layer of surgical mask under urban environmental stressors

Abundant disposable surgical masks (SMs) remain in the environment and continue to age under urban environmental stressors. This study aimed to investigate the aging characteristics of SMs and the effect of different aged layers of SMs on phenanthrene (PHE), tylosin (TYL), and sulfamethazine (SMT) under two different urban environmental stressors (UV and ozone). The results show that UV exposure causes more severe aging of the SM layers than ozone. The middle layer, made of melt-brown fabric, has displayed the highest degree of aging due to its smaller diameter and mechanical strength. The two-dimensional correlation spectroscopy (2D-COS) analysis reveals the different aging sequences of functional groups and three layers in aged SMs under the two urban environmental stressors. Whether the SMs are aged or not, the adsorptions of three organic pollutants on SMs are positively correlated with the octanol-water partition coefficient. Furthermore, except for the dominant hydrophobic interaction, aged SMs can promote the adsorption of three organic pollutants by accessory interactions (hydrogen bonding and partition), depending on their structures. These findings highlight the environmental effects of new microplastic (MP) sources and coexisting pollutants under the influence of COVID-19, which is helpful in accurately evaluating the biological toxicity of SMs.

Aging dependent plastic bag derived-microplastics as a vector of metals in lake water

The adsorption of microplastics (MPs) for metals in aquatic environment remains poorly understood due to the use of either commercial MPs, which have different property from the MPs in environments, or artificial solutions, which have not only the significantly higher concentration of metals than natural aqueous environment but also the different natures. In this study, we elaborated the adsorption throughout the aging process of plastic bag derived-MPs (initially 1-2 mm) by potassium persulfate (K₂S₂O₈) solution to metals in lake water. Comparatively, plastic bag derived-MPs had the highest adsorption capacity for Zn²⁺ followed by Fe³⁺, Pb²⁺, Mn²⁺, Cr⁶⁺, Ni²⁺, Cu²⁺ and Cd²⁺, which is not completely consistent with the literature. Both the adsorption capacity and distribution coefficients of Cu²⁺, Ni²⁺, Zn²⁺, Mn²⁺ and Pb²⁺ had significant linear correlation with carbonyl index (p < 0.05). Although the aging overall enhanced the adsorption, the adsorption capacities of MPs might fluctuate depending on metal.

Impact of coastal wastewater treatment plants on microplastic pollution in surface seawater and ecological risk assessment

This study aims to understand the influence of wastewater treatment plant discharge on the microplastic status in the surface seawater of Istanbul. For this purpose, for the first time, the distribution, composition, and ecological risk of microplastics at nine sampling stations on the southern coast of Istanbul, Marmara, were investigated at monthly intervals over a one-year period. The results showed that the microplastic abundance ranged from 0 to over 1000 particles per liter. Fibers were the dominant form at all stations. Microplastics 249-100 μm were the dominant size, and transparency was the color most found at all stations. Polyethylene and ethylene-vinyl acetate were the major types of microplastics, accounting for 50% overall. The pollution load index revealed that over 70% of sampling stations were at hazard level I. However, the hazardous index was categorized as level III with a value of 662.3 due to the presence of the most hazardous polymer named polyurethane. Further investigations into the risk assessment of MP can reveal crucial knowledge for understanding the microplastic cycle.

UV and chemical aging alter the adsorption behavior of microplastics for tetracycline

This study evaluates the "vector" effects of different microplastics (MPs) on coexisting pollutants. The adsorption of tetracycline was studied on biodegradable plastics poly(butylene adipate-co-terephthalate) (PBAT) and non-biodegradable plastics polystyrene (PS), polypropylene (PP), and polyethylene (PE) after UV aging and chemical aging. The physicochemical properties of PBAT changed more obviously after UV radiation and chemical aging comparing to PS, PP and PE. Pores and cracks appear on the surface of aged PBAT. The crystallinity increased from 29.2% to 52.62%. In adsorption experiments, pristine and aged PBAT had strong vector effects on the adsorption of tetracycline than PS, PP and PE. The adsorption capacity of tetracycline on PBAT was increased from 0.7980 mg g^-1 to 1.2669 mg g^-1 after chemical aging. The adsorption mechanism indicated that electrostatic interactions and hydrogen bonds contribute to the adsorption process. In addition, for the adsorption of tetracycline on PS, π-π interaction was the main cause, and the adsorption mechanism was not considerably changed by aging. In conclusion, this study demonstrates that biodegradable plastics have substantial vector effect on coexisting pollutants at the end of their life cycle, this contributes to assessment of the risk from microplastic pollution.

New insights into adsorption mechanism of pristine and weathered polyamide microplastics towards hydrophilic organic compounds

The widespread coexistence of hydrophilic organic compounds and microplastics (MPs) in the environment has greatly increased their associated environmental problems. To evaluate the potential carrier effect of oxygen-containing MPs on coexisting pollutants, adsorption behaviors of four hydrophilic organic compounds (benzoic acid, sulfamethoxazole, sulfamerazine and ciprofloxacin) on MPs (pristine and weathered polyamide (PA)) were studied in the aquatic environment. The results showed that the surface morphology, size, oxygen content, molecular structure, surface charge and crystallinity of PA were changed after weathering, and the weathering degree of PA treated with heat-activated potassium persulfate was the highest. The main adsorption mechanisms included hydrogen bonding, hydrophobic interaction, charge-assisted hydrogen bonding, and electrostatic interaction. Hydrogen bonding and hydrophobic interaction contributed to the adsorption, while electrostatic interaction weakened the adsorption under the specific pH conditions. The formation of charge-assisted hydrogen bonding (CAHB) was also verified through pH influence experiments, and this force can overcome the electrostatic repulsion. The high adsorption of KPA (PA weathered by K₂S₂O₈) under alkaline conditions was well explained by the formation of homonuclear CAHB due to the increase of oxygen-containing functional groups compared to the other three PA. Additionally, weathering did not always enhance the adsorption of hydrophilic organic compounds on PA, which was related to the changes in surface charge, crystallinity and hydrophilicity of PA. Overall, the physical and chemical properties (e.g., specific surface area, oxygen content, molecular structure) of PA after weathering and its trend of adsorption were different from other oxygen-free MPs in this study. This work can provide basic data for environmental risk of MPs and contribute to clarify and understand the processes of oxygenated MPs in the aquatic environment.

Physicochemical and biological ageing processes of (micro)plastics in the environment: a multi-tiered study on polyethylene

Pollution by plastic and microplastic impacts the environment globally. Knowledge on the ageing mechanisms of plastics in natural settings is needed to understand their environmental fate and their reactivity in the ecosystems. Accordingly, the study of ageing processes is gaining focus in the context of the environmental sciences. However, laboratory-based experimental research has typically assessed individual ageing processes, limiting environmental applicability. In this study, we propose a multi-tiered approach to study the environmental ageing of polyethylene plastic fragments focusing on the combined assessment of physical and biological processes in sequence. The ageing protocol included ultraviolet irradiation in air and in a range of water solutions, followed by a biofouling test. Changes in surface characteristics were assessed by Fourier transform infrared spectroscopy, scanning electron microscopy, and water contact angle. UV radiation both in air and water caused a significant increase in the density of oxidized groups (i.e., hydroxyl and carbonyl) on the plastic surface, whereby water solution chemistry influenced the process both by modulating surface oxidation and morphology. Biofouling, too, was a strong determinant of surface alterations, regardless of the prior irradiation treatments. All biofouled samples present (i) specific infrared bands of new surface functional groups (e.g., amides and polysaccharides), (ii) a further increase in hydroxyl and carbonyl groups, (iii) the diffuse presence of algal biofilm on the plastic surface, and (iv) a significant decrease in surface hydrophobicity. This suggests that biological-driven alterations are not affected by the level of physicochemical ageing and may represent, in real settings, the main driver of alteration of both weathered and pristine plastics. This work highlights the potentially pivotal role of biofouling as the main process of plastic ageing, providing useful technical insights for future experimental works. These results also confirm that a multi-tiered laboratory approach permits a realistic simulation of plastic environmental ageing in controlled conditions.

Influence of aged and pristine polyethylene microplastics on bioavailability of three heavy metals in soil: Toxic effects to earthworms (Eisenia fetida)

Virgin microplastics (MPs) would undergo aging process when entering environment, the adsorption capability of pollutants onto MPs may change during the aging process. To better understand the influence of aged polyethylene microplastics (PE-MP) on the bioavailability of three heavy metals (Zn, Pb, and Cd) in soil, hydrogen peroxide exposure (3% H₂O₂) and ultraviolet irradiation methods were employed to simulate the aging process. After aging process, different amount (0.1%, 1%, 10%) of PE-MP (pristine or aged) was added into soil to assess the ability of soil (containing PE-MP) adsorbing heavy metal. Moreover, different amount (0.01%, 0.1%, 1%) of PE-MP (pristine or aged) was added into soil to cultivate the earthworms to assess the impact of PE-MP on bioavailability of three heavy metals. Results indicated that the aged and virgin PE-MP had similar capability to adsorb heavy metal, the adsorption ability of Zn²⁺, Pb²⁺, and Cd²⁺ to pristine PE-MP were 2.42, 7.47, and 7.76 mg/g, respectively. The concentration of Zn or Pb in earthworms in treatments of metal +1% PE-MP was slightly higher than that in single metal (Zn or Pb) treatment, moreover, the concentration of Cd in earthworms in treatment of Cd + 1% PE-MP was significantly (p < 0.05) higher than that in single Cd treatment, exhibiting that 1% of PE-MP enhanced the bioavailability of heavy metals in soil. However, heavy metal concentrations in earthworms in treatments of metal + pristine PE-MP showed insignificant (p > 0.05) difference with those in treatments of metal + aged PE-MP, indicating that the aging process in this study did not change the environmental influence of PE-MP on heavy metals bioavailability. Superoxide dismutase activity, reactive oxygen species level, malondialdehyde content, and related gene expression in earthworms showed that PE-MP and heavy metals would bring toxic synergy to earthworms, therefore, the influence of MPs should be comprehensively considered when determining the environmental risk of heavy metals in soil.

Emerging investigator series: microplastic-based leachate formation under UV irradiation: the extent, characteristics, and mechanisms

Microplastics in the aquatic system are among the many inevitable consequences of plastic pollution, which has cascading environmental and public health impacts. Our study aimed at analyzing surface interactions and leachate production of six microplastics under ultraviolet (UV) irradiation. Leachate production was analyzed for the dissolved organic content (DOC), UV254, and fluorescence through excitation emission (EEM) to determine the kinetics and mechanisms involved in the release of organic matter by UV irradiation. The results suggested there was a clear trend of organic matter being released from the surface of the six microplastics caused by UV irradiation based on DOC, UV254 absorbance, and EEM intensity increasing with time. Polystyrene had the greatest and fastest increase in DOC concentrations, followed by the resin coated polystyrene. Experiments conducted at different temperatures indicated the endothermic nature of these leaching mechanisms. The differences in leachate formation for different polymers were attributed to their chemical makeup and their potency to interact with UV. The aged microplastic samples were analyzed by Fourier-transform infrared spectroscopy (FT-IR), Raman, and X-ray photoelectron spectroscopy (XPS), to determine the surface changes with respect to leachate formation. Results indicated that all microplastics had increasing carbonyl indices when aged by UV with polystyrene being the greatest. These findings affirm that the leachate formation is an interfacial interaction and could be a significant source of organic compound influx to natural waters due to the extremely abundant occurrence of microplastics and their large surface areas.

Insights into the characteristics, adsorption and desorption behaviors of microplastics aged with or without fulvic acid

Many aging experiments on microplastics (MPs) have been carried out using UV radiation or strong oxidants. Little attention has been paid to the role of water environmental factors such as dissolved organic matter (DOM). In this study, the role of fulvic acid (FA), the main component of DOM, in the UV-aging process of MPs was explored. MPs aged under UV, and UV along with 0.5 mg/L and 2 mg/L FA, were selected as subjects. The results showed that (1) FA accelerated the aging process of polyethylene (PE). PE aged with FA had a larger specific area (S_BET), with more holes and cracks on the surface. (2) FA enhanced the adsorption capacity of PE. The TC adsorption quantities of 0, 0.5, and 2 mg/L FA-aged PE were 1.100, 1.447, and 1.812 mg/L, respectively. (3) The quantity of TC desorbed by PE increased, whereas the desorption rate decreased as the FA concentration increased. The desorption rates of TC at 0, 0.5, and 2 mg/L FA-aged PE were 25.16%, 22.05%, and 19.52% in water, and 72.10%, 70.36%, and 59.51% in simulated intestinal fluid. This study explored the role of FA in the aging process of MPs. Moreover, research on the aging mechanism of MPs is enriched.