A new study challenges a 2019 World Health Organization report that microplastics in drinking water are harmless after confirming their presence in kidney, urine and bladder cancer samples.

The scoping review led by researchers from Bond University looked at 18 previous studies to assess the presence of microplastics and even smaller nanoplastics in the urinary tract. They found the contaminants were in 54% of urine samples, 70% of kidney samples and 68% of bladder cancer cases.

The review concluded that the plastic debris harmed human urinary tract cells by causing toxicity and inflammation, reducing cell survival. They also disrupt MAPK (mitogen-activated protein kinase) signaling, a process that helps cells respond to growth signals and stress.

“This scoping review highlights the rapidly emerging threat of microplastic contamination within the human urinary tract, challenging the World Health Organization’s assertion that microplastics pose no risk to public health,” the authors wrote.

“The documented cytotoxic effects of microplastics, alongside their ability to induce inflammation, reduce cell viability and disrupt signaling pathways, raise significant public health concerns relating to bladder cancer, chronic kidney disease, chronic urinary tract infections and incontinence.

“As a result, this study emphasizes the pressing need for further research and policy development to address the challenges surrounding microplastic contamination.”

Plastics have pervaded all aspects of society since their widespread adoption in the mid-20th century.

About 368 million tonnes of plastic were produced in 2019 and that is expected to double by 2039. This has resulted in the accumulation of miniscule fragments which have found their way into all aspects of the environment.

Beyond the well-documented environmental impacts of microplastics, there is emerging evidence that their presence within human organ systems is driving diseases and health issues.

The researchers were particularly interested in microplastics’ effects on the urinary tract because an estimated 404.61 million urinary tract infections occurred in 2019 alone, resulting in more than 236,000 deaths.

One of the researchers, Ph.D. candidate Liam O’Callaghan, said it was impossible to avoid microplastics.

“We’re drinking them, we’re eating them, we’re breathing them in. They can be absorbed through the skin,” Mr. O’Callaghan said.

“When you heat up plastic containers there can be millions of these tiny microplastics that leach into the food. You might filter your water but if that filter is made of plastic, over time it is going to start to degrade and pollute the water you’re drinking.

“Even tea bags—they’re coated in plastic so the paper doesn’t disintegrate when you pour in boiling water, and these bags can release billions of plastic particles into your tea.”

Mr. O’Callaghan said using glass containers and avoiding food packaging were ways to minimize exposure to microplastics.

“Why are we wrapping everything in plastic in the shops?” he said. “Does fresh produce really need to be wrapped in plastic, or could we just sell it all without the unnecessary packaging?”

The Bond researchers hope to conduct further investigations into the effects of microplastics in the human body.

“We thought we’d start with the urinary tract because the kidneys are the filter system of the body,” Mr. O’Callaghan said. “We know that microplastics are found in cancers, but do they have anything to do with forming the cancers? We don’t know yet.

“We do know they are getting into the bloodstream and a few cardiac-related papers have found that these particles can burst red blood cells.”

The study, published in the Journal of Exposure Science & Environmental Epidemiology, is believed to be the first to summarize research on the presence and effects of microplastics in the human urinary tract.

Associate Professor Lotti Tajouri, Adjunct Associate Professor Rashed Alghafri, Davinia Beaver and Professor Simon McKirdy also took part in the research.

There has been a surge in the number of studies into microplastics recently.

A study by the University of Campania Luigi Vanvitelli in Italy found that of 200 people undergoing surgery, nearly 60% had microplastics or nanoplastics in a main artery.

Meanwhile, a team at Sao Paulo University medical school found them in the brains of 8 of 15 deceased people. The pieces of plastic were found in the olfactory bulb, part of the brain that processes smell.