Green Plastics? Biodegradable Plastics Can Amplify Antibiotic Resistance in Rivers

Biodegradable plastics are not always safer for rivers and oceans, according to a new study that tracked how different plastics change the risk of antibiotic resistant bacteria over time in a real river.

A team from East China Normal University placed common plastics in a tidal river in Shanghai for 88 days to see how they shaped microbial “cities” on their surfaces, known as the plastisphere. The researchers compared a biodegradable plastic, polylactic acid (PLA), with two widely used conventional plastics, polyvinyl chloride (PVC) and polystyrene (PS).​

“Our findings show that biodegradable plastics do not simply dissolve into the environment without consequence” says corresponding author Yinglong Su. “They create a different kind of risk that peaks during degradation and should not be ignored in environmental policy.”​

Plastics Grow Their Own Microbial Worlds

When plastic floats in water it quickly becomes coated with a slimy biofilm of bacteria, viruses, and other microbes that is distinct from the surrounding water. This artificial habitat, called the plastisphere, can concentrate pathogens, antibiotic resistance genes and virulence factors that help microbes cause disease.​

In the Shanghai river experiment, all three plastics recruited unique microbial communities that looked very different from those in the river water itself. Some opportunistic pathogenic genera, including Vibrio and Acinetobacter, were consistently detected on plastic surfaces, raising public health concerns.​

The study reveals that biodegradable and conventional plastics create fundamentally different risk patterns rather than a simple “high risk versus low risk” contrast.​

• PVC acted as a long term hotspot for antibiotic resistance genes and mobile genetic elements which move DNA between microbes

• PLA created a sharp but temporary spike in risk during its mid degradation stage

On PVC, multidrug resistance genes were enriched up to 3.5 times compared with river water and remained high across the 88 day experiment. PVC also carried the highest levels of mobile genetic elements such as transposases and integrases, which can accelerate the spread of resistance through horizontal gene transfer.​

PLA showed a different pattern. Early on its surface appeared less risky, but as the material began to break down the plastisphere shifted into a hotspot enriched in opportunistic pathogens like Vibrio and Acinetobacter along with a pronounced surge in multidrug and glycopeptide resistance genes. After this mid degradation peak, the risk declined as the PLA continued to fragment and its biofilm community changed again.​

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High Risk Genomes on Plastic Surfaces

Using genome resolved metagenomics the team reconstructed 37 high quality microbial genomes to pinpoint which organisms were carrying both antibiotic resistance genes and virulence factors. This approach allowed the researchers to identify specific “high risk” strains that combine pathogenic traits with resistance and a high capacity for gene exchange.​

Some of the most concerning genomes were found on PVC and in river water where certain strains carried multiple resistance genes, dozens of virulence factors and large numbers of mobile genetic elements in the same genome. In PLA associated communities, one strain stood out as a potential “gene transfer vector” with very many mobile elements that could rapidly spread resistance once such genes are acquired.​

The authors argue that risk assessments for plastics must move beyond counting how long materials persist and instead consider the full life cycle of the plastisphere, from initial colonization through degradation. Conventional plastics like PVC pose a persistent, accumulating threat as long lived hubs for antibiotic resistance, while biodegradable PLA introduces a transient but intense risk window during breakdown when pathogenic and resistant microbes can flourish.​

“These results challenge the assumption that biodegradable plastics are automatically a safer choice in all contexts” says co first author Fengying Li. “Both biodegradable and conventional plastics can act as reservoirs and amplifiers of antibiotic resistance and potential pathogens, but they do so in very different ways.”​

The team suggests that future regulations and product design should consider how specific polymers shape microbial communities, resistance genes and virulence factors over time in real environments, not just how fast the material disappears. They also call for more monitoring of riverine plastispheres as critical interfaces between human activity, environmental pollution and the global spread of antibiotic resistance.​

Journal reference: Li F, Shen H, Pang R, Wang X, Xie B, et al. 2026. Biodegradable and non-biodegradable plastics foster unique regimes of antibiotic resistance and virulence factors in aquatic plastispheres. Biocontaminant 2: e001

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