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.
on brominated flame retardants
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.
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.
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.
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.
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.
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
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.