Plastic litter fate and contaminant transport within the urban environment, photodegradation, fragmentation, and heavy metal uptake from storm runoff

Exploring the toxicology, socio-ecological impacts and biodegradation of microplastics in Africa: Potentials for resource conservation

Achieving upcycling and circularity in the microplastic economy predominantly depends on collecting and sorting plastic waste from the source to the end-user for resource conservation. Microplastics, whether from packaging or non-packaging materials, pose a significant environmental challenge as they are often not prioritized for collection or recycling initiatives. The presence of additives impedes the quality of plastic recyclates and the persistence of microplastics as shredded resultants remain a threat to the aquatic and terrestrial ecosystem and its biodiversity. Despite the increasing global research on microplastics, the success of plastic and microplastic waste management in Africa is yet to be fully attained. Considering the improper disposal, limited recycling and upcycling intervention, lack of policy, and strict laws against plastic waste management defaulters, the ecosystems in Africa remain immensely impacted by several socio-ecological factors leading to the loss of aquatic organisms through reducing fertility and increasing stress. As a ripple consequence, the disruption of economic activities, toxic effects on animal/human health, and climate crisis are among their impact. This review therefore provides comprehensive detail of microplastic production and challenges in Africa, the toxicology concerns, socio-ecological issues associated with microplastic waste management, and insight into approaches to mitigate plastic pollution through recycling, upcycling, bioprocessing and their biodegradation with social insects and microorganisms which may form the basis for adoption by policymakers and researchers, thereby minimizing the consequences of plastic pollution in Africa.

Macroplastic surface characteristics change during wind abrasion

Mechanical abrasion is an important wind driven process which can degrade plastic litter on sandy beaches, desert environments and in agricultural settings. Wind-driven particle impacts can cause surface roughening and chemical changes and eventually complete fragmentation in high stress environments. Aeolian abrasion has been considered in the context of microplastics (< 5 mm) which can be easily mobilised by wind. However, macroplastic (> 5 mm) abrasion has primarily been confined to engineering studies using high air velocities (> 25 m s-1) and large abraders (> 6 mm) which generate greater impact forces than observed in the natural environment. Using laboratory abrasion experiments, we demonstrate that the surface microtextures and surface chemistry of three different types of plastic are substantially altered during the processes of aeolian abrasion at impact particle velocities of 0.6 m s-1. After ten days of continuous abrasion with four different erodents the macroplastic surfaces developed textures resulting from micro-cutting, denting, flaking, micro-pitting and surface flattening. The prevalence of each surface texture was dependent upon the angularity of the erodent and the type of plastic. In all cases, polymer surface chemical compositions became more complex due to embedding of shattered abrasive and the replacment of carbon with oxygen and silica.

Characterisation of tyre wear particle transport from road runoff to sea in coastal environments

Data on the fate of tyre wear particles (TWPs) within aquatic environments is limited. This study quantified TWPs entering estuaries in stormwater drainage and atmospheric fallout, and once they have reached the marine environment, within surface waters and sediments. TWPs were found at concentrations of 0.4 mg/L, 2.55 mg/m2/d, 0.00063 mg/L, and 0.96 g/kg respectively. Samples were partitioned by size to examine the distribution of TWP mass. 80-90% of TWP mass entering marine systems (stormwater and atmospheric fallout) lay between 31-125 µm. Larger particles preferentially accumulated in sediments where ∼50 % of TWP mass was >250 μm, compared to surface waters where the size class 15-63 μm accounted for ∼80 %. This study provides novel data on the sizes and concentrations of TWP pollution in coastal environments. Such data are of importance in determining biological exposures. Notably, the presence of TWPs in surface waters demonstrates their potential for transport over longer distances.

Litter in French urban areas - Part 2: transport dynamic and fluxes in stormwater

Urban areas constitute a major hotspot of litter, including plastic litter, that stormwater can wash off towards waterways. However, few studies quantified and characterized litter densities in urban areas and fluxes transported by stormwater networks. Moreover, little information is available on litter transport dynamics in stormwater, and on the factors driving this transport. This study aims at characterizing and quantifying litter amounts transported by stormwater of two nested French urban catchments (total surface area of 105 ha). Litter densities relative to land uses and rain events were investigated in the same catchments as in a compagnon paper (Ledieu et al., 2024). The present study explores the impact of rain events on the transport of urban litter in stormwater. Litter collection and characterization combined with a capture/recapture experiment using tagged litter placed in stormwater inlets show total litter fluxes of 29 kg/year, in which 14 kg/year are plastics, exported at the stormwater outlet. These fluxes confirm that stormwater runoff is a considerable pathway from urban surfaces to waterways, especially regarding small plastic litter (< 2.5 cm). Item transport dynamic is however not linear and only 0.3% of the urban litter appear remobilized. Litter transport dynamics depends on several factors (urban litter densities, hydrometeorological parameters, item composition and morphologies, and stormwater management systems) that should be considered in global models.

Antimony release from e-waste-derived microplastics in aqueous environments: Effect of plastic properties and environmental factors

Antimony (Sb) is an emerging contaminant widely concerned by researchers recently. Sb2O3, the flame-retardant synergist extensively used in plastics for electronic products, is an important source of Sb pollution. It can be released into the environment from e-waste, especially from the formed microplastics (MPs). However, the behavior and mechanisms of Sb release remain unclear. This study investigated the release behavior of Sb from two typical e-waste-derived MPs, acrylonitrile-butadiene-styrene (ABS) and high-impact polystyrene (HIPS). The effects of particle size, plastic aging, and environmental conditions (pH, humic acid, and inorganic ions) on Sb release were explored. It was found that HIPS exhibited higher total Sb (Sbtot) release than ABS, due to differences in their hydrophilicity and crystallinity. When the particle size was reduced from 2 mm to 0.15 mm, Sbtot release from HIPS and ABS increased by 620% and 350%. UV aging increased hydrophilicity and decreased crystallinity of MPs, further enhancing Sbtot release. Notably, there were about 40% Sb(III) in Sbtot released by pristine MPs, whereas in the leachate from the UV-aged MPs, Sbtot was exclusively Sb(V). Sbtot release was greatly enhanced by acidic and alkaline environments, especially at extreme pH levels, while humic acid has an inhibitory effect on the Sbtot release. These results suggest considerable amounts of Sb can be released into the environment from e-waste-derived MPs, and affected by various environmental factors. These findings improve understanding of Sb release from MPs in e-waste areas under various environmental conditions, providing insights into environmental risks tied to additive release from MPs.

Impacts of climatic stressors on dissolved organic matter leaching from microplastics and their effects on biogeochemical processes: A review

This review explores the potential impact of microplastic-derived dissolved organic matter (MP-DOM) on biogeochemical processes associated with global carbon and nitrogen cycles, with consideration given to the possible influence of irregular climate changes. We synthesize literature on MP-DOM leaching behaviors during various natural aging processes, such as heavy rainfall, heat waves, and UV irradiation, which may be intensified by climate change. MP-DOM release varies with plastic type and conditions, with organic additives significantly influencing leaching under UV exposure. Increased turbulence from hydrological events and rising temperatures also enhances MP-DOM release. While most research has focused on specific additive releases, the broader effects of polymer degradation and subsequent impacts on microbial communities and biogeochemical cycles are only recently recognized. These disruptions may affect cellular processes in algae and plant roots, enhance microbial utilization of dissolved organic carbon, and potentially increase greenhouse gas production. Our review highlights overlooked roles of MP-DOM exacerbated by climatic stressors and calls for further research to understand its broader biogeochemical impacts. We also emphasize the importance of distinguishing between polymers and commercial plastics when assessing MP-DOM's effects on biogeochemical processes associated with carbon and nitrogen cycles and recommend investigating additional aging processes influencing MP-DOM release.

Characterization, surface deformation analysis and sources of small plastic fragments collected in diverse environments of Egypt

This study investigates the sources and morphological characteristics of plastic waste across diverse Egyptian environments-marine (Mediterranean and Red Seas), freshwater (River Nile), and terrestrial (urban streets). Predominant plastics found in various marine areas include polyethylene and polypropylene, originating from both maritime and urban sources. In the Mediterranean, these plastics show higher levels of UV-induced degradation, resulting in fragments measuring 18-22 mm in size and 1-1.2 mm in thickness. The River Nile exhibits polystyrene fragments, with average sizes of 20-26 mm and thicknesses of 0.7-0.9 mm influenced by urban and agricultural runoff. Urban streets display a mix (polypropylene, polyethylene, and polystyrene), with thicker fragments (averaging 1.8 mm) due to mechanical wear and pollution. Analysis shows varying surface loss: Mediterranean (29 %), Red Sea (20-23 %), freshwater (18 %), and urban streets (up to 30 %), indicate differential degradation influenced by environmental conditions and human activities. These findings underscore the need for targeted policies to mitigate plastic pollution across Egypt's landscapes, crucial for global conservation efforts.

Potential mechanisms of aortic medial degeneration promoted by co-exposure to microplastics and lead

Microplastics (MPs) have attracted widespread attention because they can lead to combined toxicity by adsorbing heavy metals from the environment. Exposure to lead (Pb), a frequently adsorbed heavy metal by MPs, is common. In the current study, the coexistence of MPs and Pb was assessed in human samples. Then, mice were used as models to examine how co-exposure to MPs and Pb promotes aortic medial degeneration. The results showed that MPs and Pb co-exposure were detected in patients with aortic disease. In mice, MPs and Pb co-exposure promoted the damage of elastic fibers, loss of vascular smooth muscle cells (VSMCs), and release of inflammatory factors. In vitro cell models revealed that co-exposure to MPs and Pb induced excessive reactive oxygen species generation, impaired mitochondrial function, and triggered PANoptosome assembly in VSMCs. These events led to PANoptosis and inflammation through the cAMP/PKA-ROS signaling pathway. However, the use of the PKA activator 8-Br-cAMP or mitochondrial ROS scavenger Mito-TEMPO improved, mitochondrial function in VSMCs, reduced cell death, and inhibited inflammatory factor release. Taken together, the present study provided novel insights into the combined toxicity of MPs and Pb co-exposure on the aorta.

Nanoscale Abrasive Wear of Polyethylene: A Novel Approach To Probe Nanoplastic Release at the Single Asperity Level

There is a growing concern that nanoplastic pollution may pose planetary threats to human and ecosystem health. However, a quantitative and mechanistic understanding of nanoplastic release via nanoscale mechanical degradation of bulk plastics and its interplay with photoweathering remains elusive. We developed a lateral force microscope (LFM)-based nanoscratch method to investigate mechanisms of nanoscale abrasive wear of low-density polyethylene (LDPE) surfaces by a single sand particle (simulated by a 300 nm tip) under environmentally relevant load, sliding motion, and sand size. For virgin LDPE, we found plowing as the dominant wear mechanism (i.e., deformed material pushed around the perimeter of scratch). After UVA-weathering, the wear mechanism of LDPE distinctively shifted to cutting wear (i.e., deformed material detached and pushed to the end of scratch). The shift in the mechanism was quantitatively described by a new parameter, which can be incorporated into calculating the NP release rate. We determined a 10-fold higher wear rate due to UV weathering. We also observed an unexpected resistance to initiate wear for UV-aged LDPE, likely due to nanohardness increase induced by UV. For the first time, we report 0.4-4 × 10-3 μm3/μm sliding distance/μN applied load as an initial approximate nanoplastic release rate for LDPE. Our novel findings reveal nanoplastic release mechanisms in the environment, enabling physics-based prediction of the global environmental inventory of nanoplastics.

Understanding the Dynamics of Microplastics Transport in Urban Stormwater Runoff: Implications for Pollution Control and Management

The transport of microplastics (MPs) from urban environments to water resources via stormwater runoff poses significant concerns due to its adverse impacts on water safety and aquatic ecosystems. This study presents a modeling approach aimed at understanding the transport mechanisms of MPs in an urban residential setting, considering settling and buoyant MPs. To consider the effect of MP shapes, the settling velocity of various settling MPs in shapes of fibers, films, and fragments was calculated. Using an analogy of sediment transport, a Rouse number criterion was used to analyze the transport of MPs. For buoyant MPs, it was assumed that they transport as wash-load as soon as they float in the water and the travel time for them to reach the storm drain was determined. The calculation of settling velocity revealed the influence of shape on the settling velocity of MPs was particularly pronounced as the equivalent diameter of the MPs increased. The transport mechanism for the smallest settling MPs, irrespective of their shapes, density, and depth of flow, was wash-load. However, for larger MPs, the shape and size distribution of settling MPs, along with the depth of flow and slope significantly influenced their transport mechanisms compared to sediment particles. The influence of weathering on the MPs' transport mechanisms depended on their sizes and shapes. The site-specific characteristics, including slope and surface friction, significantly influenced the velocity of stormwater runoff and, consequently, the extent of MP transport during rain events. Moreover, an evaluation of the transport mechanism of settling MPs was conducted using the reported field data on MP abundance in road dust collected from residential and traffic sites. This study underscores the complexity of MP transport dynamics and provides a foundation for developing targeted strategies to mitigate MP pollution in urban environments.

Microplastic generation from field-collected plastic gauze: Unveiling the aging processes

Accumulation of plastic debris in the environment is a matter of global concern. As plastic ages, it generates microplastic (MP) particles with high mobility. Understanding how MPs are generated is crucial to controlling this emerging contaminant. In this study, we utilized high-density polyethylene (HDPE) plastic gauze, collected from urban settings, as a representative example of plastic waste. The plastic gauze was subjected to various aging conditions, including freeze-thaw cycling, mechanical abrasion, and UV irradiation. Following aging, the plastic gauze was rinsed with water, and the number of generated MPs were quantified. It was found that aged plastic gauze generated up to 334 million MP particles per m2 (> 10 µm) during rinsing, a number two orders of magnitude higher than unaged plastic. Fragmentation occurred in two dimensions for bulk MPs of all morphotypes. However, specific aging approaches (i.e., mechanical abrasion and UV irradiation) generated spheres and fibers via pseudo-3D fragmentation. Additionally, changes in molecular weight, size distribution, and surface oxidation characteristics unveiled a complex pattern (i.e., irregular changes with exposure time). This complexity underscores the intricate nature of plastic debris aging processes in the environment.

Are we underestimating stormwater? Stormwater as a significant source of microplastics in surface waters

Stormwater represent a critical pathway for transporting microplastics (MPs) to surface waters. Due to complex dynamics of MPs in stormwater, its dispersion, weathering, risk, and transport are poorly understood. This review bridges those gaps by summarizing the latest findings on sources, abundance, characteristics, and dynamics involved in stormwater MP pollution. Weathering starts before or after MPs enter stormwater and is more pronounced on land due to continuous heat and mechanical stress. Land use patterns, rainfall intensity, MPs size and density, and drainage characteristics influence the transport of MPs in stormwater. Tire and road wear particles (TRWPs), littering, and road dust are major sources of MPs in stormwater. The concentrations of MPs varies from 0.38-197,000 particles/L globally. Further MP concentrations showed regional variations, highlighting the importance of local monitoring efforts needed to understand local pollution sources. We observed unique signatures associated with the shape and color of MPs. Fibers and fragments were widely reported, with transparent and black being the predominant colors. We conclude that the contribution of stormwater to MP pollution in surface waters is significantly greater than wastewater treatment plant effluents and demands immediate attention. Field and lab scale studies are needed to understand its behavior in stormwater and the risk posed to the downstream water bodies.

Analysis and identification of degradation products in gas, particle, and liquid phases of polypropylene and polyethyleneterephthalate microplastics aging through non-thermal plasma simulation

Plastic aging can cause alterations in the physical and chemical characteristics of plastics, as well as their behavior in the environment. Due to the extremely slow natural aging process, laboratory simulated aging methods have to be used. In this study, non-thermal plasma (NTP) was adopted to investigate the aging process of polypropylene (PP) and polyethylene terephthalate (PET) microplastics. Various analytical instruments, including proton transfer reaction mass spectrometry and single-particle aerosol mass spectrometry, were employed to examine and identify the organic constituents of the gas, liquid, and particle phase degradation products, as well as to monitor the degradation process. The results showed that after 90 min of aging, both PP and PET surfaces showed yellowing, and the carbonyl index of PP increased while that of PET decreased, with an increase in crystallinity. The organic components of reaction products, such as ketones, esters, acids, and alcohols, increased with longer aging times. Gas products mainly contain aromatic hydrocarbons, while particles from aged PET contain compounds with benzene rings and metal elements. Liquid products from aged PP show a significant presence of branched alkanes. Based on this analysis, degradation mechanisms of PP and PET by NTP were proposed. This investigation represents the initial systematically exploration of the release of organic substances during the degradation of microplastics mediated by NTP. It provides significant insights into the detrimental organic compounds emitted during this process, thereby offering valuable information for understanding the environmental and human health implications of natural microplastic degradation. Furthermore, it addressed the requirements for increased attention to the potential environmental risks associated with these harmful components.

Integrated microbiota and multi-omics analysis reveal the differential responses of earthworm to conventional and biodegradable microplastics in soil under biogas slurry irrigation

As one of the promising alternatives of conventional plastic mulching film (C-PMF), biodegradable plastic mulching films (B-PMF) were employed in agronomy production to alleviate the environmental burden of C-PMF. However, information regarding the potential toxicity effects of biodegradable microplastics (MPs) in soil still in scarcity, and the available findings were found to be controversial. Additionally, little is known about the molecular toxicity effects of conventional and biodegradable MPs on terrestrial organisms. Thus, 5 % (w/w) biodegradable (polylactic acid, PLA) and conventional (polyvinylchloride, PVC; low-density polyvinylchloride, LDPE) MPs were employed to assess the toxicity effects on Eisenia fetida in agricultural soil with biogas slurry irrigation. In the present study, transcriptomic, metabolomic profiles and individual indexes were selected to reveal the toxicity mechanisms from molecular level to the individual response. Furthermore, dysbiosis of bacterial community in gut was also investigated for obtaining comprehensive knowledge on the MPs toxicity. At the end of the exposure, the number of survival earthworms after MPs exposure was significantly reduced. Compared with the initial body weight, PLA and LDPE increased the biomass of earthworms after MPs exposure, while no significant influence on the biomass was observed in PVC treatment. Microbacterium, Klebsiella and Chryseobacterium were significantly enriched in earthworm gut after PLA, PVC and LDPE exposure, respectively (p < 0.05). Transcriptomic and metabolomic analysis revealed that PLA exposure induced neurotransmission disorder and high energetic expenditure in earthworms. However, PVC and LDPE inhibited the nutrient absorption efficiency and activated the innate immunity responses of earthworms. The PLS-SEM results showed that the effects of MPs were dominated by the polymer types, and hence, significantly and directly influence the gut bacterial community of earthworms. This study provides a better understanding of the similarities and discrepancies in toxicity effects of biodegradable and conventional MPs from the perspectives of individual, gut bacterial community, transcriptome and metabolome.

Towards environmentally sustainable management: A review on the generation, degradation, and recycling of polypropylene face mask waste

There has been a considerable increase in the use of face masks in the past years. Managing face mask waste has become a global concern, as the current waste management system is insufficient to deal with such a large quantity of solid waste. The drastic increase in quantity, along with the material's inability to degrade plastic components such as polypropylene, has led to a large accumulation of plastic waste, causing a series of environmental and ecological challenges. In addition, the growing use also imposes pressure on waste management methods such as landfill and incineration, raising concerns about high energy consumption, low value-added utilization, and the release of additional pollutants during the process. This article initially reviews the impact of mask-related plastic waste generation and degradation behavior in the natural environment. It then provides an overview of various recently developed methods for recycling face mask plastic waste. The article also offers forward-looking strategies and recommendations on face mask plastic waste management. The review aims to provide guidance on harnessing the complexities of mask waste and other medical plastic pollution issues, as well as improving the current waste management system's deficiencies and inefficiencies in tackling the growing plastic waste problem.

Effects of water chemistry and flow on lead release from plastic pipes versus copper pipes, implications for plumbing decontamination

Despite being corrosion-resistant, plastic potable water pipes might accumulate heavy metals on their surface if they convey metal-contaminated tap water. This study examined the influence of water pH and flow conditions on lead (Pb) release from new and biofilm-laden potable water pipes to provide insights regarding decontamination. For this purpose, biofilms were grown onto new crosslinked polyethylene (PEX-A), high-density polyethylene (HDPE), and copper pipes for three months. Lead was then deposited onto the new and biofilm-laden pipes through 5 d exposure experiments under flow conditions. After that, lead release experiments were conducted by exposing the lead-accumulated pipes to lead-free synthetic tap water for 5 d, under both stagnant and water flow conditions. The metal accumulation study showed no significant difference in lead uptake by new pipes and their biofilm-laden counterparts under flow conditions. This could be attributed to the detachment of biofilms that have accumulated lead as water flows through the pipes. Water flow conditions significantly influenced the lead release from new and biofilm-laden water pipes. A lower water pH of 5.0 increased the release of lead from plastic pipes into the contact water, compared to pH 6.0 and 7.8. The greatest percentage of lead was released from biofilm-laden HDPE pipes (5.3%, 120 h) compared to biofilm-laden copper pipes (3.9%, 6 h) and PEX-A (3.7%, 120 h) and after exposure to lead-free synthetic tap water at pH 5.0, under stagnant conditions. On the other hand, under water flow conditions, the greatest lead release was found for new PEX-A pipes (4.4%, 120 h), new HDPE pipes (2.7%, 120 h), and biofilm-laden copper pipes (3.7%, 2 h).

Lead (Pb) deposition onto new and biofilm-laden potable water pipes

Heavy metals' interactions with plumbing materials are complicated due to the differential formation of biofilms within pipes that can modulate, transform, and/or sequester heavy metals. This research aims to elucidate the mechanistic role of biofilm presence on Lead (Pb) accumulation onto crosslinked polyethylene (PEX-A), high-density polyethylene (HDPE), and copper potable water pipes. For this purpose, biofilms were grown on new pipes for three months. Five-day Pb exposure experiments were conducted to examine the kinetics of Pb accumulation onto the new and biofilm-laden pipes. Additionally, the influence of Pb initial concentration on the rate of its accumulation onto the pipes was examined. The results revealed greater biofilm biomass on the PEX-A pipes compared to the copper and HDPE pipes. More negative zeta potential was found for the biofilm-laden plastic pipes compared to the new plastic pipes. After five days of Pb exposure under stagnant conditions, the biofilm-laden PEX-A (980 μg m-2) and HDPE (1170 μg m-2) pipes accumulated more than three times the Pb surface loading compared to the new PEX-A (265 μg m-2) and HDPE pipes (329 μg m-2), respectively. However, under flow conditions, Pb accumulation on biofilm-laden plastic pipes was lower than on the new pipes. Moreover, with increasing the initial Pb concentration, greater rates of Pb surface accumulation were found for the biofilm-laden pipes compared to the new pipes under stagnant conditions. First-order kinetics model best described the Pb accumulation onto both new and biofilm-laden water pipes under both stagnant and flow conditions.

Partitioning of heavy metals in sediments and microplastics from stormwater runoff

Microplastics could act as vehicles for transporting heavy metals from urban environments to water resources via stormwater runoff. Although the transport of heavy metals by sediments has been widely studied, there is a lack of mechanistic understanding of their competition with microplastics (MPs) for heavy metal uptake. Therefore, this study was conducted to examine the partitioning of heavy metals in microplastics and sediments from stormwater runoff. For this purpose, new low density polyethylene (LDPE) pellets were selected as representative MPs, and accelerated UV-B irradiation experiments were conducted for eight weeks to generate photodegraded MPs. The competition of Cu, Zn, and Pb species for the occupation of available surface sites on sediments and new and photodegraded LDPE MPs was examined through 48 h kinetics experiments. Additionally, leaching experiments were conducted to identify the extent of organics released into the contact water by new and photodegraded MPs. Moreover, 24 h metal exposure experiments were conducted to identify the role of initial metal concentrations on their accumulation onto the MPs and sediments. The photodegradation process altered the LDPE MPs' surface chemistry by creating the oxidized carbon functional groups [>CO, >C-O-C<], and it also enhanced their dissolved organic carbon (DOC) leaching into the contact water. The results showed significantly greater levels of Cu, Zn, and Pb accumulations on photodegraded MPs compared to the new MPs in either absence or presence of sediments. Heavy metal uptake by sediments when photodegraded MPs were present was significantly reduced. This might be due to the organic matter leached by photodegraded MPs into the contact water.

Cross-sectional microstructural analysis to evaluate the crack growth pattern of weathered marine plastics

Fragmentation of degraded plastics and release of smaller secondary microplastics is usually attributed to the growth of environmental stress cracks. Analysis of crack patterns derived from chemical degradation can be useful not only for assessing the cause of plastic fracture and evaluating the useful lifetime of a product, but it can also potentially provide valuable information on the generation of microplastics. However, the literature with respect to microplastics generation is generally limited to surface observations of polypropylene and polyethylene. Here, we used ion-beam milling to prepare cross-sections of fragments of 15 plastic products made from five commodity plastics (polypropylene, polyethylene, polystyrene, polyvinyl chloride, and polyethylene terephthalate) that were collected at two beaches in Japan, and then we examined the microstructures of those cross-sections by means of scanning electron microscopy and energy dispersive X-ray spectroscopy. Crack growth in the depth direction was examined to provide insights into microplastic generation behavior. In all of the polypropylene samples, and some of the low-density polyethylene and polystyrene samples, cracks with a depth exceeding 100 μm from the sample surface were observed. Considering that crack growth causes fracture of degraded plastic and microplastic release, these observations suggest the release of sharp-edged microplastics from the crack fracture surface. In contrast, in the high-density polyethylene and polyvinyl chloride samples, crack growth was limited to within 20 μm of the sample surface, suggesting the release of irregularly shaped microplastics and additive particles. The present results suggest that the degradation behavior of plastic products in the depth direction is dependent on the type of plastic.

Investigating the sustainability of agricultural plastic products, combined influence of polymer characteristics and environmental conditions on microplastics aging

The accelerated use of plastic products for agricultural practices has raised global concern regarding their negative impacts on soil health. This study aims to better understand the combined influence of polymer characteristics and environmental conditions on microplastic photodegradation within the agricultural soil system. For this purpose, the photodegradation behavior of low density polyethylene (LDPE) microplastics was studied through accelerated UVA radiation experiments under two different relative humidity (RH₁₀ and RH₇₀) and soil deposition conditions. The variations of plastics' surface physiochemistry due to the accelerated photodegradation were studied using Attenuated Total Reflectance-Fourier Transform Infrared spectroscopy (ATR-FTIR), X-ray Photoelectron Spectroscopy (XPS), and Field Emission Scanning Electron Microscopy (FE-SEM). The carbonyl and vinyl indices were calculated using the ATR-FTIR information to compare the degree of microplastics' photodegradation. The plastics' bulk characteristics, including the percentage of crystallinity and molecular weight distributions, were examined using the Differential Scanning Calorimetry (DSC) and Gel Permeation Chromatography (GPC). Furthermore, the extent of UVA light interaction with the microplastics was studied by determining spectral quantum yield. The results demonstrated that new LDPE microplastics with a lower molecular weight (Mw = 233 kD) were subjected to a greater extent of photodegradation than those with greater molecular weight (Mw = 515 kD). Elevated relative humidity (RH₇₀) limited the photooxidation process of microplastics and consequently reduced the surface chemistry alterations. Deposition of soil particles with respect to the plastic particles impacted the photodegradation behavior. The microplastics covered by soil particles were not degraded, unlike those deposited next to the soil particles. The knowledge developed through this study could encourage the farmers and agricultural stakeholders to apply more efficient practices to remove plastic residuals after harvesting and conduct proper plastic disposal practices to protect soil health.

Studying the combined influence of microplastics' intrinsic and extrinsic characteristics on their weathering behavior and heavy metal transport in storm runoff

The weathering and contaminant transport behavior of both primary (PMPs) and secondary microplastics (SMPs) are interrelated to their original physiochemical features and variations within the environment. This study examines the influence of PMPs' intrinsic characteristics (polymer structure and crystallinity) and SMPs' extrinsic features (surface oxidation and external sediments attachment) on the photodegradation kinetics, and subsequently Pb(II) and Zn(II) uptake from stormwater. For this purpose, high density polyethylene (HDPE) and low density polyethylene (LDPE) with different degrees of crystallinities were produced as PMPs, and their photodegradation behaviors were compared with original polymers. Furthermore, the SMPs generated by abrasion and surface oxidation of PMPs and the virgin PMPs underwent accelerated photodegradation, and the changes of their crystallinity, surface chemistry, and morphology were examined. Scanning electron microscopy (SEM) imaging and X-ray photoelectron (XPS) studies revealed the formation of cracks and different oxidized functionalities on MPs surface due to UV photodegradation. The vinyl and carbonyl indices calculated using Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy demonstrated an elevated photodegradation rate for SMPs compared to the PMPs. Moreover, the Differential Scanning Colorimetry (DSC) demonstrated an increasing percentage of crystallinity in all MPs due to the photodegradation. The percent crystallinity of HDPE pellets increased after photodegradation from 49.8 to 62.6 and it increased from 17.2 to 38.9 for LDPE pellets respectively. The greater level of increase in crystallinity for LDPE in comparison to HDPE upon photodegradation was referred to as LDPE's greater amorphous content and branched structure. A greater level of metal uptake was obtained for photodegraded LDPE pellets as 2526 μg/m² for Pb(II) and 2028 μg/m² for Zn(II) respectively.