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Photodissolution of submillimeter-sized microplastics and its dependences on temperature and light composition
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Researchers examined how temperature and light wavelength affect photodissolution of polypropylene, polystyrene, and thermoplastic polyurethane microplastics in seawater, finding that UVB radiation exclusively drives dissolution, that a 20°C temperature increase can enhance dissolved organic carbon production by 3–10 times depending on polymer, and that estimated lifetimes for these plastics in warm surface waters range from 3.6 to 6.5 years.
Photodissolution has the potential to efficiently remove microplastics from the surface ocean. Here, we examined the effects of temperature and incident sunlight composition on the photodissolution of submillimeter-sized microplastics of polypropylene (PP), polystyrene (PS), and thermoplastic polyurethane (TPU) in seawater. The photoproduction of dissolved organic carbon (DOC), chromophoric dissolved organic matter, and dissolved nitrogen (TPU only) was observed to increase exponentially within 7 days of full-spectrum irradiation. The temperature dependence of photodissolution increased with irradiation time for PP and PS but remained relatively constant for TPU. A 20 °C increase in temperature enhanced DOC photoproduction by 10 times for PP, three times for PS, and four times for TPU at 7-d irradiation, giving activation energies of 59.4-84.8 kJ mol. Photodissolution of all three polymers was exclusively driven by ultraviolet-B (UVB) radiation. PS-derived DOC was photomineralizable, while PP- and TPU-derived DOC appeared photo-resistant. Extrapolating the lab-based DOC photoproduction rates to warm surface oceans yields lifetimes of 6.5 years for PP, 3.6 years for PS, and 3.7 years for TPU. This study demonstrates that photodissolution of the tested microplastics is restricted to the thin UVB-penetrable surface ocean and that water temperature plays a critical role in controlling the photodissolution of these microplastics.
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Photochemical dissolution of buoyant microplastics to dissolved organic carbon: Rates and microbial impacts
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Common ocean surface microplastics (PE, PP, EPS) were irradiated under simulated sunlight, which fragmented and oxidized the polymers and produced dissolved organic carbon as a significant byproduct. The study identifies sunlight-driven photochemical dissolution as an important but poorly quantified removal mechanism for buoyant microplastics from the ocean surface.
Warming exponentially stimulates photoleaching of dissolved organic matter from multiple microplastics
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Researchers quantified dissolved organic matter release from four common marine microplastics (PE, PP, PET, PVC) under UV light at temperatures ranging from 10–35°C, finding that warming exponentially increased photoleaching rates — with implications for how climate change may accelerate microplastic-derived carbon cycling in ocean surface waters.
Size and Structure-Dependent Molecular Fingerprint Transformation of Microplastic-Derived Dissolved Organic Matter in Sunlit Seawater: Implication for Marine Carbon Cycles
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This study examined how the size and structure of microplastics influence the photochemical transformation of MP-derived dissolved organic matter under UV irradiation, finding that inherent plastic properties determine the molecular character of DOM released and its effects on ocean carbon cycling.
Molecular Signatures of Dissolved Organic Matter Generated from the Photodissolution of Microplastics in Sunlit Seawater
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Researchers incubated polyethylene, polypropylene, and expanded polystyrene microplastics in sunlit seawater and characterized the dissolved organic matter produced as the plastics broke down. The study found that sunlight generated hundreds of unique oxygen-containing chemical products from each plastic type, while virtually none were produced in the dark. Evidence indicates that a single process, photodegradation, can transform simple plastic polymers into a complex array of dissolved organic chemicals in ocean environments.
Solar radiation stimulates release of semi-labile dissolved organic matter from microplastics
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Researchers found that solar radiation causes microplastics to release dissolved organic matter into seawater, with low-density polyethylene releasing about five times more carbon per gram per day than polystyrene. The released organic compounds included nitrogen- and sulfur-containing molecules, and a portion overlapped with compounds found naturally in coastal waters. Incubation experiments showed that microbes could utilize 9-19% of this plastic-derived organic matter within 30 days, suggesting it becomes part of the marine carbon cycle.
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