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there are small pieces of plastic change balance Of bacteria in the human intestine in ways that resemble microbiome patterns seen in depression and bowel cancerNew research has revealed.
The study unveiled at the UEG Week 2025 medical conference suggests microplastic, particles smaller than 5 mmMay subtly but significantly change how gut bacteria behave, raising fresh concerns over the health effects of daily exposure.
The work, carried out under MicroOne, a major COMET module programme, led by Austria’s CBMed research center with international partners, is one of the first to directly explore how microplastics interact with the human gut microbiome. Researchers say the findings add to growing evidence that these pollutants, found in everything from bottled water to household dust, can affect the body in invisible ways.
To test the effects, scientists used stool samples from five healthy volunteers to grow gut microbiome cultures outside the body. They were exposed to five common types of microplastics, including polystyrene and polyethylene, at concentrations similar to typical human exposure, as well as higher doses to see how the microbes responded under stress.
While overall bacterial numbers remained stable, samples exposed to plastic became markedly more acidic, indicating a change in bacterial metabolism.
The researchers found that these disruptions also affected chemical by-products produced by the bacteria, including changes in the levels of valeric acid, lysine and lactic acid. Some of these changes reflect changes previously associated with mental health disorders and colorectal cancer.
Lead author Christian Pacher-Deutsch said the exact mechanisms behind the disruption are uncertain but several explanations are emerging. “Microplastics can alter microbial composition by creating physical or chemical environments that favor certain bacteria,” he said. “For example, biofilms can form on microplastic surfaces, providing new spaces in which certain microbes colonize more rapidly.”
He said microplastics may contain chemicals that directly interfere with the metabolism of bacteria. “This may lead to changes in acid production, which may serve as a bacterial stress response, inadvertently altering the pH of the gut,” he said. “These changes can then trigger feedback loops that further affect the balance of the microbiome.”
Pacher-Deutsch said the findings highlight how widespread exposure to microplastics can pose invisible risks. “The key thing is that microplastics have an impact on our microbiome,” he said. “Although it is too early to make definitive health claims, the microbiome is central to digestion, immunity, and even mental health. Minimizing exposure where possible is a sensible precaution.”
The prevalence of microplastics is significant. Researchers at the University of Plymouth recently found that particles found in soil can be absorbed into edible parts of crops during the growing process, after which microplastics can also become hidden in vegetables.
Nanoplastics one millionth of a centimeter in diameter were found in radish. And for the first time, experts found that these plastics can enter through the roots and spread through the plant because they are so small.
Dr Nathaniel Clarke, lecturer in physiology, said: “Plants have a layer within their roots called the Casparian strip, which acts as a filter against particles, many of which can be harmful.”