PBDEs are one of the major groups of brominated flame retardants, used in applications such as fabrics, upholstery foams, plastics and electrical equipment. The three commercial formulations - penta-BDE, octa-BDE and deca-BDE - are undergoing risk assessments under EU legislation on existing substances (ENDS Report 308, p 41 ).
The most environmentally hazardous appear to be lower brominated diphenyl ether congeners, because the molecules are small enough to cross biological membranes. They are persistent and biomagnify in food chains. Tetra- and penta-BDE congeners have been reported in fish, fish-eating birds and mammals.
Swedish researchers have also reported an exponential increase in levels of one tetra-BDE congener - BDE-47 - in human breast milk over the past 30 years (ENDS Report 283, pp 3-4 ). Human exposure to this compound is now at a similar level to some PCB congeners.
The potential for health effects from exposure to PBDEs is unknown and environmentalists have expressed concerns largely on the grounds of precaution. But research about to be published in Environmental Health Perspectives suggests that PBDEs have neurological effects similar to those attributed to PCBs.
Scientists from Uppsala and Stockholm Universities fed ten-day-old mice a single dose of either PBDE 47 or PBDE 99 - tetra- and penta-BDE congeners, respectively, which are found in human milk. The dose levels were designed to achieve concentrations in the brain comparable to those which might result in human infants less than one year old.
The researchers found no physiological effects, but behavioural analyses when the mice were two and four months old showed significant dose-related differences.
Mice put into new surroundings were monitored for activity. Normally, mice become very active for about 40 minutes as they explore a new environment, but this activity then subsides as the surroundings become more familiar - a so-called habituation response. However, mice exposed to PBDEs showed less activity in the early stages and then became relatively more active later on.
Exposed mice also showed reduced learning ability when put into a maze. Mice exposed to PBDE 99 in particular took twice as long as control animals to adjust their behaviour after changes were made to the maze.
The researchers concluded that exposure to PBDE 99, and to a lesser degree PBDE 47, were neurotoxic and affected spontaneous behaviour, learning and memory in mice. They note that exposures of human infants to PBDEs via breast milk are now significant, and that PBDEs appear to have similar neurotoxic effects to PCBs.
The findings are likely to increase pressure for a phase-out of PBDEs. The European Parliament accepted a proposal from its Environment Committee in September to ban all the three main PBDE formulations. It cited the precautionary principle and "international consensus" on the serious impacts of the products.
The European Commission proposed earlier this year that only penta-BDE should be banned (ENDS Report 312, p 48 ). Parliament's vote came ahead of the risk assessments of octa- and deca-BDEs, which will not be finalised for a few months.
The issue will now be addressed in the co-decision procedure. If Environment Ministers do not accept Parliament's vote, the two sides will have to thrash out an agreement in direct negotiations.