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Photochemical reactivity of water-soluble dissolved organic matter from microplastics and microfibers
Summary
When microplastics and microfibers sit in water, they leach dissolved organic matter (DOM) that can react with sunlight to produce reactive chemicals. This study found that the type and amount of DOM released depends heavily on polymer chemistry, with aromatic plastics like PET and polystyrene releasing more light-absorbing DOM, and microfibers releasing more DOM overall than microplastic particles. Understanding how plastic-derived DOM breaks down in sunlight is important because these chemical by-products can interact with other aquatic pollutants and affect aquatic ecosystems in ways not yet fully understood.
Plastics in aquatic environments are a source of dissolved organic matter (DOM). However, its production pathways and environmental fate remain poorly understood. This study investigated the yields, characterization, and photochemical reactivities of water-soluble DOM from seven pristine microplastics (MPs) and three microfibers (MFs). We found yields of plastic-derived DOM per unit mass of MPs or MFs, including chromophoric DOM (CDOM) and dissolved organic carbon (DOC), were significantly influenced by polymer chemical structures. Notably, MFs exhibited consistently higher DOM yields compared to MPs. In addition, plastics containing aromatic rings, such as PETE and PS, were found to generate higher CDOM yields, although PVC also showed elevated CDOM yields. The plastic-derived DOM had a diverse molecular size-range, spanning from 60 nm (polyester-DOM) to 937 nm (LDPE-DOM), while Zeta potentials, which were predominantly negatively charged, varied from -42.5 mV (nylon-DOM) to +4.6 mV (LMW-PVC-DOM). Degradation rate constants for CDOM (0.001-0.022 h) were generally higher than DOC (0.0009-0.020 h), with a shorter half-life for PETE- and PS-derived DOM. The reactivity and degradation kinetics of plastic-derived DOM were notably manifested in changes of fluorescence spectra (excitation-emission matrixes) during photochemical weathering, showing the influence of polymeric composition/structures. This baseline study provides an improved understanding of the characterization and environmental fate of microfiber- and plastic-derived DOM in aquatic environments.