Researchers have found that microplastics drifting through rivers, lakes, and oceans constantly release a complex blend of dissolved organic chemicals into the water. This chemical leakage continues over time and becomes much more intense when plastics are exposed to sunlight. The new findings offer the most detailed molecular-level picture so far of how microplastic-derived dissolved organic matter, known as MPs DOM, forms and changes in natural aquatic environments.
The research, published in New Contaminants, examined four common types of plastic and compared the chemicals they released 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 type releases its own unique chemical mixture. These chemical signatures shift as sunlight gradually breaks down plastic surfaces.
“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.”
Sunlight speeds up chemical release from microplastics
To better understand how light affects plastic breakdown, the researchers exposed polyethylene, polyethylene terephthalate, polylactic acid, and polybutylene adipate co terephthalate microplastics to water under both dark and ultraviolet conditions for up to 96 hours. Exposure to sunlight sharply increased the amount of dissolved organic carbon released by every plastic tested. Plastics labeled as biodegradable, including PLA and PBAT, released the largest amounts, reflecting their less stable chemical structures.
Kinetic modeling revealed that the release process followed zero order behavior. This means the rate was controlled by physical and chemical limits at the plastic surface rather than by how much material was already dissolved in the water. Under ultraviolet light, the researchers identified film diffusion as the main factor slowing the release process.
Plastics release a complex mix of chemical compounds
Detailed chemical analyses showed that MPs DOM contains a wide range of molecules derived from plastic additives, monomers, oligomers, and fragments formed through photo oxidized reactions. Plastics with aromatic structures, such as PET and PBAT, generated especially complex chemical mixtures.
As the plastics continued to weather, the researchers observed a rise in oxygen containing functional groups. This shift pointed to the formation of alcohols, carboxylates, ethers, and carbonyls. Chemical additives like phthalates were also detected, which aligns with their relatively weak attachment within plastic materials.
Fluorescence measurements revealed another striking difference. MPs DOM closely resembled organic material produced by microbes rather than organic matter originating from land plants and soils. This pattern contrasts strongly with natural dissolved organic matter found in rivers. Over time, the balance of protein like, lignin like, and tannin like substances shifted depending on the type of plastic and the level of sunlight exposure.
Growing environmental risks from invisible plastic pollution
The changing chemical mixtures released by microplastics could affect aquatic ecosystems in multiple ways. MPs DOM is largely made up of small, biologically accessible molecules that may stimulate or suppress microbial growth, disrupt nutrient cycles, or interact with metals and other pollutants. Previous research has shown that MPs DOM can produce reactive oxygen species, influence the formation of disinfection byproducts, and alter how pollutants attach to particles in water.
“Our findings highlight the importance of considering the full life cycle of microplastics in water, including the invisible dissolved chemicals they release,” said co author Shiting Liu. “As global plastic production continues to rise, these dissolved compounds may have growing environmental significance.”
Predicting the future chemistry of plastic pollution
Because MPs DOM is chemically complex and constantly changing, the researchers suggest that machine learning tools could help forecast how these substances behave in natural waters. Such models could improve risk assessments related to ecosystem health, pollutant transport, and carbon cycling.
The authors also point out that the flow of microplastics into rivers and oceans remains largely unregulated. As plastics continue to fragment and degrade under sunlight, the release of MPs DOM is expected to increase. Understanding how these chemicals evolve across different stages of plastic breakdown will be essential for assessing their long-term environmental impact.
