Algal blooms accelerate plastic weathering, potentially fueling microplastic formation
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Every summer, algal blooms turn rivers and lakes green. Although they are widely known as a major form of water pollution that makes water murky, a KAIST research team has now shown for the first time that algal bloom conditions can make discarded plastics, such as plastic bags, more prone to breaking apart, potentially accelerating the formation of microplastics. The study points to a new direction for the era of climate change: water pollution and plastic pollution need to be managed together rather than as separate problems.
A research team led by Professor Jaewook Myung from the Department of Civil and Environmental Engineering found, through a microcosm experiment using water collected from Duck Pond, a pond on the KAIST campus, that algal blooms alter the microbial ecosystem on the surface of low-density polyethylene (LDPE)—a common plastic used in plastic bags—and accelerate its early-stage weathering, in which the surface oxidizes and develops microscopic cracks.
The study is significant because it suggests that, in natural environments, plastic pollution and the eutrophication that drives algal blooms can interact and lead to new ecological changes.
The hidden life on plastic
Over time, plastic debris discarded in rivers and lakes becomes colonized by a wide variety of microorganisms, creating a small ecosystem of its own on the plastic surface. This ecosystem is known as the "plastisphere." The plastisphere is known to influence the spread of pathogens and the transport of microplastics, but little has been known about how algal blooms, a serious form of water pollution, affect this microbial ecosystem.
To investigate this question, the research team constructed microcosms—small-scale experimental systems that recreate natural environments in the laboratory—in which algal blooms were artificially induced by controlling light exposure and nutrient concentrations. Over the following six weeks, the researchers closely analyzed the biofilms forming on the plastic surface, the succession of microbial communities and changes in their functional gene profiles.
Thicker biofilms under bloom conditions
The analysis showed that under eutrophic conditions, in which excessive nutrients trigger algal blooms, cyanobacteria, a major group of photosynthetic bacteria, proliferated alongside a variety of other bacteria, forming a thicker biofilm on the plastic surface. Microorganisms capable of producing large amounts of extracellular polymeric substances (EPS) also became significantly more abundant. EPS is a sticky, mucilage-like material that binds microorganisms together and helps them adhere to plastic surfaces.
As the microbial ecosystem on the plastic surface changed, the early weathering of the plastic—including surface oxidation and the formation of microscopic cracks—also accelerated. The team found that microorganisms harboring genes encoding enzymes associated with plastic oxidation and early-stage degradation became more abundant under eutrophic conditions.
Analyses using Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) directly confirmed these changes. Oxygen-containing functional groups associated with oxidation, including carbonyl and hydroxyl groups, increased on the plastic surface, while more fine, hairline cracks appeared. These changes indicate that the plastic had become more susceptible to further physical weathering and fragmentation. The results suggest that these changes were driven not by a single microbial species but by the combined activity of a microbial ecosystem comprising photosynthetic and other bacteria.
A case for joint management
Myung said, "As algal blooms become more frequent because of climate change, we expect this work to provide an important scientific basis for integrated environmental management strategies that consider water quality management and plastic waste management together."
The study was led by first author Youngju Kim, a doctoral student from the Department of Civil and Environmental Engineering, and was published online in the journal Water Research on May 25, 2026.
Publication details
Youngju Kim et al, Eutrophication drives taxonomic and functional trajectories in plastic-associated biofilms, Water Research (2026). DOI: 10.1016/j.watres.2026.126183
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Citation: Algal blooms accelerate plastic weathering, potentially fueling microplastic formation (2026, July 28) retrieved 29 July 2026 from https://phys.org/news/2026-07-algal-blooms-plastic-weathering-potentially.html
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