Eriksson, P, H Viberg, E Jakobsson, U Orn and A Fredriksson. 2002. A brominated flame retardant, 2,2',4,4',5-Pentabromodiphenyl Ether: Uptake, retention, and induction of neurobehavioral alterations in mice during a critical phase of neonatal brain development. Toxicological Sciences 67:98-108.

Background on brominated flame retardants

Earlier work by Eriksson and his colleagues established that a single dose of the polybrominated flame retardant 2,2',4,4',5-pentabromodiphenyl ether, or BDE-99, undermines neurological development in mice, affecting spontaneous behavior, learning and memory. In this experiment, they show that for this effect, exposure must occur during a crucial window in post-natal development, as by day 19 after birth the effect can no longer be induced.

What did they do? Male mice were given a single moderate dose (8 mg per kg body wight, or 8 ppm) of BDE-99 on either day 4, 10 or 19 after birth. Eriksson et al. then compared spontaneous behaviors in control vs. experimental animals by observation. By dissection, they also determined where BDE-99 accumulated in the brain of experimental animals.

What did they find? Changes in spontaneous behavior were observed in animals treated on day 4 and day 10 but not on day 19. The changes indicate that the dosed animals were less able to habituate to circumstances in their cages than untreated animals. Normal mice initially are highly active in new surroundings but then settle down. The treated mice continued to be agitated in their new surroundings long after was the pattern in untreated mice. The most pronounced effect was seen in animals treated on day 10.

What does it mean? In the first few weeks of life after birth, the brains of mice undergo a period of very rapid development and organization. This period is known as the "brain growth spurt" (BGS). During the BGS, brain nerves grow rapidly and connections among nerve cells proliferate. Biochemical changes during BGS transform the fetal brain into that of an adult. It is also a period in which animals, including humans, acquire many new sensory and motor skills. In rodents BGS peaks around day 10 after birth while in humans BGS occurs during the final trimester of pregnancy and continues through the first 2 years of life after birth.

Eriksson et al.'s results are consistent with an impact of BDE-99 on processes underway in the brain growth spurt, as the maximal impact was observed on day 10 after birth and by day 19 no effect was inducible even though the dose remained the same.

The amount ingested by the mouse was relatively low... low parts per million... and the concentration the scientists estimate reached the relevant brain issues was much lower, roughly 10 parts per trillion (10.7 picomolar per gram of brain). This amount was sufficient to induce detectable effects on adult behavior months after the single exposure.

Eriksson et al. also note that the impact of BDE-99 resembles that of certain PCBs under similar exposure conditions. They raise the possibility that the presence of both types of may lead to interactions that would increase their effects either additively or synergistically. Data on human developmental neurotoxicity of PCBs has confirmed effects of those compounds, while no relevant epidemiological studies of neurodevelopmental effects in humans have been reported.