KAIST finds algal blooms accelerate microplastic formation

Algal blooms, one of the most common forms of water pollution, accelerate the breakdown of discarded plastic and speed up the generation of microplastics, according to new research.

KAIST announced Wednesday that a research team led by Myung Jae-wook, a professor in the Department of Civil and Environmental Engineering, has identified how algal blooms alter the microbial ecosystem on the surface of low-density polyethylene (LDPE) film — the plastic used in products such as plastic bags — and promote early-stage weathering of the material. The finding came through ecosystem simulation experiments using samples collected from a pond.

The study is significant because it shows that plastic pollution and the eutrophication that causes algal blooms can interact in natural environments, together driving new ecological changes.

Plastic discarded in rivers and lakes gradually accumulates microorganisms on its surface, forming a miniature ecosystem known as the "plastisphere." While the plastisphere is known to influence the spread of pathogens and microplastics, little had been understood about how algal blooms — a serious form of water pollution — affect this microbial community.

The research team built miniature ecosystems in which algal blooms were artificially induced by controlling light levels and nutrient concentrations. Over six weeks, the team closely analyzed the biofilms and microbial communities forming on plastic surfaces, as well as changes in gene expression.

The analysis found that under eutrophic conditions — where excess nutrients trigger algal blooms — cyanobacteria, a representative photosynthetic bacterium, proliferated alongside a range of other bacteria, forming thicker biofilms on plastic surfaces. Microorganisms that produce extracellular polymeric substances, the sticky material that helps bind microbes together and adhere them to plastic surfaces, also increased significantly.

As the microbial ecosystem on plastic surfaces changed, early-stage weathering — the oxidation of the surface and the formation of microscopic cracks — also accelerated. The team confirmed that microorganisms carrying genes for enzymes that aid plastic oxidation and early decomposition became more abundant under eutrophic conditions.

The research team concluded that the changes were driven not by any single microbial species but by the broader microbial ecosystem formed through the interaction of photosynthetic and general bacteria.

"As climate change increases the frequency of algal blooms, these findings show that the behavior of plastic waste in aquatic environments may change in the future," Myung said. "This research can provide a theoretical foundation for building an integrated water quality management platform to address plastic pollution in aquatic environments."

The findings were published in Water Research, an international academic journal in the field of environmental science.