Microplastics in aquatic environments are not merely visible pollutants; they continuously leak complex chemical mixtures into surrounding water, a process accelerated by sunlight. New research reveals that these invisible plumes, derived from various plastic types, differ significantly from natural organic matter and could impact ecosystems. The study, published in New Contaminants, provides detailed insights into this phenomenon.
Researchers have uncovered how microplastics drifting in rivers, lakes, and oceans emit invisible clouds of dissolved organic chemicals, known as microplastic-derived dissolved organic matter (MPs DOM). This leakage intensifies under sunlight exposure, transforming plastics into sources of evolving chemical signatures that may alter aquatic life.
The study examined four common plastics: polyethylene (PE), polyethylene terephthalate (PET), polylactic acid (PLA), and polybutylene adipate co-terephthalate (PBAT). Samples were exposed to water under dark and ultraviolet conditions for up to 96 hours. Sunlight sharply boosted the release of dissolved organic carbon from all types, with biodegradable options like PLA and PBAT yielding the highest amounts due to their unstable structures.
Using techniques such as kinetic modeling, fluorescence spectroscopy, high-resolution mass spectrometry, and infrared analysis, the team found that each plastic produces a unique mix of additives, monomers, oligomers, and photo-oxidized fragments. Aromatic-structured plastics like PET and PBAT generated particularly intricate mixtures. Over time, oxygen-containing groups such as alcohols, carboxylates, ethers, and carbonyls increased, alongside detectable additives like phthalates.
"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."
Fluorescence analysis indicated that MPs DOM mimics microbially produced organic material more than land-derived matter, with shifting balances of protein-like, lignin-like, and tannin-like substances based on plastic type and light exposure. The release follows zero-order kinetics, limited by surface factors, and under UV light, film diffusion plays a key role.
These chemical plumes pose risks by potentially stimulating or inhibiting microbial growth, disrupting nutrient cycles, interacting with metals and pollutants, generating reactive oxygen species, and affecting disinfection byproduct formation. "Our findings highlight the importance of considering the full life cycle of microplastics in water, including the invisible dissolved chemicals they release," noted co-author Shiting Liu. As plastic production rises, unregulated flows into waterways could amplify these effects, prompting calls for machine learning models to predict MPs DOM behavior and inform risk assessments.
