PBDEs are flame retardants of the additive type , i.e . they are physically combined with the material being treated . Because of the chemical and toxic properties of its components , in particular isomers of hexabromodiphenyl ether ( HexaBDE ) and heptabromodiphenyl ether ( HeptaBDE ) , and their wide spread occurrence in the environment and in humans c-OctaBDE causes concern in many regions in the world .