Polybrominated diphenyl ethers or PBDEs, are a class of organobromine compounds that are used as flame retardants. Like other brominated flame retardants, PBDEs have been used in a wide array of products, including building materials, electronics, furnishings, motor vehicles, airplanes, plastics, polyurethane foams, and textiles. They are structurally akin to polychlorinated diphenyl ethers (PCDEs), polychlorinated biphenyls (PCBs) and other polyhalogenated compounds, consisting of two halogenated aromatic rings. PBDEs are classified according to the average number of bromine atoms in the molecule. The health hazards of these chemicals have attracted increasing scrutiny, and they have been shown to reduce fertility in humans at levels found in households. Because of their toxicity and persistence, the industrial production of some PBDEs is restricted under the Stockholm Convention, a treaty to control and phase out major persistent organic pollutants (POPs). Classes of PBDEs The family of PBDEs consists of 209 possible substances, which are called congeners (PBDE = C12H(10−x)BrxO (x = 1, 2, ..., 10 = m + n)). The number of isomers for mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-, and decabromodiphenyl ethers are 3, 12, 24, 42, 46, 42, 24, 12, 3 and 1, respectively. In the United States, PBDEs are marketed with the trade names DE-60F, DE-61, DE-62, and DE-71 applied to pentaBDE mixtures, DE-79 applied to octaBDE mixtures, and DE 83R and Saytex 102E applied to decaBDE mixtures. The available commercial PBDE products are not single compounds or even single congeners but rather mixtures of congeners. Lower brominated PBDEs These species average 1–4 bromine atoms per molecule and are regarded as more dangerous because they more efficiently bioaccumulate. Lower-brominated PBDEs have been known to affect hormone levels in the thyroid gland. Studies have linked them to reproductive and neurological risks at certain concentrations or higher. Higher brominated PBDEs These species have average 5 or more bromine atoms per molecule. The commercial mixture, named pentabromodiphenyl ether contains the pentabromo derivative predominantly (50–62%); however, the mixture also contains tetrabromides (24–38%) and hexabromides (4–8%), as well as traces of the tribromides (0–1%). In similar manner, commercial octabromodiphenyl ether is a mixture of homologs: hexa-, hepta-, octa-, nona-, and decabromides. Health and environmental concerns Since the 1990s, environmental concerns were raised because of the high hydrophobicity of PBDEs and their high resistance to degradation processes. People are exposed to low levels of PBDEs through ingestion of food and by inhalation. PBDEs bioaccumulate