The war against microplastics continues to wage. Researchers now say they are finding the small, invisible plastic particles in human waste.

Microplastics were found in stool samples of every participant from a small pilot study. According to researchers from the Environment Agency Austria and the Medical University of Vienna, the microstudy followed eight healthy volunteers from different countries (Finland, Italy, Japan, the Netherlands, Poland, Russia, United Kingdom and Austria).

For one week, the eight participants kept a diary of the food and drink they consumed. Then, researchers tested their stool for 10 different types of plastics.

Of the 10 tested, nine different types of plastics were found in the samples. An average of 20 microplastic particles measuring between 50 and 500 micrometers were found per 10 grams of stool.

Researchers said this is the first study of its kind and the group wants to expand its investigation so is seeking funding for further research, said Philipp Schwabl, lead researcher.

"Personally, I did not expect that each sample would be tested positive," Schwabl said.

Where did the plastics that each of the eight participants ingested come from? Researchers say they are not sure. However, Schwabl did say that most participants drank liquids from plastic bottles and also ate seafood, which could be bringing microplastics from ocean pollution up the food chain. No vegetarians or vegans were involved in the study.

Of course, the sample size of the study was very, very small, thus potentially limiting the outcomes. Despite this, Schwabl said he wants to know more about diet and lifestyle, which might contribute to the plastic ingestion. This is not the first study to find that these small plastics are headed for the human gut.

Another study published recently examined 259 water bottles from brands sold across nine countries, which found that 93 percent of them were contaminated with microplastics.

Additionally, even some tap water has tested positive for tiny plastic particles.

"Recent studies have found plastics in seafood, wildlife, tap water and now in salt. It’s clear that there is no escape from this plastics crisis, especially as it continues to leak into our waterways and oceans," said Mikyoung Kim, campaigner at Greenpeace East Asia, in a statement. The study revealed 90 percent of the sea salt sold globally contains microplastics.

Tap water samples from more than a dozen nations were recently analyzed by scientists for an investigation by Orb Media, who shared the findings with The Guardian. Overall, 83 percent of the samples were contaminated with plastic fibers.

The U.S. had the highest contamination rate, at 94 percent, with plastic fibers found in tap water sampled at sites, including buildings of Congress, the Environmental Protection Agency’s headquarters, and Trump Tower in New York. Lebanon and India had the next highest rates of contamination.

The average number of fibers found in each 500-milliliter sample ranged from 4.8 in the U.S. to 1.9 in Europe.

"We have enough data from looking at wildlife, and the impacts that it’s having on wildlife, to be concerned," said Dr. Sherri Mason, a microplastics expert at the State University of New York in Fredonia, who supervised the analyses for Orb. "If it’s impacting [wildlife], then how do we think that it’s not going to somehow impact us?"

Microplastics are also known to contain and absorb toxic chemicals, and research on wild animals shows they are released in the body. Professor Richard Thompson at Plymouth University in the U.K. told Orb, "It became clear very early on that the plastic would release those chemicals and that actually, the conditions in the gut would facilitate really quite rapid release." His research has shown microplastics are found in a third of fish caught in the U.K.

How microplastics end up in drinking water is for now a mystery, but the atmosphere is one obvious source, with fibers shed by the everyday wear and tear of clothes and carpets. Tumble dryers are another potential source, with almost 80 percent of U.S. households having dryers that usually vent to the open air.

"We are increasingly smothering ecosystems in plastic and I am very worried that there may be all kinds of unintended, adverse consequences that we will only find out about once it is too late," said professor Roland Geyer, from the University of California, Santa Barbara, who led a recent study.