Firesafe but not failsafe: flame retardants cause neurotoxic effects. (Science Selections).

Polybrominated diphenyl ethers (PBDEs), widely used as flame retardants, are emerging contaminants of concern. A 1998 study of Swedish women showed that PBDE concentrations in mothers' milk increased exponentially from 1972 to 1997, doubling every five years. PBDEs have been compared to polychlorinated biphenyls (PCBs) because of their similar ubiquitous distribution throughout the global environment, their structure, and their properties, including persistence and the ability to bioaccumulate. In light of these findings, Per Eriksson of the Department of Environmental Toxicology at Uppsala University and colleagues investigated the developmental neurotoxic effects of two PBDEs and another type of brominated flame retardant, tetrabromo-bisphenol-A (TBBPA), on young mice [EHP 109:903-908]. They report that PBDE 47 and PBDE 99 can cause behavioral disturbances similar to those caused by PCBs in laboratory experiments with mice--aberrations in motor behavior worsening with age and reduced learning and memory--while TBBPA produced no adverse effects.

The scientists investigated the spontaneous behavior and learning ability of groups of mice that were given one of two dosages of PBDE 47, PBDE 99, or TBBPA at 10 days after birth. At 2 and 4 months postdosing, the spontaneous behavior of randomly selected groups of eight males was monitored for three consecutive 20-minute periods. The researchers observed habituation behaviors moving around a new space, rearing up, and general exploration, all of which tend to decrease as a mouse gets used to a new environment. At both 2 and 4 months, during the first 20-minute period the PBDE-treated animals were less active than the controls, and this decrease correlated with increasing dose. During the second period the activities in all groups were comparable. During the third period the PBDE-treated animals appeared to be more active than the controls, with the increase again apparently dose-related. The authors report that this nonhabituating behavior worsens with age, as they are more pronounced in 4-month-old mice than in 2-month-old mice.

At 5 months postdosing, groups of 16-18 randomly selected males were tested using a Morris water maze. This is a common behavioral test in which mice use visual cues to find and remember the location of a platform submerged in a pool of water. This task provides a measure of many cognitive abilities, including analytical skills, learning and memory, and the ability to form strategies.

The decrease in the time taken to locate the platform over a total of 20 trials was used to demonstrate the animals' spatial learning ability. On day 5 the platform was relocated and the animals' performance of the maze test was measured over another 5 trials. The decrease in the time taken to find the relocated platform over the 5 trials was used as a measure of the animals' relearning ability. During the first part of the swim maze study, both treated and control animals performed to an equivalent standard. In the relearning stage of the study, mice exposed to the higher dose of PBDE 99 performed significantly worse than control animals, but those dosed with PBDE 47 were not significantly different from controls.

Based on the results of the 2-, 4-, and 5-month tests, the authors conclude that although both PBDEs cause adverse neurodevelopmental effects, PBDE 99 is the more potent neurotoxicant.