(HealthDay)—Microplastics have been detected in stool samples of healthy volunteers, according to research published online Sept. 3 in the Annals of Internal Medicine.

Philipp Schwabl, M.D., from the Medical University of Vienna, and colleagues conducted a prospective case series in which eight aged 33 to 65 years completed a food diary and collected stool samples according to instructions. Fourier-transform infrared microspectroscopy was used to analyze the presence and shape of 10 common types of in stool samples following chemical digestion.

The researchers found that all of the tested positive for microplastics. Per 10 g of human stool, a median of 20 microplastic particles were identified. Nine types of plastic were detected overall; the most abundant were polypropylene and polyethylene terephthalate.

"This small prospective case series showed that various microplastics were present in human stool, and no sample was free of microplastics. Larger studies are needed to validate these findings," the authors write. "Research on the origins of microplastics ingested by humans, potential intestinal absorption, and effects on is urgently needed."