development of the brain can cause permanent changes in behavior, including hyperactivity. Swedish scientists first reported substances related to pentaBDE were accumulating in human breast milk. Studies by the Swedish Society for Nature Conservation found for the first time very high levels of more highly brominated PBDEs (BDE-209) in eggs of peregrine falcons. Two forms of PBDEs, penta- and octaBDE, are no longer manufactured in the United States because of health and safety concerns. Based on a comprehensive risk assessment under the Existing Substances Regulation 793/93/EEC, the European Union has completely banned the use of penta- and octaBDE since 2004. However, both chemicals are still found in furniture and foam items made before the phase-out was completed. The most common PBDEs used in electronics are decaBDE. DecaBDE is banned in Europe for this use and in some U.S. states. For PBDE, EPA has set reference dose of 7 micrograms per kilogram of body weight, which is "believed to be without appreciable effects". However, Linda Birnbaum, PhD, a senior toxicologist formerly with the EPA (now at NIEHS) notes concern: "What I see is another piece of evidence that supports the fact that levels of these chemicals in children appear to be higher than the levels in their parents; I think this study raises a red flag." A previous study by the Environmental Working Group in 2003 published test results showing that the average level of fire-retardants in breast milk from 20 American mothers was 75 times higher than the average levels measured in Europe. Increasing levels of PBDEs in the environment may be responsible for the increasing incidence of feline hyperthyroidism. A study in 2007 found PBDE levels in cats 20- to 100-fold greater than median levels in U.S. adults, although it was not adequately powered to establish an association between hyperthyroid cats and serum PBDE levels. Subsequent studies have indeed found such an association. An experiment conducted at Woods Hole Oceanographic Institution in 2005 showed that the isotopic signature of methoxy-PBDEs found in whale blubber contained carbon-14, the naturally occurring radioactive isotope of carbon. Methoxy-PBDEs are produced by some marine species. If the methoxy-PBDEs in the whale had come from artificial (human-made) sources, they would have contained only stable isotopes of carbon because virtually all PBDEs that are produced artificially use petroleum as the source of carbon; all carbon-14 would have long since completely decayed from that source. The isotopic