Microplastics carry chemical, biological contaminants: Review

Microplastics can carry both chemical and biological contaminants, transporting toxic chemicals, microorganisms, and antibiotic resistance genes through water, soil, food webs, and across environmental boundaries, in addition to causing pollution, a new review shows.

While microplastics are known for harmful effects in organisms and ecosystems, their environmental impact may extend far beyond the plastic particles themselves, researchers said.

The review, published in the journal Energy and Environment Nexus, also introduces a three-tiered framework for understanding the physical, chemical and biological factors that determine when these transport effects may become major ecological risks.
“Microplastics should not be considered isolated particles in the environment,” author Jingliang Shi, from Jiangxi Agricultural University in China, said.

“They can interact with chemicals and microorganisms, transport them between environmental compartments and, under certain conditions, amplify their ecological effects.

Understanding when these processes become dominant is essential for realistic risk assessment,” Shi said.

A major concern is the ‘Trojan horse effect’, where microplastics can adsorb persistent organic pollutants, heavy metals and other contaminants on the surfaces, the researchers said.

The pollutants may be released in the digestive systems of the organisms upon ingestion- conventional microplastics generally deliver contaminants through the gastrointestinal tract, while nanoplastics smaller than a micrometre may cross biological membranes and distribute pollutants to internal organs, they found.

Further, the team said surfaces of microplastics can develop microbial communities known as the plastisphere, which can provide a protected habitat for pathogens and antibiotic resistance genes.

Within the biofilms, a close contact between microorganisms may promote horizontal gene transfer, potentially accelerating the spread of antimicrobial resistance, the review found.

“Microplastics serve as pivotal mobile vectors enabling long-distance and cross-media transport of chemical and biological pollutants,” it said. “These two vector effects act synergistically to amplify ecological hazards,” the authors write.

They also show that the chemical and biological effects may reinforce each other- pollutants attached to microplastics can create a selective pressure on microbial communities, while biofilms can alter plastic surface properties and increase subsequent pollutant adsorption, they said.

The bi-directional positive feedback may intensify both contaminant accumulation and the transfer of antibiotic resistance genes, the team said.

They proposed a three-tiered regulatory framework involving physical, chemical and biological drivers.

Particle size, shape and aging can influence transport and surface reactivity, while polymer chemistry and environmental conditions control adsorption and desorption, the researchers said.

Further, biological processes, including the formation of biofilm, ingestion and food-web transfer, determine how contaminants ultimately reach organisms, they said.

Conditions under which the combined chemical and biological vector effects may become particularly important were also identified, including a prolonged exposure exceeding 30 days.

The study reframes microplastics not simply as contaminants, but as dynamic platforms capable of connecting chemical pollution, microbial ecology and antimicrobial resistance across ecosystems, the authors said.