Study Shows Sunscreen Chemicals Hinder Plastic Decomposition in Oceans

The chemical compound ethylhexyl methoxycinnamate, commonly known as EHMC, may slow down the degradation of discarded plastics in the ocean and may help biofilm bacteria thrive—these bacteria are better protected under harsh conditions.

Scientists at the University of Stirling, led by Dr. Sabine Matallana-Surget, conducted this analysis, which is the first study of co-pollution—where plastics in the ocean act as carriers for other chemical pollutants, including UV filters from sunscreen.

Dr. Matalana Sujit, Associate Professor at the School of Natural Sciences, is now calling on policymakers to take urgent action to address what she describes as the invisible threat of sunscreen.

She said, "These changes are important. By suppressing aerobic bacteria that help degrade plastics and selecting those aerobic bacteria that stabilize or strengthen biofilms, ultraviolet filters will extend the lifespan of plastics in the ocean—making them more resistant to decomposition by sunlight or microbes."

“Therefore, there is an urgent need for targeted research and policy interventions to mitigate these complex ecological threats.

Plastic debris in the ocean provides a new surface for microbial growth, forming a sticky layer known as the plastisphere. In addition to forming the plastisphere, plastics also absorb other pollutants, including water-insoluble sunscreen washed off from human skin, which can then adhere to the surface of marine plastics.

Sunscreen, like oil, is hydrophobic—this means it is insoluble in water. This makes them a comprehensive threat because they can accumulate on plastics and remain in the environment.

Scientists have previously studied the role of plastic rings, but know little about how other chemicals like EHMC affect microorganisms living on the plastic.

This new study shows that when plastics are co-contaminated with EHMC, not only...Marinomonas unicellularisSuch pollutant-degrading bacteria will decrease, and likePseudomonasSuch bacteria produce more proteins to stabilize biological membranes and enhance their survival ability.

The bacteria include species known for their resilience in polluted environments and their ability to degrade various pollutants, including pesticides, heavy metals, and hydrocarbons. However, somePseudomonasThe strain is also classified as an opportunistic pathogen capable of causing serious infections that may require antibiotic treatment, raising potential public health concerns that researchers hope to further investigate.

A key finding of the study is that exposure to EHMCMonococcusThe level of a protein called outer membrane porin F (OprF) is much higher. This protein plays a crucial role in maintaining the structure of the biofilm, which serves as a protective layer that helps bacteria survive in harsh environments.

Researchers also observed a shift to anaerobic respiration—cells can produce energy without oxygen—revealing a complete transformation in the metabolism of microorganisms within the plastic circle.

Research shows that EHMC can inhibit the development of beneficial aerobic bacteria by promoting the formation of more pressure-resistant anaerobic biofilms, thereby aiding in the early-stage degradation of plastic pollutants.

Dr. Matallana-Surget added, "The UV protection properties of EHMC, combined with its inhibitory effect on hydrocarbon-degrading bacteria, can indirectly protect plastics from photodegradation and biodegradation, further contributing to their persistence in the marine environment."

“This impact, coupled with the enrichment of potential pathogenic bacteria, has raised serious concerns about ecosystem stability and human health, especially in coastal areas with high tourism rates and severe plastic pollution.。”

The paper "Sunscreens as an Invisible Threat of Plastic Co-Pollutants: Effects of Common Organic UV Filters on the Formation and Metabolic Function of Biofilms on New Marine Plastic Gyres" was published in the Journal of Hazardous Materials.

Dr. Matallana-Surget co-led the study in collaboration with Dr. Charlotte Lee, who was responsible for the core experiments, Dr. Lauren Messer from the University of Stirling, and Professor Ruddy Wattiez from the University of Mons in Belgium.

This project originated from Dr. Matallana-Surget’s initial concept of investigating emerging dual pollution issues and builds upon 15 years of collaborative work between the teams at Stirling and Mons.

The study was funded by the UKRI Natural Environment Research Council (NERC) and the Singapore National Research Foundation. The program was further supported by the European Regional Development Fund and the Walloon Region of Belgium.

It builds upon the previous research published last year by Dr. Matallana-Surget, which revealed the key role of bacteria living on plastic debris.

Dr. Matallana-Surget also published a study evaluating the impact of the Deepwater Horizon oil spill on microscopic marine bacteria that play an important role in ecosystem functioning.