Researchers Studied How Sunlight Breaks Down Plastics

Northwestern University scientists found that ocean conditions hinder the natural degradation of polystyrene.

Updated on Sept. 24, 2026 in Environmental

A close-up shot of a white plastic fragment submerged in clear seawater, illuminated by a focused beam of light. — Researchers at Northwestern University found that salt and organic matter in seawater significantly slow the natural breakdown of polystyrene plastics by sunlight. AI Illustration. Upload story photo >

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Researchers in Evanston investigated how ultraviolet light and bacteria interact to break down polystyrene plastic. The team discovered that salt and organic matter in seawater significantly slow this degradation process compared to purified water.

Why it matters

Engineers aim to use these findings to design future plastics that are more susceptible to sunlight-driven decay. Understanding why polystyrene persists in aquatic environments is key to addressing the long-term accumulation of floating debris.

The study subjected 2.6-inch polystyrene squares to simulated sunlight at 68°F for 90 days. Testing showed that organic matter increased oxidation markers by 2.3-fold in purified water while inhibiting the process in salty solutions.

The players

Northwestern University

This private research institution in Illinois hosted the team of engineers who conducted the study.

National Science Foundation

This federal agency provided the funding necessary to carry out the environmental research study.

The details

Ultraviolet rays typically crack plastic surfaces and bind oxygen atoms onto polymer chains, allowing bacteria to feed on the resulting molecules. The researchers found that while bacteria helped in freshwater, the structural properties of seawater salts impede this sun-induced oxidation.

1971: The year plastic foam was first spotted in the ocean.
90 days: The duration of the simulated sunlight exposure experiment.
24 days: The duration of the bacterial degradation experiments.
2025: The year Oceana published a report on foam damage.
June 8: The date of the annual observance of World Oceans Day.

The Big Picture

This discovery marks a shift in understanding how environmental variables, rather than just material composition, dictate plastic persistence. It follows the precedent of the RIKEN Center for Sustainable Resource Science in identifying biological pathways to combat synthetic waste.

The study suggests that current plastic waste may remain in the ocean for over a century due to these inhibiting chemical factors. Future consumer goods might eventually be manufactured with specific additives designed to accelerate breakdown when exposed to natural light.

The takeaway

Plastic foam is exceptionally resistant to natural decay because its ring-studded molecular structure remains stable in saltwater. Reducing reliance on such materials remains the most effective way to prevent long-term environmental pollution.