Development of a digestion method for determining microplastic pollution in vegetal-rich clayey mangrove sediments

Continuous-flow separation and preconcentration of microplastics from natural waters using countercurrent chromatography

Microplastics is known to be ubiquitous in aquatic environment. Quantification of microplastics in natural waters is an important problem of analytical chemistry, the solution of which is needed for the assessment of water quality and potential risks for water inhabitants and consumers. Separation methods play a key role in the correct quantification of microplastics in natural waters. In the present study the applicability of countercurrent chromatography to the continuous-flow separation and preconcentration of microplastics from water samples in rotating coiled column (RCC) using water-oil systems has been demonstrated for the first time. The effect of column rotation speed and mobile phase (water) flow rate on the retention of the stationary (oil) phase in RCC is studied. The retention parameters of 10 vegetable and 2 synthetic oils are determined. Castor, olive, rapeseed, soybean, linseed, sesame, and sunflower oils are found to be applicable to the separation of microplastics from water samples using RCC. Taking as example polyethylene microparticles of different size (40-63, 63-100, and 100-250 μm), the high recovery of microplastics (about 100 %) from aqueous phase into castor and rapeseed oils is shown. The method has been proven to be efficient for the separation of microplastics from simulated fresh and sea natural waters. It may be perspective not only for the quantification of microplastics in natural waters but as well as for the purification of wastewaters containing microplastics.

Effects of lakeshore landcover types and environmental factors on microplastic distribution in lakes on the Inner Mongolia Plateau, China

Microplastic pollution in freshwater environments has received increasing attention. However, limited research on the occurrence and distribution of microplastics in plateau lakes. This study investigated the microplastic characteristics and influencing factors in lakes with different land cover types on the Inner Mongolia Plateau. Results showed that microplastic abundance ranged from 0.5 to 12.6 items/L in water and 50-325 items/kg in sediments. Microplastics in water were predominantly polypropylene (50.5%), fragments (40.5%), and 50-200 µm (66.7%). High-density (27.9%), fibrous (69.3%), and large-sized microplastics (47.7%) were retained primarily in lake sediments. The highest microplastic abundance in water was found in cropland lakes and grassland lakes, while that in sediments was in descending order of desert lakes > cropland lakes > grassland lakes > forest-grassland lakes. Differences among lake types suggest that agriculture, tourism, and atmospheric transport may be critical microplastic sources. Microplastic distribution was positively correlated with farmland and artificial surface coverage, showing that land cover types related to human activities could exacerbate microplastic pollution in lakes. Redundancy analysis showed that ammonia nitrogen and pH were the key physicochemical factors affecting microplastic distribution in lakes, indicating the potential sources of microplastics in lakes and the uniqueness of microplastic occurrence characteristics in desert saline-alkaline lakes, respectively.

Comparison of three digestion methods for microplastic extraction from aquaculture feeds

Microplastics (MPs) are ubiquitous pollutants found in aquaculture animals that may threaten human health through the food chain. However, there is a lack of effective methods for extracting MPs from aquaculture feeds containing complex components such as organic matter and fish bones. Therefore, in the present study, the extraction efficiency of three digestion methods using 30 % H2O2, Fenton reagent, and 30 % H2O2 + HNO3 for different particle sizes and types of MPs in aquaculture feeds was investigated and compared. The total digestion efficiency of the aquaculture feeds by 30 % H2O2 was 97.3 ± 0.1 %, while the recovery efficiency of MPs was 91.3 ± 1.1 % -103.1 ± 0.9 %. However, there was a large deviation in the extraction efficiency of MPs from aquaculture feeds by the Fenton reagent and 30 % H2O2 + HNO3. Notably, the surface morphology, particle size distribution, and oxidation degree of MPs hardly changed after 30 % H2O2 digestion. More importantly, the changes in the spectral features and carbonyl index of MPs after 30 % H2O2 digestion were smaller than those of the Fenton reagent and 30 % H2O2 + HNO3, which did not affect the identification of MPs. Overall, 30 % H2O2 was more efficient in extracting MPs from aquaculture feeds, and no significant effect on the characteristics of MPs was observed. This work provides novel insights into the effect of chemical pretreatment on the extraction of MPs in aquaculture feeds and provides an optimal protocol for the detection of MPs in aquaculture feeds.

The consequences of reduced anthropogenic activities during the COVID-19 pandemic on microplastic abundance in a tropical estuarine region: Goa, India

Plastic pollution is pervasive, as it has infiltrated every corner of the planet and the COVID-19 pandemic has caused a depletion in the production, consumption, and disposal of plastics. To find out the effect of the COVID-19 pandemic, a comparative assessment of microplastics (MPs) observed before and after the pandemic was evaluated in surface water and sediment from the major rivers of Goa, i.e. Mandovi and Zuari. To comprehend the relative difference in the abundance, characteristics, and source of MPs, samples were examined in both the dry and wet seasons. We found a sharp decrease in the concentration of MPs immediately after the isolated pandemic. During the dry and wet seasons, two to seven times less concentration of MPs was recorded for water and sediments after the pandemic period compared to the prior pandemic. MPs size, >300 μm were relatively abundant after the pandemic period in contrast to the prior pandemic (<300 μm sized MPs were more). Polyamide (PA), polyvinyl alcohol (PVAL), and polyvinyl chloride (PVC) were the dominant polymers after the pandemic whereas earlier the dominant polymers were polyacetylene, polyacrylamide (PAM), and polyvinyl pyrrolidone (PVP). The risk assessment of MPs in sediments (Polymer load index) was higher prior to the pandemic. The water quality parameters also indicated an improvement in the water quality during the pandemic. The present study clearly exhibited that due to the reduction of overall anthropogenic activities during the COVID-19 pandemic period, a sharp decline of plastic waste and MP abundance in the coastal water body in Goa, west coast of India was found. This study unveils the controlling factors (such as total solid waste generation, plastic waste, tourism activities, and the effect of monsoon) which influence the abundance and distribution of macro- and microplastics.

Microplastics in mangroves with special reference to Asia: Occurrence, distribution, bioaccumulation and remediation options

Microplastics (MPs) are a new and lesser-known pollutant that has intrigued the interest of scientists all over the world in recent decades. MP (<5mm in size) can enter marine environments such as mangrove forests in a variety of ways, interfering with the health of the environment and organisms. Mangroves are now getting increasingly exposed to microplastic contamination due to their proximity to human activities and their position as critical transitional zones between land and sea. The present study reviews the status of MPs contamination specifically in mangrove ecosystems situated in Asia. Different sources and characteristics of MPs, subsequent deposition of MPs in mangrove water and sediments, bioaccumulation in different organisms are discussed in this context. MP concentrations in sediments and organisms were higher in mangrove forests exposed to fishing, coastal tourism, urban, and industrial wastewater than in pristine areas. The distribution of MPs varies from organism to organism in mangrove ecosystems, and is significantly influenced by their morphometric characteristics, feeding habits, dwelling environment etc. Mangrove plants can accumulate microplastics in their roots, stem and leaves through absorption, adsorption and entrapment helping in reducing abundance of microplastic in the surrounding environment. Several bacterial and fungal species are reported from these mangrove ecosystems, which are capable of degrading MPs. The bioremediation potential of mangrove plants offers an innovative and sustainable approach to mitigate microplastic pollution. Diverse mechanisms of MP biodegradation by mangrove dwelling organisms are discussed in this context. Biotechnological applications can be utilized to explore the genetic potential of the floral and faunal species found in the Asian mangroves. Detailed studies are required to monitor, control, and evaluate MP pollution in sediments and various organisms in mangrove ecosystems in Asia as well as in other parts of the world.

Combined approaches for detecting polypropylene microplastics in crop plants

Microplastics (MPs) pollution in the terrestrial environment causes accumulation in crop plants. Consumption of these plants may have negative effects on human health. Therefore, it is crucial to analyze MPs accumulation in the plants. The aim of this study is to determine polypropylene (PP) particles in plants exposed to label-free PP for 75 days. In order to extract PP from organic matter, a two-step alkaline and wet peroxide oxidation chemical digestion method was applied to the roots, stems, and leaves of maize and wheat. The PP particles in the digested solutions were detected by the Nile red staining method, which has not been used previously in the detection of MPs in plants. Nile red stained PP particles mostly accumulated in the roots of wheat and the stems of maize plants. Statistical analysis revealed that the maize deposited more and larger PP particles regardless of the location. Moreover, the presence of PP particles in the digestion solutions was proved by the heating method. The PP particles on the glass slides were transformed into different shapes due to melting.

Recent Study of Separation and Identification of Micro- and Nanoplastics for Aquatic Products

Micro- and nanoplastics (MNPs) are polymeric compounds widely used in industry and daily life. Although contamination of aquatic products with MNPs exists, most current research on MNPs focuses on environmental, ecological, and toxicological studies, with less on food safety. Currently, the extent to which aquatic products are affected depends primarily on the physical and chemical properties of the consumed MNPs and the content of MNPs. This review presents new findings on the occurrence of MNPs in aquatic products in light of their properties, carrier effects, chemical effects, seasonality, spatiality, and differences in their location within organisms. The latest studies have been summarized for separation and identification of MNPs for aquatic products as well as their physical and chemical properties in aquatic products using fish, bivalves, and crustaceans as models from a food safety perspective. Also, the shortcomings of safety studies are reviewed, and guidance is provided for future research directions. Finally, gaps in current knowledge on MNPs are also emphasized.

Effect of ultrasonication conditions on polyethylene microplastics sourced from landfills: A precursor study to establish guidelines for their extraction from environmental matrices

Establishing concentration of microplastics (MPs), designated as CMP, in aqueous, semi-solid and solid samples originating from unscientifically created landfills/dumpsites (UCLDs) and engineered landfills (ELFs) is of utmost importance to assess their impact on the geoenvironment. However, the accuracy of CMP will be guided by the extraction efficiency of MPs from these samples. The extraction of MPs from semi-solid and solid samples of UCLDs/ELFs would be cumbersome, mainly due to their trapping in solid aggregates (including organic matter). Such aggregates need to be dispersed to release the MPs, which can be achieved through the assistance of ultrasonication (US) in the presence of an appropriate dispersing agent. However, mere dispersion of solid aggregates during the US might not result in the complete release of MPs adhered (AMPs) to MPs native (NMPs) to these samples. This is because MPs would adhere to the surface of the adjacent ones due to various physical-mechanical-thermal-chemical processes that prevail in landfills. Hence, guidelines for US-assisted extraction of MPs should be developed by considering an approach that would ensure (i) cleaning of NMPs' surface and (ii) release of AMPs without damaging the former. This necessitates understanding the influence of US parameters such as energy applied (Eus), time (tus) and direct/indirect exposure of NMPs from landfills that would control CMP. In this context, the influence of above mentioned US parameters on the (i) surface cleaning of polyethylene NMPs and (ii) release of AMPs and their concentrations (CAMP) was investigated. It was observed that Eus equal to 500 kJ/L during the indirect method of US would result in surface cleaning of NMPs and complete release of AMPs without damaging the farmer's structure. The present work acts as a precursor study to establish the guidelines for the US-assisted extraction of MPs in environmental samples. Also, a generalized relationship between Eus and CAMP, which can be employed to study the impact of landfill type on the release of MPs during the US was developed.

A Complete Guide to Extraction Methods of Microplastics from Complex Environmental Matrices

Sustainable development is a big global challenge for the 21st century. In recent years, a class of emerging contaminants known as microplastics (MPs) has been identified as a significant pollutant with the potential to harm ecosystems. These small plastic particles have been found in every compartment of the planet, with aquatic habitats serving as the ultimate sink. The challenge to extract MPs from different environmental matrices is a tangible and imperative issue. One of the primary specialties of research in environmental chemistry is the development of simple, rapid, low-cost, sensitive, and selective analytical methods for the extraction and identification of MPs in the environment. The present review describes the developments in MP extraction methods from complex environmental matrices. All existing methodologies (new, old, and proof-of-concept) are discussed and evaluated for their potential usefulness to extract MPs from various biotic and abiotic matrices for the sake of progress and innovation. This study concludes by addressing the current challenges and outlining future research objectives aimed at combating MP pollution. Additionally, a set of recommendations is provided to assist researchers in selecting appropriate analytical techniques for obtaining accurate results. To facilitate this process, a proposed roadmap for MP extraction is presented, considering the specific environmental compartments under investigation. By following this roadmap, researchers can enhance their understanding of MP pollution and contribute to effective mitigation strategies.

Accumulation and re-distribution of microplastics via aquatic plants and macroalgae - A review of field studies

The aquatic plants and macroalgae are primary producers with major roles regarding the maintenance of ecosystems but their interaction with microplastics (MPs) has received less attention than animals. We summarize the methodologies used, the MPs abundances and their characteristics across the literature on MPs pollution in aquatic plants and macroalgae. The sampling and quantification of MPs still lacks consistency between studies, which increased the uncertainty in cross-comparisons. The abundance of MPs varied by orders of magnitude between species and were mostly fibers and polymers with large degrees of production and applications. Filamentous species contained more MPs than others. The average ratio of MPs between vegetated and unvegetated sites reached 3:1. The average ratio of MPs between the biotic and abiotic fractions reached 2193:1, suggesting a high level of retention in fields. Our findings supported that aquatic plants and macroalgae are critical in the plastic flux within the marine environments.

Distribution and risk assessment of microplastics in typical ecosystems in the South China Sea

Microplastic pollution in the marine environment has attracted worldwide attention. The South China Sea is considered a hotspot for microplastic pollution due to the developed industries and high population density around the South China Sea. The accumulation of microplastics in ecosystems can adversely affect the health of the environment and organisms. This paper reviews the recent microplastic studies conducted in the South China Sea, which novelty summarizes the abundance, types, and potential hazards of microplastics in coral reef ecosystems, mangrove ecosystems, seagrass bed ecosystems, and macroalgal ecosystems. A summary of the microplastic pollution status of four ecosystems and a risk assessment provides a more comprehensive understanding of the impact of microplastic pollution on marine ecosystems in the South China Sea. Microplastic abundances of up to 45,200 items/m³ were reported in coral reef surface waters, 5738.3 items/kg in mangrove sediments, and 927.3 items/kg in seagrass bed sediments. There are few studies of microplastics in the South China Sea macroalgae ecosystems. However, studies from other areas indicate that macroalgae can accumulate microplastics and are more likely to enter the food chain or be consumed by humans. Finally, this paper compared the current risk levels of microplastics in the coral reef, mangrove, and seagrass bed ecosystems based on available studies. Pollution load index (PLI) ranges from 3 to 31 in mangrove ecosystems, 5.7 to 11.9 in seagrass bed ecosystems, and 6.1 to 10.2 in coral reef ecosystems, respectively. The PLI index varies considerably between mangroves depending on the intensity of anthropogenic activity around the mangrove. Further studies on seagrass beds and macroalgal ecosystems are required to extend our understanding of microplastic pollution in marine environments. Recent microplastic detection in fish muscle tissue in mangroves requires more research to further the biological impact of microplastic ingestion and the potential food safety risks.

Abundance and characteristics of microplastics in the Wanquan River estuary, Hainan Island

As the nexus where rivers and oceans meet, estuaries are vulnerable to microplastic (MP) pollution derived from rivers. However, few studies have focused on the pollution status of MPs in small estuarine areas. Here, the abundance and characteristics of MPs in surface water and sediment samples from a small estuary, the Wanquan River estuary, were studied. The average abundance of MPs was 6573 ± 2659 n/m³ in surface water and 1065 ± 696 n/kg dw in sediment samples from the Wanquan River estuary. Most of the MPs in water samples and sediments were red (92.9 % and 88.1 %) fragments (87.4 % and 95.5 %) with sizes <1.0 mm (90.8 % and 92.4 %) made up of antifouling paint particles (APPs) (83.5 % and 89.8 %), respectively. A significant positive correlation (p < 0.01) was found between the concentration of Cu²⁺ and the abundance of APPs in sediment samples from the Wanquan River estuary. The APPs in the sediments can act as a continuous source of toxic chemicals (e.g., Cu²⁺) to marine environments. The results of this study expand our knowledge about MP pollution in small estuaries, and the ecological risk of APPs in the Wanquan River estuary to aquatic organisms should not be ignored.

Vertical distribution, accumulation, and characteristics of microplastics in mangrove sediment in China

Mangroves in tropical and subtropical regions worldwide are recognized as important sinks for microplastics (MPs). However, recent studies have focused on surface sediments, and in China, the vertical distribution and characteristics of MPs in mangrove sediments remain poorly understood. In this study, sediment cores of 100 cm depth were collected from six representative mangroves in China to investigate MPs via chronological analysis. Futian had the highest abundance of MPs (0-3123 n/kg), followed by Dongfang, Yunxiao, Zhanjiang, Dongzhaigang and Fangchenggang. The earliest MPs occurring in mangroves were dated back to 1955, and their abundance increased exponentially from bottom to surface sediments. MPs were mainly white in color, fiber-shaped, 1000-5000 μm in size, and of polypropylene/polyethylene polymer types. Furthermore, the MPs in the urban mangrove also showed a higher diversity in color. The results showed that the MP stocks in the urbanized Futian mangrove reached 1828 mg/m³, an order of magnitude higher than in other areas (251 ± 180 mg/m³), contributing to 0.0057 % of the carbon storage of the sediment. The abundance of MPs in mangrove sediments is expected to increase by 2.38-9.54 times by 2030, and therefore deserve further attention.

A comparative study on the distribution behavior of microplastics through FT-IR analysis on different land uses in agricultural soils

Plastic materials have been variously exposed to arable land for decades through soil mulching, plastic housing, and sewage sludge composting. Their mechanical abrasion and biochemical degradation induce the proliferation of myriad microplastics that can further be broken into smaller nano-sized pieces that can be further accumulated in living organisms (including soil invertebrates, fruits, and vegetables); they can also be widely dispersed in neighboring environments. Despite the intensive use of plastics in agriculture, little is known about their origin of occurrence and environmental fate, especially with a size below 100 μm. Therefore, in this study, microplastics with a size in the range of 20-2,000 μm were investigated in soil samples obtained from three different conditions of land uses: tilled with plastic mulch, bare ground (i.e., uncultivated land), and in between the greenhouses of the farmland D located in Namyangju-si, Gyeonggi-do, Republic of Korea. They were primarily identified using Fourier transform infrared (FT-IR) spectroscopy coupled with a microscope. Prior to performing the analysis, microplastic extraction from the soil samples was validated using standardized high-density polyethylene (HDPE) microplastics of various sizes ranging from 20 to 500 μm. As a result, the number of microplastics was estimated to be (241 ± 52), (195 ± 37), and (306 ± 56) particles per kg of dry soil in tillage, bare ground, and in between greenhouses, respectively. They consist of polyethylene (PE), polypropylene (PP), and poly(ethylene terephthalate) (PET), which are the basic constituents of commonly used agricultural products. The particle size distribution depends on the type of plastic, the time elapsed since their usage, and the degree and duration of environmental exposure; the plastic particle sizes were smaller in tillage and around the greenhouses since agricultural films have been weathered for a long time, whereas those with relatively large sizes were found in the uncultivated.

Urban mangrove ecosystems are under severe threat from microplastic pollution: a case study from Mangalavanam, Kerala, India

The prevalence of microplastics in urban mangrove ecosystems has received little scientific attention despite their immense ecological significance. An investigation was conducted to assess the microplastic abundance and characteristics in three different environmental compartments viz; soil (933 ± 564 particles/kg), sediment (1275 ± 532 particles/kg d.w.), and water (101.6 ± 24 particles/liter) of the Mangalavanam bird sanctuary, a protected mangrove forest in the Cochin city of India. Microplastic fibres were predominant in water, while soil and sediment contained a higher proportion of microplastic fragments. Importantly, surrounding urban features and tidal fluctuation were considered to be influencing microplastic metrics in the area. The colour composition of microplastics was found to be similar in all three environmental compartments and most of the identified polymers were those which are scarcely recycled. Altogether, this study highlights the importance of adopting location-specific measures to protect the area from microplastic pollution and provides the baseline data required for further assessing the impacts of microplastic pollution on mangroves, avifauna, and other components of biodiversity in the region.

Current status and trends of research on microplastic fugacity characteristics and pollution levels in mangrove wetlands

Microplastics have been widely detected in the environment, while mangrove wetlands are considered barriers to land-based plastic transport to the ocean, requiring special attention. However, the current literature is distributed and broad besides limited information on the fate characteristics and pollution levels. This study uses a systematic literature review method to analyze the current research status and future trends. In this study, the literature is summarized and concluded that Characteristics including color, shape, size, polymer chemistry and surface microstructure are the basic information for microplastic research in mangrove wetlands. Size is the key to studying distribution and convergence without international standards. The shape is vital to study its sources and environmental processes. Color affects biological predation and is important information for studying ecological risk. The chemical composition of plastics is the key to studying microplastics’ fingerprint information, source, and sink. The surface microstructure is an important basis for studying adsorption behavior and aging processes. Mangrove microplastic studies in China are mainly on the southern and southeastern coasts, and microplastic pollution is more severe in Fujian, Guangdong, and Guangxi than in Hainan. In contrast, studies on mangrove microplastics abroad are mainly concentrated in Southeast Asia, the Middle East, and South America. Overall, microplastic contamination was detected in the major distribution areas of mangroves worldwide and was correlated with mangrove density and human activities.

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.

The effects of weathering-induced degradation of polymers in the microplastic study involving reduction of organic matter

The analysis of microplastics in complex environmental samples requires the use of chemicals to reduce the organic matrix. This procedure should be evaluated in terms of the preservation of the microplastic's integrity, typically done with pristine reference microplastics. However, real microplastics are most likely degraded due to weathering, so pristine reference microplastics might not depict the appropriateness of the process. This study performed a purification process using sodium dodecyl sulfate and hydrogen peroxide on sewage sludge containing LLDPE, HDPE, PP, PS, PET, PA66 and SBR samples exposed to simulated environmental weathering. The degradation of the polymers was assessed by analyzing surface morphology, mass variation, and mechanical, thermal and chemical properties. Comparison with pristine polymers revealed that the purification process can lead to more detrimental effects if the polymers are weathered. After the purification process, some important observations were: 1) LLDPE, PP and SBR surfaces had cracks in the weathered samples that were not observed in the pristine samples, 2) weathered LLDPE, PP and PA66 experienced greater mass loss than pristine, 3) the fragmentation propensity of weathered LLDPE, HDPE, PP, PS and SBR increased compared to pristine samples and 4) the main characteristic peaks in FTIR spectrum could be identified and used for chemical identification of most polymers for pristine and weathered samples. Based on the findings of this study, when analyzing the efficiency and adequacy of a purification process with methods based on surface morphology, mass variation and particle counting indicators, it is recommended to consider the differences that potentially arise between pristine and weathered microplastics, especially for polyolefins (PEs and PP).

Widespread microplastic pollution in mangrove soils of Todos os Santos Bay, northern Brazil

Microplastics have been studied in sediments from coastal and aquatic environments, but contamination of mangrove soils is still relatively unknown in most mangroves around the world. In this study, the presence of microplastics was investigated in six mangrove soils around the Todos Santos Bay (TSB), the largest and most important navigable bay on the Brazilian coast. Samples were collected at three depths (surface, 10 cm, and 30 cm) at three different distances from the lower tidal area. Ten grams of soil were sieved in a 150 μm mesh and centrifuged with ZnCl₂ solution (density of 1.5 kg dm^-3) for the extraction of microplastics. The microplastics were quantified, measured, and described using a systematic photographic method and the ImageJ program. Microplastics were abundant in all samples, with a mean of 10,782 ± 7,671 items kg^-1 (max.: 31,087 items kg^-1, only one sample <2,000 items kg^-1), higher than any other value reported worldwide. The abundances varied among the six mangroves studied, with a predominance of fibers and mean size of 196 μm. Even remote mangroves were highly polluted, reflecting a large dispersion of the pollutants. The abundance did not differ significantly between soil depths, evidencing a continuous input and burial of microplastics in the soil up to 30 cm. The investigation of the source of microplastics and their presence in water and biota is urgent in this Brazilian region, and these results emphasize the need for global actions to protect coastal ecosystems.

Study of microplastics pollution in sediments and organisms in mangrove forests: A review

Microplastics (MP) are an emerging and lesser-known pollutant that has attracted the attention of researchers around the world in recent decades. Size of PM is smaller than 5 mm and can be entered in different ways into marine environments like mangrove forests and interfere with the health of the environment and organisms. The present study reviews 53 studies in the field of microplastics in different parts (sediments and organisms) of mangrove forests. About 26% of the 53 studies was published in 2020. In most studies, MP particles were categorized based on the shape, color, size, and polymer genus. The number of microplastics per kilogram of mangrove sediments has been reported as 1.22-6390. The effect of sediment texture on the frequency of microplastic particles and the relationship between sediment pH and MP abundance were also discussed. The fiber and bright color PMs were more common in living organisms (mollusks, crustaceans, and fish). The PM particles with different genus (polypropylene, polyethylene, polystyrene, and polyethylene terephthalate) were reported for sediment samples. In sediments with smaller sizes and lower pH, microplastics have been detected more frequently. It was reported that sediments and roots of mangrove forests act as livestock and retain microplastics for a long time. The highest concentration of MP in different parts of mangrove forests (sediment and organisms) has been reported for China. Few reports were observed on microplastics in water in mangrove forests. Also, the concentration of microplastics in sediments and organisms in mangrove forests exposed to fishing, coastal tourism, urban, and industrial wastewater was higher than those in pristine areas. It is necessary to conduct comprehensive studies to monitor, control, and evaluate the MP pollution in sediments and various organisms in mangrove forests worldwide.

Effects and Impacts of Different Oxidative Digestion Treatments on Virgin and Aged Microplastic Particles

Although several sample preparation methods for analyzing microplastics (MPs) in environmental matrices have been implemented in recent years, important uncertainties and criticalities in the approaches adopted still persist. Preliminary purification of samples, based on oxidative digestion, is an important phase to isolate microplastics from the environmental matrix; it should guarantee both efficacy and minimal damage to the particles. In this context, our study aims to evaluate Fenton’s reaction digestion pre-treatment used to isolate and extract microplastics from environmental matrices. We evaluated the particle recovery efficiency and the impact of the oxidation method on the integrity of the MPs subjected to digestion considering different particles’ polymeric composition, size, and morphology. For this purpose, two laboratory experiments were set up: the first one to evaluate the efficacy of various digestion protocols in the MPs extraction from a complex matrix, and the second one to assess the possible harm of different treatments, differing in temperatures and volume reagents used, on virgin and aged MPs. Morphological, physicochemical, and dimensional changes were verified by Scanning Electron Microscope (SEM) and Fourier Transformed Infrared (FTIR) spectroscopy. The findings of the first experiment showed the greatest difference in recovery rates especially for polyvinyl chloride and polyethylene terephthalate particles, indicating the role of temperature and the kind of polymer as the major factors influencing MPs extraction. In the second experiment, the SEM analysis revealed morphological and particle size alterations of various entities, in particular for the particles treated at 75 °C and with major evident alterations of aged MPs to virgin ones. In conclusion, this study highlights how several factors, including temperature and polymer, influence the integrity of the particles altering the quality of the final data.

A straightforward method for microplastic extraction from organic-rich freshwater samples

The extraction of microplastics from organic-rich freshwater samples is challenging and limited information is available in the literature. This study aims at developing efficient methods for water volume reduction and organic matter removal in freshwater samples, while focusing on the reduction of the economic and environmental costs, maintaining microplastics integrity and avoiding contamination. For the water volume reduction approach, centrifuging freshwater samples (water, sediment, algae, leaves, driftwood, fish tissue) at different speeds (3500, 6000 rpm) and times (5, 10 min) showed that 3500 rpm for 5 min was efficient to settle the mineral and organic material, while preserving the polymers and showing high microplastic recovering rates (93 ± 6%). These recovery rates were significantly higher than the traditional sieving approach (77 ± 22%). The posterior minimal consumption of reagents resulting from the reduction of water volume helped to reduce the economic and environmental costs of the devised methodology, becoming more aligned with green chemistry principles. For biogenic organic matter removal, four digestion solutions were tested on freshwater samples, namely 10% potassium hydroxide, Fenton reagent (30% H₂O₂ + Fe(II)), 7% and 10% sodium hypochlorite (NaClO), under 3 periods of time (1, 6 and 15 h), at 50 °C. Both 7% and 10% NaClO showed the highest rates of organic matter removal (86 ± 1% and 90 ± 1%, respectively), after 6 h at 50 °C. Exposure of virgin and aged polymers (polyethylene, polypropylene, polystyrene, polyvinyl chloride, nylon, polyethylene terephthalate) to NaClO showed no weight, visual, surface structure, Fourier transform infrared spectra and carbonyl index changes, except for nylon, although not to an extent that affected its identification. This method resulted in high recovery rates of polymers (92 ± 6%). Thus, 7% NaClO at 50 °C for 6 h (or overnight) may be efficiently used for microplastic analysis in organic-rich freshwater samples.

Fate and Effects of Macro- and Microplastics in Coastal Wetlands

Coastal wetlands trap plastics from terrestrial and marine sources, but the stocks of plastics and their impacts on coastal wetlands are poorly known. We evaluated the stocks, fate, and biological and biogeochemical effects of plastics in coastal wetlands with plastic abundance data from 112 studies. The representative abundance of plastics that occurs in coastal wetland sediments and is ingested by marine animals reaches 156.7 and 98.3 items kg^-1, respectively, 200 times higher than that (0.43 items kg^-1) in the water column. Plastics are more abundant in mangrove forests and tidal marshes than in tidal flats and seagrass meadows. The variation in plastic abundance is related to climatic and geographic zones, seasons, and population density or plastic waste management. The abundance of plastics ingested by pelagic and demersal fish increases with fish length and dry weight. The dominant characteristics of plastics ingested by marine animals are correlated with those found in coastal wetland sediments. Microplastics exert negative effects on biota abundance and mangrove survival but positive effects on sediment nutrients, leaf drop, and carbon emission. We highlight that plastic pollution is widespread in coastal wetlands and actions are urged to include microplastics in ecosystem health and degradation assessment.

Distribution, characteristics, and human exposure to microplastics in mangroves within the Guangdong-Hong Kong-Macao Greater Bay Area

In this study, three mangroves in the Guangdong-Hong Kong-Macao Greater Bay Area- Qi'ao Island in Zhuhai, Nansha in Guangzhou, and Futian in Shenzhen-were selected for investigating the distribution of microplastics and their characteristics The average microplastic abundance in each descended in the order: Futian (1600 n/kg) > Nansha (1100 n/kg) > Qi'ao Island (440 n/kg), with values from the forest fringe being significantly higher than those in the forest interior. The microplastics were mainly fibers, 1-5 mm in size, and white/black in color; they consisted of polypropylene and polyethylene, with foam and polystyrene accounting for a high proportion in Nansha. The exposure of humans to microplastics in the Futian forest fringe reached 35.95 ng/d·kg; it was one order of magnitude higher than the exposures in Qi'ao Island and Nansha. Furthermore, ingestion accounted for approximately 74% of the total exposure to the human body, dermal contact constitutes 25%, and sediment inhalation accounted for less than 1%.

Microplastics in China Sea: Analysis, status, source, and fate

Microplastics (MPs) in marine environments have raised increasing concerns worldwide in recent years. China is one of the largest plastic producers in the world. In this review, available information on MPs in China Sea was reviewed, including studies on seawater, sediment, and biota. The status and limits of sampling methods of MPs were summarized, such as sampling tools, sampling volume, and depth of sampling. The analytical methods of MPs were outlined, such as sieving, density separation, purification, filtration, and visual sorting. The characteristics of MPs, such as abundances, sizes, shapes, polymer types, sources, and fates were analyzed. The abundances of MPs in China Sea varied from 0.1 to 27,840.0 items m^-3 in seawater, and from 13.0 to 14,712.0 items kg^-1 d.w. in sediments. Furthermore, MPs were mainly featured with sizes ranging from 0.001 to 0.5 mm, with colors of transparent and black, and polymer types of polypropylene and polyethylene. To promote research on MPs in China Sea, the sampling and analytical methods were insufficiently standardized and should be improved. As for microplastic (MP) pollution in China Sea, laws and regulations have already been established to manage and control plastic waste. Furthermore, several suggestions to control plastic pollution were as follows: (1) control marine plastic pollution at the source; (2) strengthen technological innovations; (3) urge people to minimize disposable plastic products in their daily lives; (4) strengthen international cooperation in the treatment of marine plastic waste.

Sodium hypochlorite as an oxidizing agent for removal of soil organic matter before microplastics analyses

The omnipresence of microplastics (MPs) across Earth's surface has raised concerns about their environmental impact and created an urgent need for methods to identify them in complex soil and sedimentary matrices. However, detecting MPs in the O horizons of soils is difficult because plastic polymers share many physical and chemical properties with natural soil organic matter (SOM). In this study, we assessed whether sodium hypochlorite (NaOCl), a reagent that can oxidize SOM and simultaneously preserve mineral constituents, can be used for MP analysis and characterization in soil environments. In addition, we scrutinized how factors such as MP size, polymer type, extraction methods, and soil matrix affect the recovery of microplastic particles. We used both hydrophobic and density-dependent separation methods to assess the effects of our oxidation treatment on the recovery of MP. We observed that NaOCl effectively removed SOM without greatly altering the surface properties of resistant MP polymers (polypropylene, polylactic acid, low-density polyethylene, and polyethylene terephthalate), which were characterized using scanning electron microscopy and Fourier-transform infrared spectroscopy after SOM removal. The NaOCl treatment caused some chlorination and formation of additional C-OH bonds on polymer surfaces, which likely contributed to the reduced efficiency of the hydrophobic-based (oil) extraction. We conclude that NaOCl treatment can improve detection of MPs in SOM-rich soil and that recovery of MPs from soils is influenced by MP size, polymer type, extraction method, and soil type, which makes it challenging to develop a universal analytical method.

Micro/nano-plastics occurrence, identification, risk analysis and mitigation: challenges and perspectives

Micro/nanoplastics (MP/NPs) are emerging global pollutants that garnered enormous attention due to their potential threat to the ecosystem in virtue of their persistence and accumulation. Notably, United Nations Environment Programme (UNEP) yearbook in 2014 proposed MPs as one among ten emergent issues that the Earth is facing today. MP/NPs can be found in most regularly used products (primary microplastics) or formed by the fragmentation of bigger plastics (secondary microplastics) and are inextricably discharged into the environment by terrestrial and land-based sources, particularly runoff. They are non-degradable, biologically incompatible, and their presence in the air, soil, water, and food can induce ecotoxicological issues and also a menace to the environment. Due to micro size and diverse chemical nature, MP/NPs easily infiltrate wastewater treatment processes. This communication reviews the current understanding of MP/NPs occurrence, mobility, aggregation behavior, and degradation/assimilation in terrestrial, aquatic (fresh & marine), atmospheric depositions, wetlands and trophic food chain. This communication provide current perspectives and understanding on MP/NPs concerning (1) Source, occurrence, distribution, and properties (2) Impact on the ecosystem and its services, (3) Techniques in detection and identification and (4) Strategies to manage and mitigation.

Protocol for microplastic pollution monitoring in freshwater ecosystems: Towards a high-throughput sample processing - MICROPLASTREAM

Robust and reproducible quantification of microplastic pollution in freshwater ecosystems requires the processing of a large amount of samples collected in varying environmental conditions. Such samples are characterized by a high amount of organic matter compared to microplastics and are highly variable in terms of the quantity and the composition of matrices, requiring a standardized analytical protocol for sample treatment and analysis. However, two important and time-consuming steps for microplastic recovery are the elimination of organic matter and microscopic inspection of samples. Here, we developed and validated a protocol, targeting particles with length ranging from 700 µm to 5 mm, that includes a double-step digestion of organic matter, consisting of incubation with potassium hydroxide followed by hydrogen peroxide solutions, and two stereomicroscopic analyses. In addition, we developed several technical improvements allowing reducing the time needed to process samples, such as the design of an adapted filter-cap to improve the content transfer. The absence of physical and chemical alterations in the investigated microplastic pellets and the average reduction of 65.8% (± 9.59 SD) of organic matter in real samples demonstrated that our protocol is fit for purpose. We recommend a second stereomicroscopic analysis to avoid underestimating microplastic concentration and particle size distribution biased towards larger particles. When used for a large-scale monitoring of microplastic pollution, this protocol resulted in an estimated time of 38 h for one person for the treatment of a batch of 24 samples, allowing a higher throughput sample processing and reproducible quantification. • Protocol customization towards high-throughput sample processing • Double step digestion to improve organic matter elimination • Importance of stereomicroscopic analysis for microplastic recovery.

Methods for separating microplastics from complex solid matrices: Comparative analysis

Microplastics (MPs) are widely found in complex solid matrices such as soil, sediments and sludge. The separation procedure is crucial for effective analysis of MPs, but existing methods varied among studies. Here, we systematically summarize and compare separation methods including density, oil, electrostatic, magnetic, and solvent extraction separation. Density separation is the most commonly used approach, but time-consuming and discharging hazardous materials dependent on extraction solutions. In contrast, oil, electrostatic, magnetic separation and solvent extraction separation are emerging approaches with advantages of low-cost, quick, or environmentally-friendly, but with high request of instruments. Despite variation among these approaches, the separation efficiency is closely related to characteristics of MPs including polymer types, sizes and shapes. The treatment of digestion and fluorescence staining can facilitate the detection of MPs. This analysis suggests that further optimization and improvement of existing approaches can facilitate the development of new separation technology for assaying MPs in complex environmental matrices.

How mangrove plants affect microplastic distribution in sediments of coastal wetlands: Case study in Shenzhen Bay, South China

Microplastic pollution is common in marine and coastal ecosystems, especially in mangrove wetlands. However, factors affecting the distribution of microplastics, such as plants, have not been sufficiently studied. We investigated the effect of different plant species on the distribution of sediment microplastics in two Nature Reserves in South China, viz. Futian Mangrove and Mai Po Mangrove. In Futian Mangrove, the abundance of total microplastics among three monospecific mangrove stands dominated by Sonneratia caseolaris, Kandelia obovata, and Sonneratia apetala was similar. The abundance of microplastics in the mudflat was similar to that in the forest interior, except for the fact that more fiber was found in the mudflat than in the interior of Sonneratia apetala. This suggested that the dense pneumatophores at the fringe prevented fibers from entering the mangrove forest. The significant positive dependence (p < 0.05) between the density of Sonneratia pneumatophores and the abundance of fibers highlighted the importance of pneumatophores. The abundance of total microplastics, predominantly in the form of fibers, in sediments at the forest fringe (2835 ± 713 items/kg d.w. and 2070 ± 224 items/kg d.w. in Futian and Mai Po, respectively) was higher than that in the forest interior and mudflat. There was no difference between the two latter locations in both mangroves, which demonstrated the significance of the fringe effect. This paper reports for the first time that the spatial distribution of microplastics in mangrove sediments was affected by plant species, which provides useful information for environmental processes of microplastics in coastal wetlands.

From source to sink: Review and prospects of microplastics in wetland ecosystems

The source, distribution, migration, and fate of microplastics (MPs) in aquatic and terrestrial ecosystems have received much attention. However, the relevant reports in wetland ecosystems, the boundary area between water and land, are still rare. Where are the sources and sinks of MPs in the wetland? The latest researches have shown that the sources of MPs in wetlands include sewage discharge, surface runoff, and plastic wastes from aquaculture. Fibers and fragments are the most common shapes, and PE, PP, PS can be detected in water or sediment matrices, and biota of wetlands. The distribution is affected by hydrodynamic conditions, sediment properties, and vegetation coverage. Factors affecting the vertical migration of MPs include their own physical and chemical properties, the combination of substances that accelerate deposition (mineral adsorption and biological flocculation), and resuspension. Minerals tend to adsorb negatively charged MPs while algae aggregates have a preference for positively charged MPs. The wetlands vegetation can trap MPs and affect their migration. In water matrices, MPs are ingested by organisms and integrated into sediments, which makes them seem undetectable in the wetland ecosystem. Photodegradation and microbial degradation can further reduce the MPs in size. Although recent research has increased, we are still searching for a methodological harmonization of the detection practices and exploring the migration rules and fate patterns of MPs. Our work is the first comprehensive review of the source, distribution, migration, and fate of MPs in wetland ecosystems. It reveals the uniqueness of wetland habitat in the research of MPs and indicates the potential of wetlands acting as sources or sinks for MPs.

Characterization of microplastics in mangrove sediment of Muara Angke Wildlife Reserve, Indonesia

An investigation of microplastic abundance and its characteristics was conducted in Muara Angke Wildlife Reserve, a relic mangrove forest in the Jakarta metropolitan, to contribute to marine microplastics' national data inventory. Microplastics were found in all the stations, with an average of 28.09 ± 10.28 particles per kg of dry sediment (n kg^-1). Sediments in the outside mangrove area contained more microplastics than the inside area. Foam form was the most dominant in all the samples and was found more abundant on the outside. More than half of microplastics were of size <1000 μm, and nearly 50% were polystyrenes. This polymer is widely used for food packaging, which is prone to be fragmented. Polypropylene and polyethylene form another 50% of microplastics, which are widely used for textiles and fishing gears. As Jakarta is the largest city in Indonesia, this microplastic dataset may be the benchmark for other mangroves around the country.

Microplastics pollution in mangrove ecosystems: A critical review of current knowledge and future directions

Over the last decade, microplastics (MPs, plastic particles <5 mm) as emerging contaminants have received a great deal of international attention, not only because of their continuous accumulation in both marine and terrestrial environment, but also due to their serious threats posed to the environment. Voluminous studies regarding sources, distribution characterization, and fate of MPs in the different environmental compartments (e.g., marine, freshwater, wastewater, and soil) have been reported since 2004, whereas MPs pollution in unique marine ecosystems (e.g., coastal mangrove habitat) receives little scientific attention. Mangrove ecosystem, an important buffer between the land and the sea, has been identified as a potential sink of MPs caused by both marine and land-based activities. Moreover, the source and distribution characteristics of MPs in this ecosystem are significantly different from other coastal habitats, mainly owing to its unique features of high productivity and biomass. With the impetus to provide a more integrated view of MPs pollution in mangrove habitats, a literature review was conducted based on the existing studies related to this topic. This is the first review to present the current state of MPs pollution in mangrove ecosystems, specially including (i) the possible sources of MPs in mangrove areas and their pathways entering into this habitat; (ii) MPs pollution in the different mangrove compartments (including surface seawater, sediments, and biotas); and (iii) factors influencing MPs distribution in mangrove areas. Toward that end, the research gaps are proposed to guide for future research priorities.

Degradation of common polymers in sewage sludge purification process developed for microplastic analysis

To enable and/or facilitate analysis of microplastics from environmental samples, a purification process is required to reduce the organic matter content. The development of such process has as one main concern, besides achieving efficient organic matter reduction, the preservation of the microplastics. In this study, a three-step method for sewage sludge purification was proposed employing sodium dodecyl sulfate and hydrogen peroxide. The effects of the purification method on seven polymers (LLDPE, HDPE, PP, PS, PET, PA66 and SBR) were evaluated in terms of mass change, surface characteristics, mechanical properties, thermal properties and functional groups change. It was also assessed how the polymers were affected by the purification chemicals without the presence of sewage sludge. The purification process led to changes in all tested plastics, but in different intensities. LLDPE, HDPE, PP, PS and PET did not suffer considerable degradation. PET was more affected by hydrolysis than oxidation. On the other hand, the integrities of PA66 and SBR were noticeably affected. The effects of the purification process were considered to be due to the plasticizer behavior of water and oxidation on PA66 and loss of filler and oxidation on SBR. For both polymers there was a reduction on the tensile strength of around 50-60% after the purification, indicating they could be prone to fragmentate into smaller pieces along the process. After purification, PA66 also started to decompose at a temperature around 10 °C lower comparing to virgin samples. Except for SBR, the presence of sewage sludge and its oxidation was more harmful to the polymers than the purification chemicals without the presence of sewage sludge. This study serves as an evaluation of the effects of the purification process on the degradation of microplastics and a methodology for such assessment when designing a purification process.

Sample Preparation Techniques for the Analysis of Microplastics in Soil—A Review

Although most plastic pollution originates on land, current research largely remains focused on aquatic ecosystems. Studies pioneering terrestrial microplastic research have adapted analytical methods from aquatic research without acknowledging the complex nature of soil. Meanwhile, novel methods have been developed and further refined. However, methodical inconsistencies still challenge a comprehensive understanding of microplastic occurrence and fate in and on soil. This review aims to disentangle the variety of state-of-the-art sample preparation techniques for heterogeneous solid matrices to identify and discuss best-practice methods for soil-focused microplastic analyses. We show that soil sampling, homogenization, and aggregate dispersion are often neglected or incompletely documented. Microplastic preconcentration is typically performed by separating inorganic soil constituents with high-density salt solutions. Not yet standardized but currently most used separation setups involve overflowing beakers to retrieve supernatant plastics, although closed-design separation funnels probably reduce the risk of contamination. Fenton reagent may be particularly useful to digest soil organic matter if suspected to interfere with subsequent microplastic quantification. A promising new approach is extraction of target polymers with organic solvents. However, insufficiently characterized soils still impede an informed decision on optimal sample preparation. Further research and method development thus requires thorough validation and quality control with well-characterized matrices to enable robust routine analyses for terrestrial microplastics.