Scientists have for the first time found microplastic particles in human stool samples, suggesting that the food chain is contaminated with plastic.

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

The Environment Agency Austria tested samples eight subjects from Europe, Japan, and Russia, and detected 20 particles of microplastic were found in each 10g of excreta.  Polypropylene and polyethylene terephthalate were the most common.  For every 10 grams of poop, the researchers found 20 particles of microplastic, which is defined as particles of less than five millimeters.  Some of it was tiny plastic beads created for the cosmetics or personal care industry, but others were the result of breaking down of larger pieces of plastic, often in the sea.

The Austrian researchers guess that "more than 50 percent of the world's human population might have microplastics in their stools".  Larger scale studies will be needed to confirm this.

Microplastic has already been found in tap water and in the oceans, in the guts of fish and even in flying insects.  An Italian investigation found it in popular soft drinks.  This is a health threat because they disrupt iron absorption and add to stress on the liver.  Plastic particles in the gut could affect the digestive system's immune response or could aid the transmission of toxic chemicals and pathogens.

"The smallest microplastic particles are capable of entering the bloodstream, the lymphatic system, and may even reach the liver," said Schwabl, who will introduce his research at report on the study at at gastroenterology conference in Vienna on Tuesday.  "Now that we have the first evidence for microplastics inside humans, we need further research to understand what this means for human health."