The porpoises and dolphins investigated were stranded on the coasts of Scotland, Ireland, the Netherlands, Belgium, France and northwest Spain. By far the most HBCD was found in the blubber of animals from the Irish Sea and the West Coast of Scotland. Therefore the researchers suspect that this HBCD originates from a source discharging into the Irish Sea.
The alpha isomer of HBCD forms at most fifteen percent of the HBCD formulation used in commercial flame retardants. The three isomers differ in how the bromine atoms are bound to the carbon atoms of HBCD and a new analytical technique can distinguish between the different isomers. Using this technique, Boon and his colleagues discovered that only the alpha isomer accumulates in sea mammals such as dolphins. They used liver material from laboratory rats and a recently dead seal washed up on a beach on Texel, the island off the Dutch coast where Royal NIOZ is located, to investigate the reason for these differences in bioaccumulation between the different HBCD isomers.
The beta and gamma isomers of HBCD are metabolised by the animals. The enzyme complex cytochrome P450 in the liver plays an important role in this. This complex adds oxygen to the HBCD but it cannot react with the alpha isomer. This is due to subtle differences in the spatial structure of the alpha, beta and gamma isomer molecules. As it is not metabolised, the alpha isomer accumulates in the fat-rich tissues of sea mammals, such as the blubber.
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