Researchers have mapped the molecular changes that unfold as sunlight causes plastics to leach dissolved organic matter, findings that could reshape understanding of ecosystem health, water quality, and global carbon cycling.
Scientists have found that microplastics drifting through rivers, lakes, and oceans steadily release a wide range of dissolved organic chemicals into the water. These chemicals change over time, with sunlight playing a major role in how they form and break down. The research offers the most detailed molecular-scale look so far at how microplastic-derived dissolved organic matter, known as MPs DOM, develops and changes in natural aquatic environments.
The study, published in New Contaminants, examined four widely used types of plastic and compared the chemicals they release with naturally occurring dissolved organic matter found in rivers. By combining kinetic modeling with fluorescence spectroscopy, high-resolution mass spectrometry, and infrared analysis, the team showed that each plastic produces its own chemical signature. These signatures shift as sunlight alters the surface of the polymers.
“Microplastics do not just pollute aquatic environments as visible particles. They also create an invisible chemical plume that changes as they weather,” said lead author Jiunian Guan of Northeast Normal University. “Our study shows that sunlight is the primary driver of this process, and that the molecules released from plastics are very different from those produced naturally in rivers and soils.”
To explore this process, the researchers placed microplastics made of polyethylene, polyethylene terephthalate, polylactic acid, and polybutylene adipate co terephthalate in water under both dark conditions and ultraviolet light for periods of up to 96 hours. Exposure to sunlight sharply increased the amount of dissolved organic carbon released by all four plastics. Materials designed to be biodegradable, such as PLA and PBAT, released the highest levels, which the researchers linked to their less stable chemical structures.
