PLA plastic is biodegradable, yet its behavior in real environments is nuanced. Biodegradable materials burn bright in labs but may not degrade quickly in the sea, unlike some petroleum-based plastics such as polyethylene or polystyrene, which persist longer in marine settings.
This understanding comes from a study led by the Barcelona Institute of Marine Sciences (ICM-CSIC) with participation from Vigo’s Institute for Marine Studies (IIM-CSIC). The research, published in Marine Environmental Studies, consolidates these insights for a broader audience.
Previously, researchers found that these plastics fail to biodegrade at temperatures below 60º C, a condition not present in ocean waters. Experts expect photodegradation from sunlight to be a factor that could help break down components, but the resulting products may still be challenging for marine bacteria to fully degrade.
The biodegradability of plastic does not guarantee degradation under all conditions. For instance, compostable plastic needs temperatures above 50º C to biodegrade, which oceans and many natural environments do not reach, says a scientist from ICM-CSIC, Cristina Romera-Castillo.
A plastic glove at sea
To conduct the study, researchers exposed different plastic types to ocean temperatures and sunlight and then tracked the organic carbon released during degradation. They also measured how effectively marine bacteria could break down that carbon. The findings show that biodegradable PLA releases similar or less carbon than petroleum-based plastics, and bacteria are about as effective at handling PLA photodegradation products as they are with polystyrene.
Old plastic pollutes more
Laboratory experiments also indicated that aged plastic becomes more polluted over time.
Specifically, the results indicate that plastic dumped into the sea releases about 57,000 tons of dissolved organic carbon each year, more than double estimates from studies using fresh pieces. This occurs because plastics lose additives that shield them from sunlight and physical erosion, releasing more chemical compounds into the water, whether from the polymer itself or from additives that influence color, flexibility, and other properties, Romera explained.
plastics in the sea
Another study, published in Frontiers in Marine Science, warned about the impact of this pollution on the marine ecosystem and the carbon cycle.
The good news is that some bacteria can break down certain compounds released by plastics, which helps lessen their environmental footprint. This observation is noted by Romera and colleagues as a potential opening for bioremediation strategies—using living organisms to help restore contaminated environments—though this avenue remains under exploration.
Marta Sebastián, another ICM-CSIC researcher, notes that some release products may resist degradation but could still be metabolized by specific bacteria. The research team now aims to explore whether marine microbes could be harnessed to remediate or recover other plastic-contaminated habitats, advancing our understanding of biological pathways that could mitigate plastic pollution in oceans.