Mangrove forests, long valued for protecting coastlines and supporting marine life, are increasingly turning into long-term traps for plastic and coastal waste, according to new research from Colombia. Scientists warn that while mangroves naturally slow water movement and capture sediment, the same characteristics now make them hotspots for accumulating human-generated debris, posing serious risks to ecosystems and nearby communities.
Mangroves grow where rivers meet the sea, forming dense root systems that shelter fish, crabs and birds while supporting coastal livelihoods. Recent findings show these roots also trap plastic bottles, bags, food containers and other waste, allowing debris to persist for decades within mangrove soils.
Colombian Study Reveals How Mangroves Trap and Store Plastic for Decades
Researchers from the University of Barcelona surveyed 29 mangrove sites across Colombia, combining on-ground waste assessments with interviews of more than 670 coastal residents. The study revealed that the structure and location of mangrove forests strongly influence how much waste they collect.
Fringe mangroves, which grow along open coastlines and lagoons, were found to trap the highest levels of waste, averaging about 2.5 items per square metre. Tidal action pushes floating debris toward the forest edge, where complex root systems block its movement. In contrast, riverine and basin mangroves collected far less waste, often below 0.4 items per square metre.
Distance from human settlements also played a key role, with mangroves closer to towns accumulating significantly more rubbish. Factors such as tree size, age or forest density showed little influence, underscoring human activity as the primary driver of pollution.
Plastic made up nearly 90 percent of all recorded waste. Over time, sunlight, tides and animal activity break plastic into smaller fragments that become buried in mangrove soils, creating what researchers describe as long-lasting “soil plastic carbon.”
Pollution Threatens Wildlife, Food Security and Coastal Communities
Mangrove roots, especially the stilt roots of red mangroves and the aerial roots of black and white mangroves, are highly effective at trapping debris. While some fragments may return to open waters during storms, many remain locked in sediment, slowly fragmenting into microplastics that can enter marine food webs.
This pollution harms wildlife through ingestion and entanglement, weakens mangrove health, and threatens fisheries that coastal communities depend on. Toxic substances linked to plastic can move through the food chain, reducing fish quality and undermining flood protection provided by healthy mangrove systems.
Interviews revealed that most residents understand the ecological value of mangroves and recognize pollution as a growing threat. Many pointed to inadequate waste collection systems, open dumping and plastic-heavy packaging as major contributors. Community members identified better waste management, education, reduced single-use plastics and local recycling programs as essential solutions.
Researchers stress that protecting mangroves requires stopping waste before it reaches coastal forests. Improving sanitation services and reducing plastic use are seen as critical steps to prevent mangroves from becoming permanent waste repositories.
The study has been published in the journal Environmental Pollution highlighting the urgent need to address plastic pollution to safeguard mangrove ecosystems for future generations.