Microplastic pollution in freshwater systems in Southeast Asia: contamination levels, sources, and ecological impacts

Microplastics and nanoplastics co-exposure modulates chromium bioaccumulation and physiological responses in rats

The environmental fragmentation of plastics generates a mixture of plastic particles of various sizes, which frequently co-occur with other mobile and persistent environmental pollutants. Despite the prevalence of such scenarios, the interaction between micro- and nanoplastics (MNPs) and their combined effects with environmental pollutants, such as highly toxic hexavalent chromium (Cr(VI)), remain almost entirely unexplored in mammalian species. This study demonstrated that nanoplastic and microplastic particles co-aggregate and together influence Cr bioaccumulation patterns and related physiological alterations in rats. Following a four-week repeated intragastric exposure of Wistar rats to MNPs and Cr(VI), either alone or in combination, MNPs significantly enhanced Cr bioaccumulation in the liver, heart, brain, and skin. Under co-exposure conditions, Cr(VI) was the primary driver of cellular effects observed in the blood, including shifts in immune cell subpopulations (e.g., neutrophils, lymphocytes) and alterations in red blood cell indices, while serum biochemistry reflected limited physiological stress. MNPs per se decreased creatine kinase activity and increased cholesterol levels. In summary, polystyrene MNPs increase Cr(VI) distribution and bioavailability, but co-exposure does not uniformly exacerbate toxicity. Instead, their interaction may selectively alter physiological responses, emphasizing the need for a deeper understanding of their combined effects and potential health risks.

Sex differences in cardiac fibrosis induced by gestational exposure to polystyrene nanoplastics in mice offspring

The increasing accumulation of plastics in the environment has raised concerns regarding their potential health hazards. Nanoplastics (NPs) can get transported across the placental barrier, resulting in detrimental effects on developing offspring. To date, the effects of maternal exposure to NPs during pregnancy on the cardiac toxicity in adult offspring have not been conclusively evaluated. Herein, the potential for cardiac injury in the progeny of adult mice that were gestationally exposed to 80 nm polystyrene NPs (PS-NPs) at different doses (0, 0.5, 1, and 5 µg µL-1) through oropharyngeal aspiration was investigated. Gestational exposure to PS-NPs resulted in cardiac fibrosis and cardiomyocyte apoptosis, and induced an increase in malondialdehyde (MDA) levels in adult offspring hearts, which were sex-specific and dose-dependent. The mRNA expression levels of estrogen receptor (ER)-related genes, such as Esr1, Esr2, and GPER1, were found to be significantly decreased on exposure to low-dose PS-NPs but elevated on exposure to high-dose PS-NPs in offspring hearts. Furthermore, the magnitude of this elevation in male offspring significantly exceeded compared to that of the female offspring. Additionally, the expression levels of Esr2 and GPER1 in male offspring that were gestationally exposed to high-dose PS-NPs were found to be higher than those observed in female offspring. The observed sex difference in cardiac fibrosis may be correlated with oxidative stress and changes in ER-related gene expression in the offspring's heart. Overall, our study demonstrated that gestational PS-NP exposure induces significant cardiac injury in adult offspring, providing crucial data on the transgenerational effects of PS-NP exposure in mice.

First Evidence of Microplastic Ingestion by Riverine Fish From the Freshwater of Northwest Peninsular Malaysia

In a baseline study, we investigated microplastic contamination in fish from the Pinang and Kerian Rivers in Northwest Peninsular Malaysia. In recognition of the growing concern over microplastic pollution in aquatic environments, we aimed to assess the abundance and characteristics of microplastics ingested by various fish species. Fish samples were collected from local fishermen, followed by a digestion process using 10% potassium hydroxide (KOH). Microplastics were isolated and analyzed through visual examination and attenuated total reflectance Fourier transform infrared spectroscopy. The results revealed a high prevalence of microplastics, with Johnius borneensis and Oreochromis sp. exhibiting the highest abundance, averaging 48.6 and 42.8 microplastics/g, respectively. The predominant shapes were fibers (55.6%) and fragments (25.9%), with colors primarily transparent (48.19%) and black (30.12%). Our results indicate significant contamination levels in freshwater fish, emphasizing the need for further research and effective mitigation strategies. These findings provide crucial baseline data on microplastics in Malaysian freshwater ecosystems. Environ Toxicol Chem 2024;43:2189-2198. © 2024 SETAC.

Microplastics monitoring in freshwater systems: A review of global efforts, knowledge gaps, and research priorities

The escalating production of synthetic plastics and inadequate waste management have led to pervasive microplastic (MP) contamination in aquatic ecosystems. MPs, typically defined as particles smaller than 5 mm, have become an emerging pollutant in freshwater environments. While significant concern about MPs has risen since 2014, research has predominantly concentrated on marine settings, there is an urgent need for a more in-depth critical review to systematically summarize the current global efforts, knowledge gaps, and research priorities for MP monitoring in freshwater systems. This review evaluates the current understanding of MP monitoring in freshwater environments by examining the distribution, characteristics, and sources of MPs, alongside the progression of analytical methods with quantitative evidence. Our findings suggest that MPs are widely distributed in global freshwater systems, with higher abundances found in areas with intense human economic activities, such as the United States, Europe, and China. MP abundance distributions vary across different water bodies (e.g., rivers, lakes, estuaries, and wetlands), with sampling methods and size range selections significantly influencing reported MP abundances. Despite great global efforts, there is still a lack of harmonized analyzing framework and understanding of MP pollution in specific regions and facilities. Future research should prioritize the development of standardized analysis protocols and open-source MP datasets to facilitate data comparison. Additionally, exploring the potential of state-of-the-art artificial intelligence for rapid, accurate, and large-scale modeling and characterization of MPs is crucial to inform effective strategies for managing MP pollution in freshwater ecosystems.

First-of-Its-Kind: Nationwide meta-analysis of microplastic pollution and risk assessment in Thailand

Thailand ranks as the sixth largest contributor to global microplastic pollution, which is exacerbated by extensive plastic use. Despite rising concerns, no comprehensive review is available on microplastic contamination and its potential risk in Thailand. This review synthesised data on microplastic abundance and characteristics within the country from 118 peer-reviewed publications (2017-2024). We found predominant microplastic presence in crustaceans (1.69-160.15 items/g), followed by Mollusca (0.03-9.5 items/g) and fishes (0.01-28.17 items/g), with higher abundances in wastewater (4 × 102 to 6.09 × 105 items/m3) compared to that in freshwater (1.44-2.92 × 106 items/m3) and seawater (2.70 × 10-1 to 6.25 × 104 items/m3). Marine sediments (48.3-2.13 × 104 items/kg) also showed significantly higher microplastic concentrations than terrestrial sediments (3-2.92 × 103 items/kg). Predominant microplastics were identified as fibers (59.36% and 35.05% for biological and environmental samples, respectively) and fragments (24.14%, 30.68%) in blue (25.95%, 18.64%), and colourless/transparent (20.01%, 14.47%), primarily composed of polyethylene terephthalate (19.46%, 9.19%), nylon (3.23%, 9.99%), polypropylene (19.78%, 24.23%), and polyethylene (14.81%, 11.66%). The potential ecological risk was low in all ecosystems except for wastewater. Shrimp and fish were more susceptible to microplastics compared to other studies in the region. Additionally, the sources, transport, and pathways of microplastic pollution in Thailand's aquatic territories and the current measures and policies implemented by the government to address plastic pollution are discussed. This review has compiled up-to-date insights into the prevalence, distribution, and risks associated with microplastics, which is instrumental in formulating effective strategies for contaminant control and ultimately reducing plastic pollution.

Severe microplastic pollution risks in urban freshwater system post-landfill fire: A case study from Brahmapuram, India

To investigate the escalating issue of microplastic (MP), pollution in urban water bodies, this study focuses on the aftermath of the Brahmapuram landfill fire in Kochi, India, analyzing its impact on MP concentrations in nearby freshwater system. The study conducted sampling sessions at the landfill site immediately before and after the fire. Post-fire, findings demonstrated a substantial increase in MP concentrations in surface waters, with levels rising from an average 25793.33 to 44863.33 particles/m³, featuring a notable presence of larger, predominantly black MPs. Sediment samples showed no significant change in MP count, but there was a significant increase in mass concentration. SEM/EDS analysis revealed changes in surface morphology and elemental composition, suggesting thermal degradation. Risk assessment using the Microplastic Pollution Index (MPI) and Risk Quotient (RQ) methods indicated heightened MP pollution risk in surface water post-fire. Hierarchical cluster analysis revealed the landfill's proximity as a significant factor influencing MP characteristics in the aquatic system. The study highlights the escalated challenge of MP pollution in urban water bodies following environmental disasters like landfill fires, underscoring the urgent need for policy and environmental management strategies.

Southeast Asia's environmental challenges: emergence of new contaminants and advancements in testing methods

Emerging contaminants, including pharmaceuticals, personal care products, microplastics, and per- and poly-fluoroalkyl substances, pose a major threat to both ecosystems and human health in Southeast Asia. As this region undergoes rapid industrialization and urbanization, the increasing presence of unconventional pollutants in water bodies, soil, and various organisms has become an alarming concern. This review comprehensively examines the environmental challenges posed by emerging contaminants in Southeast Asia and recent progress in toxicity testing methods. We discuss the diverse range of emerging contaminants found in Southeast Asia, shedding light on their causes and effects on ecosystems, and emphasize the need for robust toxicological testing methods. This review is a valuable resource for researchers, policymakers, and environmental practitioners working to mitigate the impacts of emerging contaminants and secure a sustainable future for Southeast Asia.

Impact of flooding on microplastic abundance and distribution in freshwater environment: a review

Due to smaller particle size (0.1 µm-5 mm), non-biodegradable or slowly degradable nature, and high accumulation capacity in the environment, microplastics are becoming a cause of concern throughout the globe. The abundance and distribution of microplastics in aquatic compartments are strongly influenced by various natural and anthropogenic variables. Hydrodynamic conditions like flood events, caused due to extreme precipitation, accelerate the transport and settlement of microplastics in freshwater bodies. This review highlights the current literature which focuses on the effect of flooding on microplastic abundance, characterization, and distribution in freshwater environments worldwide. However, only limited research papers are identified through focused literature search, as this area of research is relatively new. Most of the studies reported increased and decreased abundance of microplastics in water and sediment samples, respectively, during post-flooding period with the exception of few studies. We also evaluate the post-flooding abundances of different morphological shape and polymer type of microplastics. Fragments, fibers, beads, and film were the most frequently reported microplastic shape and polystyrene, and polyethylene was the dominant polymer type found in freshwater environments. Future research should focus on more advanced techniques to understand microplastic fluxes under flood condition and the dominance of various natural and human-induced factors over one another in determining microplastic abundance. This will further enhance to mitigate microplastic pollution in freshwater environments.

Evaluation of vertical distribution characteristics of microplastics under 20 μm in lake and river waters in South Korea

Following the alarming reports of microplastic pollution in the marine environment, increased attention has been given to microplastics in other environmental media. Despite the attention, there is limited research available on the depth-distribution of microplastics in freshwater. Specifically, in the case of water sources used for drinking or tap, the height of intake facilities varies, and it is highly likely that there is a correlation between the vertical distribution of microplastics and these water intake structures. Further, because the size of microplastics varies widely in the environment, the commonly used sampling devices are not suitable for selectively extracting microplastics without causing cross-contamination. Thus, we developed a suitable device for microplastics of size 5-20 µm and studied microplastic distribution in freshwater at various depths by considering various types of microplastics and aqueous systems. Lake and river, two major water sources, were selected for the study of microplastics distribution in water system. The microplastic distribution characteristics in both water systems showed that polypropylene and polyethylene were the most abundant across all depths because of their production volume. Plastic types with higher density were found only at the lower layers, and polystyrene was found in the upper layers because of the environmental effects on its buoyancy caused pore diameter and surface area. The lake and river had higher microplastic distribution in the lower layer and upper layer, respectively. This was because the flow rate in river was higher than that of lake. The higher flow rate reduced the settling velocity in river. Thus, hydrodynamic stability influences the vertical distribution and concentrations of microplastics in the water systems. These results are expected to be used for understanding the behavioral characteristics of microplastics in water systems and to manage water sources.

Discovering untapped microbial communities through metagenomics for microplastic remediation: recent advances, challenges, and way forward

Microplastics (MPs) are ubiquitous pollutants persisting almost everywhere in the environment. With the increase in anthropogenic activities, MP accumulation is increasing enormously in aquatic, marine, and terrestrial ecosystems. Owing to the slow degradation of plastics, MPs show an increased biomagnification probability of persistent, bioaccumulative, and toxic substances thereby creating a threat to environmental biota. Thus, remediation of MP-pollutants requires efficient strategies to circumvent the mobilization of contaminants leaching into the water, soil, and ultimately to human beings. Over the years, several microorganisms have been characterized by the potential to degrade different plastic polymers through enzymatic actions. Metagenomics (MGs) is an effective way to discover novel microbial communities and access their functional genetics for the exploration and characterization of plastic-degrading microbial consortia and enzymes. MGs in combination with metatranscriptomics and metabolomics approaches are a powerful tool to identify and select remediation-efficient microbes in situ. Advancement in bioinformatics and sequencing tools allows rapid screening, mining, and prediction of genes that are capable of polymer degradation. This review comprehensively summarizes the growing threat of microplastics around the world and highlights the role of MGs and computational biology in building effective response strategies for MP remediation.

Seasonal pollution and surface characteristics of microplastics in surface water in the Wanzhou section of the Three Gorges Reservoir, China

The pollution of freshwater environments with microplastics (MPs) has attracted increasing attention owing to their threats to aquatic ecosystems and human health. Here, we sampled and analyzed MPs from mainstream, tributary, and backwater areas in the Wanzhou section of the Three Gorges Reservoir (TGR) in impoundment and flood periods. Microplastic pollution was the most severe in the backwater areas. The average abundance of MPs reached the highest value in the flood period (5.27±3.47×107 items km-2), which was 3-5 times that in the impoundment period. In the 0.3-5 mm size class, the 1-5 mm fraction was the most abundant, accounting for more than 81% in the flood period and 68% of the total MP particle abundance in the impoundment period in the mainstream and backwater areas. However, 0.3-1 mm MPs contributed more than 50% in the tributaries during the impoundment period. Polystyrene, polypropylene, and polyethylene MPs were detected in foam, fragment, sheet, and line-shaped MP particles. White, opaque, foamed polystyrene MPs contributed 32-81% to total MP particle abundance in the watershed. Microplastic particle surfaces showed signs of damage and oxidation, and ten different elements were found. Oxygen was clustered on the surface of foam and fragment MPs. Microplastic pollution was severe in the Wanzhou watershed. Especially in the backwater areas, oxidized MPs of variable shapes derived mainly from surface runoff in the flood period and sewage discharge in the impoundment period were abundant. The results of this study contribute to understanding seasonal pollution patterns and surface characteristics of MPs in the TGR and similar watersheds.

Microplastic concentrations in river water and bed sediments in a tropical river: implications for water quality monitoring

Recent increase in awareness of the extent of microplastic contamination in marine and freshwater systems has heightened concerns over the ecological and human health risks of this ubiquitous material. Assessing risks posed by microplastic in freshwater systems requires sampling to establish contamination levels, but standard sampling protocols have yet to be established. An important question is whether sampling and assessment should focus on microplastic concentrations in the water or the amount deposited on the bed. On three dates, five replicated water and bed sediment samples were collected from each of the eight sites along the upper reach of the Semenyih River, Malaysia. Microplastics were found in all 160 samples, with mean concentrations of 3.12 ± 2.49 particles/L in river water and 6027.39 ± 16,585.87 particles/m² deposited on the surface of riverbed sediments. Fibres were the dominant type of microplastic in all samples, but fragments made up a greater proportion of the material on the bed than in the water. Within-site variability in microplastic abundance was high for both water and bed sediments, and very often greater than between-site variability. Patterns suggest that microplastic accumulation on the bed is spatially variable, and single samples are therefore inadequate for assessing bed contamination levels at a site. Sites with the highest mean concentrations in samples of water were not those with the highest concentrations on the bed, indicating that monitoring based only on water samples may not provide a good picture of either relative or absolute bed contamination levels, nor the risks posed to benthic organisms.

Dispersal and transport of microplastic particles under different flow conditions in riverine ecosystem

Microplastic (MP) pollution is a global issue owing to its potential threats to ecosystems and human health. MP pollution in river ecosystems is widely investigated, but the transport process under different hydrological conditions remain unclear. In this study, an approach of particle tracking in conjunction with hydrodynamic modeling was developed to investigate the dispersal and transport processes of microplastic particles in riverine ecosystem. The concentration and dispersal pattern of polyamide (PA), polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyethylene terephthalate (PET) particles under base flow and flood events with recurrence intervals of 10-year, 20-year and 50-year were identified. Results indicated that rainfall intensity had a significant impact on the microplastic transport in rivers. Higher suspension concentration and lower sedimented concentration were observed in high flow periods, and the sedimented concentration showed a slow increasing trend in the flood recession stage. High water velocity facilitated the microplastic particles to be migrated for a longer distance, and high water flow was conducive to transport more microplastics from source points. Besides, microplastic particles with high density had worse mobility in water and more prone to deposition. PET were likely to be transported for a relatively shorter distance, while PP had higher mobility and took less time to reach the same simulation point. This study put forward an effective approach to understand the transport of MPs in the river. The results obtained are useful to identify pollution hotspots and track pollution paths.

Microplastics in ASEAN region countries: A review on current status and perspectives

A literature assessment was conducted to determine the current state of microplastics research in ASEAN countries focusing on 1) microplastics in water, sediment, and water organisms; 2) microplastics' sources and dispersion; and 3) microplastics' environmental consequences, including human toxicity. ASEAN countries contributed only about 5 % of the global scholarly papers on microplastics, with Indonesia contributing the most followed by Malaysia and Thailand. The lack of standard harmonized sampling and processing methodologies made comparisons between research difficult. ASEAN contributes the most to plastic trash ending up in the ocean, indicating a need for more work in this region to prevent plastic pollution. Microplastics are found in every environmental compartment; however, their distribution and environmental consequences have not been sufficiently investigated. There are very few studies on microplastics in the human blood system as well as respiratory organs like the lungs, indicating that more research is needed.

Priorities to inform research on marine plastic pollution in Southeast Asia

Southeast Asia is considered to have some of the highest levels of marine plastic pollution in the world. It is therefore vitally important to increase our understanding of the impacts and risks of plastic pollution to marine ecosystems and the essential services they provide to support the development of mitigation measures in the region. An interdisciplinary, international network of experts (Australia, Indonesia, Ireland, Malaysia, the Philippines, Singapore, Thailand, the United Kingdom, and Vietnam) set a research agenda for marine plastic pollution in the region, synthesizing current knowledge and highlighting areas for further research in Southeast Asia. Using an inductive method, 21 research questions emerged under five non-predefined key themes, grouping them according to which: (1) characterise marine plastic pollution in Southeast Asia; (2) explore its movement and fate across the region; (3) describe the biological and chemical modifications marine plastic pollution undergoes; (4) detail its environmental, social, and economic impacts; and, finally, (5) target regional policies and possible solutions. Questions relating to these research priority areas highlight the importance of better understanding the fate of marine plastic pollution, its degradation, and the impacts and risks it can generate across communities and different ecosystem services. Knowledge of these aspects will help support actions which currently suffer from transboundary problems, lack of responsibility, and inaction to tackle the issue from its point source in the region. Being profoundly affected by marine plastic pollution, Southeast Asian countries provide an opportunity to test the effectiveness of innovative and socially inclusive changes in marine plastic governance, as well as both high and low-tech solutions, which can offer insights and actionable models to the rest of the world.

Dual drive acute lethal toxicity of methylene blue to Daphnia magna by polystyrene microplastics and light

Microplastics (MPs) can adsorb and influence the toxicity of traditional pollutants significantly. Although the complex toxicity of MPs and molecular pollutants were frequently reported, rare work has been done on the influence of MPs on the phototoxicity of photosensitive pollutants under light illumination condition. Herein, polystyrene microplastics (PS) (~1 μm in diameter, 5.0 mg/L) was used as a model MP to investigate its influence on the phototoxicity of a soluble blue dye, methylene blue (MB) using Daphnia magna as a model organism. The results indicate that PS could adsorb MB effectively and quickly, thus led to concentrated MB on PS/water interface. D. magna ingested MB-adsorbed PS very quickly within tens of minutes. Although MB or PS alone led to negligible lethal phototoxicity to D. magna, PS significantly enhanced the lethal phototoxicity of MB (0.25 mg/L) to D. magna after light illumination (10 h) with the survival rate decreased by 63.3 % compared with the control in the dark. Further, the phototoxicity of MB was found positively consistent with PS concentration from 0.50 mg/L to 7.50 mg/L. The singlet oxygen fluorescence assay indicates that the presence of PS did not increase the total amount of singlet oxygen in the aquatic environment but increased the local concentration in the gut area via non-selective ingestion of D. magna. High level singlet oxygen generated in the gut might possibly be the main reason that led to the massive death of D. magna. Surface adsorption of photosensitive pollutants may transform inert MPs into persistent solid sources of singlet oxygen production and become a new potential lethal threat to aquatic small organisms and ecological equilibrium. This kind of MPs and light dual drive phototoxicity of photosensitive pollutants needs to paid more attention in understanding the uncertain ecological risk of MPs.

Relative contributions of different local sources to riverborne microplastic in a mixed landuse area within a tropical catchment

Information on the relative contributions of microplastics coming from different sources is important to help prioritise measures to reduce river contamination levels and limit human and ecological health risks. This paper reports on work which aimed to quantitatively assess the relative concentrations and types of microplastic delivered from differed sources to a second order river. The study was undertaken in a mixed landuse area within a rapidly urbanising catchment in Malaysia. Over a six-week period, water samples were collected from road culverts and drains in residential and industrial areas across the area to assess microplastic concentrations, while inputs from atmospheric deposition and wastewater treatment plants (WWTPs) were also quantified. Microplastic fibres and fragments were the dominant material in all sources, with the majority consisting of styrene-butadiene rubber and nylon. Culverts draining main roads were the main contributor to riverborne microplastic, delivering 42.20 ± 35.29 particles/L directly to the river channel. Road inputs were up to seven times greater than those from residential (8.53 ± 9.91 particles/L) and industrial (5.67 ± 4.88 particles/L) areas. The five WWTPs had removal efficiencies of between 30.95 ± 5.51% and 69.94 ± 22.17%, with their outflows delivering microplastics to the river in concentrations similar to those in uncontrolled residential and industrial drains. Atmospheric deposition across the study area was estimated to be 76.07 ± 32.85 particles/m²/day (=8.35 ± 5.11 particles/L). Mitigation strategies in the study area should focus on improving management of water draining roads, and re-routing discharges from domestic and industrial areas to WWTPs rather than allowing them to flow directly to the river. The low efficiencies of some of the WWTPs are not unusual, and indicate the need for additional water treatment to deal with microplastic present in wastewater.