Microplastics in watershed: extraction, identification, and environmental risk assessment from the real sample

There has been an increase in plastic production and consumption in recent years, which has become a major global environmental challenge due to the persistence of plastics in nature. Microplastics (MPs) contamination signifies a serious environmental challenge, yet discrepancies among analytical methodologies and sample matrices continue to limit the harmonization and cross-comparability of reported data. This study investigates MPs’ extractions from the soil collected from the Sukhna Lake Watershed, Chandigarh, India. This research employs systematic sampling for soil collection by dividing a single sampling site into a 4 × 4 grid. Furthermore, the density separation method was employed for the extraction of MPs from the soil samples. The extracted MPs were comprehensively characterized using a fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscope (FE-SEM), energy-dispersive X-ray Spectroscopy (EDS)-mapping, X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma mass spectrometry (ICP-MS), which was used to elucidate the molecular structure, morphology, surface chemistry, and elemental composition of the MPs. The MPs were further solubilized in various solvents and analyzed using UV-visible spectroscopy. The results from the FTIR and FE-SEM demonstrated the presence of various types of plastics at the collecting site, including polyethylene, polypropylene, polyvinyl chloride, and polyethylene terephthalate in different morphologies. These techniques also confirmed that plastics had undergone prolonged interactions with the environment, enabling them to interact with contaminants. Furthermore, the results from XPS, ICP-MS and UV-Visible spectroscopy suggested the presence of organic and inorganic contaminants, including heavy metals, in the MPs. The combined results emphasize that the MPs present in the watershed can function as potential vectors for the accumulation and transport of potent and persistent contaminants. This research delivers new insights into MPs as environmentally aged, oxidized materials with mineral-organic surface coatings, highlighting their enhanced capacity to act as carriers of pollutants and their broader environmental implications.

As the use of durable, reusable materials like wood, ceramics, and glass declines, production and reliance on plastic products continue to grow. This transition has fueled global plastic production, which increased from two megatons in 1950 to approximately 380 megatons in 2015 (Sharma et al., 2023). With the increasing amount of plastic being produced and consumed, there is a global strain on the management of plastic and its components, which have become a point of heavy contention worldwide. The mismanagement of plastics has created a new and major source of pollution, known as microplastic (MP) pollution.

MPs are defined as any plastic smaller than 5 mm in size and have emerged as a critical source of environmental pollution. MPs originate from diverse sources such as tire abrasion (47%), city dust (22%), road markings (20%), washing of textiles (8%), marine coatings (2%), preindustrial pellets (1%), and microbeads from personal care products (<1%) (Manshoven et al., 2022). Due to their small size, abundance, and persistence, MPs are now ubiquitous across terrestrial, freshwater, and marine environments.

These plastics are primarily categorized into two types: primary microplastics and secondary microplastics. Primary MPs are deliberately manufactured at microscopic sizes for their applications in products such as cosmetics, toothpaste, industrial abrasives, and synthetic textiles. Secondary MPs result from the breakdown of larger plastic items due to physical, chemical, and biological degradation processes (Zhao et al., 2024). This can include abrasion of discarded plastic, which degrades over time due to UV radiation, weathering, and microbial activity. This continuous breakdown of macroplastics contributes substantially to the increasing environmental load of MPs.

The extensive use of plastics across domestic, commercial, and industrial sectors has led to the release of diverse polymer types into the environment. Among the most common plastics contributing to MPs pollution are polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), Polyvinyl chloride (PVC), and Polyester (PES), etc. These plastics can persist in the environment for many decades. Additionally, the production of these plastics causes environmental degradation, greenhouse gas release and human and environmental health issues (Alfarisi and Primadasa, 2018; Junaid et al., 2024; Chen et al., 2026).

Once these plastics enter the environment, they are translocated across ecosystems by wind, ocean currents, and even living organisms, which is the main reason that MPs are being detected in some of the most remote areas of the planet (Chaudhary et al., 2024). This further poses threats to food chains and food webs globally and locally, as MPs can absorb contaminants (inorganic and organic) from one area and then release them into another (Raj and Das, 2023; Hoque et al., 2024; Musah, 2024; Genchi et al., 2020; Bernard, 2008; Akhtar et al., 2021). Many factors also affect the ability of MPs to absorb environmental contamination, for example, surface roughness, porosity, pH medium, surface area, and hydrophobicity (Rafa et al., 2024; Joo et al., 2021).

Currently, there is a significant imbalance in MP research, where research in marine and aquatic environments are favored as opposed to terrestrial environments, known as the terrestrial gap. Like aquatic systems, terrestrial ecosystems act as major MP sinks, particularly agricultural and urban soils, which harbor up to 24 times more MP pollution than oceanic basins (Horton et al., 2017). In terrestrial environments, MPs accumulate in soil and can impact the soil structure, including porosity, aeration, water retention, and plant growth. Furthermore, the microbiomes present within the soil are affected, further altering the biogeochemical cycling of nutrients. One of the larger concerns of MPs contamination in soil is the absorption of these MPs by plant roots, which affects the nutrient reuptake and plant growth. Overall, this will affect terrestrial fauna as these MPs are now entering food webs (Azeem et al., 2021). Pollutants that are found in terrestrial environments or in soil have a high capacity to become mobile and enter aquatic ecosystems. This is especially true for watershed systems as the physical and chemical properties of the watershed directly impact the water body (Hassan et al., 2025).

The Sukhna Lake is a 3 km 2, man-made, rain-fed reservoir located in the foothills of the Himalayas, in Chandigarh, India, popularly known as the ‘City Beautiful’ of India. The Sukhna Lake watershed is created around the 3,000-ha watershed in the Shivalik Hills and its surrounding area. Adjacent to this lake are the Reserved Forest Area, Lake Reserves, and the Sukhna Wildlife Sanctuary, which are all ecologically vital features of the Chandigarh planned city. This lake was engineered by impounding the Sukhna Choe, which is a seasonal stream coming down from the Shivalik Hills. The Lake acts as the catchment area for this stream. This watershed is a geologically sensitive system that is prone to erosion, pollution, and other runoff. Especially in the monsoon season, the heavy rainfall causes siltation from the surrounding area into the lake, which further causes any pollutants present within the terrestrial environment to be deposited into the lake. The urbanization activities, tourism, and litter sources in and around the watershed can cause immense amounts of MP accumulation in the lake, which can have major consequences on the ecological and biological health of the reservoir.

This study aims to extract and analyze the MPs collected from soil in Chandigarh, India. For this study, a random sample collection was applied, and the samples were separated using the density separation method. Furthermore, the samples were analyzed using advanced analytical techniques. The main objective of this study is to investigate the occurrence and possible effects of MPs in soil samples collected from the Sukhna Lake Watershed by characterizing the physical, chemical and morphological properties of these particles. Additionally, this study aims to investigate the association of MPs with organic and inorganic pollutants, including heavy metals. While MPs have been extensively studied in aquatic systems, overall, there is still limited information regarding the analysis of MPs present in terrestrial or soil environments. Specifically, there is scarce data on the polymer composition, weathering state, elemental contamination, and pollutant-carrying potential in soils of North Indian urban watersheds. These findings will contribute to a better understanding of MP pollution dynamics and inform future environmental management strategies, especially in the context of the Sukhna Lake Watershed in Chandigarh (India).

Materials

All chemicals were used in their original state without any later modification or purification. All experiments were conducted at room temperature in double-distilled water (ddH 2 O). Sodium Chloride (NaCl) from Fisher Scientific was used for MPs separation. Methanol (99% pure), and hexane (n-Hexane 99%) were purchased from FINAR. Acetonitrile was purchased from Cynor Laboratories, India. Alcohol stabilized chloroform was purchased from Rankem Labs, India.

Methods

Selection of study site

The study site/sample collection area selected is in Chandigarh, India (30°43ʹ16.59ʹʹ N, 76°49 ʹ 11.95ʹʹE), within the Sukhna Lake watershed (Figure 1). A recent increase in construction and industrial activity around this area was observed, which is expected to influence environmental contamination levels, specifically MPs.

The surrounding area also includes Reserved Forest Area, Lake Reserves, Sukhna Wildlife Sanctuary, public gardens and parks, local plant nurseries, residential backyards used for farming, and urban infrastructure. Ongoing activities such as new housing development, freshwater pipeline upgrades, road construction, and maintenance works characterize the site as a mixed land-use zone with both ecological and anthropogenic influences, making it suitable for soil impacts.

Soil sample collection

For soil sample collection, one collection side was selected. Systematic grid sampling was used to decrease sampling bias. A 4 × 4 ft quadrant was established at the designated site and subdivided into four 60.96 × 60.96 cm sections. From each section, four random subsamples were extracted, yielding a total of 16 samples. The top 0–1 cm of the soil layer was excavated as the majority of the pollutants accumulate in this layer. A test tube was filled 2 inches in depth with the samples from each sample site. The contents of the collection tubes were transferred into a clean glass beaker and manually mixed to produce a homogeneous composite sample prior to analysis. Soil sampling was conducted using a systematic grid-based approach. The original methodology was modified by implementing a design appropriate for the Sukhna Lake Watershed and the objectives of the present investigation (Chia et al., 2024). A total of 113.34g of soil was extracted during soil collection.

Separation of microplastics and characterization of microplastics

Initially, the larger soil particles were strained using a stainless steel 5 mm sieve. Any visible MPs were physically removed from the soil after sieving. MPs were further isolated from soil using a 225 mL heavy water solution, where 40g of NaCl was used for 50g of soil. The soil sample was added to this solution, shaken vigorously, and then left to settle. The top layer was then decanted and dried, then washed again, to remove any remaining NaCl. This density separation procedure was adapted from Strady et al. (2021) (Strady et al., 2021). Vacuum filtration of the remaining liquid was then performed on a filter paper with a 3 µm pore size to remove any excess water. Approximately 5.1g of MPs were extracted using this method. These MPs (0.5g) were added into 3 mL of 4 separate solvents-: methanol, chloroform, hexane, acetonitrile (Figure 2). These were then sonicated for 30 min. The solvents were then analyzed using UV-visible spectroscopy. The MPs’ functional group analysis was carried out using FTIR, utilizing the attenuated total reflectance (ATR) (Perkin Elmer - Spectrum RX-1 FT-IR spectrophotometer). To obtain information about the morphology of MPs and elemental analysis, the FE-SEM model Hitachi SU8010 with EDS and mapping S-Bruker SDD XFlash 6130 detector was used. Extracted dried MPs samples were cast on carbon tape at an aluminum stub and coated with a gold sputter coating machine (15 mA for 20 s). For mapping and EDS analysis, the working distance was 15 mm, and the operating voltage was fixed at 15 kV. X-Ray photoelectron spectroscopy was used to analyze the composition and state of elements at the surface of different MPs samples using the ThermoFisher K-ALPHA model. Elemental analysis was performed using an ICP–MS system (iCAP RQ, Thermo Scientific, USA). For further analysis, multi-elemental calibration solutions of 1–200 μg mL -1 by serial dilution was prepared. Argon plasma generated by a 27 MHz radiofrequency source was used for ionization.

Recovery and extraction efficiency

From 113.34g of soil total excavated from the 16 collection points, there were about 5.1g of MPs recovered. While the abundance of MPs 4.5% is relatively high, it may suggest the effectiveness of the extraction procedure. Residual particles attached to MPs may also contribute to the higher mass during recovery. Sometime presence of mineral-associated elements on the MP surfaces suggests that soil-derived minerals remain attached to the particles despite washing and filtration. This strong attachment may be due to oxidation, chemical bonding or other hydrophobic attachments (Sajjad et al., 2022).

FTIR

FTIR was used to determine the peaks of five random plastic samples from the MPs batch (Figure 3). All five samples were identified by comparing spectra with reference spectra that have been previously reported in the literature. The assignments of the polymer type were based on peak positioning and characteristic functional groups that are associated with the given sample.

In Plastic Sample PI. Sm.1, the predominant peaks were observed at 2955 cm -1, 2919 cm -1, 2850 cm -1, which generally correspond to asymmetric and symmetric C-H stretching vibration of–CH 3 and–CH 2 groups (Yadav, 2005). Additional peaks at 1237 cm -1, 1265 cm -1, and 1102 cm -1 can be attributed to the C-C stretching and CH bending vibrations, with a strong C=O stretching peak at 1723 cm -1, which showed the possibility of carbonyl-containing polymer presence (Fang et al., 2012). In Pl. Sm.2. sample peaks are seen around 2956 cm -1, 2919 cm -1 and 2857 cm -1, corresponding to C–H stretching vibrations (Umamaheswari and Murali, 2013), while peaks at 1728 cm -1, 1558 cm -1, and 1377 cm -1 can be associated with C=O, C=C, aromatic ring vibrations and CH bending (Prasad et al., 2011). The presence of a band near 1027 cm -1 indicates a C-O stretching in the ester group. These are all consistent with the reported peaks of a pure PET sample or weathered PP/PE containing oxidation products (Kauts et al., 2023). Sources of PP/PE and PET predominantly include packaging and single use food containers, which are often seen littered in this specific area of the Sukhna Lake Watershed. Breakdown of synthetic textiles may also contribute to the presence of PP in the sample.

In PI. Sm.3 strong bands are seen at 2960 cm -1, 2918 cm -1, 2854 cm -1 correspond to asymmetric and symmetric stretching of–C-H, which are characteristic of polyethylene. The peak at 721 cm -1 is assigned to CH 2 rocking vibrations, a diagnostic feature of long-chain aliphatic hydrocarbons (Guo and Bustin, 1998). The weak band observed around 1707 cm -1 may indicate slight oxidation (carbonyl formation), which is commonly observed in aged polyethylene samples. These peaks correspond to peaks seen in literature of a pure HDPE/LDPE sample at 3743 cm -1, 2913 cm -1, 2847 cm -1, 1742 cm -1, and 721 cm -1. Sources of these plastics include single-use packing containers, or agriculture materials. The presence of numerous greenhouses and commercial nurseries may explain the source of HDPE/LDPE in the homogenous sample. In Pl. Sm. 4, a major band is observed in the sample at 2912 cm -1, which can be attributed to the C–H stretching. The peaks at 1249 and 961 cm -1 correspond to C–H bending and wagging vibrations. The bands observed at 870 and 608 cm -1 are characteristic of C–Cl stretching vibrations, which are a key identifying feature of PVC (Ramesh et al., 2007). Peaks in pure PVC samples are observed at 2911 cm -1, 1254 cm -1, 956 cm -1, 834 cm -1, and 616 cm -1, which match closely with the literature results (Ul-Hamid et al., 2015). Other than PVC, there is a possibility of the presence of PET, due to the presence of the C=O peak around 1725 cm -1 with other characteristic peaks. The major sources of PVC include construction activities, where these PVC pipes are used for plumbing or other structures. The new construction activities around the Lake may be responsible for the increasing PVC presence in the sample. In PI. Sm.5 peaks seen at 2917 cm -1, 2852 cm -1, correspond to aliphatic C–H stretching, while the band at 1459 cm -1 is associated with CH 2 bending. The peaks at 771 cm -1 and 720 cm -1 correspond to CH 2 rocking and skeletal vibration (Fang et al., 2010).

FTIR analysis revealed that the extracted MPs are dominated by polyolefin materials, particularly polyethylene (PE), which is consistent with global reports showing PE as the most abundant MPs in terrestrial environments due to its extensive use in packaging materials, mulch films, agricultural films, and disposable products (Table 1).

FE-SEM

Morphological identification of MPs was carried out using FE-SEM analysis. Figures 4A,E shows very angular and well-defined MP particles with uniform shape. Particles seen in Figures 4B,F) shows a flatter morphology, with uneven layering and sharper edges. Figure 4F also shows some fracturing and other surface irregularities, which can indicate erosion or weathering. Figures 4C,G shows fibrous particles that may have a filmlike structure. This can be correlated to the weathering of thin plastic sheets or bags. Figure 4D shows a spherical structure with a collapsed appearance, which is generally seen in microbeads or other plastics that have been exposed to higher temperatures (such as plastic burning). Lastly, Figure 4H shows an irregular and aggregated mass of porous plastic. This may be caused primarily by absorption of environmental contaminants or advanced weathering.

EDS

The results for EDS of MPs samples showed the presence of a few predominant elements. These elements included carbon, oxygen, chlorine, aluminum, silicone, calcium, and nitrogen. The detection of these elements can further prove the properties of plastics as well as the additives/leachates within the plastic. Spectrum in Figure 5A shows that the MP contains inorganic elements, such as Ca, Al, and Si, indicating possible mineral absorption from the environment from particles like clays, calcium carbonate, or fly ash residues. However, the high amounts of carbon and chlorine present in the sample also suggest a plastic polymer base, potentially PVC (polyvinyl chloride) or a plastic that has the capacity to absorb mineral particles. Spectrum in Figure 5B shows the surface of a nearly pure plastic, as there is a very high detection of carbon (C: 88.39 wt%), which is the base of plastics. These can include polyethylene (PE), polypropylene (PP), or polystyrene (PS). Spectrum in Figure 5C shows a high presence of N and Cl which may indicate various properties of the MP. For example, the MP may be a nitrogen containing polymer such as nylon, polyurethane, or acrylonitrile. Alternatively, these elements can also indicate the absorption of nitrogenous compounds, such as fertilizers, urea, or nitrates, which are common in agricultural runoff. The presence of Cl further suggests exposure to contaminated environmental pollution. The presence of inorganic elements such as Si, Al, Ca, Cl, and N further indicates the possible environmental history and surface conditioning of the particles. The detection of Si and Al are significant as these elements are constituents of minerals and aluminosilicate particles commonly present in clay soils. The presence of these further suggests the development of mineral coatings on MPs and/or strong adsorption of clay particles by the MPs. These mineral attachments on the MP surface can further indicate prolonged contact between the particle with the soil matrix.

The Cl seen in MPs may have originated from multiple sources. One possible source is PVC, which was among the polymer types identified through FTIR analysis. Alternatively, chlorine may originate from environmental salts, road dust, irrigation water, or residual inorganic deposits associated with the soil matrix. The simultaneous detection of sodium and chlorine in some samples supports the possibility of adsorbed salt residues or environmental contamination contributing to the elemental composition of the particle surface. Collectively, the presence of these elements within the sample provides strong evidence that the MPs have undergone surface environmental aging and surface modifications.

XPS

The XPS spectra (Figures 6, 7) for the different MPs samples explain the characteristic elements present on the surface of the particles after extraction from the soil. The results in Figure 6 illustrate the chemical composition of the polymer, any potential contamination from the soil, and the possible effects of weathering on the sample. Carbons (C 1s) present in the sample depict the carbon backbone of the plastics such as PP, PE, PS, etc. Oxygen (O 1s) depicts any oxidation caused by ageing or weathering of the sample or any polymers that contain oxygen. Any trace minerals, such as Si, Al, Ca, Na, K, or Mg, show dust or soil attached to the surface of the samples. Elements such as Chlorine and Nitrogen can be additives, degradation products or other salts from experimental procedures or soil. On the contrary, Figure 7 depicts a core-level XPS spectrum, which illustrates any surface chemistry changes and chemical bonding in the microplastics. For these samples, peak deconvolution was performed to distinguish between any polymer-derived functionalities and soil-associated functionalities.

Figure 6a has a dominant C 1s peak (89.87 at%) with a minor O 1s contribution (10.13 at%), indicating the surface has a composition of carbonaceous material. There is a lack of inorganic elements, which suggests that this sample may not have had much interaction with surrounding soil minerals, making it highly pure. Additionally, a lower oxygen content implies limited surface oxidation, consistent with a weakly aged polymeric material. This composition is characteristic of polyolefin-type microplastics such as polyethylene or polypropylene. In comparison to Figures 6a and 6b showed a reduced carbon content (81.6 at%) and increased oxygen concentration (14.52 at%), accompanied by trace amounts of Si (2.66 at%), Al (0.95 at%), and Na (0.27 at%). The higher levels of O 1s may indicate surface oxidation, which is caused by degradation of the particle. Additionally, the presence of silicon and aluminum suggests adsorption of silicate and aluminosilicate soil particles. These results indicate early environmental aging and some mineral attachment on the microplastic surface. Figure 6c displayed a substantial amount of surface alteration, which was reflected by the elevated O 1s levels at 49.87%, which is almost double the C 1s levels (22.93 at%). Other elements present in this sample include Si (13.99 at%), Al (8.3 at%), and minor amounts of K, Mg, and N. Nevertheless, the high amount of oxygen indicates long-term oxidative weathering of the polymer surface, and the high abundance of inorganic elements indicates persistent association with soil minerals. These findings indicate that the particle was likely present in the soil environment for a prolonged period, which resulted in the weathering and mineral-rich surface of the microplastic. Figure 6d displayed a predominantly carbon-based surface (C 1s: 62.25 at%), though with elevated O 1s (19.99 at%) and notable levels of Cl (7.89 at%), Na (5.26 at%), Si (2.97 at%), and trace Ca and N. Sodium and chloride in the sample suggest the adsorption or salts from the soil or during experimentation. The presence of calcium can be attributed to carbonate minerals, and the nitrogen may have originated from organic matter or other microbial residues. The elemental findings of this particle indicate advanced environmental aging by depicting a complex surface contamination that involves mineral and ionic species.

Furthermore, a high-resolution XPS analysis was performed on MP identified in the survey spectrum presented in Figure 6d, and the corresponding narrow spectra is presented in Figure 7. Figure 7a demonstrates a C 1s spectrum which contains peaks at 284.5 eV, attributed to C–C/C–H bonds, characteristic of the hydrocarbon backbone of polyolefin microplastics. Additional components at 285.8 eV and 288.5eV correspond to C–O and C=O/O–C=O, respectively. The presence of oxygen bonding indicates oxidation of the polymer, which is most likely due to its exposure to the environment, photo-oxidation, and other microbial activity. The formation of O-containing functional groups augments the surface polarity of the microplastics, enabling the adsorption of natural organic matter and metal ions, consistent with the elemental composition observed in the survey spectrum. Figure 7b displays an O 1s spectrum, which mainly consists of peaks at ∼531.8 eV, 533.4 eV, and ∼536.2 eV, corresponding to C=O, C–O, and adsorbed oxygen species, respectively. The lower binding energy can be assigned to carbonyl oxygen or other metal-oxygen bonds, while the higher binding energy can be associated with C-O bonds and other silicone and oxygen species. Oxygen presence can be attributed to both oxidation of the polymer and absorption of mineral phases, which further confirms the ageing of the MP within soil. Figure 7c shows a Si 2p spectrum, which displays a central peak at ∼102 eV, which is characteristic of Si–O bonds. These bonds are typically found within silicate minerals such as quartz and clay. The absence of the peak near 99–100 eV confirms that the Si is not present in pure elemental silicon. Also, silicon is not a property of plastics; its existence specifies that the polymer strongly adheres to soil particles. This can further suggest the formation of a mineral coating over the MP during environmental residence.

In addition to the dominant C1s and O1s signals, high-resolution XPS spectra of Cl 2p, Ca 2p, N 1s, and Na 1s are presented in Figures 7d–g, respectively. The Cl 2p doublet at 198–200 eV and Na 1s peak at 1072 eV are consistent with adsorbed inorganic salts, likely Cl-containing residues. The Ca 2p doublet at 347 and 350.5 eV confirms the existence of Ca 2+ bearing mineral phases, such as calcium carbonate or related soil-derived residues. The N 1s peak centered at ∼399–400 eV suggests N-containing organic species, likely originating from adsorbed natural microbial residues or organic matter. Together, these results specify that the MP surfaces were not pristine, but were environmentally conditioned and coated with an inorganic-organic eco-corona derived from the surrounding soil matrix.

The combined analytical results obtained from FTIR, FE-SEM, EDS, and XPS provide strong evidence that the recovered MPs have undergone significant environmental weathering during their residence within the Sukhna Lake watershed soil matrix. The recovered particles display prominent physical and chemical signatures associated with long term environmental exposure. The FTIR shows the presence of uncharacteristic carbonyl absorption bands. These absorption bands generally suggest the oxidative degradation of a polymer through prolonged exposure to sunlight, oxygen, moisture, and microbial activity, and provides an indicator of the environmental age of the MP (Withana et al., 2025). The FE-SEM further supports this claim via the assessment of the morphological characteristics of the MPs. These particles displayed fractured edges, irregular surfaces, porosity, aggregation, and structural deformation, which are all commonly observed during the plastic breakdown. This also increases the surface area for contamination adsorption and mineral attachment. The EDX revealed the presence of inorganic elements, indicating adsorption of soil-derived minerals, carbonate particles, salts, and organic matter onto the MP surface. XPS testing further confirmed advanced surface modification through elevated oxygen concentrations, reduced carbon content, and the presence of oxygen-containing functional groups such as C=O and C–O. These are characteristic of oxidative degradation. Furthermore, Si–O and other mineral-associated species were detected in both analyses which suggests the formation of an inorganic–organic eco-corona resulting from prolonged interaction with the surrounding soil matrix. These surface alterations indicate long-term environmental exposure which may enhance the ability of the MPs to adsorb and transport contaminants across the Sukhna Lake watershed.

ICP-MS

The ICP-MS was operated via a single quadrupole mode with helium Kinetic Energy Discrimination (He KED) mode for interference removal. This analysis was performed for the detection of specific elements, including heavy metals (Mg, P, As, Cd, and Pb) in the microplastic sample (Table 2). Magnesium was the most abundant element detected, with an average concentration of 272,309.6 ppb. This element displayed a low relative standard deviation (RSD = 0.5%) which indicates excellent analytical precision and suggests a uniform distribution of magnesium within the analyzed sample. Mg is generally added into plastics in the form of magnesium hydroxide or magnesium oxide to enhance the plastics’ safety, boost manufacturing, or act as a thickener. The detection of this element suggests the possibility of additives in the plastic.

Phosphorus was also detected at an average concentration of 68,689.2 ppb. The high RSD value (54.4%) may be attributed to heterogeneity of the sample, matrix effects, or instrumental fluctuations. Similar to Mg, compounds of phosphorus are also added to plastics as flame retardants, plasticizers or stabilizers. Chemicals such as red phosphorus or organic phosphinates contain flame-retardant properties. The presence of the element can further indicate the additives in the plastic. Arsenic and cadmium were not detected in the sample. These are negative concentrations reported of these elements at the RSD value of 20.0% and 47.1%, respectively.

Lead, which is a potent heavy metal, was also detected in the MP sample at a high average concentration of 695.96 ppb. Measurable levels of lead were present at a high RSD (59.3%). Pb is a heavy metal that is added to plastics as a heat stabilizer, UV blocker or pigment. The exposure to this heavy metal can have detrimental neurotoxic effects. These five elements were specifically tested as they serve as core contaminants in microplastic pollution. These elements include a mixture of common plastic additives and heavy metals.

Overall, the four tested solvents show similar peaks in UV. Methanol (Figure 8A) showed peaks primarily in the 200–330 nm region. The UV-Visible spectrum for acetonitrile (Figure 8B) shows sharp absorbance peaks in the 270–395 nm region, a broader shoulder around 300–400 nm and a duller peak in the 570 nm region. MPs in chloroform (Figure 8C) displayed one dominant, broad band from 200 to 350 nm. Lastly, it was observed that the UV-Visible spectrum of MPs dissolved in hexane (Figure 8D) displayed strong peaks from 200 to 250 nm, after which the peaks dropped off, with a small hub between 550 nm and 600 nm. Physical color changes were seen in all the solvents after sonication. There is also a visible color change that was observed within each solvent after sonication. Methanol changed from a clear to a bright blue color, and acetonitrile changed from a clear to a pale grey. There was considerably less color change seen in chloroform, as there was less color change observed as compared to the other solvents. Color change was also observed in hexane where the solvent changed from a clear to a pale blue color (Figure 9). Using these results, MPs likely contain oxidized organic functional groups or leachable organic additives such as UV stabilizers, plasticizers, antioxidants, or degradation products present in the samples (Fang et al., 2012; Masrat et al., 2013; Galisinova et al., 2013; Mohd et al., 2018; Abo et al., 2016; Chen et al., 2014; Zhang et al., 2023; Pavanello et al., 2022; Basu et al., 2009). The appearance of visible region absorption band indicates the presence of chromophoric compounds, which may originate from synthetic dye, pigments or adsorbed organic contaminants on MPs (Mohd et al., 2018; Jiang et al., 2025; Sharma et al., 2024; Bartasun et al., 2013; Zhao et al., 2022).

The terrestrial and aquatic environments of the Sukhna Lake watershed are largely impacted by MP pollution. While the MPs themselves pose a threat due to their persistence, their ability to absorb, transport, and accumulate pollution further escalate its effects. Evidence collected via FTIR, FE-SEM EDS, XPS, ICP-MS, and UV-Visible spectroscopy suggests that the recovered MPs have undergone extensive environmental weathering (Sharma et al., 2025). This has further resulted in the surfaces of the MPs being oxidized, developing mineral coatings, and accumulating organic and inorganic contaminants. If the contaminants present in the soil matrix become mobile, they possess the ability to travel across watersheds, into this vulnerable aquatic environment. This mobilization can occur via wind erosion, rainfall, surface runoff, or flooding events, especially during the monsoon season in Chandigarh, where seasonal streams (choes) act as a transportation pathway, carrying MPs and associated pollutants across the ecosystem, ultimately into the Sukhna Lake. Overall, this increases the bioavailability of the contaminant and may cause the MPs to act as both a physical pollutant and a carrier for the redistribution of chemicals across the watershed.

This present research is one of the first studies that investigates the MPs on the site of origin rather than the site of deposition in this area. In a recent study MPs were examined within the Sukhna lake (5–75 particles per L) and sediment (170–2320 particles per kg) (Ajay et al., 2026); however, in this study, the soils around the lake were assessed as a source of MP pollution. These pollutants enter the lake via runoff, erosion or flooding-especially during the rainy season. By examining them individually and as carriers of pollutants, this study highlights the environmental significance of MPs in the Sukhna Lake and in other similar environments. Nevertheless, this research can be further expanded by adding multiple sample collection sites, so the spatial viability of the MPs across the watershed can be assessed. While only the Choe was studied, the surrounding watershed includes forests, agricultural land, and urban areas, all of which offer different insights into the MP pollution of the Lake. By expanding the study site, a more comprehensive study can be produced, which may better explain the fate of MP and their associated pollutants.

This study highlights the significant role that MPs play as carriers of pollutants within the soil of the Sukhna Lake Watershed. Because these samples were collected from the Sukhna Lake Choe, as they become mobilized seasonally. Thus, these pollutants have a high capacity for further polluting the main water body. A systematic sampling approach and advanced analytical techniques enabled the identification and characterization of MPs and their associated contaminants. The results obtained from the FTIR analysis determined the type of plastics present in the area, including PP, PE, PET, HDPE/LDPE, PVC and PS, which demonstrate the prevalence and diversity of MPs in the sampled soil. The shape, size, and elemental composition of these MPs were also determined via FE-SEM, EDS-Mapping, and XPS, respectively. It was observed that plastics had undergone prolonged interactions with the environment. This has resulted in the formation of rough and abraded surfaces on the MPs, which allow them to be highly capable of interacting with contaminants.

Furthermore, ICP-MS and solvent extraction followed by UV-Visible spectroscopy were used to identify any possible additives. The results suggested the presence of organic and inorganic contaminants was associated with the MPs, including heavy metals. The combined results emphasize that the MPs present in the watershed can function as potential vectors for the accumulation and transport of potent and persistent contaminants.

Overall, this study provides valuable insights into the environmental risks posed by MPs and their associated pollutants by employing multiple analytical techniques to assess the composition, weathering state, and contaminant-carrying potential. These results emphasize the need for improved waste management strategies, stricter regulations on plastic usage, and further research to better understand the long-term impacts of this pollution on terrestrial and aquatic ecosystems, especially given the sensitivity of the Sukhna Lake ecosystem.