Brominated flame retardants

Brominated flame retardants are industrial chemicals produced to fire-protect construction materials, indoor decorations, furniture, textiles, electronics, and electrical appliances. One of the major classes of BFRs are the polybrominated diphenyl ethers (PBDEs). PBDEs are not chemically bound to the product material, so they are prone to migrate into the environment and adsorb to particles such as household dust.

Unlike the legacy POPs (e.g. the organohalogen compounds [OHCs]), where dietary intake is an important route of exposure, BFRs also have indoor dust as a significant source of exposure via inhalation and hand-to-mouth activities, a special concern for small children and cats. An exposure assessment study on PBDE burdens in Americans found that the food intake of PBDEs explained less than 20% of the total body burden and that 82% of the body burden of PBDEs could be accounted for through house dust exposure. This large contribution from indoor dust is proposed as an explanation for the elevated levels of PBDEs in serum observed in North Americans. In Europe we have not used the same amounts of PBDE in our products due to different standards of fire protection.

The analysed BFRs and other OHCs were reported in 2015 for the first time, when Jessica Engdahl Norrgran defended her thesis at Stockholm University (Thesis SU 2015), and secondly when the publication came out in 2017 (Norrgran Engdahl et al. 2017). The analysis were performed on the individual household dust from three rooms (n=41), cat serum (n=28 cats were sampled but as  several families had more than one cat these samples were pooled), and cat food (dry and wet, n=28), according to what the cat owners reported that the cats ate. Here we discuss the BFRs, i.e. polybrominated diphenylethers (PBDEs), polybrominated biphenyls (PBB) and decabromodiphenylether (DBDPE).

Figure 1. Individual dust levels of BFR found in child rooms (1), adult bedrooms (2) or living rooms (3) from 17 families. The dust from home 12, 14 and 16 needed to be pooled from all rooms due to limited sample volumes, and in family 9 only one sample was taken. In home 3 and 4 the children slept in the adults bedroom.

Both the levels of BFR analysed in the dust samples and the chemical profile (of the individual BFRs) differed between the households, much more than for example phthalates and OPFRs. This indicates that the sources of these compounds are quite product specific and that active choices of household products can affect the chemical exposure indoor. The total BFR (incl. PBDEs, PBB, and DBDPE) concentration found in the household dust were from 60 ng/g dust and up to 12800 ng/g dust. In general, the BFR composition were similar between the three rooms, but the levels were a bit higher in the living rooms. This is expected as most electronics and textiles to which flame retardants are applied to are found there (exceptions could be seen though).

Figure 2. BFR levels (on a lipid weight basis) analyzed in cat serum from 17 households. The blood serum was pooled for the household with several cats, except for two cats in household 9 and 17.

The serum levels of BFRs was dominated by the 6-OH-BDE47, which is coming from cat food and not from household dust. It’s a natural contaminant from the marine environment where it is believed to be synthesized by algae among others, probably as a defense system. It is believed to enter the cat food via the fish content that is blended in. Also, the 2,4,6-tribromophenol (2,4,6-TBP) can have a marine origin, although it is also used as a pesticide and industrial intermediate for chemical synthesis. Both these two compounds are potent endocrine disruptors on the thyroid system.

Further, it was surprising to find the fully brominated biphenyl (BB-209) in all cat serum samples at high levels. A compound phased out two decades ago and to which the current source is still unknown. The BB-209 could only be found in a few dust samples, which could not explain the high levels found in cats. To the authors knowledge BB-209 has not been determined in human samples. Within MiSSE we have performed some additional studies to search for the source of BB-209 specifically. We did not find any traces of BB-209 in cat litter sand (10 different brands tested), nor in cat toys (7 commercially popular toys with a wide span of material) and we tested the veterinarian equipment to rule out any contamination of the serum during handling. We also compared the chemical profile in blood serum between cats, dogs and horses for BFR and some classical organohalogen compounds (N. Fijol Bachelor thesis 2017, Stockholm University). We could there confirm that BB-209 was only determined in the cat’s serum and not in dog’s or horse’s. We do still not have an answer to where this compound is coming from, but one suggestion could be the cat’s lowered metabolic character could interfere and increase the accumulation of these highly lipophilic compounds.

The levels of the PBDEs in cat serum consisted mainly of the penta- (5 bromine) BDE-47 and BDE-99 and the fully brominated BDE-209.

The data were thoroughly evaluated statistically and the main conclusions from the study were;

  • A significant correlation between dust levels and cat serum levels of certain PBDEs could be established, which indicate that dust is a relevant exposure pathway for cats. Also, the congener profile BDE47/99 correspond to the dust profile.
  • Cats and humans are similarly exposed to these compounds and it is believed that cats can work as sentinel for small children and toddlers exposure.

Further reading:

Norrgran Engdahl Thesis 2015

Norrgran Engdahl et al 2017