Considerations on salts used for density separation in the extraction of microplastics from sediments

Spatio-temporal variation and ecological risk assessment of microplastics along the touristic beaches of a mediterranean coast transect (Valencia province, East Spain)

Annually, the Mediterranean region attracts around one-third of the global coastal tourism, which is acknowledged as a substantial contributor to plastic pollution. Coastal municipalities mitigate this through periodic sand and shore cleaning. However, the efficacy of these measures remains uncertain. In this study, the occurrence of MPs (10 μm-5 mm) in sand from seven different, regularly cleaned, touristic beaches of the coastline of Valencia province (E Spain) was assessed. Two different sampling campaigns were performed in winter and in summer (2022) to compare the results and understand the influence of the high touristic activity, as well as, the efficiency of the measures taken against MPs pollution. The methodology used was designed specifically for the matrix and employed density separation using a Sediment Microplastic Isolation (SMI) Unit. In addition to conventional visual inspection and ATR-FTIR, automatic quantification and identification of the polymers of lower size was performed by μFTIR. The average MPs concentration in the summer (339 ± 92 MP kg-1 by stereomicroscopy and 339 ± 189 MP kg-1 by μFTIR) was significantly higher than in the winter (71 ± 92 MP kg-1 and 143 ± 85 MP kg-1) (p < 0.05). The combination of these analytical tools provides comprehensive information about the MPs present in beach sand. Fibers were the most abundant form of MPs, while most of the polymers analyzed were polyethylene (PE) and halogenated polystyrene (Cl-PS and Br-PS) with food packaging, swimming equipment and fishing nets being their most probable sources. Ecological risk assessment was performed through the Pollution Load Index (PLI), the Hazardous Index (HI) and the Risk Quotient (RQ), with the results indicating potential risk that ranges from moderate to high depending on the applied approach.

Unraveling the land-based discharge of microplastics from sewers to oceans - A comprehensive study and risk assessment in wastewaters of Goa, India

Owing to their pervasive dispersion in the environment and their potential ramifications on both marine life and human health, microplastics (MPs) are of increasing concern. However, there is still a lack of research on the release of MPs from different land-based pathways like creeks, drainage outfalls, and conduits into coastal water systems in India. This study represents comprehensive research into the attribution of MPs in the estuarine system, specifically those emanating from wastewater sources in Panjim City, Goa, India. Urban wastewater collected from different locations in and around Panjim City exhibited values ranging from 79 ± 21 to 338 ± 7 MPs/L, with a prevalence of fibrous and black MP particles. The size range of the MPs at all sampling sites was 100-300 μm. Analysis by μ-FTIR revealed 35 distinct polymeric compositions in wastewater, with a dominance of polyacrylamide (PAM), polyvinyl chloride (PVC), and polyamide (PA). Additionally, primary and secondary MPs were studied to unravel the contributions from land-based sources. This included the quantification of MPs in ten samples from personal care products (PCPs) and twenty samples from washing machine effluents (WMEs). MPs in PCPs ranged from 1.8 to 1554 MPs/g. Microfibres and fragments were predominant in WMEs (3986 to 4898 MPs/L). This study suggests a strong relation between polymers found in wastewater effluent and those present in PCPs and WMEs. The identified polymers showed high polymer hazard indices (IV and V), posing a significant threat to the ecosystem and a potential risk to human health.

Contamination of Thames Estuary sediments by retroreflective glass microbeads, road marking paint fragments and anthropogenic microfibres

Surface and subsurface sediment samples (n = 16) from the highly urbanised inner Thames Estuary (UK) have been physically and chemically characterised and analysed for anthropogenic microdebris. Sediments were gravelly sands throughout and were heavily contaminated by lead (Pb, up to 12,500 mg kg-1) and zinc (Zn, up to 9500 mg kg-1). Microfibres of mm-dimensions and retroreflective glass microbeads (median diameter = 188 μm) used in road markings were the most abundant types of microdebris present, and concentrations (as numbers, N) on a dry weight basis were spatially heterogeneous (ranging from about 4000 to 60,000 N kg-1 and 100 to 28,000 N kg-1, respectively). Nevertheless, concentrations of the two types of particle were significantly correlated and both displayed an inverse, non-linear relationship with sediment grain size. Road marking paint fragments of different colours were detected in most cases (n = 13) but quantification was difficult because of analytical constraints related to size, shape, colour, fragmentation and encrustation. Concentrations of up to about 500 mg kg-1 Pb were determined in isolated paint fragments but road paint particles are unlikely to make a significant contribution to Pb pollution in Thames Estuary sediments. Overall, our observations suggest that stormwater runoff is a significant source of multiple types of anthropogenic microdebris in urban estuaries, with additional, direct atmospheric deposition contributing to microfibre accumulation. More generally, it is recommended that studies of microplastics consider additional debris and sediment characteristics for a better understanding of their sources and transport.

Identification and physico-chemical characterization of microplastics in marine aerosols over the northeast Arabian Sea

Microplastics (MPs) in the atmosphere can undergo long-range transport from emission regions to pristine terrestrial and oceanic ecosystems. Due to their inherent toxic and hazardous characteristics, MPs pose serious risks to both human well-being and the equilibrium of ecosystem. The present study outlines the comprehensive characterization, spanning physical and chemical attributes of MPs associated with atmospheric aerosols. Total suspended particulates (TSPs) were collected on a quartz fibre filter by operating a high-volume sampler for 24 h during distinct years (March, 2016 and November, 2020) at a coastal location in the northeast Arabian Sea. Subsequent to the sampling, a series of techniques were applied including density separation. The assessment and scrutiny of the MPs was carried out using stereo-zoom microscopy with supplementary validation using advanced fluorescence microscopy for enhanced precision in identification. Our comparative assessment suggests peroxide treatment followed by density separation could be a robust procedure for the definitive identification and characterization of MPs in the atmosphere. Average total abundance of MPs was found to be 1.30 ± 0.14 n/m3 in 2016 and 1.46 ± 0.12 n/m3 in 2020 with fibres, fragments and films having similar relative contributions (41 %, 31 %, 28 % in 2016 and 40 %, 35 %, 25 % in 2020). Fibres were found to be dominant morphotype followed by fragments and films over the coastal region of the Arabian Sea. In order to unravel the detailed chemical nature of these MPs, spectral analysis using μ-FTIR was carried out. The outcome of the analysis showed prevailing polymers as polyvinyl chloride and polymethyl methacrylate (50545 %) as dominant polymers followed by polyester (15 %), styrene butyl methacrylate (11 %), and polyacetal (9 %). MPs present in the vicinity of the Arabian Sea have potential to supply nutrients and toxicants, consequently can contribute to the modulation of the surface water biogeochemical processes.

Emerging isolation and degradation technology of microplastics and nanoplastics in the environment

Microplastics (MPs, less than 5 mm in size) are widely distributed in surroundings in various forms and ways, and threaten ecosystems security and human health. Its environmental behavior as pollutants carrier and the after-effects exposed to MPs has been extensively exploited; whereas, current knowledge on technologies for the separation and degradation of MPs is relatively limited. It is essential to isolate MPs from surroundings and/or degrade to safe levels. This in-depth review details the origin and distribution of MPs. Provides a comprehensive summary of currently available MPs separation and degradation technologies, and discusses the mechanisms, challenges, and application prospects of these technologies. Comparison of the contribution of various separation methods to the separation of NPs and MPs. Furthermore, the latest research trends and direction in bio-degradation technology are outlooked.

Suspected sources of microplastics and nanoplastics: Contamination from experimental reagents and solvents

There is an increasing concern about the potential effects of microplastics (MPs) and nanoplastics on human health and other organisms. For the separation and detection of MPs, there are various approaches, and the distinct procedures led to different results. However, the presence of MPs in the reagents was not addressed, which could cause false and/or inaccurate results during MPs detection. In this study, the chemical reagents commonly used for the separation and detection of MPs were selected to ascertain whether these reagents introduce MPs. It was shown that a large number of MPs were detected in the reagent and solvent samples. The largest number of MPs (>1 μm) was detected in the KOH reagent, with the abundance of 3070 items/g. The order of MPs abundance in the selected reagents was: KOH > NaCl > CaCl2 > SDS > NaI > H2O2. The types of MPs were the same as the body and stopper of the reagent packaging bottles. MPs size detected in reagent bottles was primarily smaller than 10 μm. The abundance of MPs in the reagents were independent of their purity, however, there was a certain difference in MPs abundance in reagents from different manufacturers. Furthermore, the presence of nanoplastics (< 1 μm) was verified in the reagents through Py-GCMS, with the abundance (39.47-43.01 mg/kg) higher than that of MPs. The obtained results in this study raised specific requirements and cautions for MPs and nanoplastics related research in terms of quality control. Also, this work can facilitate a more accurate assessment of MPs concentrations in the environment.

Characterization and source apportionment of microplastics in Indian composts

Microplastics (MP), small plastic particles under 5 mm, are pollutants known to carry heavy metals in ecosystems. Composts are a significant source of soil microplastics. This study examined MSW composts from Kochi and Kozhikode in India for microplastic concentrations and heavy metals' accumulation thereon. Microplastics were isolated using zinc chloride density separation, with Fenton's reagent used for organic matter oxidation. Resin types were identified using FTIR analysis that showed the presence of PE, PP, PS, nylon, PET, and allyl alcohol copolymer. In Kozhikode's compost, the average concentration of microplastics was 840 ± 30 items/kg, while Kochi had 1600 ± 111 items/kg, mainly polyethylene films. PE was the most prevalent resin, comprising 58.3% in Kozhikode and 73.37% in Kochi. Heavy metal analysis of MP showed significant concentrations of lead, cadmium, zinc, copper, and manganese adsorbed on the surface of microplastics. The concentrations of heavy metals in the MP before Fenton oxidation ranged from 1.02 to 2.02 times the corresponding concentrations in compost for Kozhikode and 1.23 to 2.85 times for Kochi. Source apportionment studies revealed that 64% of microplastics in Kozhikode and 77% in Kochi originated from single-use plastics. Ecological risk indices, PLI and PHI, showed that composts from both locations fall under hazard level V. The study revealed that compost from unsegregated MSW can act as a significant source of microplastics and heavy metals in the soil environment, with single-use plastics contributing major share of the issue.

Characteristics and removal efficiency of microplastics at secondary wastewater treatment plant in Lithuania

Wastewater treatment plants (WWTPs) are the most significant barrier between anthropogenic microplastics and environmental ecosystems. The distribution and characteristics of microplastics in WWTPs remain uncertain and incompletely understood, particularly in northeastern Europe (Baltic States), where there is a lack of data on microplastic pollution and distribution. This study presents the removal efficiency and variation in characteristics of microplastics in different stages of the secondary WWTP during a 3-month sampling campaign in Lithuania. The abundance, size, shape, color, and chemical composition of microplastics in the wastewater at different treatment stages were thoroughly examined, in a size range from 20 to 1000 μm. On average, 2962 ± 25 particles/L of microplastic enter the studied WWTP. The obtained microplastic removal efficiency was 55.4% ± 3.9%, highlighting the necessity to enhance wastewater treatment strategies focusing on microplastic removal. Fragment-type microplastics smaller than 100 μm were removed from wastewater samples with the highest removal efficiency. Furthermore, our study includes recommendations to improve microplastic removal efficiency and contribute to mitigating microplastic pollution. PRACTITIONER POINTS: A large number of MPs in the size range of 20-1000 μm enter Lithuanian WWTP. Small-sized MPs within a range of 20-50 μm and 50-100 μm were removed with the highest efficiency of 54.07 ± 1.68% and 56.4 ± 2.43%, respectively. The shape and size of MPs have a major impact on the efficiency of their removal. Future research should prioritize the development of economical and energy-efficient systems, specifically designed for the removal of MPs in WWTPs.

Characterization and removal efficiencies of microplastics discharged from sewage treatment plants in Southeast Spain

Microplastics (MPs) are ubiquitous pollutants that can effectively harm different ecosystems. The information on the relative contribution of wastewater treatment plants (WWTPs) to the surrounding environment is important, in order to understand ecological health risks and implement measures to reduce their presence. This focus article presents a quantitative assessment on the relative concentration and types of MPs delivered from four WWTPs located at the Southeast of Spain. Samples from WWTPs were collected throughout a four-year period, comprising more than 1,200 L of analyzed wastewater and 3,215 microparticles isolated. Density extraction with 1.08 g/mL NaCl salt solution was systematically used as the main separation method, in a simple and reliable manner, and repeat extraction cycles did not play any significant impact on the study outcomes. The four WWTPs had removal efficiencies between 64.3% and 89.2% after primary, secondary, and tertiary treatment phases, without diurnal or daily variations. Advanced treatment methods displayed a lower removal rate for fibers than for particulate MPs. The abundance of MPs was always higher and with a lower mean size in wastewater samples collected in Autumn than for the rest of seasons. MPs dumped from WWTPs in large quantities into the environment are meant to be regarded as an important point source for aquatic and terrestrial environments.

Long-term release kinetic characteristics of microplastic from commonly used masks into water under simulated natural environments

Masks-related microplastic pollution poses a new threat to the environment and human health that has gained increasing concern. However, the long-term release kinetics of microplastic from masks in aquatic environments have yet to studied, which hampers its risk assessment. Four types of masks, namely cotton mask, fashion mask, N95 mask, and disposable surgical mask were exposed to systematically simulated natural water environments to determine the time-dependent microplastic release characteristics at 3, 6, 9, and 12 months, respectively. In addition, the structure changes of employed masks were examined by scanning electron microscopy. Moreover, Fourier transform infrared spectroscopy was applied to analyze the chemical composition and groups of released microplastic fibers. Our results showed that the simulated natural water environment could degrade four types of masks and continuously produce microplastic fibers/fragments in a time-dependent manner. The dominant size of released particles/fibers was below 20 μm across four types of face masks. The physical structure of all four masks was damaged to varying degrees concomitant with photo-oxidation reaction. Collectively, we characterized the long-term release kinetics of microplastic from four types of commonly used masks under a well-mimic real word water environment. Our findings suggest that urgent action must be taken to properly manage disposable masks and ultimately limit the health threats associated with discarded masks.

Spatio-temporal distribution of microplastics in water and sediment samples of the Plankenburg river, Western Cape, South Africa

Microplastic (MPs) pollution has become a subject of environmental concern due to its wide ubiquity in the environment. Microplastics are possible sources of other hazardous chemicals to aquatic organisms due to their composition and sorption properties. In this study, MPs occurrence in water and sediment samples of the Plankenburg River, Western Cape, South Africa was investigated. The physicochemical characterization of the river water was done onsite. 30 L water samples were collected and filtered in 10 L triplicates through a 250 μm mesh onsite using a metal bucket. An additional 12 L sample was collected and filtered in 4 L triplicates through 20 μm mesh in the laboratory. The extraction of MPs from water in the laboratory was by density separation. Sediment samples were also collected at the selected sites, oven-dried and microplastics in the laboratory. Sampling was conducted over four seasons - spring, summer, autumn, and winter. Microplastics were classified by visual observation and Fourier Transform Infrared Spectroscopy (FTIR-ATR). The seasonal distribution of MPs in the surface water samples varied across all sites. However, spring samples had the highest MPs occurrence (5.13 ± 6.62 MP/L) and the least, in autumn (1.52 ± 2.54 MP/L). The MPs in sediment samples were observed in spring (1587.50 ± 599.32 MP/kg). Fibres were the most dominant microplastic particle type (shape), with a size range of 500-1000 μm at the different sites. The infrared spectroscopic analysis confirmed the dominant polymer type to be polyethylene. This study provides an understanding of the microplastic occurrence in the Plankenburg River system and gives a baseline for future monitoring and assessment of water and sediment in the South African freshwater systems.

Decontamination of neutron-activated radioactive concrete waste by separating Eu, Co, Fe, and Mn-containing sand particles using dense medium separation

Neutron-activated concrete waste is one of the most challenging radioactive wastes to decontaminate because the radionuclides exist in a chemically stable binding state, and it is very difficult to break those bindings with the conventional acid decontamination method. Here, we suggest a new dense medium separation (DMS) of felsic and mafic minerals from simulated neutron-activated concrete waste using sodium-polytungstate (SPT) solution because most elements (Eu, Co, Fe, and Mn) that can be activated by neutrons are concentrated in mafic minerals. We also determined the optimal density of the SPT solution as ∼ 2.70 g/cm³, and a high degree of decontamination was achieved for sand particles ranging from 75 to 500 µm in size. Under these optimized conditions, DMS (80.02%) exhibits much higher radionuclide removal efficiency (RRE) than 5 M acid decontaminations (23.27-31.29%) for Eu. Furthermore, DMS (59.38-63.36%) shows similar RRE to 5 M acid decontaminations (41.67-73.94%) for Fe, Mn, and Co. We believe this DMS process could be useful and applicable to the decontamination of neutron-activated concrete wastes because it is possible to perform a large-scale process compared to conventional acid decontamination methods, which is also advantageous in reducing secondary waste generation and facile radionuclide recovery.

Microplastic pollution in the intertidal and subtidal sediments of Vava'u, Tonga

Plastic pollution research on a global scale intensified considerably in the current decade; however, research efforts in the South Pacific are still lagging. Here, we report on microplastic contamination of intertidal and subtidal sediments in the Vava'u archipelago, Tonga. While providing the first baseline data of its type in Tonga, the study also advances methods and adjusts them for low-budget research. The methods were based on density separation of microplastics from the sediment using CaCl₂, a high-density salt which due to its high solubility, low cost and availability. Once separated, microplastics were quantified by microscopic analysis and polymers characterized via FTIR spectroscopy. Microplastics in intertidal and subtidal sediments were found in concentrations of 23.5 ± 1.9 and 15.0 ± 1.9 particles L^-1 of sediment, respectively. The dominant type of microplastics in both intertidal (85 %) and subtidal sediments (62 %) were fibres.

Microplastic contamination in terrestrial ecosystems: A study using barn owl (Tyto alba) pellets

Microplastics (MPs) are recognised as an emerging environmental problem that needs to be carefully monitored. So far, MPs have been widely recorded in marine and freshwater ecosystems. Still, few studies have focused on MP occurrence in terrestrial ecosystems, although soils are suspected to be one of the main MP reservoirs. To test a non-invasive method for assessing MP contamination in terrestrial ecosystems, we analysed the pellets of a top terrestrial predator, the barn owl (Tyto alba). Sixty pellets were collected from three agricultural areas (20 pellets each) and analysed to assess both barn owl diet and MP content. Thirty-four MPs were confirmed by micro-Fourier Transform Infrared Spectroscopy (μ-FTIR) analysis in 33% of the pellets (min-max 1-5 MPs per pellet). Most of the detected items were microfibres (88.2%). Polyethylene terephthalate, polyacrylonitrile and polyamide were the most abundant polymers. One of the three sites was significantly less contaminated. In the two sites with the highest MP occurrences, barn owl diet was characterised by predation on synanthropic rodents, particularly brown rats (Rattus norvegicus), which may indicate habitat degradation and increased exposure to MPs. Analyses also suggest that Savi's pine vole (Microtus savii) is the prey least at risk of MP contamination, probably due to its strictly herbivorous diet. We argue that the analysis of barn owl pellets may represent a cost-effective method for monitoring MP contamination in terrestrial ecosystems.

Potential Artifacts and Control Experiments in Toxicity Tests of Nanoplastic and Microplastic Particles

To fully understand the potential ecological and human health risks from nanoplastics and microplastics (NMPs) in the environment, it is critical to make accurate measurements. Similar to past research on the toxicology of engineered nanomaterials, a broad range of measurement artifacts and biases are possible when testing their potential toxicity. For example, antimicrobials and surfactants may be present in commercially available NMP dispersions, and these compounds may account for toxicity observed instead of being caused by exposure to the NMP particles. Therefore, control measurements are needed to assess potential artifacts, and revisions to the protocol may be needed to eliminate or reduce the artifacts. In this paper, we comprehensively review and suggest a next generation of control experiments to identify measurement artifacts and biases that can occur while performing NMP toxicity experiments. This review covers the broad range of potential NMP toxicological experiments, such as in vitro studies with a single cell type or complex 3-D tissue constructs, in vivo mammalian studies, and ecotoxicity experiments testing pelagic, sediment, and soil organisms. Incorporation of these control experiments can reduce the likelihood of false positive and false negative results and more accurately elucidate the potential ecological and human health risks of NMPs.

Comparison of different salt solutions for density separation of conventional and biodegradable microplastic from solid sample matrices

Microplastics are the new emerging pollutants ubiquitously detectable in aquatic and terrestrial ecosystems. Fate and behavior, as well as ecotoxicity, are of increasing environmental concern, particularly in sediments and soils as natural sinks. For a global environmental risk assessment, reliable and easy to apply analytical methods are mandatory to obtain comparable data. This is based on the isolation of microplastics out of the solid sample matrices prior to instrumental detection. Thus, this study provides an easy to apply approach for density separation. The technique emerged from a comparative study using different salt solutions to isolate conventional, and for the first time biodegradable, microplastics from different solid sample matrices, i.e., sand, artificial soil, and compost. Four solutions (water, sodium chloride, sodium hexametaphosphate, and sodium bromide) of different densities were applied followed by oxidizing digestion. Finally, the impact of the procedures on size and surface properties of microplastics was tested. Dependent on the sample matrix, the highest recovery rates of 87.3-100.3% for conventional polymers, and 38.2-78.2% for biodegradable polymers, were determined with sodium bromide. It could be shown that the type of solid sample matrix influences the recovery rates and has to be considered when choosing a sample preparation technique.

New separation protocol reveals spray painting as a neglected source of microplastics in soils

Microplastics are recently discovered contaminants, yet knowledge on their sources and analysis is limited. For instance, paint microplastics are poorly known because soil separation protocols using flotation solutions cannot separate paint microplastics due to the higher density of paint microplastic versus common microplastics. Here, we designed a new two-step density separation protocol for paint microplastics, allowing paint microplastics to be separated from the soil without digestion. Paint particles were separated from soil samples collected around the graffiti wall at the Mauerpark, Berlin, then quantified according to their shape and color characteristic. The presence of polymers as binders in the paint particles was verified by Fourier transform infrared spectroscopy. Results show concentrations from 1.1 × 10⁵ to 2.9 × 10⁵ microplastics per Kg of dry soil, representing the highest microplastic concentration ever reported in the literature. Particle concentrations decreased and the median size increased with soil depth. Our results provide first evidence that spray painting, a technique with a wide range of applications from industry to art, leaves a legacy of environmental microplastic in soils that has so far gone unnoticed.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10311-022-01500-2.

Comparison of pre-treatment methods and heavy density liquids to optimize microplastic extraction from natural marine sediments

The ubiquitous occurrence of anthropogenic particles, including microplastics in the marine environment, has, over the last years, gained worldwide attention. As a result, many methods have been developed to estimate the amount and type of microplastics in the marine environment. However, there are still no standardized protocols for how different marine matrices should be sampled or how to extract and identify these particles, making meaningful data comparison hard. Buoyant microplastics are influenced by winds and currents, and concentrations could hence be expected to be highly variable over time. However, since both high density and most of the initially buoyant microplastics are known to eventually sink and settle on the seafloor, marine sediments are proposed as a suitable matrix for microplastics monitoring. Several principles, apparatuses, and protocols for extracting microplastics from marine sediments have been presented, but extensive comparison of the different steps in the protocols using real environmental samples is lacking. Thus, in this study, different pre-treatment and subsequent density separation protocols for extraction of microplastics from replicate samples of marine sediment were compared. Two pre-treatment methods, one using inorganic chemicals (NaClO + KOH + Na₄P₂O₇) and one using porcine pancreatic enzymes, as well as one with no pre-treatment of the sediment, were compared in combination with two commonly used high-density saline solutions used for density separation, sodium chloride (NaCl) and zinc chloride (ZnCl₂). Both pre-treatment methods effectively removed organic matter, and both saline solutions extracted lighter plastic particles such as polyethylene (PE) and polypropylene (PP). The most efficient combination, chemical pre-treatment and density separation with ZnCl₂, was found to extract > 15 times more particles (≥ 100 µm) from the sediment than other treatment combinations, which could largely be explained by the high presence and efficient extraction of PVC particles.

Influence of sediment texture on HDPE microplastics recovery by density separation

Microplastics (MPs) are an emerging environmental pollutant, threatening marine and terrestrial ecosystems. Because of their properties and their widely varying size (5mm-0.1 μm), it is still difficult to define a valid and efficient method for extracting MPs from solid matrices. Among the several methods proposed, density separation is the most practical and cost-effective one. Progress is still ongoing towards a deeper understanding of the advantages and limitations related to the application of density separation for MPs extraction, the recovery yields and the factors that may influence it. In this context, we introduce the following work, which provides an early-stage insight into how the sediment texture may influence the efficiency of this extraction method, and how parameters, such as sedimentation time and extraction cycles, can be modified to always achieve the best recovery. Our focus has been directed on evaluating the extraction efficiency of HDPE MPs by density separation using NaCl, from three types of sediment: sandy (SS), sandy loam (SLS) and sandy-clay loam (SCLS). We investigated the impact of sedimentation time (1, 6, 12, 24 h) and extraction cycles (3 cycles for each sedimentation time) on MPs recovery. Finally, we determined the minimum amount of MPs (MPs g/g sediment) below which it is not possible to quantify MPs with the method used. The results have shown that the recovery efficiency of MPs from sediment is structure dependent. The highest recoveries are reached after a settling time of 1 and 6 h. Furthermore, for samples with minimum clay content (SS), only one extraction cycle is needed, whereas two extraction cycles are required for SLS and SCLS. The outcomes about the detection limit (LOD) of the method, showed the existence of an interaction MPs-clay/sediment, which allowed us to understand how far this extraction method is suitable in field, thus defining the minimum grade of MPs pollution (MPs g/g sediment) below which this method is no longer capable to extract MPs from contaminated samples.

Seasonal heterogeneity and a link to precipitation in the release of microplastic during COVID-19 outbreak from the Greater Jakarta area to Jakarta Bay, Indonesia

To reduce microplastic contamination in the environment, we need to better understand its sources and transit, especially from land to sea. This study examines microplastic contamination in Jakarta's nine river outlets. Microplastics were found in all sampling intervals and areas, ranging from 4.29 to 23.49 particles m^-3. The trend of microplastic contamination tends to increase as the anthropogenic activity towards Jakarta Bay from the eastern side of the bay. Our study found a link between rainfall and the abundance of microplastic particles in all river outlets studied. This investigation found polyethylene, polystyrene, and polypropylene in large proportion due to their widespread use in normal daily life and industrial applications. Our research observed an increase in microplastic fibers made of polypropylene over time. We suspect a relationship between COVID-19 PPE waste and microplastic shift in our study area. More research is needed to establish how and where microplastics enter rivers.

Methodology for removing microplastics and other anthropogenic microparticles from sludge dewatering system

Anthropogenic microparticles (e.g., microplastics) are present in sewage plants, especially in sludge streams. However, the lack of standardized protocols to scrutinize the presence of anthropogenic microparticles in sludge makes the comparison between studies unfeasible. To tackle the knowledge gap regarding the efficiency of methodologies on the extraction of anthropogenic microparticles from the complex organic matrix, dewatered sludge, and digested sludge was treated with peroxidation and density separation, and the recovery of microparticles from these samples was investigated. The results showed that with the use of a higher density solution (NaI, 1.5 g/cm³) a much better recovery of anthropogenic microparticles from sludge samples (approximately 1000 microparticles/g-dw and 2000 microparticles/g-dw, from dewatered and digested sludge, respectively) was achieved in comparison with the use of a lower density solution (NaCl, 1.2 g/cm³) (200 microparticles/g-dw and 600 microparticles/g-dw from dewatered and digested sludge, respectively). Moreover, although the use of peroxidation is an essential step to break down the sludge structure and to release microparticles to the liquid phase, the use of peroxidation after or before density separation did not affect the overall recovery of microparticles. Polyethylene, polypropylene, and copolymer ethylene-ethyl-acrylate were the main microplastic fragments identified in digested sludge and dewatered sludge. However, no relation was observed between the method applied and the polymer recovered. Regarding the presence of anthropogenic microparticle in centrifuge effluent, 450 ± 212 microparticles/L were counted, and although little is known about this stream, in can be a relevant source of anthropogenic microparticles.

Quality assessment of research studies on microplastics in soils: A methodological perspective

Microplastics have become a global concern, and soil acts as a major sink for plastic pollution. Due to rapid development of soil microplastics research, various analysis methods have been developed, but require proper consistency and standard procedures. The objective of this study was to appraise a quality assessment concerning soil microplastics from a methodological perspective. Nine studies were selected for the quality assessment exercise based on methodological investigations on soil microplastics and were evaluated based on the adapted Criteria for Reporting and Evaluating Ecotoxicity Data (CRED) method. The highest score obtained by an individual study was 21 while the lowest was 14, leaving a wide score gap which indicated inconsistency amongst the studies. Criterion with the highest average score of 2.0 was obtained for sample size and data reporting. The lowest average score of 0.89 was for the negative control. In conclusion, the total average scores for all eleven criteria were 1.56. Current quality assessment perceived that there was room for improvement and betterment of quality assurance for studies on microplastics and a form of guideline on methodological aspects of soil microplastics studies. It was suggested that future microplastics studies should methodically include quality assurance/quality control (QA/QC) protocols in every process to ensure that good quality data is produced and applied in the risk assessment process.

Mugilidae fish as bioindicator for monitoring plastic pollution: Comparison between a commercial port and a fishpond (north-western Mediterranean Sea)

In the last decade, interest in monitoring and managing plastic pollution has greatly increased. This study compared levels of microplastic contamination in stomachs of Mugilidae fish, suggesting this family as a target for plastic pollution monitoring in areas with different degrees of anthropisation. Two sites characterised by low and high anthropic impact, a fishpond (S'Ena Arrubia, Italy) and a port (Genoa, Italy), respectively, were compared. This study highlighted a stronger microplastic contamination in the port, with a higher percentage of fish showing the presence of microplastics and a larger polymeric variability compared to the fishpond. The microplastic number in fish from the port was higher than in the literature, but it was not significantly different from S'Ena Arrubia in terms of the microplastic percentage found in single individuals. Biomonitoring of microplastic contamination in Mugilidae fish resulted in a valid tool for the investigation of areas differently affected by human activity.

Microplastics retained in stormwater control measures: Where do they come from and where do they go?

Stormwater control measures (SCM) can remove and accumulate microplastics and may serve as a long-term source of microplastics for groundwater pollution because of their potential for downward mobility in subsurface. Furthermore, the number of microplastics accumulated in SCM may have been underestimated as the calculation typically only accounts for microplastics accumulated via episodic stormwater loading and ignores microplastic accumuation via continuous atmospheric deposition. To evaluate the source pathways of accumulated microplastics and their potential for downward mobility to groundwater, we analyzed spatial distributions of microplastics above ground on the canopy around SCM and below ground in the subsurface in and outside the boundaries of fourteen SCM in Los Angeles. Using an exponential model, we link subsurface retardation of microplastics to the median particle size of soil (D₅₀) and land use. Despite receiving significantly more stormwater, microplastic concentrations in SCM at surface depth or subsurface depth were not significantly different from the concentration at the same depth outside the SCM. Similar concentration in and outside of SCM indicates that stormwater is not the sole source of microplastics accumulated in SCM. The high concentration of microplastics on leaves of vegetation in SCM confirms that the contribution of atmospheric deposition is significant. Within and outside the SCM boundary, microplastics are removed within the top 5 cm of the subsurface, and their concentration decreases exponentially with depth, indicating limited potential for groundwater pollution from the microplastics accumulated in SCM. Outside the SCM boundary, the subsurface retardation coefficient decreases with increases in D₅₀, indicating straining of microplastics as the dominant removal mechanism. Inside the boundary of SCM, however, the retardation coefficient was independent of D₅₀, implying that microplastics could have either moved deeper into the filter layer in SCM or that compost, mulch, or organic amendments used in the filter media were pre-contaminated with microplastics. Overall, these results provide insights on microplastics source, accumulation, and downward mobility in SCM.

Dynamics of airborne microplastics, appraisal and distributional behaviour in atmosphere; a review

The use of plastics is common across all aspects of human life owing to its durable and versatile nature. The generation and utilization of plastics are directly related to the anthropogenic activities. The extensive use of plastics and adoption of inappropriate waste-management frameworks has resulted in their release into the environment, where they may persist. Different environmental factors, such as, photochemical, thermo-oxidation, and biological degradation, can lead to the degradation of plastics into micro- (MPs) and nano-plastics (NPs). The behaviour and concentration of MPs in the terrestrial environment can depend on their size, density, and local atmospheric conditions. Microplastics and nanoplastics may enter the food web, carrying various organic pollutants, which bio-accumulate at different trophic levels, prompting organism health concerns. Microplastics being airborne identifies as new exposure route. Dietary and airborne exposure to MPs has led researchers to stress the importance of evaluating their toxicological potential. The primary goal of this paper is to explore the environmental fate of MPs from sources to sink in the terrestrial environment, as well as detail their potential impacts on human health. Additionally, this review article focuses on the presence of airborne microplastics, detailed sample pre-processing methods, and outlines analytical methods for their characterization.

Selection of a density separation solution to study microplastics in tropical riverine sediment

Microplastics (MPs) are small (< 5 mm) plastic particles that are widely found in marine, freshwater, terrestrial and atmospheric environments. Due to their prevalence and persistence, MPs are considered an emerging contaminant of environmental concern. The separation and quantitation of MPs from freshwater sediments is a challenging and critical issue. It is necessary to identify the fate and sources of MPs in the environment, minimise their release and adverse effects. Compared to marine sediments, standardised methods for extracting and estimating the amount of MPs in freshwater sediments are relatively limited. The present study focuses on MP recovery efficiency of four commonly used salt solutions (NaCl, NaI, CaCl₂ and ZnCl₂) for isolating MPs during the density separation step from freshwater sediment. Known combinations of artificial MP particles (PS, PE, PVC, PET, PP and HDPE) were spiked into standard river sediment. Extraction using NaI, ZnCl₂ and NaCl solutions resulted in higher recovery rates from 37 to 97% compared to the CaCl₂ solution (28-83%) and varied between polymer types. Low-density MPs (PE, HDPE, PP and PS) were more effectively recovered (> 87%) than the denser polymers (PET and PVC: 37 to 88.8%) using NaCl, NaI and ZnCl₂ solutions. However, the effective flotation of ZnCl₂ and NaI solutions is relatively expensive and unsafe to the environment, especially in the context of developing countries. Therefore, considering the efficiency, cost and environmental criteria, NaCl solution was selected. The protocol was then tested by extracting MPs from nine riverine sediment samples from the Red River Delta. Sediments collected from urban rivers were highly polluted by MPs (26,000 MPs items·kg^-1 DW) compared to sediments located downstream. Using a NaCl solution was found to be effective in this case study and might also be used in long-term and large-scale MP monitoring programmes in Vietnam.

Fourier transform infrared (FTIR) analysis identifies microplastics in stranded common dolphins (Delphinus delphis) from New Zealand waters

Here we provide a first assessment of microplastics (MPs) in stomach contents of 15 common dolphins (Delphinus delphis) from both single and mass stranding events along the New Zealand coast between 2019 and 2020. MPs were observed in all examined individuals, with an average of 7.8 pieces per stomach. Most MPs were fragments (77%, n = 90) as opposed to fibres (23%, n = 27), with translucent/clear (46%) the most prevalent colour. Fourier transform infrared (FTIR) spectroscopy revealed polyethylene terephthalate (65%) as the most predominant polymer in fibres, whereas polypropylene (31%) and acrylonitrile butadiene styrene (20%) were more frequently recorded as fragments. Mean fragment and fibre size was 584 μm and 1567 μm, respectively. No correlation between total number of MPs and biological parameters (total body length, age, sexual maturity, axillary girth, or blubber thickness) was observed, with similar levels of MPs observed between each of the mass stranding events. Considering MPs are being increasingly linked to a wide range of deleterious effects across taxa, these findings in a typically pelagic marine sentinel species warrants further investigation.

Nile Red staining for detecting microplastics in biota: Preliminary evidence

Nile Red is a lipophilic, metachromatic and solvatochromic dye used as an alternative or complementary method to aid identification of microplastics in routine analysis of biological samples. It was rarely used in biota since organic residues after the digestion step can be co-stained with possible overestimation of microplastics. The limits of using Nile Red in biota were investigated in marine mussels experimentally contaminated with low-density polyethylene (LDPE) microplastics. Stained particles were detected through magnified images obtained by stitching together thirty photographs of the filter surface of each sample. LDPE particles appeared yellowish and fluorescent and could be confused with certain organic residues. The smaller the fragments, the greater the difficulty in recognizing them. In particular, it was difficult to recognize LDPE particles based on their fluorescence if <180 μm in size. Regardless of the size, fluorescence of the items aids the operator in LDPE particles identification also in biota.

Identifying microplastic litter with Laser Induced Breakdown Spectroscopy: A first approach

The broad diversity of microplastic litter requires a selection of analytical techniques to reliably determine the particle's chemical composition. This study demonstrates that Laser Induced Breakdown Spectroscopy (LIBS) can identify microplastic particles based on their spectral fingerprints. By studying the spectral features of polymer reference spectra, microplastic litter can be distinguished from non-plastic materials. The results show that LIBS can be used as a fast in-situ technique for pre-characterization of the microparticle's material and is a possible tool for environmental studies on microplastics.

Disparities in Methods Used to Determine Microplastics in the Aquatic Environment: A Review of Legislation, Sampling Process and Instrumental Analysis

Plastic particles smaller than 5 mm, i.e., microplastics, have been detected in a number of environments. The number of studies on microplastics in marine environments, fresh water, wastewater, the atmosphere, and the human body are increasing along with a rise in the amounts of plastic materials introduced into the environment every year, all contributing to a range of health and environmental issues. Although the use of primary microplastics has been gradually reduced by recent legislation in many countries, new knowledge and data on these problems are needed to understand the overall lifecycle of secondary microplastics in particular. The aim of this review is to provide unified information on the pathways of microplastics into the environment, their degradation, and related legislation, with a special focus on the methods of their sampling, determination, and instrumental analysis. To deal with the health and environmental issues associated with the abundance of microplastics in the environment, researchers should focus on agreeing on a uniform methodology to determine the gravity of the problem through obtaining comparable data, thus leading to new and stricter legislation enforcing more sustainable plastic production and recycling, and hopefully contributing to reversing the trend of high amounts of microplastics worldwide.