Distribution and Characteristics of Microplastics in

Indian Water Bodies: Present Understanding and Future Challenges

Babita Markande, Shubhra Sinha, Suryakant Manikpuri, Rajiv Nayan, Vikash Patel, Khushi Ganjir, Manas Kanti Deb*

School of Studies in Chemistry, Pt. Ravishankar Shukla University, Raipur, Chhattisgarh, India

Abstract

Microplastics (MPs), defined as plastic particles smaller than 5 mm, have become emerging environmental contaminants due to their adverse effects on aquatic ecosystems. In India, increasing plastic production coupled with inadequate recycling practices has significantly contributed to MP pollution, attracting growing scientific attention in recent years. This review presents a comprehensive assessment of MPs in Indian freshwater systems and examines their potential impacts on ecosystem services. Most existing studies have primarily concentrated on the occurrence and abundance of MPs, while limited information is available regarding their sources, transport mechanisms, environmental behaviour, and long-term ecological consequences. Current findings indicate that white-colored Fibres and fragments, mainly composed of polypropylene (PP), polyethylene terephthalate (PET), and   polyethylene (PE), are the predominant MP types detected in Indian freshwater environments. Analytical techniques vary according to particle size, with larger MPs (>500 μm) commonly identified using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), whereas smaller particles (<500 μm) are generally characterized through μ-FTIR imaging. However, inconsistencies in sampling strategies and analytical methodologies hinder reliable comparisons among studies. Therefore, future research should emphasise the development of standardized protocols, rigorous contamination control, long-term monitoring programs, advanced analytical methods, and expand ed investigations of freshwater ecosystems, particularly in central India, to enhance understanding and   facilitate effective management of MP pollution.

Keywords: Microplastics, India, Standardized analytical methods, polypropylene, polyethylene terephthalate, polyethylene

1. Introduction

Plastics are versatile polymer-based materials synthesized through the polymerization of organic monomers. Their lightweight characteristics and high flexibility allow them to be molded into a wide variety of shapes and sizes, making them useful as both synthetic and semi-synthetic materials (Chakraborty et al., 2023; Ebere et al., 2019). In recent decades, the production and accumulation of plastic waste have increased at an alarming rate worldwide. According to the Plastics Europe report (2023), global plastic production reached approximately 4 × 10⁶ metric tons in 2022, with China, North America, and other Asian countries contributing the largest share. Despite the massive scale of production, effective waste management remains a major challenge, as less than 10% of the nearly seven billion tons of plastic waste generated globally has been recycled (Mushtak et al., 2024; Wu et al., 2023).

The continuous discharge and spread of plastic debris into the environment are expected to further intensify in the coming years, with estimates suggesting that plastic waste could reach nearly 250 million tons by 2025 (Murugan et al., 2023; Jambeck et al., 2015). This growing accumulation of plastic pollution poses serious environmental concerns and highlights the urgent need for improved recycling technologies and sustainable waste management strategies. Based on size, plastic debris is commonly classified into macroplastics, mesoplastics, and   MPs (Qiu et al., 2016). MPs represent the smallest fraction and are generally defined as plastic particles with dimensions less than 5 mm (Thompson et al., 2004). However, definitions vary slightly across standards and literature. For instance, ISO/TR 21960:2020(E) defines MPs as insoluble polymer particles ranging from 1 to 1000 μm (1 mm), whereas most studies consider a broader size range of 1 μm to 5 mm (Ghanadi et al., 2024; Ghanadi et al., 2023).

MPs comprise a wide variety of polymer types, including polypropylene (PP), polyethylene (PE), polyamide (PA), polyethylene terephthalate (PET), polystyrene (PS), polyurethane (PUR), polycarbonate (PC), rayon (RY), nylon (NY), and polyvinyl chloride (PVC). Among these, PE and   PS are most frequently detected in aquatic environments (Tiwari et al., 2019). Apart from particle size, MPs are also categorized according to their morphology and physical appearance. They are found in a variety of forms, including spheres such as beads, pellets, and granules; fibres like filaments and threads; as well as Films, Fragments, and   Foams. shown in Table 1, Spherical forms are typically associated with primary MPs, whereas fibres, fragments, and Films are predominantly derived from secondary sources. Colour variations are also significant, with MPs appearing as white, transparent, or translucent. Translucent particles constitute the largest proportion (approximately 47%), followed by yellow to brown (about 26%) and blue to green shades (around 9%), as shown in Figure 1 (Kavya et al., 2020; Covernton et al., 2019).

Table 1. Major Microplastic Polymers and Their Associated Shapes

Figure 1. Classification of MPs based on size, shape, type, and   colour

Figure 2. Sources of microplastics based on their origin

MPs are further categorized into primary and secondary types based on their origin, shown in Figure 2. Primary MPs are intentionally manufactured at sizes smaller than 5 mm and are commonly found in products such as textiles, pharmaceuticals, and personal care items, including toothpaste and exfoliating scrubs (Elkhatib & Oyanedel -Craver, 2020). In contrast, secondary MPs are generated through the degradation of larger plastic materials via processes such as mechanical abrasion, ultraviolet radiation, and microbial activity. It is widely recognised that secondary MPs constitute the majority of environmental MPs, originating from sources such as industrial plastic pellets, household waste, and other discarded plastic materials (Xu et al., 2019).

Because of their extremely small size, microplastics (MPs) have emerged as significant environmental and economic pollutants, contaminating a wide range of ecosystems such as aquatic environments, sediments, air, salt, biota, wastewater treatment systems, and even honey (Veerasingam et al., 2021; Xu et al., 2019). Their widespread occurrence has prompted numerous investigations into plastic pollution across different freshwater bodies, including rivers, lakes, and ponds (Upadhyay & Bajpai, 2024; Thandavamoorthy Rajeswari et al., 2023; Selvam et al., 2021).

The pollution of freshwater bodies by MPs is closely linked to the terrestrial environment (Gupta et al., 2023), particularly in areas where rivers intersect with urban centres. In these areas, factories and sewage discharge plastic pollutants into wastewater, which eventually ends up in nearby rivers and surface water through runoff from rain and irrigation in agricultural areas. This exacerbates the pollution, as MPs migrate into nearby water bodies (Du et al., 2021). This presence of MPs in marine and freshwater environments has sparked significant concern among scientists and the general public due to its adverse impacts on aquatic life (Elkhatib & Oyanedel-Craver, 2020). Furthermore, MPs can act as carriers for hazardous waterborne pollutants, thereby posing significant risks to aquatic organisms (Sinha et al., 2023; Saha et al., 2021). The ingestion of toxin-contaminated MPs may adversely affect living organisms and lead to bioaccumulation of harmful substances. In humans, MP particles have been detected in different tissues and organs, where they may interfere with immune system functions and contribute to various health-related disorders (Turkey & Upadhyay, 2021; Wang & Wang, 2018).

The identification and   characterization of MPs in aquatic environments remain technically challenging due to their small size and heterogeneous nature. Accurate detection typically involves a multistep analytical workflow, beginning with visual inspection or microscopic screening, followed by advanced instrumental techniques such as Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), Raman spectroscopy, pyrolysis–gas chromatography–mass spectrometry (Py-GC–MS), and thermal extraction desorption–gas chromatography–mass spectrometry (TED–GC–MS) (Du et al., 2021; Qiu et al., 2016; Neelavannan & Sen 2023; Primpke et al., 2020).

Plastic contamination has emerged as a significant environmental issue, particularly in densely populated countries such as India. The growing burden of plastic pollution has raised serious concerns regarding its impact on freshwater ecosystems, especially river systems that directly or indirectly sustain nearly one billion people across the Indian subcontinent. India is characterized by an extensive and complex hydrological network, including major rivers as well as lakes, ponds, canals, estuaries, floodplains, coastal waters, and marine environments (Gani et al., 2024; Kumar et al., 2024).

These freshwater systems are integral to India’s socio-economic framework, supporting agriculture, aquaculture, navigation, hydropower generation, and a wide range of industrial and commercial activities. However, increasing anthropogenic pressures have led to substantial environmental degradation. The discharge of untreated or inadequately treated wastewater from industrial, urban, and agricultural sources, along with urban runoff, has resulted in widespread contamination of both surface and groundwater resources. These waters are now burdened with diverse pollutants, including organic compounds, inorganic substances, and plastic-derived contaminants (Kumar et al., 2024; Malla-Pradhan et al., 2023).

 MPs have been widely reported in both freshwater and marine environments globally, with elevated concentrations of ten observed in densely populated urban regions. They have been detected across multiple environmental matrices, including precipitation, sewage sludge, treated wastewater effluents, and even drinking water. In recent years, research on microplastic pollution has expanded considerably, with a substantial proportion of studies focusing specifically on freshwater systems (Malla-Pradhan et al., 2023; Muthulakshmi et al., 2023).

MPs enter freshwater environments through a variety of pathways, including agricultural runoff, industrial effluents, fishing activities, tourism, atmospheric deposition, improper disposal of plastic waste, stormwater and road runoff, flooding events, wastewater treatment plant discharges, and domestic sewage. Despite the increasing global focus, studies investigating microplastic contamination in Indian freshwater systems remain limited (Gani et al., 2024; Neelavannan & Sen, 2023; Sonbhadra & Pandey, 2023; Vaid et al., 2021; Veerasingam et al., 2020).

Current research in India has primarily concentrated on MPs in freshwater bodies, sediments, and urban tropical ponds and lakes. Nevertheless, there exists a notable gap in comprehensive data regarding the distribution, abundance, and physicochemical characteristics of MPs, particularly in the water bodies of central India. Additionally, there is insufficient understanding of plastic waste mismanagement practices and the environmental factors governing the transport, fate, and dispersion of MPs.

Therefore, the current study aims to provide a comprehensive review of the available scientific literature on MPs in India's water bodies, with the aim of improving understanding of the impacts of MP pollution on ecosystem services associated with freshwater resources.

2. Potential Threat of MPs

 Extensive plastic pollution has resulted in the widespread distribution of MPs throughout aquatic ecosystems, enabling their penetration across biological barriers and ingestion by a wide range of aquatic organisms. Due to their extremely small size, MPs can be easily consumed by organisms at different trophic levels, including zooplankton, molluscs, fish, and other aquatic species (Kumar et al., 2024). The uptake and bioavailability of MPs are influenced by multiple factors, such as their size, shape, colour, density, surface properties, and mobility. In addition, organism-related characteristics, including feeding habits, morphology, and metabolic activity, also play a significant role in determining MP ingestion and accumulation (Sonbhadra & Pandey, 2023; Su et al., 2019). MPs are highly stable and persistent in the environment, resulting in long residence times once released into nature. Their continuous fragmentation into smaller particles increases their surface area and enhances their ability to adsorb toxic contaminants such as persistent organic pollutants (POPs), including benzo(a)pyrene (BaP), heavy metals, and other hydrophobic chemicals. Consequently, MPs act not only as pollutants themselves but also as carriers and vectors for hazardous substances, thereby amplifying their ecological toxicity (Kumar et al., 2024; Sonbhadra & Pandey, 2023; Mashirin & Chitra, 2022).

Once ingested, MPs may translocate across biological membranes and migrate within organisms through the gastrointestinal tract, gills, or lungs into the circulatory system, liver, kidney, and other tissues. The movement and toxicological effects of MPs vary depending on environmental conditions and species-specific physiological characteristics. Numerous studies have reported that MP ingestion can adversely affect aquatic organisms by impairing digestive efficiency, nutrient absorption, feeding behaviour, immune response, reproduction, and growth. In addition, exposure to MPs can induce oxidative stress, neurotoxicity, reduced predatory performance, increased mortality, and behavioural alterations, ultimately contributing to population decline in natural ecosystems (Kumar et al., 2024; Su et al., 2019).

The accumulation of MPs within aquatic organisms also raises significant concerns regarding food chain transfer and human health risks. Humans may consume MPs indirectly through contaminated seafood and aquatic food products, potentially leading to similar physiological and pathological abnormalities. The persistence and bioaccumulation of MPs therefore represent a serious threat to ecosystem stability, biodiversity, environmental quality, and public health (Kumar et al., 2024; Mashirin & Chitra, 2022).

Globally, increasing attention is being directed towards the environmental and ecological impacts of plastic debris and   MP contamination. India, one of the world’s major plastic consumers, generates approximately 8 million tons of plastic waste annually, of which nearly 5.7 million tons become waste each year. Improper plastic waste management, rapid urbanization, industrialization, and population growth have significantly contributed to MP contamination in Indian freshwater and marine environments (Verma et al. 2016).Top of Form

3. Bottom of FormStatus of Plastics in India

Plastic pollution has become a critical global environmental issue, with nearly 8–12 million tonnes of plastic waste entering marine environments every year as a result of inadequate waste management and improper disposal practices (Meijer et al., 2021; Jambeck et al., 2015).

In India, the problem has intensified due to rapid urbanization, increasing population density, industrial development, and rising plastic consumption.

 According to the Central Pollution Control Board (CPCB), India generates approximately 3846936 tonnes of plastic waste annually (CPCB Annual Report, 2021-22).

 Recognition of the growing environmental risks associated with plastic pollution has led to the implementation of several regulatory measures across the country. India was among the first nations to ban single-use plastics on ships in 2019, demonstrating early policy intervention toward plastic waste reduction. Prior to this, the state of Sikkim had already enforced a ban on single-use plastics in 1998, serving as a model for other Indian states. These initiatives eventually contributed to the nationwide restriction on single-use plastics introduced in 2022 (Neelavannan et al.2022; Wong et al., 2020).

The Indian plastics industry originated in the 1950s but began receiving significant governmental attention only during the 1970s. Since then, the sector has expanded rapidly and has become an important contributor to the national economy, supporting numerous industrial and commercial sectors. However, despite its economic significance, the plastics industry continues to face major challenges related to sustainable waste management, recycling efficiency, and the reduction of environmental impacts associated with plastic production and disposal.

4. Sampling procedure and   tools

Despite nearly two decades of research on MPs, there is still no standardized methodology for sample collection, pretreatment, identification, and quantification. This lack of standardization creates inconsistencies in analytical protocols, making it difficult to compare results across different studies. These variations mainly arise from differences in sampling methods, extraction techniques, and preservation approaches, shown in Figure 3, which are often selected based on the research objective, available resources, and the type of environmental matrix being studied. MPs have been reported in various freshwater compartments, including surface water, water columns, sediments, and aquatic organisms, and the sampling strategy is chosen accordingly. Generally, three main sampling approaches are used: selective sampling, bulk sampling, and volume-reduced sampling. Selective sampling involves directly collecting visible MPs from the environment, typically from shore sediments, and is suitable for larger particles (1–5 mm). Bulk sampling involves collecting the entire sample without reducing its volume, ensuring comprehensive analysis. In contrast, volume-reduced sampling involves collecting a portion of the sample during the sampling process, which is commonly applied to water samples to make handling and analysis more practical. These methodological differences highlight the need for standardized protocols to improve consistency and   reliability in microplastic research (Neelavannan & Sen, 2023; Veerasingam et al., 2020; Mendoza et al., 2019; Li et al., 2018).

Figure 3. The procedural steps involved in the sampling, extraction and   characterization processes of microplastics

4.1. Water

Several studies have investigated the occurrence and distribution of MPs along the Indian coast and in freshwater systems. Sampling is considered the most critical step in the quantification of MPs, as it directly influences the accuracy and comparability of results.

Two primary sampling approaches are commonly employed: volume-reduced sampling and bulk sampling. In volume-reduced sampling, the volume of water is reduced during collection using nets or filtration systems. Instruments such as manta trawl nets, plankton nets, zooplankton nets, and pump filtration systems are widely used. A flow meter is typically attached to the mouth of the net to determine the volume of water filtered, enabling accurate estimation of MP concentration. In contrast, bulk sampling involves collecting water without reducing its volume, using tools such as stainless-steel buckets or Teflon pumps. The selection of a sampling method depends on the research objective, available resources, and the environmental compartment under investigation.

Manta trawl nets with varying mesh sizes (112, 200, 300, 333, and   335 µm) have been extensively used for sampling MPs from surface waters, typically at depths ranging from 20 cm to 3–5 m (Veerasingam et al., 2020; Mendoza et al., 2019; Li et al., 2018; Hidalgo-Ruz et al., 2012). However, several methodological limitations have been reported. In some studies, the use of a flow meter was not specified, which can introduce significant errors when the sampling volume is estimated solely based on towing distance. Inaccuracies may also arise if the net is not fully submerged, becomes clogged with debris, or is affected by vessel movement. Additionally, sampling direction, such as towing from the windward side or from the rear of a boat, can influence MP quantification. Fully submerged nets may also fail to capture floating MPs concentrated at the water surface.

Mesh size plays a crucial role in determining the abundance and size distribution of collected MPs. Reported mesh sizes range from 20 µm to 335 µm, with 300–335 µm being the most commonly used range (accounting for approximately 31.43% of studies). However, larger mesh sizes may lead to underestimation of smaller MPs (Mendoza et al., 2019; Li et al., 2018). In freshwater environments, MPs have been studied in lakes, rivers, and groundwater systems. Sampling depths typically range from 20 cm to 3–5 m, using plankton nets with mesh sizes of 20, 100, 120, 300, 333, and   335 µm. Alternative methods include the use of stainless-steel buckets combined with sieving, or hand-operated bilge pumps, as demonstrated by Napper et al., who collected surface water samples (0.5 m depth) from the Ganga River and filtered them through a 330 µm nylon mesh (Napper et al., 2021).

Despite these advancements, there remains a lack of stand ardization in sampling methodologies. Key parameters such as the use of flow meters, towing speed, sampling duration, and immersion depth are not consistently reported, which affects data reliability and comparability across studies. Furthermore, limited attention has been given to sampling from wastewater treatment plants, which are recognized as significant sources of MPs. MP concentrations in water samples are reported using various units, including items/km², items/m³, items/1000 m³, items/L, and   particles/L (Veerasingam et al., 2020; Mendoza et al., 2019; Li et al., 2018). This variation further complicates cross-study comparisons and highlights the need for standardized protocols in MP sampling and analysis.

4.2.  Sediment          

The occurrence and abundance of MPs in sediments from beaches, coastal regions, islands, and lakes have been investigated in approximately 24 studies. Sediment sampling in beach and coastal environments is commonly performed using a quadrat-based approach, where a metal or wooden frame is placed on the sediment surface and   inserted to a depth of 0–5 cm. The enclosed sediment is then collected using stainless steel spoons or shovels. Various frame dimensions have been employed in India, including 25 × 25 cm, 30 × 30 cm, 50 × 50 cm, 100 × 100 cm and   200 × 200 cm, depending on the study design.

Grab samplers, including the Van Veen and   Peterson grab, are commonly employed for the collection of underwater sediment samples from bottom surfaces. In some studies, larger microplastic particles and plastic pellets have also been manually retrieved using stainless steel tweezers or through hand-picking methods. However, the majority of existing investigations have primarily concentrated on surface sediments, while studies involving sediment core sampling to evaluate the vertical distribution of microplastics remain limited (Neelavannan & Sen, 2023; Neelavannan et al., 2022; Veerasingam et al., 2020).

In freshwater environments, approximately thirteen studies have examined the distribution of MPs in lakes and rivers across India. Sampling methodologies in these systems are largely similar to those used in coastal environments. Shoreline sediments are typically collected using stainless steel spoons or scoops, with sampling depths ranging from 0 to 6 cm, while submerged sediments are obtained using Van Veen grab samplers.

The abundance of MPs in sediment samples is reported using various units, most commonly as items/kg or items/g of dry weight. Some studies also express concentrations in terms of items/m², while others report results as particles/kg or particles per unit dry weight. This variability in reporting units, along with differences in sampling strategies, highlights the lack of standardization in sediment-based microplastic studies (Neelavannan et al., 2022; Singh et al., 2021; Amrutha et al., 2020; Veerasingam et al., 2020).

5. MPs SEPARATION METHODS

Most published studies on MPs involve the separation of MPs from bulk sediment and volume-reduced water samples. Density separation is the most commonly employed technique; however, some studies utilise filtration or sieving prior to sorting. The isolated particles are then identified either through visual inspection or with the aid of magnification tools such as microscopes. The variability in these processing methods indicates the absence of a standardized protocol for the isolation of MPs from environmental samples.

5.1 Water

In all 20 studies, collected water samples were initially subjected to filtration or sieving for size-based separation. Subsequent processing steps typically include organic matter digestion, density separation, and final filtration, which are essential for the accurate identification and quantification of MPs.

5.1.1 Organic Matter Digestion

To eliminate organic matter from the sample matrix, most studies employed chemical degradation methods, including oxidative, acidic, or alkaline digestion. Approximately 85.71% of the reviewed studies incorporated a digestion step. Hydrogen peroxide (H₂O₂), often at a concentration of 30%, was the most widely used reagent for organic matter removal. In several cases, it was combined with ferrous ions (Fe²⁺) to form Fenton’s reagent, which generates highly reactive oxidative species capable of efficiently degrading organic material (Malla-Pradhan et al., 2023; Veerasingam et al., 2020). Alternative digestion methods included acid treatment using hydrochloric acid (HCl) and alkaline digestion using sodium hydroxide (NaOH), sometimes in combination with surfactants such as sodium dodecyl sulfate (SDS). The digestion process was typically carried out at temperatures ranging from room temperature to 75 °C for durations between 12 and   72 hours. Material (Neelavannan & Sen 2023).

Enzymatic digestion, although known for its high efficiency and minimal impact on microplastic integrity, was not employed in the reviewed studies. This is likely due to its higher cost and longer processing time compared to chemical methods (Malla-Pradhan et al., 2023; Li et al., 2018).

5.1.2 Density Separation

Density separation is one of the most widely employed techniques for the isolation of MPs, as it utilises differences in polymer density for effective separation. However, its application in freshwater studies remains relatively limited, with only approximately 31.43% of the reviewed lake water studies adopting this method. Various density separation solutions have been used for MP extraction. Saturated sodium chloride (NaCl; density ~1.2 g/cm³) is the most frequently applied solution because of its low cost, easy availability, and non-toxic nature, although it is mainly effective for the recovery of low-density polymers. To improve the extraction of a broader range of MPs, higher-density solutions such as zinc chloride (ZnCl₂; ~1.5 g/cm³), potassium formate (~1.54 g/cm³), sodium iodide (NaI), and lithium metatungstate (~1.6 g/cm³) have also been utilised. In some studies, a combination of NaCl and   NaI has been employed to enhance separation efficiency and improve polymer recovery. Although high-density solutions increase the recovery efficiency of denser MPs, certain reagents, particularly ZnCl₂, require careful handling due to their corrosive and hazardous properties.

5.1.3 Filtration

Filtration constitutes the final stage of sample processing. After digestion and density separation, the resulting supernatant is subjected to vacuum filtration using filter papers with appropriate pore sizes (e.g., 0.7 µm or 0.8 µm). In certain cases, sieves may be employed as an alternative to filter membranes. The retained material is subsequently dried at temperatures ranging from room temperature to approximately 55°C and   then preserved in Petri dishes for further analysis (Malla-Pradhan et al., 2023; Neelavannan & Sen, 2023; Li et al., 2018)

5.2 Sediment

Sediment samples are typically dried and sieved using a range of mesh sizes to achieve size-based fractionation of MPs, with commonly used sieves including 10 mm, 5 mm, 3 mm, 2 mm, 1 mm, 0.3 mm, 850 μm, and   63 μm. In several studies, additional sieve sizes such as 300 μm and   100 μm are also employed to improve separation efficiency. Following sieving, density separation was widely applied for MP extraction, using saturated salt solutions such as NaCl, ZnCl_₂, NaI, CaCl_₂, and, in some cases Na_₂WO_₄.2H_₂O, depending on the required density and recovery efficiency. To remove organic matter, most studies incorporated a digestion step using 30% H₂O₂ either before or after density separation, although a few exceptions omitted this treatment. After digestion and density separation, the supernatant containing MPs was filtered through filter papers of varying pore sizes, including 0.2 μm, 0.45 μm, 0.7 μm, 0.8 μm, 1.2 μm, and up to 38 μm, depending on the targeted particle size range. In some cases, sieves of 1 mm and   0.3 mm were used to further fractionate the supernatant before transferring it onto watch glasses. The filtered residues were then dried either at room temperature or in an oven and subsequently analyzed using microscopic and spectroscopic techniques for identification and   characterization of MPs (Neelavannan & Sen, 2023; Amrutha et al., 2020; Veerasingam et al., 2020).

6. Assessment Techniques for Detecting MPs

6.1 Visual Inspection

Visual identification is one of the most commonly used methods for the detection and quantification of MPs in environmental samples, particularly in freshwater systems in India. This method involves either direct observation with the naked eye for larger particles or the use of stereomicroscopes and light microscopes for smaller MPs. Identification is primarily based on key visual characteristics such as colour, brightness, and the absence of cellular or organic structures. Typically, larger fragments can be identified directly, while smaller particles require microscopic examination. In some cases, visual identification is further supported by the hot-needle test, where plastic particles melt upon contact, helping to distinguish them from non-plastic materials (Qiu et al., 2016; Derraik, 2002).

During visual inspection, certain criteria are followed to improve accuracy: particles should lack cellular organization, exhibit uniform colouration, and   fibres should not appear segmented or twisted like natural materials. Despite being simple, cost-effective, and   widely adopted, this method has limitations. The manual process of inspecting and   counting MPs is time-consuming and   may lead to overestimation or underestimation due to observer bias and   misidentification of non-plastic particles. However, the use of digital counting software can help reduce these limitations. Studies have shown that light microscopy can achieve high recovery rates (e.g., around 96% (Crichton et al., 2017), making visual identification a useful initial screening method. Even so, it is generally recommended to combine this approach with more advanced analytical techniques for accurate and   reliable microplastic characterization (Neelavannan & Sen 2023; Veerasingam et al., 2020; Li et al., 2018).

Figure 4. Analytical Approaches for MPs Detection

6.2 Fourier Transform Infrared Spectroscopy

Fourier Transform Infrared (FTIR) spectroscopy is among the most commonly applied analytical techniques for the identification and characterization of microplastics (MPs). The technique operates by transmitting infrared radiation through a sample, where specific molecular bonds absorb characteristic frequencies of the radiation. Using a beam splitter, the instrument creates an interference pattern from two infrared beams, which is subsequently processed through Fourier transformation to generate an infrared spectrum. The resulting spectrum displays distinct wavenumbers corresponding to molecular vibrations, thereby providing a unique spectral fingerprint that enables precise identification of different polymer types (Neelavannan & Sen, 2023; Li et al., 2018).

For microplastic analysis, the mid-infrared region (400–4000 cm⁻¹) is most commonly used because it contains characteristic absorption bands of polymers. The two most frequently used modes of FTIR are attenuated total reflectance (ATR) and transmission mode (Sinha et al., 2024; Saha et al., 2021). ATR-FTIR is generally applied for larger MPs (>500 µm), especially in water and sediment samples, while smaller particles (<500 µm) are analyzed using micro-FTIR (µ-FTIR) or FTIR coupled with a confocal microscope, enabling chemical imaging (Sonbhadra & Pandey 2023).

FTIR has been extensively used in microplastic research, appearing in nearly 90% of reviewed studies for identifying polymer types in environmental samples. In addition to identification, FTIR can also be used to study the weathering or ageing of MPs, often evaluated using parameters like the carbonyl index, which reflects oxidation levels in polymers. Despite its advantages, FTIR has several limitations. Spectra obtained from different modes (ATR vs transmission) may vary, which can complicate comparisons. Sample preparation is essential, as MPs must be properly placed on a substrate; however, filters or substrates can introduce spectral interference. FTIR also has a size limitation and cannot effectively analyze particles smaller than ~10 µm. Furthermore, chemical degradation of plastics can alter spectral features, making interpretation more complex. Many studies also overlook important steps like spectral preprocessing and chemometric analysis, which could improve accuracy and reliability (Neelavannan & Sen, 2023; Veerasingam et al., 2020; Li et al., 2018).

6.3 Raman spectroscopy

Raman spectroscopy, including both microscopy and spectroscopy modes, is a widely used technique for identifying MPs polymer types. It is a non-destructive method that provides detailed structural and chemical information based on the interaction of light with the sample. The technique works on the principle of inelastic scattering of light, where the wavelength of scattered radiation changes due to interactions with molecular vibrations. This produces a unique Raman fingerprint spectrum that helps identify different polymers (Song et al., 2014).

Raman spectra for microplastic analysis are typically collected in the range of 200–3500 cm⁻¹, although specific studies of ten focus on regions like 500–3200 cm⁻¹ or 600–1800 cm⁻¹ for polymer identification. In practical applications, extracted MPs from environmental samples such as water and sediments are analyzed using laser sources, commonly a 785 nm laser, under controlled conditions of power, exposure time, and multiple scans to improve signal quality. Advanced techniques like micro-Raman (µ-Raman) imaging allow detailed characterization of MPs, including their polymer type, size distribution, morphology, and particle count. This method can detect particles as small as 1 µm, offering significantly higher spatial resolution compared to FTIR (approximately 1 µm vs 20 µm). It also has advantages such as minimal water interference, broader spectral coverage, and   highly distinct spectral fingerprints (Neelavannan & Sen, 2023; Primpke et al., 2020)

Raman microscopy is particularly useful for analyzing smaller MPs (<20 µm), where techniques like FTIR become limited. For example, particles larger than 100 µm can be easily scanned, while smaller particles are analyzed using imaging approaches that build detailed maps of the sample area. However, Raman spectroscopy has some limitations. The Raman scattering signal is inherently weak, which often requires longer acquisition times to achieve a good signal-to-noise ratio. Additionally, fluorescence interference from coloured or degraded plastics and biofouling can affect spectral quality. The spectra of weathered or aged plastics may also change, making identification more challenging. Another important limitation is the lack of comprehensive spectral databases for weathered MPs, which reduces identification accuracy in environmental samples (Neelavannan & Sen 2023; Primpke et al., 2020; Sonbhadra & Pandey 2023).

To overcome these challenges, combining Raman spectroscopy with multivariate or chemometric analysis has proven to be an effective approach for improving the identification and quantification of MPs.

6.4 Scanning Electron Microscope and   Energy Dispersive X-ray Spectrometer.

Scanning Electron Microscopy (SEM) is widely used to study the physical properties, surface morphology, origin, and ageing of MPs. In this technique, a focused beam of electrons scans the surface of a sample, producing high-resolution images that reveal detailed surface features. For improved analysis, SEM is often combined with Energy Dispersive X-ray Spectroscopy (EDS). This combined SEM/EDS approach not only provides surface morphology but also gives qualitative information about elemental composition, helping to better understand the nature and origin of MPs (Han et al., 2020; Veerasingam et al., 2020).

SEM has been effectively used to analyze MPs smaller than 200 µm, revealing various surface characteristics such as fibres, eroded fibres, particles attached to fibres, rod-like structures, and fragmented forms. For example, smoother fibres are typically associated with primary MPs that have not undergone weathering, while rough, cracked, or eroded surfaces indicate aged or degraded plastics.

The SEM/EDS technique has been applied in multiple studies, including in India, to characterize MPs from water and sediment samples. It helps in understanding not only morphology but also the processes of degradation and environmental exposure (Sharma et al., 2020; Reddy et al., 2006). However, SEM/EDS has several limitations. The technique is relatively expensive and time-intensive, and it requires careful sample preparation prior to analysis. Moreover, the reliability of chemical characterization may be affected by selection bias, since the results largely depend on the efficiency of microplastic isolation and the representative selection of particles for examination (Neelavannan & Sen, 2023; Veerasingam et al., 2020).

6.5 Atomic Force Microscopy

Atomic Force Microscopy (AFM) is an advanced technique used to study the surface morphology and nanoscale features of MPs. It can produce very high-resolution images (at the nanometer scale), making it useful for examining fine surface details that are not visible with other techniques

AFM works using a sharp nanoscale tip attached to a flexible cantilever. When the tip scans the surface of a sample (in contact or non-contact mode), the cantilever bends due to interaction forces between the tip and the sample. This bending is detected using a laser and   photodetector system, and   the data is converted into a detailed surface image (Neelavannan & Sen, 2023; Sharma et al., 2020)

This technique is particularly useful for studying weathering and abrasion patterns of MPs, such as cracks, pits, flakes, roughness, and particles attached to the surface. It has been applied to analyze MPs from various environmental samples, including groundwater, surface water, and estuarine regions in India (Selvam et al., 2021; Sharma et al., 2020). In addition to imaging, AFM can also provide nanomechanical and thermal information. For example, AFM-based nanomechanical mapping has been used to study the mechanical properties of semicrystalline polymers, while nano-thermal analysis can help determine properties like melting point (Wu et al., 2018). Despite its advantages, AFM has some limitations. The scanning process is slow, which makes it less suitable for large sample analysis. Also, artifacts can arise due to interactions between the probe tip and the sample or during image processing, which may affect accuracy (Neelavannan & Sen, 2023; Sonbhadra & Pandey, 2023; Veerasingam et al., 2020)

7. Abundance and   Distribution of MPs in Water Bodies

MPs are widely distributed across diverse freshwater and coastal ecosystems in India, including rivers, lakes, ponds, wetlands, estuaries, and marine environments. Considerable spatial variation in MP abundance was observed among different regions and environmental compartments such as surface water, subsurface water, bottom water, and sediments shown in Table 2.

India has the second-highest burden of microplastic (MP) pollution in river systems globally after China, highlighting the growing concern regarding plastic contamination in aquatic ecosystems. The occurrence and distribution of MPs in Indian water bodies are strongly influenced by regional and environmental factors, including population density, urbanization, industrial activities, hydrological conditions, tourism, and waste management practices. Densely populated regions generally contribute greater MP inputs through domestic wastewater, personal care products, and other anthropogenic sources. Northern Indian rivers often pass through highly populated urban areas, whereas many southern rivers exhibit seasonal flow patterns that may facilitate MP retention within sediments (Amrutha & warrier 2020; Napper et al., 2021)

Hydrological and climatic factors also play an important role in MP transport and distribution. River discharge often shows a negative relationship with MP concentration, where increased water flow can dilute MP levels. For example, lower MP concentrations have been reported in the Ganga River during monsoon periods due to flushing effects, whereas increased runoff and sediment resuspension contributed to higher MP concentrations in Manipal Lake during the rainy season (Warrier et al.,2022; Kumar et al., 2021). In addition, MP sources are associated with both atmospheric deposition and human activities, including tourism, vehicle emissions, textile industries, packaging materials, and domestic waste.

Among freshwater systems, rivers showed substantial contamination levels. For instance, the Mula River in Pune recorded very high concentrations ranging from 1561 ± 167 to 1808 ± 697 particles/L during post-monsoon and pre-monsoon seasons, respectively, indicating the strong influence of seasonal runoff and anthropogenic activities. Similarly, the Narmada River exhibited high MP abundance with 4738 ± 5303 particles/m³ in surface water and 290071 ± 199929 particles/m³ in sediments. In contrast, lower concentrations were reported in rivers such as the Thamirabarani River (1.1 ± 0.99 MP/L) and   Kaveri River (2.15 ± 1.9 MP/L).

Lake ecosystems also showed significant MP accumulation. Anchar Lake in the northwestern Himalaya contained 233 to 1533 particles/kg in sediments, while Veeranam Lake sediments showed 309 items/kg. Kodaikanal Lake water contained 24.42 ± 3.22 items/L, and   Renuka Lake recorded 21 ± 13 particles/L. Urban lakes such as Bhoj Wetland, Kolavai Lake, and lakes in Indore also exhibited noticeable contamination levels, reflecting the impact of urbanization, domestic discharge, tourism, and recreational activities.

Sediments generally showed greater MP accumulation than surface waters because sediments act as long-term sinks for plastic debris. For example, Dal Lake sediments contained 416 ± 38 MP/kg, while Kaveri River sediments showed values up to 699 ± 66 items/kg. The Indus and   Brahmaputra River sediments also contained substantial MP loads ranging from 20 to 340 MP/kg dry weight.

Overall, the table indicates that microplastic contamination has emerged as a widespread environmental concern across Indian aquatic ecosystems. Variations in abundance and distribution are strongly influenced by population density, urbanization, industrial discharge, tourism, hydrodynamic conditions, seasonal rainfall, and waste management practices. The widespread occurrence of MPs in both water and sediment matrices indicates the urgent need for continuous monitoring, standardized analytical methods, and effective plastic waste management strategies in India.

Table 2. MPs Studies in Water Bodies of India

8. Shapes and   chemical characterization of microplastics

MPs present in Indian aquatic environments exhibit a wide diversity of shapes and polymer compositions, reflecting their multiple sources, degradation pathways, and environmental behaviour shown in Table 2. Morphological and chemical characterization of MPs is important because particle shape and polymer type influence their transport, persistence, toxicity, and interaction with aquatic organisms.

Among the various microplastic morphologies, fibres and fragments were identified as the predominant forms in Indian freshwater and coastal ecosystems, including rivers, lakes, ponds, wetlands, estuaries, and coastal regions. Fibres were commonly reported in water samples collected from major water bodies such as the Ganges River, Yamuna River, Kaveri River, Vembanad Lake, and several urban lakes. These fibrous microplastics are primarily linked to sources such as domestic sewage discharge, laundering of synthetic textiles, fishing-related activities, and the degradation of synthetic ropes and fishing gear. Fragment-shaped MPs were also highly abundant and likely originated from the breakdown of larger plastic items such as bottles, containers, packaging materials, and household waste through physical, chemical, and biological weathering processes. In addition to fibres and fragments, several other morphologies, including Films, foams, pellets, beads, sheets, glitter particles, spheres, and thin pieces, were identified in different environmental matrices. Films were commonly associated with plastic bags and packaging materials, whereas foams likely originated from thermocol and insulation materials. Pellets and beads represent primary MPs that may enter aquatic systems directly from industrial raw materials or cosmetic products. The occurrence of multiple MP shapes indicates the contribution of both primary and secondary microplastic sources in Indian freshwater ecosystems.

Chemical characterization showed that polyethylene (PE) and polypropylene (PP) were the most frequently detected polymer types across nearly all studied locations. These polymers are widely used in single-use plastics, packaging materials, containers, bottles, and household products, which explains their dominance in aquatic environments. Other commonly identified polymers included polyethylene terephthalate (PET), polystyrene (PS), polyvinyl chloride (PVC), polyamide (PA or nylon), high-density polyethylene (HDPE), and low-density polyethylene (LDPE).

Certain studies also reported less common polymers such as polytetrafluoroethylene (PTFE), poly(methyl methacrylate) (PMMA), polycarbonate (PC), polyurethane (PU), polyoxymethylene (POM), ethylene vinyl alcohol copolymer resin, and acrylonitrile-butadiene-styrene (ABS). The presence of these specialized polymers suggests contributions from industrial activities, electronic waste, paints, automobile sectors, and construction materials. The predominance of PE and   PP can also be attributed to their lower density and buoyant nature, which favours their transport and persistence in surface waters. In contrast, denser polymers such as PET, PVC, and   PA are more likely to accumulate in sediments. This explains why sediment samples from lakes and rivers often showed higher diversity and abundance of polymer types compared to surface water samples.

Overall, the morphological and chemical characterization of MPs in Indian aquatic environments reveals that synthetic polymers from domestic, industrial, agricultural, fishing, and urban activities are continuously entering freshwater systems. The dominance of fibres, fragments, PE, and PP indicates the major role of municipal plastic waste and textile-derived pollution, while the occurrence of diverse polymer types highlights the complexity of MP contamination in aquatic ecosystems.

9. Discussion

Research on microplastics (MPs) has received significant scientific attention over the past decade, resulting in considerable advancements in understanding their occurrence, distribution, and environmental impacts. Nevertheless, several critical challenges and knowledge gaps still persist. Most existing studies have largely focused on the abundance and occurrence of MPs, whereas detailed information regarding their sources, transport pathways, environmental fate, and long-term ecological and toxicological effects remains insufficient.

In India, MP investigations have primarily been concentrated in selected geographical regions, while many freshwater ecosystems, particularly those located in central India, remain inadequately explored. States such as Madhya Pradesh, Chhattisgarh, and   Odisha can be regarded as potential “white spots” in MP research because of the scarcity of field-based studies despite their ecological and hydrological significance. Several major river systems flowing through these regions, including the Tapti, Mahanadi, Godavari, Krishna, Chambal, Betwa, and   Son rivers, have received very limited attention with respect to microplastic detection and characterization. Investigating MP contamination in these river systems is important not only for assessing pollution levels within freshwater environments but also for understanding land-to-ocean transport pathways and evaluating the contribution of Indian rivers to marine plastic pollution.

A major challenge in current MP research is the lack of standardised methodologies for sampling, extraction, identification, and quantification. Variations in mesh sizes, sampling duration, trawling speed, digestion methods, density separation techniques, and reporting units make comparisons among studies difficult and can affect data reliability. Previous studies have suggested that net sampling is one of the most effective techniques for quantifying MPs in water because it allows sampling over larger areas while reducing sample processing time. However, sampling conditions strongly influence the measured abundance of MPs. For example, smaller mesh sizes generally retain a greater number of particles and therefore produce higher reported MP concentrations. Consequently, future studies should focus on establishing harmonized sampling and analytical protocols to improve reproducibility and enable reliable comparisons among datasets generated from different environmental matrices and geographical regions.

Strict contamination control measures should also be incorporated throughout field sampling and laboratory procedures to ensure the accuracy and reliability of MP data. Potential contamination can be minimized by covering solutions and materials with glass lids or aluminium foil, using glass containers for storage, including procedural and field blanks, avoiding plastic equipment, wearing cotton laboratory coats, maintaining clean working environments such as laminar flow systems, and using high-quality glass fibre filters. Implementing such measures can substantially reduce external contamination and improve the overall quality of analytical results.

Future research should also emphasize understanding the transport mechanisms and seasonal dynamics of MPs across different environmental compartments, including surface water, groundwater, sediments, and aquatic organisms. Long-term monitoring programs are required to identify pollution hotspots and evaluate temporal trends in MP contamination. Furthermore, studies investigating interactions between MPs and heavy metals, persistent organic pollutants, and other emerging contaminants are essential because MPs can act as carriers of toxic substances and potentially increase ecological and health risks.

Future studies should increasingly adopt advanced analytical techniques to enhance the detection and   characterization of microplastics (MPs). While Fourier Transform Infrared (FTIR) spectroscopy and   Raman spectroscopy are widely utilized for polymer identification, their integration with automated imaging technologies, machine learning-based analysis, pyrolysis–GC-MS, and high-resolution microscopic methods could significantly improve analytical accuracy and efficiency, especially for smaller MPs and nanoplastics. Nanoplastics, in particular, remain poorly investigated due to current analytical constraints, despite posing potentially higher environmental and biological risks because of their greater surface area, enhanced reactivity, and increased mobility.

Overall, future research on microplastics (MPs) should progress beyond merely descriptive assessments and focus more on mechanistic, process-oriented, and risk-based studies. Greater emphasis should be placed on understanding the ecological, toxicological, and human health impacts associated with MP contamination. Such comprehensive investigations will improve knowledge of the behaviour, transport, and fate of MPs in aquatic environments, while also supporting the development of efficient monitoring programs, management policies, and mitigation strategies to address microplastic pollution.

10. Conclusions

Microplastics (MPs) have become significant environmental pollutants in aquatic ecosystems across the globe. Over the past few years, considerable attention has been given by researchers, policymakers, and the public to understanding the occurrence, distribution, and potential impacts of MPs in rivers and lakes. Despite the increasing concern, knowledge regarding the abundance, spatial distribution, sources, transport mechanisms, and environmental fate of MPs in freshwater ecosystems is still limited. In India, research on MPs in freshwater environments has mainly progressed during the past decade. Most investigations have focused on the detection and occurrence of MPs in river and lake waters, sediments, and aquatic organisms, while broader studies addressing their transport pathways, ecological risks, and long-term environmental implications remain relatively scarce.

Investigations have also emphasized MP size distribution and the development of monitoring and analytical techniques for water and sediment samples. Nevertheless, baseline information regarding MP contamination in many major Indian river systems is still lacking, particularly in central Indian freshwater ecosystems. Although substantial progress has been made globally in understanding the toxicological effects of MPs, further studies are still required to comprehensively evaluate their abundance, sources, transport mechanisms, and ecological impacts. In particular, detailed investigations are needed in the central regions of India to better understand the distribution, pathways, and long-term environmental consequences of MPs in freshwater systems.

Acknowledgements

The authors are thankful to DST-PURSE Project (SR/PURSE/2022/145) for financial assistance. Additionally, BM gratefully acknowledges the research fellowship NFSC granted by (UGC) under letter no. NSFDC/E-81088. 

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