A study led by researchers from the University of Barcelona and the Marine and Coastal Research Institute (INVEMAR) in Colombia warns of the presence of potentially pathogenic bacteria in microplastics extracted from water, sediments and the digestive tract of fish in the Ciénaga Grande de Santa Marta, the largest and most productive coastal lagoon system in the Colombian Caribbean. Bacteria form biofilms on the surface of microplastics and give rise to what are known as plastispheres, ecosystems associated with plastic waste that are highly resistant to environmental changes. Microplastics have also been found in fish consumed by the local population, posing an even greater risk to the entire natural ecosystem and human health.

These conclusions are now revealed in an article in the Journal of Hazardous Materials, led by researchers Ostin Garcés-Ordóñez and Miquel Canals, from the Marine Geosciences Consolidated Research Group of the UB’s Faculty of Earth Sciences.

The study opens a new perspective on the microorganisms that colonize microplastics in coastal lagoons, an area still little explored by the scientific community. The findings also provide unpublished data on the interactions between microplastics and potentially pathogenic bacteria in ecosystems under increasing environmental pressure.

Plastics and bacteria that also threaten the local population

Covering 1,321 km², the Ciénaga Grande de Santa Marta is a shallow (1-1.8m) lake ecosystem that receives freshwater from four rivers and seawater through a channel connecting it to the Caribbean Sea. Flanked by mangroves, it is home to two national parks — recognized as a Ramsar site — and is a strategic lagoon complex for biodiversity conservation. In this ecoregion of rich fauna and flora, fishing is essential for the livelihoods of local communities.

Despite its ecological value, “the Ciénaga Grande de Santa Marta is seriously threatened by high microbiological contamination and microplastics that affect the water, sediments and organisms. These pollutants alter the quality of the habitat and fishery products and, ultimately, the food security of the local population”, says researcher Ostin Garcés-Ordóñez, a member of the UB’s Consolidated Research Group in Marine Geosciences and INVEMAR’s Marine Environmental Quality Research Group.

The study identified nineteen potentially pathogenic bacterial species in the microplastics tested. The most prevalent species, Aeromonas caviae, can cause gastroenteritis and was found together with Pantoea sp. in microplastics extracted from water samples, sediment samples and the digestive tract of commonly consumed fish.

“Enterobacter roggenkampii and Pseudomonas fluorescens species, which can also cause infections, were found on microplastics extracted from water and on fish. The bacterium responsible for cholera — Vibrio cholerae — was the second most abundant bacteria, although it was only found on microplastics in water. To find out whether these bacteria are capable of triggering outbreaks of disease in fish and humans around the Ciénaga Grande de Santa Marta, the presence of the virulence genes needed to do so would have to be confirmed, so this would be one of the lines of research to be pursued in future studies”, says Garcés-Ordóñez.

Plastisfera: plastics that facilitate gene exchange between bacteria

In the Ciénaga Grande de Santa Marta, microplastics harbour a high bacterial diversity. Analyses have identified a total of 65 bacterial phyla that predominate in marine and coastal environments, and the most abundant were Proteobacteria (52 %), Firmicutes (15 %) and Bacteroidetes (8 %). A total of 1,760 bacterial genera were also identified, with a predominance of Aeromonas (9 %), Romboutsia (6 %) and Acinetobacter (6 %).

“The most abundant microbial taxa varied according to the environmental matrix analysed: Aeromonas predominated in waters, Rhodocyclaceae in sediments, and Romboutsia in fish. However, genera such as Acinetobacter, Pseudomonas and Aeromonas — which include potentially pathogenic species — were also found in microplastics in water, sediments and fish”, says Professor Miquel Canals, from the UB’s Department of Earth and Ocean Dynamics.

“These microorganisms form biofilms that facilitate interaction between bacterial species and the exchange of genes that may be related to virulence and antibiotic resistance”, note the experts.

These coastal lagoons are particularly vulnerable to microplastic pollution. With limited water circulation and shallow depth, they are exposed to a constant influx of pollutants via rivers, sewage discharges or direct spills that favour the accumulation of plastics and the proliferation of potentially pathogenic bacteria in the natural environment.

“Positively buoyant microplastics — polyethylene, polypropylene, etc. — can facilitate bacterial growth because they keep colonies in the water column or near the surface, where they have easy access to oxygen, light and nutrients. Their specific density is different from those of natural particles, allowing them to act as vectors and facilitate the flow of bacteria from the water and sediments to the fish that ingest them”, say the experts.

Seeking solutions for coastal lagoons around the world

Establishing an Early Warning System (EWS) could help identify risk situations and forecast them well in advance. Rapid communication and emergency protocols — involving scientists, health workers and local communities — could warn of potential infectious disease outbreaks in the area. Governance should also be strengthened, sanitation infrastructure and health care improved, as well as education and training of different social actors for long-term monitoring.

“Our diagnosis of the situation underlines the need to implement integrated environmental management and public health strategies”, note the experts, who are also authors of a previous study (Environmental Pollution, 2022) that warned about the alarming situation caused by microplastic pollution in 50 coastal lagoons around the world. “This new study presents a conceptual model of the environmental risks to the lagoon and surrounding human communities. This is a very vulnerable scenario because it is a semi-enclosed system, with a limited economy, poor health care and a high dependence on fishery resources”.

Experts say that the Ciénaga Grande de Santa Marta represents an ideal model for analysing a health and environmental problem that affects many lagoons around the world. “Studying this system will help not only to generate new knowledge, but also to develop effective strategies to manage the environmental risks associated with these types of pollution, as well as to extrapolate strategies to improve the environmental status of affected coastal lagoons in other regions of the world”, the team concludes.
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