Published online 20 May 2011 | Nature | doi:10.1038/news.2011.311

News: Explainer

A burning issue

Should flame-retardant chemicals be banned?

babyMany baby products contain fire retardants, but how much do we know about these chemicals?BSIP/Photoshot

Mothers reading one of the several hundred news stories this week that covered a study of flame retardants in US baby products could be forgiven for panicking. "Study: 80 Percent of Baby Products Are Toxic" screamed Fox News.

The research that triggered this media storm, and published this week in Environmental Science and Technology1, does highlight a major issue with toxicology research, consumer products and chemical regulation. But not in the way that might be expected from a glance at the general media coverage.

What does the study actually tell us?

Heather Stapleton at Duke University in Durham, North Carolina and her colleagues set out to find how widespread flame-retardant chemicals were in upholstery foam used in babies' and children's items, and which chemicals were present. They asked members of the general public to send them small cuttings of foam from items such as child car seats, baby-changing mats and crib mattresses, and also purchased some new products themselves to analyse.

They found a number of different flame-retardant chemicals in 80% of the foams. Most common were TDCPP (tris(1,3-dichloroisopropyl) phosphate) and a proprietary product called Firemaster550, a widely-used flame-retardant in the United States. Stapleton and her team also reported detection of polybrominated diphenyl ethers (PBDEs) in five samples out of 101, suggesting the presence of a type of PBDE called PentaBDE whose use was discontinued in 2004.

"The paper confirms what all scientists in my area of research know," says Larissa Takser, who studies environmental contaminants at the University of Sherbrooke in Canada, and was not involved in the study. "Our exposure is composed of old, for example PBDE, and new, recently developed chemicals, which will be used for years before their careful evaluation, if it will be done at all."

The products containing the PBDEs date from before 2004, so the chemicals' presence is not surprising, and study author Thomas Webster says he expected that the majority of the flame retardants found would be TDCPP and Firemaster. Two other flame retardants were found, one that is sold as 'V6' and one that was unknown to the researchers.

Webster, an environmental epidemiologist at the Boston University School of Public Health in Massachusetts, says one key aim of the research was to find out what is actually being used, as baby products can remain in use for a long time after purchase.

"There's really only flame-retardant standards in California about this kind of thing," says Webster, about the US. "We don't know about, say, Massachusetts. It's very hard to find out what's being used."

What does the study not tell us?

California has tough standards that mandate the use of flame retardants in upholstery foams and as this state is a big part of the US market it is sometimes assumed that products will automatically be manufactured to contain these chemicals.

"Obviously all these items have to respond to the California legislation. The only way to address this law is to have flame retardants. Its not surprising that they found flame retardants in these items," says Lucio Costa, a neurotoxicology researcher at the University of Washington, Seattle.

"The issue is whether these new flame retardants that are used instead of the old PBDEs actually leak into the environment, and whether there is exposure and whether these chemicals have a toxicological profile," he says.

This latest study does not address that. It was not designed to measure what actual exposure babies and their parents face from the presence of these chemicals in foam inside cushions, and whether the chemicals leak out of the foam.

Nevertheless, this doesn't mean that people are not exposed to PBDEs and other flame retardants. These chemicals are extremely persistent and so become widely distributed in the environment when they do escape. Studies – including some from the same authors as this latest paper – have detected the chemicals in household dust2, in breast milk3 and even in polar bears4.

So do we actually know that these chemicals are harmful?

PBDEs are chemically similar to the polychlorinated biphenyls or PCBs, which were banned in many countries in the late 1970s and early 1980s. Although the toxicity of some PCBs is well documented, much less can be said with certainty about PBDEs.

Holly LaVoie at the University of South Carolina School of Medicine in Columbia says we do not have enough proof at this point to say for certain that PBDEs are harmful to human health.

"Most of the work has come from animal studies at very high doses," she says. "Animal studies hint that there could be some problem."

High doses of the chemicals have been found to trigger neurological problems in lab rats. They also appear to mimic the effect of thyroid hormones, which have a similar chemical structure, and can cause problems in this way. LaVoie's team recently reported the first study showing that low doses could interfere with thyroid function in rats.

Approaching the problem from the other side are epidemiological studies. These try to puzzle out links between chemical exposure and health problems in humans using statistical analysis of population surveys.

Several epidemiological studies on flame retardants are in progress, says Takser, but they take time to get results. And researchers are often late to the game because of problems that include funding and delays in recognizing potential problems.

A major epidemiological study is GESTE, which is looking at the relation between PBDE exposure, thyroid disruption and child development.

Takser will present the first results from GESTE at a conference in June. "GESTE is designed to specifically address the question of thyroid disruption by PBDE and related chemicals and long-term effects on child psychomotor development and behaviour," she explains. "We clearly confirm thyroid disruption as found in animal studies," Takser says.

"Really, we know that they are thyroid disrupters in animals. Also, they are probably involved in behavioural dysfunction (for example, hyperactivity) in developing animals and in children," she summarizes

What do we know about the flame-retardant compounds other than PDBEs?

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There are some studies suggesting that TDCPP may be harmful. Both it and a related compound were the subject of some scrutiny in the 1970s, when they appeared in children's pyjamas.

"It wasn't banned, but it was removed," explains Webster. "The research back then suggested it was mutagenic. It looks like it might be a carcinogen. There's some new data that suggest it might be neurotoxic."

The state of the art here is still far less than with PBDEs however, and there are even fewer studies on Firemaster550.

Webster also says he was surprised to find the "weird" compounds in this new study: the V6 and the unknown chemical. While we don't know very much about PBDEs and TDCPP, we know even less about these newer compounds.

Webster calls it a "hydra problem", after the mythical monster which sprouted two new heads every time one of its existing heads was chopped off.

As Costa says, "This is the problem we always have when we find a compound is toxic and we ban it. In most cases we know less about the new compound than we know about the old ones."

Many researchers believe that the way the United States deals with chemicals needs shaking up to ensure that more testing on such products is done before they hit the market, an approach used to some extent in Europe.

But they do prevent fire right?

The effectiveness of flame retardants on saving lives is hard to tease out, as their use overlaps with other initiatives such as smoke alarms and also with a decline in smoking — a major cause of household fires. Another question is whether such flame retardants need to be in baby products.

"How many babies smoke?" asks Webster.

Industry association the American Chemical Council, based in Washington DC, says that flame retardants "provide important fire-safety benefits". Campaign groups dispute this, saying that their introduction has not reduced deaths and they do not provide very much protection.

The issue is up for discussion at the forthcoming conference: "We've got some people saying they're effective and some people saying they're not so effective," says Webster

In the age-old sign off of science reporters everywhere: more research is needed, say scientists. 

  • References

    1. Stapleton, H. et al. Environ. Sci. Technol. doi:10.1021/es2007462 (2011).
    2. Stapleton, H. et al. Environ. Sci. Technol. 43, 7490-7495 (2009). | Article | PubMed | ISI | ChemPort |
    3. Schecter, A. et al. Environ. Health. Perspect. 111, 1723-1729 (2003). | Article | PubMed | ISI | ChemPort |
    4. Muir, D. et al. Environ. Sci. Technol. 15, 449-55 (2006).
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