Four types of MPs (mPE, mPP, mPS, and mPVC) were selected for based on their high abundance in nearshore waters surrounding Hainan Island, China (Gao et al., 2022b). MPs with three distinct particle sizes (i.e., approximately 13, 165, and 550 μm), representative of the 10 μm–1 mm range prevalent in marine environments, were mechanically generated by Shunjie Technology Co., Ltd. (Dongguan, China). Key properties of the MPs are summarized in Supplementary Table S1 . Spectroscopic grade potassium bromide was obtained from Aladdin Biochemical Technology Co., Ltd., Shanghai, China. Natural seawater was collected from Haikou, Hainan Province, China (20°3′48″E, 110°24′54″N), filtered through a 0.22 μm filter membrane. The physicochemical properties and compositions of seawater were shown in Supplementary Table S2 , and specific determination methods were detailed in Supporting Information Text S1 . A UVA-340 nm lamp (Q-Lab Corporation, USA; 20 W output, peak wavelength: 340 nm) was employed to simulate solar ultraviolet radiation.

Pristine MPs were sequentially rinsed with deionized water, air-dried, and mixed with natural seawater in glass culture dishes (MPs: 3.5 g, seawater: 40 mL). Subsequently, all culture dishes were transferred to a custom-designed aging chamber (dimensions: 90 × 180 × 40 cm; Supplementary Figures S1a, b ) maintained at 25°C for 15, 30, 90, and 180 days, with triplicate samples per timepoint. UVA possesses strong penetration capabilities, enabling it to traverse glass. Each chamber layer contained two UVA-340 tubes, delivering irradiance comparable to midday summer sunlight (0.70–0.80 μW/cm²) (Brennan, 1987). The UVA intensity was verified using a calibrated photometer (Sanpo Instrument Co., Ltd., China), measuring 78.1 μW/cm² at the lamp surface and 68.8 μW/cm² through the seawater-covered culture dish. To minimize evaporation, dishes were sealed with lids, and deionized water was replenished periodically ( Supplementary Figure S1c ). Post-aging, MPs were collected, surface-cleaned with deionized water, air-dried at room temperature, and stored in brown glass bottles for subsequent analysis (see Supporting Information 1 Text S2 for collection protocols).

The size of MPs was determined with a laser diffraction particle size analyzer (MAZ3000, Mastersizer, UK). The surface structures of MPs were examined by using Field Emission Scanning Electron Microscopy (FESEM, Verios G4 UC, Thermo Fisher Scientific, USA). The elemental composition of MPs surfaces was analyzed by using an X-ray Fluorescence Spectrometer (XRF, ArL Perform x, Thermo Scientific, USA). A Fourier Transform Infrared Spectrometer (FTIR, Tensor 27, Bruker, Germany) was employed to analyze the functional groups of MPs. An X-ray Diffractometer Spectrometer (XRD, DX-2700BH, Tianrui, China) was used to analyze the crystallinity of MPs. Triplicate measurements ensured reproducibility, with representative spectra selected for analysis. Details were provided in Supporting Information 1 Text 3 .

The CI is employed to quantitatively assess the degree of aging and oxidation in polymers, which is determined through analysis of FTIR spectra (Dong et al., 2022; Su et al., 2024). The CI calculation method was shown in Table 1 . Initial attempts to model CI using a first-order kinetic equation yielded poor fits ( Supplementary Table S3 ). Consequently, a modified first-order model incorporating an empirical parameter A and the Elovich kinetic model were applied to fit the CI ( Table 1 ).

One-way analysis of variance (ANOVA) was performed using IBM SPSS 25 for statistical analysis, with significant differences assessed using the LSD multiple range test (P <0.05). The FESEM images were annotated and combined using Adobe Photoshop 2021. The FTIR and crystallinity spectra were examined using the Thermo Scientific OMNIC Series and MDI Jade 6.5 software, respectively. Experimental data, CI fitting, and data visualization were conducted using Excel 2019 and Origin 2018.

The aging process induced distinct structural alterations across MP types under UVA irradiation ( Figure 1 ). While mPE, mPP, and mPS exhibited no significant color changes, mPVC developed a pronounced yellow hue after 180 days of exposure, indicative of surface oxidation and chromophore formation via photoinduced reactions (Sun et al., 2020). Plastic aging typically occurs through cracking and peeling. Initial surface analysis revealed smooth textures for pristine MPs (550 μm). However, progressive aging introduced structural defects, including flakes, cracks, protrusions, and oxidized particles ( Figure 1 ), likely due to UVA radiation (Liu et al., 2020; Mao et al., 2020). Notably, the extent of deterioration varied with material and duration. For example, after 15-day aging, mPE and mPP developed noticeable particles, fragments, and cracks, while mPS showed minor fragmentation and mPVC remained mostly smooth with only a few fragments. After 30 days of aging, the aforementioned aging phenomenon became more pronounced. With prolonged aging time, the surfaces of MPs gradually transitioned from an initial smooth to rough. After 180-days aging, mPE and mPP exhibited disordered surface structures characterized by prominent pits, deep holes, and fractures; whereas mPS and mPVC displayed multiple cracks, numerous fragments, and particles.

Specifically, mPE contains unsaturated bonds (C=C) within the main chain or end chains, and exhibits frequent active branching points. These points are susceptible to oxidation by O₃, NO_x, or atmospheric free radicals, forming highly unstable hydrogen peroxide that subsequently transforms into stable carbonyl groups with UVA absorption properties (Chamas et al., 2020; Rabek, 1995). mPP, especially in amorphous or low-order forms, is prone to oxidation at tertiary carbon atoms, leading to the formation and decomposition of hydrogen peroxides (Oswald and Turi, 1965). The migration of mPS free radicals within the polymer matrix induces degradation under UVA radiation, forming brittle regions or layers on their surface (Cooper, 2012; Yousif and Haddad, 2013). In contrast, mPVC’s disordered open structure makes it less sensitive to UVA radiation and less susceptible to peeling (Arnold, 1995; Christensen et al., 2018). Furthermore, the accelerated aging in seawater compared to freshwater systems underscores the synergistic role of salinity. Chloride ions likely catalyzed hydrolysis and oxidative chain cleavage, enhancing surface roughness (Ding et al., 2020; Gao et al., 2021).

Moreover, some elements were detected on the surface of aged MPs, including Ag, Br, Ca, Cl, Fe, Ho, K, Lu, Mg, Si, Sr, Sx, Ti, Yb, and Zn ( Figures 2a–d ), indicating that MPs release internal structural elements during aging. The content of Ag, Br, Cl, Fe, K and Mg increased with prolonged aging time, suggesting progressive release of intrinsic additives (e.g., catalysts, plasticizers) from polymer matrices. For instance, Zn and Fe residues likely originated from Ziegler-Natta catalysts used in polyolefin synthesis (Groh et al., 2019; Turner and Filella, 2021). The emergence of surface cracks facilitated oxygen diffusion and elemental leaching, creating a feedback loop that accelerated oxidative degradation (Luo et al., 2020). Such elemental redistribution poses ecological risks, as heavy metals (e.g., Zn, Fe) may interact with marine biota or adsorb co-pollutants.

Comparative analysis of MPs across sizes (13 μm, 165 μm, 550 μm) revealed divergent aging trajectories ( Supplementary Figure S2 , S3 ). Larger MPs (550 μm) exhibited earlier onset of surface roughening (15 days vs. 30 days for 13 μm MPs). This may be attributed to higher surface-to-volume ratio in smaller particles, which delays crack initiation by distributing stress more evenly. Shorter diffusion pathways for oxygen and radicals in smaller MPs, promoting uniform oxidation over localized degradation (Liu et al., 2020). Paradoxically, smaller MPs (13 μm) displayed higher surface elemental concentrations ( Supplementary Figure S3 ), attributed to their greater specific surface area enhancing additive exposure and leaching (Mao et al., 2020). This inverse relationship between particle size and elemental release underscores the complexity of MPs aging mechanisms, necessitating multi-parameter assessments (e.g., CI, crystallinity) for holistic evaluation.

XRD analysis revealed insights into the structural reorganization of MPs during UVA-induced aging. While mPVC exhibited complex diffraction patterns with overlapping peaks, precluding quantitative analysis, distinct crystallinity trends were observed for mPE, mPP, and mPS ( Figures 2e–h ).

No notable changes in the peak positions were observed in the four types of aged 550 μm MPs. mPE exhibited strong peaks at 21.5° and 23.9°, while mPP showed distinct peaks at 14.2°, 16.9°, and 21.9°. The primary peak for mPS was identified at 19.6°. Notably, the XRD spectra of aged MPs exhibited a noticeable increased peak intensity compared to pristine MPs. This suggests that aging affects MPs crystallinity, which is consistent with previous studies (Liu et al., 2018; Ma et al., 2019; Su et al., 2024). Additionally, this study revealed an intriguing phenomenon whereby the crystallinity of MPs diminishes over time. The crystallinity of aged 15 d MPs peaked, while the crystallinity of aged 180 d MPs only marginally surpassed that of pristine MPs. This may be attributed to the preferential degradation of amorphous regions during early aging stages, which temporarily increases crystallinity (Rouillon et al., 2016; Sun et al., 2020). Velzeboer et al. (2014) noted that oxidative damage to molecular chains can hinder crystal formation, reducing crystallinity after aging. The decrease of crystallinity of MPs may affect the change of the mass of the crystal region. UV aging can cause molecular chain breakage, leading to lower molecular weight and reduced crystal mass (Zhang et al., 2025). Additionally, new defect areas such as micropores and cracks may form during aging, further degrading crystal quality (Anshari et al., 2025).

Prolonged aging of MPs leads to the oxidation of amorphous regions, generating oxygen-containing functional groups and diminishing crystallinity. This phenomenon is mostly caused by oxidative reactions during continuous degradation of plastics, leading to chain fragmentation and incorporation of diverse polar functional groups. In particular, carbonyl groups tend to be enriched in the amorphous regions of polymers (Anshari et al., 2025). These groups can disrupt the regularity of molecular long chains and induce their entanglement, forming amorphous regions within MPs (Litvinov et al., 2020; Singh and Sharma, 2008). For instance, polyethylene terephthalate (PET) exposed to air shows higher CI values from peresters or anhydrides, indicating significant degradation in amorphous regions (Matsumoto et al., 2023). Various functional groups introduce compositional and structural diversity, causing variable changes in MPs’ crystallinity levels. Decreased crystallinity enhances material brittleness while reducing toughness, accelerating plastic fracture (Dong et al., 2022).

Smaller MPs (165 μm) exhibited enhanced crystallinity compared to larger counterparts (550 μm). For mPE and mPP, peak intensities doubled in 165 μm MPs ( Supplementary Figures S4a, b ), attributable to higher surface area accelerating amorphous phase oxidation (Ma et al., 2019). Notably, 13 μm mPS showed a progressive peak shift from 19.6° to 14.5° after 90 days ( Supplementary Figures S4e-g ), signaling nanoscale structural reorganization via chain fragmentation. Though excluded from quantitative analysis, mPVC exhibited unique behavior: maximal diffraction intensity at 15 days ( Supplementary Figures S4d, h ), followed by progressive broadening. This suggests rapid additive leaching (e.g., plasticizers) initially stabilizes the structure, followed by chlorine loss-induced amorphization (Christensen et al., 2018). Overall, UVA radiation exposure increases MPs crystallinity and alters surface structure.

The interaction and cross-linking of free radicals in MPs can occur under UVA radiation, leading to external forces that impede segmental motion. This reduces elongation at break and increases brittleness (Galloway and Lewis, 2016; Liu et al., 2020). Besides surface morphology changes, the composition, properties, and functionalities of MP surfaces also modify during aging.

As shown in Figures 2i–l , FTIR spectra of pristine and aged MPs are similar. However, subtle changes and new peaks were observed in the functional groups corresponding to aged MPs, indicating modifications in the surface chemical structure of aged MPs. For instance, aged mPE displayed peaks at 2921, 2848, 1657, and 1466 cm^-1; aged mPP showed peaks at 3340, 3030-2780, 1720, 1460-1380, and 1170 cm^-1; aged mPS demonstrated peaks at 3440, 3130, 2820, 1880, 1600, 1490, and 694 cm^-1; whereas aged mPVC presented bands at wavelengths of 2920, 1720, and 1630–609 cm^-1 (e.g., 1430, 879 cm^-1). These deviations from pristine MPs suggest increased degradation with aging. Peak intensities of functional groups on MPs’ surfaces become more prominent over time, especially after 180 days, confirming the detrimental impact of extended UVA radiation on the surface structure of MPs. This is consistent with previous studies showing that MPs undergo photooxidation under UVA exposure (Gao et al., 2022a).

The spectral range of 3750–3000 cm^-1 corresponded to hydroxyl (-OH) stretching vibration. The peak intensity of aged mPP and mPS was enhanced at 3440 cm^-1, indicating intensified -OH bonds stretching. Within the range of 3000–2700 cm^-1, novel peaks (mPP, mPS, mPVC) or stronger peak intensities (mPE) were observed, suggesting the presence of surface-bound C-H stretching ( Table 2 ). UVA irradiation-induced degradation of MPs increases oxygen exposure, leading to extensive oxidation reactions (Cai et al., 2018; Yu et al., 2023). Moreover, the higher concentration of chloride ions in seawater facilitates substitution reactions, enhancing -OH stretching (Mao et al., 2020). The FTIR spectra of aged mPE, mPP, mPS, and mPVC exhibited significant changes in the carbonyl stretching vibration region (1900–1650 cm^-1), indicating C=O stretching ( Table 2 ). Previous study showed that -OH and C=O serve as prominent indicators of polymer oxidation, with increased C=O implying the incorporation of oxygen into carbon-hydrogen bonds (Brandon et al., 2016). Additionally, aged samples also exhibited C=C double bond stretching in the 1690–1500 cm^-1. Within the 1475–1000 cm^-1 range, MPs displayed X-H in-plane bending vibrations, X-Y stretching vibrations, C-H in-plane bending or C-O stretching and skeletal vibrations associated with C-C single bonds ( Table 2 ). The phenomenon may be attributed to the adsorption of substances, such as Laurocapram (aliphatic) and Phthalic anhydride (aromatic), by MPs in seawater ( Supplementary Table S2 ). Previous studies demonstrated that MPs surfaces were rich in bisphenol A, polychlorinated biphenyls, nonylphenols, and other organic substances (Hirai et al., 2011; Mato et al., 2001; Pascall et al., 2005). Some research also indicated that mPE and micro-poly (butyleneadipate-co-terephthalate) (mPBAT) exhibited varying degrees of changes in aromatic and aliphatic C-O and C=O bonds under H₂O₂ influence (Du et al., 2024). MPs aging modifies surface morphology and functional groups, primarily due to fractured surfaces facilitating oxygen ingress and accelerating aging (Luo et al., 2020). After a 15-day aging period, novel peaks emerge within the range of 1000–650 cm^-1 for aged mPS; whereas for aged mPP and mPVC, new peaks begin to manifest after 90 days of aging, predominantly associated with out-of-plane bending vibrations of olefins and aromatics such as ortho-disubstituted benzene rings (770–735 cm^-1), meta-disubstituted benzene rings (710–690 and 810–750 cm^-1), and para-disubstituted benzene rings (830–810 cm^-1).

FTIR spectroscopy of MPs with smaller particle sizes (165 and 13 μm) showed that as aging time increased, differences in their infrared spectra became more pronounced. Aged MPs exhibited significant changes in C-H stretching vibrations (3000–2700 cm^-1), while aged mPS and mPVC showed more pronounced variations in out-of-plane bending vibrations (1000–650 cm^-1). In seawater conditions, long-wave ultraviolet irradiation affects MPs-oxygen interaction, leading to polymer chain breakage and crosslinking.

Meanwhile, FTIR spectroscopy of MPs with smaller particle sizes (i.e., 165 and 13 μm) revealed that as aging time increased, differences in their infrared spectra became more pronounced ( Supplementary Figure S5 ). All aged MPs exhibited significant changes in functional groups within the C-H stretching vibration region (3000–2700 cm^-1), while aged mPS and mPVC showed more pronounced variations in the out-of-plane bending vibration region (1000–650 cm^-1). In conclusion, during photodegradation under seawater conditions, long-wave ultraviolet irradiation can affect MPs-oxygen interaction, leading to a cascade of physicochemical reactions such as polymer chain breakage and crosslinking.

The CI serves as a reliable indicator of MPs aging, quantifying changes in carbonyl content and facilitating the evaluation of polymer chain breakage (Di Pippo et al., 2020). As shown in Figures 3a–d , the CI of aged MPs increased significantly over time: 180 d >90 d >30 d >15 d >0 d. Significant variations were observed before each treatment (P <0.05), except for mPE-550 μm, mPE-165 μm, and mPP-550 μm. This result was consistent with previous research and can be primarily attributed to oxidation reactions on the surface of MPs under UVA irradiation (Dong et al., 2022; Zhang et al., 2023). The 550 μm mPE exhibited a higher CI value than the other two sizes of mPE (i.e., 165 and13 μm), likely due to its initially higher CI. The mPE and mPS exhibited higher CI values followed by mPVC, while mPP had the lowest. This indicated that different types of MPs exhibited varying degradation rates.

Simultaneously, the CI rate was calculated to quantify the aging rate of MPs. The mPE exhibited a significantly higher rate at 30 days of aging compared to other aging time (P <0.05), ranging from 0.0200-0.0457% per day ( Supplementary Table S4 ). A similar trend was observed for mPVC, while mPP and mPS demonstrated peak CI rates at 15 or 30 days of aging. The result is interpreted as substantial oxidation during the early stages of MP aging, consistent with previous findings on direct photolysis in early weathering (Dong et al., 2022). Moreover, smaller-sized MPs (i.e., 165 and 13 μm mPS, and 13 μm mPVC) exhibited lower CI rates, indicating slower degradation rate for small-sized MPs in the environment. The result was consistent with FESEM observations (Section 3.1). Therefore, more attention and concern should be paid to the small-sized MPs, particularly their potential environmental impact.

To gain a more profound insight into the aging process of MPs, this study aimed to correlate CI with aging time. Initially, a first-order kinetic model was employed to fit CI values; however, these fitting results were deemed unsatisfactory ( Supplementary Table S3 ). Previous study also indicated that standard kinetic models were inadequate in explaining the degree of MPs aging or fragmentation (Di Pippo et al., 2020). While suitable for simple degradation processes, the first-order model is limited in complex scenarios with nonlinear behaviors and specific environmental conditions (Bekins et al., 1998; Wang et al., 2018). For example, factors such as temperature, pH levels, salinity, and microorganisms can influence reaction rates, leading to deviations from first-order kinetics. Although this study was conducted under UVA-340 irradiation and constant temperature, the presence of microorganisms in seawater complicates the degradation of MPs, thereby reducing the effectiveness of the first-order model.

To improve fitting accuracy, we incorporated an additional parameter into our modified first-order kinetic model. The fitting results demonstrated high accuracy ( Figures 3e–h ), with R² ranging from 0.88 to 0.99 ( Supplementary Table S5 ). In contrast, previous study reported significantly lower R² of 0.774, 0.849, and 0.891 when employing first-order kinetics to fit mPP, mPET, and mPLA, respectively (Su et al., 2024), which contrasted sharply with our improved model in this study. However, further validation is necessary to confirm the significance of the parameters utilized in first-order kinetic improvement model. The Elovich model performed noticeably worse than our modified first-order model but showed satisfactory fits for 165 and 13 μm mPE, 165 μm mPP, as well as 550 μm mPVC, with R² ranging from 0.73 to 0.89. However, it performed poorly for mPS, with a maximum R² of 0.57 ( Figures 3i–l and Supplementary Table S5 ). This highlights the complexity of MPs degradation in marine environments under UVA irradiation and underscores the limitations of simple kinetic models. This may be attributed to the material characteristics of MPs, including molecular weight, structure, and additives distribution significantly influence MPs degradation mechanism (Di Pippo et al., 2020; Liu et al., 2022).

In summary, the aging behavior of MPs is a complex environmental phenomenon requiring consideration of multiple factors for thorough investigation. These factors encompass elements such as temperature, UV radiation, coexisting pollutants, and inherent material properties. Consequently, exploring the aging behavior of MPs remains a formidable challenge.

The main chains of mPE, mPP, mPS, and mPVC are composed of carbon atoms, leading to similar photodegradation mechanisms in seawater. This process can be categorized into four steps: light initiation, free radical reaction, chain scission and surface oxidation ( Figure 4 ). UVA irradiation cleaves C-H bonds, generating alkyl radicals (R•) that react with dissolved oxygen to form peroxyl radicals (ROO•) (Dimassi et al., 2022). These reactive intermediates abstract hydrogen from adjacent polymer chains, propagating radical chains and forming hydroperoxides (ROOH) (Ashfaq et al., 2020). Hydroperoxide photolysis (ROOH→RO• + •OH) induces backbone cleavage, reducing molecular weight and generating low-molecular-weight fragments (LMWFs) (Bracco et al., 2018). Concurrently, radical recombination promotes crosslinking, forming brittle three-dimensional networks (Gryn’ova et al., 2011). Oxidative functionalization introduces hydroxyl, carbonyl, and carboxyl groups ( Figures 2i–l ), enhancing hydrophilicity and microbial colonization (Gao et al., 2021; Gewert et al., 2015). FTIR spectra confirmed progressive CI increases, with mPE and mPP showing the highest oxidation levels after 180 days ( Supplementary Table S4 ).

The degradation process of mPE in seawater is relatively straightforward. mPE degradation initiates via C-H bond cleavage at branching points, forming allylic radicals that rapidly oxidize to peroxides ( Figure 4 ). This mechanism represents the crucial initial step in photodegradation (Bracco et al., 2018; Zhu et al., 2024), which was supported by the FTIR spectrum ( Figure 2i ). Chain scission produces LMWFs (<1 kDa), including aldehydes and ketones, which are readily metabolized by marine microbes to CO₂ and H₂O (Ghatge et al., 2020). Crosslinking dominates at later stages, creating surface microcracks that accelerate embrittlement.

The tertiary carbons in mPP’s -CH₃ side chains are highly susceptible to radical attack, leading to faster peroxide formation than mPE (Oswald and Turi, 1965). This results in 22.2% higher CI values for mPP compared to mPE after 180 days ( Supplementary Table S4 ). Degradation generates methyl ketones and carboxylic acids, which enhance bioaccessibility but also increase ecotoxicity due to additive leaching (Gewert et al., 2015). Both mPE and mPP exhibited surface roughening under ultraviolet radiation, but the specific manifestations of these two types of MPs differ ( Figure 1 ). Therefore, when investigating the weathering or degradation of MPs, it is important to consider the distinct degradation characteristics among different types of MPs.

The primary distinction in the degradation mechanism between mPS and mPE lies in the benzene ring, which can stabilize free radicals, slowing down the degradation rate of mPS (Yousif and Haddad, 2013). Prolonged UV exposure forms phenylperoxyl radicals (PhOO•), which decompose into benzaldehyde and benzoic acid—substances with demonstrated allelopathic effects on phytoplankton (Nakatani et al., 2022). FESEM images show that mPS has significantly lower surface roughness compared to mPE and mPP ( Figure 1 ). Additionally, the CI for mPS was notably lower than that of mPE, especially after 180 days of aging. For instance, the CI for 13 μm mPE reached 0.0117 ± 0.0008, compared to 0.0076 ± 0.0007 for mPS ( Supplementary Table S4 ).

The molecular structure of mPVC includes chlorine atoms, leading to a distinct photodegradation process in seawater compared to other MPs. mPVC undergoes dechlorination under UVA, cleaving C-Cl bonds to release HCl and chlorine radicals (Cl•) (Peng et al., 2022). The dechlorination process leads to a complex and slow degradation of mPVC (Kudzin et al., 2024), and the surface roughness of mPVC was significantly lower than other MPs ( Figure 1 ). These radicals propagate chain scission, producing chlorinated LMWFs (e.g., dichloroethanes) that resist biodegradation and exhibit acute toxicity (Novotný et al., 2022). Surface Cl content increased by 18% after aging ( Figures 2a, d, h ), correlating with inhibited microbial activity in coastal sediments (Gao et al., 2023).

MPs degradation in seawater involves photodegradation and biodegradation, both influenced by environmental conditions such as salinity, temperature, and pH (Kaing et al., 2024). Elevated salinity and ionic diversity in seawater can affect MPs’ surface properties, impacting pollutant adsorption and degradation. Lower seawater temperatures further inhibit both the rates of photodegradation and free radical reactions, but localized conditions (such as near hydrothermal vents or warm currents) can result in higher temperatures that may accelerate thermal degradation of MPs. pH influences the stability of oxidation products and microbial activity. In marine environments, physical processes such as wave action and sediment interactions cause mechanical abrasion of MPs (Sipe et al., 2022; Song et al., 2017). Additionally, microorganisms in marine environments can decompose MPs, but biodegradation is slow due to low oxygen levels and seawater temperatures. Meanwhile, MPs additives release substances during degradation, affecting the overall process (Gewert et al., 2015). The size and type of MPs also serve as influential factors on their degradation. In conclusion, the degradation rates of MPs can be ranked as follows: mPP >mPE >mPS >mPVC. A better understanding of these factors will aid in developing effective strategies for managing plastic waste and mitigating marine pollution.