Your brand of dental floss might be leaving you with more than squeaky-clean teeth and fresh breath. It could also be depositing traces of a potentially dangerous class of chemicals known as per- and polyfluoroalkyl substances (PFAS).

A recent study looked for forms of PFAS in the blood of volunteers after quizzing them on their lifestyle habits. The results highlight the challenges involved in avoiding these concerning toxins.

In collaboration with the Public Health Institute in California, researchers from the Silent Spring Institute set out to identify common daily habits that risk raising exposure to these potentially dangerous chemicals.

A little under a year ago, the US Environmental Protection Agency held a summit to address allegations of high levels of PFAS in the drinking water of 33 states.

Unfortunately, media was banned from the event, so it's not clear what the government's current assessment of the risks are.

But drinking water is just one place we can expect to find these potentially nasty substances. They've been in production since the mid-20th century, used for their slick, water-repellent properties on everything from furniture fabrics to food packaging.

To say these chemicals are virtually everywhere is an understatement. And to makes matters worse, PFASs don't break down very easily, and can accumulate in the tissues of animals.

But is it all as bad as it sounds?

Once word got out that these and related classes of organic fluorides were detectable in significant amounts in the environment and our own bodies, there was a surge of interest in their health effects.

Research has intensified in recent decades, with field and laboratory models suggesting elevated levels of such chemicals risk depressing the immune system, damaging the liver, crossing the placenta to affect foetal development, and maybe giving certain cancers a boost.

While there's no clear indication of a safe level, the fact the material clings to proteins and builds up in tissues such as the liver and kidneys makes it a serious concern.

Localised bans are debated by policy makers, so we can can expect this class of chemicals to remain in use for some time yet. In the meantime, researchers have busied themselves with tracking down the various pathways PFASs take to get into our bodies.

In this case, 178 women – half of which identified as African American – were recruited to provide blood samples, which were analysed for signs of 11 different types of PFAS. The participants also provided details of their lifestyle through structured interviews.

Levels of two PFSA compounds, perfluorooctanoic acid and perfluorohexanesulfonic acid, were found to be lower in the African American participants than in the rest of the sample, indicating differences in concentrations between racial demographics.

Frequent consumption of food from PFSA-coated cardboard containers also seemed to raise the levels of four PFSA compounds in African American women, but not in the other groups.

Living in a city with PFSA in the water supply, unsurprisingly, also correlated with high levels of some types of the potential toxin.

But the most surprising source of contamination was dental floss.

Analysis of the threads in 18 different brands showed levels of fluorine indicative of PFSA being used as coatings. Specifically, several types of Oral-B Glide were implicated, and two similar generic brand competitors.

"This is the first study to show that using dental floss containing PFAS is associated with a higher body burden of these toxic chemicals," says lead author Katie Boronow from Silent Spring.

None of this should be taken as hard evidence that PFASs in dental floss will lead to health problems – at least, not on their own.

The study stopped short of collecting information on medical history or disease risks, providing little more than comparative concentrations of various organic fluorides.

But with these chemicals found in so many places, and alarm bells ringing on their potential for causing harm in sufficient doses, it might pay to make concessions where possible.

Mind you, that doesn't mean you need to give up flossing.

"The good news is, based on our findings, consumers can choose flosses that don't contain PFAS," says Boronow.

There's no doubt we'll be hearing more on these chemicals in the future, as researchers continue to investigate their biological impact and industries seek ways to limit their use and find alternatives.

For now, it's important this potentially nasty contaminant stays on our radar.

This research was published in Nature.