Microplastics are everywhere. They have been detected in polar regions, at the peak of Mount Everest and even in the depths of the Mariana Trench. The environmental abundance of microplastic particles, defined as measuring less than 5 mm in size, has increased substantially in recent years, including in the food we eat, our drinking water and the air we breathe1. This pollution can originate from primary microplastics manufactured for a specific application, for example, personal care products, or the degradation of larger plastic waste such as synthetic textiles, tyres and food packaging. Given the prevalence of this plastic debris, investigations into potential impacts on human health are emerging.

A Nature Medicine article recently hit the headlines reporting that microplastics and nanoplastics (measuring less than 1 μm) were detected in post-mortem human tissues (kidney, liver and brain) using sensitive chemical analysis2. Polyethylene was the most prevalent microplastic, particularly in brain tissues. Although there was no association between plastic concentration and age, sex, race or ethnicity, or cause of death, there was a link with time of sampling. Individuals who died in 2024, compared with 2016, had higher concentrations of micro- and nanoplastics in the liver and brain. This suggests that longer exposure to these plastic particles, and therefore uptake, most commonly via ingestion or inhalation, can increase accumulation in tissues.

This is not the first time microplastics have been detected in human samples. However, direct evidence linking their presence to human health was previously limited. Interestingly, the authors of the Nature Medicine article also found that samples from individuals with a documented dementia diagnosis had more accumulation of microplastics in cerebrovascular walls and immune cells2. Indeed, a link between microplastic accumulation and disease was observed in patients with cardiovascular disease — carotid artery plaques with detectable microplastics and nanoplastics had a higher risk of cardiovascular events, such as myocardial infarction or stroke3.

But what about microbes? Microbes are closely interlinked with environmental and host health, so any negative microplastic-driven effects on microbial physiology, behaviour or metabolism will undoubtedly impact the broader ecosystem. At the same time, microbes may be influenced indirectly by plastic-driven impacts on the host or environment. So far, most research has focused on the so-called plastisphere — microbial communities that are capable of attaching and growing on plastic debris, which can then be dispersed throughout an ecosystem4. Some of these microbes can be harnessed for their ability to breakdown microplastics and remove them from the environment5,6, yet others may have detrimental effects.

A growing body of work has reported microplastic contamination of animals, particularly those at higher risk of ingesting debris, and impacts on their gut microbiome. Wild seabird gut microbiome diversity and composition was linked to the concentration of microplastics present in the gut7. Microplastics were associated with decreases in commensals and increases in pathogens — both zoonotic and antibiotic-resistant microbes — as well as plastic-degraders. Experiments in mice have revealed similar shifts in gut microbiota composition, as well as functional changes such as increased inflammation8. Interestingly, other work in humans has reported a link between faecal microplastic concentration and inflammatory bowel disease, although the authors did not characterize the microbiota9.

Environmental microbes and their biogeochemical impacts are also being investigated. As with the gut microbiome, terrestrial and aquatic microbiomes have altered composition associated with microplastic contamination. A microplastic-driven signature emerges — a reduction in beneficial or commensal microorganisms, and an increase in pathogenic microbes harbouring antibiotic resistance genes7,10. Although the compositional impacts are clear, limited functional insights have been revealed. A recent study in Nature Communications measured increased bacteria-mediated nitrification within plastisphere biofilms compared with surrounding water and control biofilms in ex situ estuarian samples11. Whether metabolisms in this microenvironment make a broader contribution to biogeochemical cycling is unclear.

Work so far, while mostly descriptive, underscores the need for more research into interactions between microbes and microplastics. Mechanistic insights are needed to understand how microplastics enrich for pathogens and their associated antibiotic resistance genes, and whether these observed shifts are having consequential impacts on host health or ecosystem functioning. This will not be without challenges. Identifying environmentally relevant exposure levels and timescales, as well as the diversity of microplastic shape, size and chemical composition, are issues across the microplastic field and standards should be developed. This will require improved surveillance and regular measurements to ensure that experiments are reflecting real-world scenarios. Invisible nanoplastics are of particular concern owing to their minute size, which may enable them to cross cellular barriers. They also require sensitive detection methods, which may be prohibitive for many researchers1.

This area of research is still in its infancy, but with growing concerns regarding microplastic pollution, investigations into their impacts on our microbial partners are vital.