Embedded in our furniture and our clothing, our electronics and our food, our carpets and our walls, flame resistant chemicals are everywhere. They're even in our dust.
Brominated flame retardants (BFRs) have been in use since the 1970s, but in recent decades they've become the subject of intense scientific scrutiny.
One type, known as polybrominated diphenyl ethers (PBDEs), have taken a lot of the heat. Not only can they easily leach into the environment, these retardants are commonly inhaled and ingested, where they begin to build up in the body.
We still don't know what the human health effects are, if they exist, but numerous animal studies and some epidemiological research suggests exposure is linked to adverse hormonal, reproductive and behavioural effects.
PBDEs have been restricted in Canada since 2008, but new research has found these retardants still persist in the dust of some homes.
Using X-ray spectroscopy techniques, which allow for non-destructive probing of a material, researchers in Canada tested 20 dust samples collected from the vacuum cleaners of homes in Newfoundland.
"We were able to show that there was a noticeable amount of bromine present in all of the dust samples we analysed and in a select few we were able to identify bromine species that were characteristic of brominated flame retardants," says Peter Blanchard who works at the Canadian Light Source (CSL).
It's the first time scientists have been able to connect bromine particles back to specific BFRs, and it could help us better understand our lifetime exposure to these chemicals.
The concentrations of bromine in this particular study ranged from 2-19 μg/g, which is admittedly very low. Yet because these chemicals can accumulate in the body over time, long-term exposure to even minimal amounts may be harmful, especially when you consider other routes for exposure, including dermal uptake from treated fabrics, from the diet, and via human milk for breast-fed infants.
Overall, the concentrations of bromine were comparable to other recent studies of household dust in Ireland and Australia, and below the safe reference dose, or 'hazard quotient', designated by the United States Environmental Protection Agency.
But while the research in Ireland shows BFR levels in dust are in the safe zone, another recent study in the United Kingdom found BFR levels in dust were actually higher than the US EPA hazard quotient.
Measuring the chemicals within dust is difficult. These are tiny concentrations we're talking about and identifying specific species within those tangles is even more challenging.
While growing evidence suggests concentrations of BFRs are higher indoors, methods for measuring these chemicals have varied from study to study, and we might be overlooking the smallest ones.
In previous dust samples, for instance, BFRs were at their highest concentration in particle sizes smaller than 250 μm. But in the current study, particle sizes were generally larger than 500 μm.
"The accuracy of using [X-ray absorption near-edge spectroscopy] to identify BFRs is highly dependent on the source and size of the dust samples," the authors write.
"Therefore, for future research, it is important to take into account the sources of dust sample and to focus on fine dust particles."
Far more research needs to be done before we can properly estimate our cumulative lifetime exposure to specific BFRs, and figure out at what stage they put our health at risk.
In the meantime, Europe has prohibited the use and marketing of several PBDEs, including 'decaBDE', which has a similar structure to a known human carcinogen.
North American legislation has lagged behind and been far more lax. In 2009, the US EPA added 'decaBDE' to the list of phase-out chemicals in favour of 'greener' alternatives, and yet some industry scientists are still defending its use.
In response to recent results from Ireland, which show decaBDE in dust and air within the home, researchers funded by the American Chemistry Council's North American Flame Retardant Alliance argued there would be no adverse health effects.
"Thus, their paper clearly demonstrates that one can measure flame retardants at extremely low levels, but exposure to these amounts are not likely biologically or physiologically relevant," the response reads.
That would be nice, but it might not be true. While oral ingestion and skin absorption of house dust is a major pathway of BFR exposure, especially among toddlers who put things in their mouth a lot, there are other ways it can get into our bodies.
In response to the response, the authors of the original study once again backed up their original concern, especially for a type of fire retardant known as decabromodiphenyl ethane (DBDPE), which has been linked to neurodevelopmental effects.
Not only did the response rely on the lowest reference dose for rats, they say, it doesn't take into account the combined effects of other forms of exposure, including skin against fabric, seafood, and breast milk.
"Taking such additional exposures into account will inevitably increase the Hazard Quotient and in conclusion we stand firmly by our statement that 'detailed study of the health implications of exposure to DBDPE is thus recommended'," the authors write, declaring no conflicts of interest.
In the meantime, there are few practical measures people can take. Educating the public on which fire retardants may pose the greatest health risks could help, but further research needs to be done so we can give more definitive advice and hopefully implement stronger regulations.
It's also really important that new flame retardants are also tested for safety as recent studies show these chemicals are also accumulating in our dust and bodies.
"Public awareness is very important," says public and environmental health scientist Atanu Sarkar from Memorial University in Canada.
"Maybe we need more frequent vacuuming of all the dust."
The authors plan on visiting the same households several years from now to see how the concentrations may have changed over time.
Let's hope there are less next time.
The study was published in Environmental Science and Pollution Research.