A research team examined how MPs DOM forms and evolves by running controlled leaching experiments on four common microplastics polyethylene, polyethylene terephthalate, polylactic acid, and polybutylene adipate co terephthalate under dark and ultraviolet light conditions. The researchers compared dissolved organic matter released from these plastics with natural dissolved organic matter, or N DOM, to determine how light exposure and polymer type influence the quantity and chemistry of the leached material.
The team tracked dissolved organic carbon release over time and analyzed the kinetics using zero order and pseudo second order models, along with intraparticle diffusion and Boyd type approaches to identify rate limiting steps. They combined these bulk measurements with a suite of spectroscopic and mass spectrometric tools, including FT IR for functional groups, fluorescence excitation emission matrices with PARAFAC modeling for component dynamics and indices such as FI, BIX, and HIX, and ultrahigh resolution FT ICR MS for molecular formulas, elemental classes, and van Krevelen style compositional trends.
Under dark conditions, dissolved organic carbon rose steadily for both natural and plastic derived sources, but N DOM released substantially more DOC than MPs DOM, and biodegradable plastics yielded more DOC than conventional polymers. Kinetic and diffusion analyses indicated that MPs DOM release was constrained mainly by intraparticle diffusion, while N DOM release was governed by film diffusion at the water interface.
Ultraviolet exposure sharply increased DOC release rates from all plastics and accelerated MPs DOM production, particularly from biodegradable polymers such as PLA and PBAT, which reflected their less stable chemical structures. Zero order kinetics remained valid under UV, indicating that DOC release was controlled by polymer properties and irradiation conditions rather than by DOC concentration in the water. Under UV, diffusion control shifted toward film diffusion for both MPs DOM and N DOM, showing that sunlight alters not only the amount but also the transport regime of dissolved material from microplastics and natural sources.
The ratio of UV irradiated to dark DOC production increased over time, with UV sensitivity ordered PBAT greater than PLA greater than PET greater than PE, and all plastics more responsive than natural dissolved organic matter. This ranking confirmed that ultraviolet radiation acts as the main driver of MPs DOM formation and highlighted biodegradable polymers as important contributors to dissolved plastic derived carbon under sunlit conditions.
Spectroscopic data showed that UV light promoted the release of polymer monomers, oligomers, and additives, including phthalate plasticizers, and generated oxygen containing functional groups through hydrolysis and photochemical reactions. These changes shifted MPs DOM toward lower molecular weight, more oxidized compounds that differ from the more stable, terrestrially derived humic character of natural dissolved organic matter.
Fluorescence analyses indicated that MPs DOM moved from additive dominated signatures toward more protein like and low molecular weight humic like components as irradiation progressed, whereas N DOM remained dominated by humic like material with relatively stable fluorescence indices. FT ICR MS further resolved polymer specific molecular pathways, showing that PET derived DOM became more oxidized and aromatic, while PLA derived DOM shifted toward carbohydrate and tannin like formulas and other MPs DOM trajectories diverged from those observed for natural DOM.
These molecular fingerprints demonstrate that MPs DOM behaves as a distinct and dynamic fraction of dissolved organic matter rather than a simple extension of natural DOM. The results indicate that sunlight exposed microplastics create evolving clouds of dissolved compounds with compositions controlled by polymer type, additives, and irradiation history, introducing new chemical diversity into aquatic systems.
The study concludes that MPs DOM functions as a chemically active agent in aquatic environments, not just as an extra carbon source. Its relatively low molecular weight and oxidized character make it highly bioavailable, with the potential to either stimulate or inhibit microbial activity and to modify food web structure.
According to the authors, MPs DOM can bind trace metals, influence mineral transformation, and interfere with pollutant adsorption and transport, thereby reshaping contaminant behavior in surface waters and treatment systems. The material may also serve as a precursor for disinfection byproducts during water treatment and can generate reactive oxygen species under sunlight, which in turn can participate in contaminant degradation and nanoparticle formation.
By mapping how microplastic derived dissolved organic matter forms, evolves, and interacts with other components of aquatic chemistry under light and dark conditions, the work provides a mechanistic basis for including MPs DOM in assessments of water quality and carbon cycling. The findings suggest that accounting for this dissolved pollution pathway is important when evaluating the long term environmental footprint of plastics and the effectiveness of biodegradability strategies in sunlit surface waters.
Research Report:Molecular-level insights into derivation dynamics of microplastic-derived dissolved organic matter
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