Young zebrafish exposed to flame retardants through their mothers swam up to 60 percent slower and had reduced gene expression important for nervous system development, a new study has found. In natural settings, slower swimmers are easier targets for predators. The new study, published in Environmental Science & Technology, is unique because it shows in fish that exposure to PBDEs, found in some furniture and electronics, can lead to developmental and behavioral changes in their offspring. Such early life changes to the neurological system can lead to learning and behavioral problems later in life.
The results are unique because the zebrafish larvae were exposed to the PBDEs through their parents. The pentaBDE chemicals accumulated in the exposed parents during the five-month exposure time, and the mothers transferred some of these chemicals into their eggs.
This research contributes to an increasing number of studies that shows early life exposure to PBDEs can impact locomotion. Previous studies have found that zebrafish embryos exposed to the pentaBDE mixture — or one of its main chemical components (BDE 47) — swim slower as larvae during similar light-dark tests.
But in a similar study in which the parents were exposed to the decaBDE flame retardant mixture, larvae actually swam faster during the light and dark tests. Although this suggests that locomotion behavior may be a common target for different PBDEs, the actual effect may vary.
These findings have direct implications for predator-prey avoidance in fish, but also have implications for humans and other mammals. This is because scientists use these types of locomotion tests as a measure of how individuals interact with their surrounding environment. Impaired environmental interaction is characteristic of behavioral impacts such as ADHD.
In the study, the fish were subjected to alternating dark-light cycles. Under normal conditions when switching from light to dark conditions, fish will initially swim faster and then gradually slow down. The slower swimming speed in the pentaBDE-exposed fish may indicate that they did not respond as quickly to the changes in light conditions. This may indicate a reduced ability to interpret changes in their environment.
The scientists do not know the way the pentaBDE chemicals damaged the brain, but they think it may be related to the thyroid hormone system. Thyroid hormones are essential for proper brain development, and it is well known that PBDEs can disrupt thyroid hormones.
The study investigated a commercial flame retardant mixture, called pentaBDE. This mixture is now banned, but the chemicals that are in the penta-BDE mixture are still widely detected in the environment, including house dust.
A limitation of the study is that the fish were exposed to very high levels of PBDEs, about 1,000 times higher than typical environmental levels. It is not known if similar effects would have been observed with lower, environmentally relevant PBDE levels.
Future work should examine if the effects on swimming persist through the fish's life. Also, additional work should investigate if the harmful effects are transferred to future generations, such as the grandchildren.