Sources, concentrations, distributions, fluxes and fate of microplastics in a hypersaline lake: Maharloo, south-west Iran

Unveiling microplastics pollution in a subtropical rural recreational lake: A novel insight

While global attention has been primarily focused on the occurrence and persistence of microplastics (MP) in urban lakes, relatively little attention has been paid to the problem of MP pollution in rural recreational lakes. This pioneering study aims to shed light on MP size, composition, abundance, spatial distribution, and contributing factors in a rural recreational lake, 'Nikli Lake' in Kishoreganj, Bangladesh. Using density separation, MPs were extracted from 30 water and 30 sediment samples taken from ten different locations in the lake. Subsequent characterization was carried out using a combination of techniques, including a stereomicroscope, Fourier transform infrared spectroscopy (FTIR) and field emission scanning electron microscopy (FE-SEM). The results showed a significant prevalence of MPs in all samples, with an average amount of 109.667 ± 10.892 pieces/kg3 (dw) in the sediment and 98.167 ± 12.849 pieces/m3 in the water. Small MPs (<0.5 mm), fragments and transparent colored particles formed the majority, accounting for 80.2%, 64.5% and 55.3% in water and 78.9%, 66.4% and 64.3% in sediment, respectively. In line with global trends, polypropylene (PP) (53%) and polyethylene (PE) (43%) emerged as the predominant polymers within the MPs. MP contents in water and sediment showed positive correlations with outflow, while they correlated negatively with inflow and lake depth (p > 0.05). Local activities such as the discharge of domestic sewage, fishing waste and agricultural runoff significantly influence the distribution of polypropylene. Assessment of pollution factor, pollution risk index and pollution load index values at the sampling sites confirmed the presence of MPs, with values above 1. This study is a baseline database that provides a comprehensive understanding of MP pollution in the freshwater ecosystem of Bangladesh, particularly in a rural recreational lake. A crucial next step is to explore ecotoxicological mechanisms, legislative measures and future research challenges triggered by MP pollution.

Microplastics in Asian rivers: Geographical distribution, most detected types, and inconsistency in methodologies

Microplastics pose a significant environmental threat, with potential implications for toxic chemical release, aquatic life endangerment, and human food chain contamination. In Asia, rapid economic growth coupled with inadequate waste management has escalated plastic pollution in rivers, positioning them as focal points for environmental concern. Despite Asia's rivers being considered the most polluted with plastics globally, scholarly attention to microplastics in the region's freshwater environments is a recent development. This study undertakes a systematic review of 228 scholarly articles to map microplastic hotspots in Asian freshwater systems and synthesize current research trends within the continent. Findings reveal a concentration of research in China and Japan, primarily investigating riverine and surface waters through net-based sampling methods. Polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET) emerge as the predominant microplastic types, frequently observed as fibers or fragments. However, the diversity of sampling methodologies and reporting metrics complicates data synthesis, underscoring the need for standardized analytical frameworks to facilitate comparative analysis. This paper delineates the distribution of microplastic hotspots and outlines the prevailing challenges and prospects in microplastic research within Asian freshwater contexts.

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

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

Leakage of plastics and other debris from landfills to a highly protected lake by wintering gulls

GENERAL CONTEXT

Gulls ingest plastic and other litter while foraging in open landfills, because organic matter is mixed with other debris. Therefore, gulls are potential biovectors of plastic pollution into natural habitats, especially when they concentrate in wetlands for roosting.

NOVELTY

We quantified, for the first time, the flow of plastic and other anthropogenic debris from open landfills to a natural lake via the movement of gulls. We focused on Fuente de Piedra, an inland closed-basin lake in Spain that is internationally important for biodiversity.

METHODOLOGY

In 2022, we sampled gull pellets regurgitated in the lake by lesser black-backed gulls Larus fuscus that feed on landfills, as well as their faeces, then characterized and quantified debris particles of ≥0.5 mm. By combining GPS and census data from 2010 to 2022, together with plastic quantification based on FTIR-ATR analysis, we estimated the average annual deposition of plastic and other debris by the wintering gull population into the lake.

MAIN RESULTS

86 % of pellets contained plastics, and 94 % contained other debris such as glass and textiles. Polyethylene (54 %), polypropylene (11.5 %) and polystyrene (11.5 %) were the main plastic polymers. An estimated annual mean of 400 kg of plastics were moved by gulls into the lake. Only 1 % of plastic mass was imported in faeces.

DISCUSSION

Incorporating the biovectoring role of birds can provide a more holistic view of the plastic cycle and waste management. Biovectoring is predictable in sites worldwide where gulls and other waterbirds feed in landfills and roost in wetlands. We discuss bird deterrence and other ways of mitigating debris leakage into aquatic ecosystems.

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.

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.

A review of microplastic threat mitigation in Asian lentic environments

Microplastic (MP) pollution has evolved into a significant worldwide environmental concern due to its widespread sources, enduring presence, and adverse effects on lentic ecosystems and human well-being. The growing awareness of the hidden threat posed by MPs in lentic ecosystems has emphasized the need for more in-depth research. Unlike marine environments, there remain unanswered questions about MP hotspots, ecotoxic effects, transport mechanisms, and fragmentation in lentic ecosystems. The introduction of MPs represents a novel threat to long-term environmental health, posing unresolved challenges for sustainable management. While MP pollution in lentic ecosystems has garnered global attention due to its ecotoxicity, our understanding of MP hotspots in lakes from an Asian perspective remains limited. Hence, the aim of this review is to provide a comprehensive analysis of MP hotspots, morphological attributes, ecotoxic impacts, sustainable solutions, and future challenges across Asia. The review summarizes the methods employed in previous studies and the techniques for sampling and analyzing microplastics in lake water and sediment. Notably, most studies concerning lake microplastics tend to follow the order of China > India > Pakistan > Nepal > Turkey > Bangladesh. Additionally, this review critically addresses the analysis of microplastics in lake water and sediment, shedding light on the prevalent net-based sampling methods. Ultimately, this study emphasizes the existing research gaps and suggests new research directions, taking into account recent advancements in the study of microplastics in lentic environments. In conclusion, the review advocates for sustainable interventions to mitigate MP pollution in the future, highlighting the presence of MPs in Asian lakes, water, and sediment, and their potential ecotoxicological repercussions on both the environment and human health.

Depth profiles of microplastics in sediments from inland water to coast and their influential factors

Microplastics, plastic particles with a size smaller than 5 mm, are widely observed in the global environments and pose a growing threat as they accumulate and affect the environments in numerous ways. These particles can be transported from inland water to coast and disperse from surface water to deep sediments, especially the latter, while knowledge of the hidden microplastics in sediment layers is still lacking. Understanding the characteristics and behavior of microplastics in deep sediments from inland water to coast is crucial for estimating the present and future global plastic budget from land to seas. Herein, present knowledge of microplastic sedimentation from inland water to coast is reviewed, with a focus on the physical characteristics of microplastics and environmental factors that affect sedimentation. The abundance, shape, composition, and timeline of microplastics in sediment layers in rivers, floodplains, lakes, estuaries and coastal wetlands are presented. The abundance of microplastics in sediment layers varies across sites and may exhibit opposite trends along depth, and generally the proportion of relatively small microplastics increases with depth, while less is known about the vertical trends in the shape and composition of microplastics. Timeline of microplastics is generally linked to the sedimentation rate, which varies from millimeters to centimeters per year in the reviewed studies. The spatiotemporal characteristics of microplastic sedimentation depend on the settling and erosion of microplastics, which are determined by two aspects, microplastic characteristics and environmental factors. The former aspect includes size, shape and density influenced by aggregation and biofouling, and the latter includes dynamic forces, topographic features, bioturbation and human activities. The comprehensive review of these factors highlights the needs to further quantify the characteristics of microplastic sedimentation and explore the role of these factors in microplastic sedimentation on various spatiotemporal scales.

Microplastics identification in water by TGA-DSC Method: Maharloo Lake, Iran

Nowadays, one of the biggest challenges is the lack of coordination between the microplastic identification methods used by researchers. To advance our global understanding of microplastic contamination and address the knowledge gaps, we require acceptable or similar identification methods or instruments designed to support the quantitative characterization of the microplastics data. In the current study, we focused on the thermogravimetric analysis (TGA) with differential scanning calorimetry (DSC) method which is usually used experimentally by other researchers, while we tried to look at this method in a real aquatic environment, Maharloo Lake and its Rivers. A number of 22 sites were chosen for sampling microplastics from water. The mean and median of total organic matter percentage for rivers samples (mean = 88%;median = 88%) was similar to the Maharloo lake (mean = 88.33%; median = 89%), suggesting the existence of a robust potential sink. The differentiation of the organic matter part into labile (e.g., carbon aliphatic and polysaccharides), recalcitrant (e.g., aromatic compounds and most plastics), and refractory fractions was implemented and the results indicated that labile organic matter was dominant in both the lake and the rivers, while recalcitrant and refractory fractions were lower. The river's average labile and refractory fractions were similar to the lake. Although the overall results of the study show combining TGA techniques with other analytical procedures can improve the technical quality of polymers, interpreting the complex information of those measurements requires a high level of expertise and the technology is still maturing.

Environmental fate of microplastics in an urban river: Spatial distribution and seasonal variation

Rivers are recognized as an important pathway for transport of microplastics (MPs) from land to sea, but limited information is available on the spatial distribution and seasonal variation of riverine MPs from upper reaches to estuaries. Such information is critical for source apportionment and development of effective management measures for riverine MPs. To fill the knowledge gap, we investigated the occurrence of MPs in surface water along an urban river in Guangzhou, southern China in wet and dry seasons. The abundances of MPs from 16 sampling sites in the wet and dry seasons varied from 0.123 to 1.84 particles m^-3 and from 0.046 to 4.21 particles m^-3, respectively. The spatial distribution of MP abundances showed an increasing trend from upstream to midstream and a decreasing trend from midstream to downstream and estuaries. The abundances of MPs peaked at the midstream, which is surrounded by a highly urbanized region with high population density (∼2530 persons per km²). The large surface water runoff during the wet season elevated the MP abundance in riverine water, except for that flowing through the central urban area where the abundance of MPs collected in the dry season was higher than that in the wet season. This was mainly ascribed to the large input from extensive anthropogenic activities and slow water flow rate in urban areas. The estimated monthly riverine MP fluxes from Humen, Hongqili, and Jiaomen were 7.42, 2.38, and 2.3 billion particles, respectively, in the wet season, and 0.86, 0.71, and 0.19 billion particles, respectively, in the dry season. An increase of riverine MP fluxes from Humen, Hongqili, and Jiaomen in the past three years was evident. The results from the present study provide valuable information for source apportionment of riverine MPs and support the initialization of possible MPs controlling measures.

Distribution of microplastics in the catchment region of Pallikaranai marshland, a Ramsar site in Chennai, India

Microplastics are persistent toxic pollutants, detected in different environmental compartments. Numerous studies on the characteristics and distribution of microplastics present in different environmental matrices are being carried out. However, limited studies have been performed in environmental systems like eco-sensitive freshwater marshlands. Therefore, to enrich the existing knowledge and understanding, this current study has analysed the distribution and characteristics of microplastics present in the catchment region of Pallikaranai marshland, Chennai, India. Both surface water and sediment samples were contaminated with microplastics in the range of 740-2826 items/m³and 700 to 5833 items/kg of dry sediment, respectively. Compared to other shapes, fibrous microplastics were predominant in most of the surface water (n = 11) and sediment (n = 8) samples. The abundant presence of smaller microplastics (<1 mm) in the surface water suggests elevated impacts on the aquatic species owing to their higher bioavailability. Elevated anthropogenic activities and frequent movement of people in urban and residential areas were noted to possibly influence the spatial distribution of microplastics. Furthermore, heavy metals' occurrence on microplastics was investigated using X-Ray Fluorescence Analyser (XRF) and Zn, Fe, Ti, and Ni are the commonly detected (>50% of the samples) elements. The estimated average pollution load index of 2.5 indicates the polluted state of Pallikaranai catchment region.

Variation of microplastics in the shore sediment of high-altitude lakes of the Indian Himalaya using different pretreatment methods

Microplastics pollution is a growing environmental concern. However, microplastics studies in high altitude remote lakes are scarce. In this study, microplastics pollution was assessed in the shore sediment of three high altitude lakes in Ladakh of the Indian Himalaya, namely Pangong Lake, Tsomoriri Lake and Tsokar Lake. Sampling of lakes shore sediment was performed in August 2019. Two different pretreatment methods were implemented with sediment samples from same sites, resulting two sets of samples. One set of samples was pretreated utilizing enzymatic degradation together with Fenton reactions. Another set of samples from the same sites were pretreated with 30 % hydrogen peroxide (H₂O₂) and Fenton reaction. Enzymatically pretreated samples resulted in higher microplastics concentrations than the set of H₂O₂ pretreated samples, which indicated that microplastics concentrations in sediment samples varies even among samples from the same site and that the pretreatment procedure may impact on the reported microplastics concentrations. Considering both sets of samples, microplastic concentration was 160-1000 MP/kg dw in Pangong Lake, 960-3800 MP/kg dw in Tsomoriri Lake, and 160-1000 MP/kg dw in Tsokar Lake. Blank correction based on the limit of detection and the limit of quantification indicated that microplastics concentrations at some sites of the studied lakes are higher than the limit of detection and the limit of quantification. The findings of this study indicated that the studied lakes in the Indian Himalaya are contaminated with microplastics. In addition, the comparison of microplastics using different pretreatment methods illustrated the importance of harmonization of microplastics studies to enable a reliable comparison among microplastics data. Therefore, this study contributes towards an assessment of microplastics in the high-altitude lakes in Indian Himalaya. The findings attributed towards clearer understanding regarding the need of harmonization of pretreatment methods and demonstrated the importance of reporting complete information in microplastics research.