A new study found microplastic particles in human waste for the first time, a worrying sign of the prevalence of plastic in the food chain, the Guardian reports.

In the small study of participants from Europe, Russia and Japan — presented at United European Gastroenterology’s meeting in Vienna — all eight were found to have microplastic particles in their stool samples. Out of 10 varieties tested for, nine different plastics were identified in the human waste, with polypropylene and polyethylene terephthalate the most common.

Based on their findings, the study researchers expect that tiny bits of plastics may be widespread in the human digestive system.

“This is the first study of its kind and confirms what we have long suspected, that plastics ultimately reach the human gut. Of particular concern is what this means to us, and especially patients with gastrointestinal diseases,” said Philipp Schwabl, the study’s lead and a researcher at the Medical University of Vienna, in a statement.

The study, conducted by the Environment Agency Austria, hypothesizes that “more than 50% of the world population might have microplastics in their stools,” according to the Guardian. However, the authors underscored the need for more research on a larger sample size before drawing conclusions.

Microplastics are tiny pieces of plastic smaller than 5 millimeters, either found in products like exfoliants or disintegrated from larger pieces of plastic such as those that often end up in the ocean.

One study earlier this year found that fish in Hong Kong were ingesting plastic which could end up in humans. Another found that microplastic contamination in bottled water was nearly universal.

Researchers say microplastics circulating in the human body could endanger health, affecting the immune system or facilitating the exchange of toxins, according to the Guardian.

By the World Economic Forum’s estimation, the world’s oceans will be filled with more plastic than fish by weight by 2050. Every year, 8 million metric tons of plastic end up in the oceans—a that figure could increase by ten-fold over the next decade if actions are not taken, according to another 2015 study.

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