Heat and ultraviolet light broke down an advanced flame-retardant chemical, commonly used in polystyrene building insulation, into by-products containing the environmental toxin bromine, according to a recent study. A buildup of bromine in humans and animals can disrupt thyroid hormone function, negatively affect liver enzyme production, and potentially be toxic to the immune and nervous systems.
“There is the claim that this flame retardant is more environmentally friendly,” said Christoph Koch, a graduate student in aquatic ecology at the University of Duisburg-Essen in Germany and lead author on the study. If manufacturers intend to begin using this flame retardant for personal items, Koch said, a better understanding of how it degrades is needed before it becomes common in clothing, electronic equipment, or furniture.
From Simple to Complex Flame Retardants
Recently, environmental protection agencies in Europe and the United States prohibited the use of flame retardants with simple chemical structures, called monomers. Monomers quickly break down into by-products with bromine, which builds up in terrestrial and marine sediments and biota across the world. Regulations now advise the use of polymer-based flame retardants (polyFR).
Polymers “are bigger, less mobile in the environment, and cannot be taken up by any type of cells very quickly or at all,” said coauthor Bernd Sures. Sures is Koch’s Ph.D. adviser and a professor of biology at the University of Duisburg-Essen.
“Everyone seems to be okay with this new type of flame retardant because [the molecule] is so big,” he added. However, little is known about how polyFRs break down and what the by-products may be, Sures said.
Breaking Down a Polymer
“Due to its size, polyFR is probably a better environmental option,” Koch said. “But we know that other polymers outside of flame retardants can break down through ultraviolet radiation and through heat. These are known mechanisms for degradation. We thought to apply those mechanisms to polyFR.”
Koch and his team incorporated a common polyFR, brominated polybutadiene, into expanded polystyrene foam. They tested how the chemical degraded when exposed to 60°C heat, to ultraviolet light (UV) of a moderate intensity, and a combination of both.
These are conditions polystyrene insulation might experience on an average summer’s day in the Northern Hemisphere if it’s installed in an attic or left to degrade in an outdoor landfill, Koch said. The UVB exposure was the same as that from 9 days of natural sunlight, and the UVA exposure was the same as that from only 6 hours of natural sunlight.
Under these conditions, the team found that polyFR degraded into up to 75 by-products, about 10% of which were brominated compounds. The polyFR degraded into more products when exposed to UV light than when it was exposed only to heat.
Whether the degradation products may accumulate in the environment similar to the way monomers do is still unknown, the researchers said. The team published these findings in Environmental Science and Technology on 9 January.
The possible environmental impact “is especially important at the end of life of these substances,” Sures said. If polyFR “is used in insulation materials and it goes to a landfill or is not treated in a proper way at the end, then we could have negative effects like degradations.”
Ecotoxicity Still Unknown
“Many of these different degradation products contained bromine and thus could potentially present a toxicity hazard,” Adrian Covaci, a professor of environmental toxicology and chemistry at the University of Antwerp in Wilrijk, Belgium, told Eos. Covaci, who was not involved with this research, called the study “environmentally relevant” but said that there was too little information at the moment to comment on the potential for toxicity in people.
“This work indicates that more experiments are necessary to characterize this material and, as such, the potential for toxicity to the environment and humans,” Covaci said.
The researchers noted that they have tested only how the polyFR degraded when incorporated into polystyrene but not when incorporated into a commercial insulation product. The polyFR may break down differently in a commercial product, they said, and should be tested before the flame retardant becomes common in everyday products.
In a public response to this research, DowDuPont, which manufactures polyFR for insulation, stated that it “has conducted extensive testing on the safety profile of polymeric FR, including degradation” and that independent government tests have shown that it is a “suitable substitute” for previously used flame retardants. The company added that the chemical’s “potential environmental impact should have been validated [by Koch et al.] by studying degradation within polystyrene foam insulation.”
—Kimberly M. S. Cartier (@AstroKimCartier), Staff Writer
Correction, 1 February 2019: DowDuPont contacted Eos after publication of this article and requested their response to the study by Koch et al. be included.