Volunteers from eight countries participated in a Europe-wide study to test dangerous particles present in the human digestive system.
Researchers tested participants’ stools and found several toxic chemicals present, suggesting the particles were ingested through food.
One of the components included two different types of plastic – polypropylene (PP) and polyethylene terephthalate (PET).
As part of the study, participants kept food diaries which were studied to figure out how the substances entered their bodies.
Scientists believe the plastic was ingested through plastic-wrapped food or drinking from plastic bottles.
Other possible sources included fish that have been exposed to micro-particles at sea, beer, tap water and cosmetic products.
Dr Philipp Schwabl, who led the research, said: “This is the first study of its kind and confirms what we have long suspected — plastics ultimately reach the human gut.
“Of particular concern is what this means to us, and especially patients with gastrointestinal diseases.
“While the highest plastic concentrations in animal studies have been found in the gut, the smallest particles are capable of entering the bloodstream, the lymphatic system and may even reach the liver.
“Now that we have the first evidence for micro-plastics inside humans, we need further research to understand what this means for human health.”
Ingested particles could lead to gastrointestinal diseases, affecting the blood stream and other organs, scientists have warned.
Participants from Britain, Austria, Finland, Italy, Japan, the Netherlands, Poland and Russia took part in the research project.
An estimated 5 percent of plastic waste ends up in the sea, which is then consumed by sea animals.
Significant amounts of plastic have been found in foods such as tuna, lobster and shrimp.
Some scientists believe plastic particles can even be ingested through the air.
Environmental expert professor Alistair Boxall, from the University of York, said: “I’m not at all surprised or particularly worried by these findings. Micro-plastics have been found in tap water, bottled water, fish and mussel tissue and even in beer.
“We will also be exposed to particles from house dust, food packaging materials and the use of plastic bottles. It’s therefore inevitable that at least some of these things will get into our lungs and digestive systems.”