Monster Seminar JAM - Evaluating the Potential Health Impacts of Polybrominated Diphenyl Ether (PBDE) Flame Retardants using Teleost Fish Models
Dr. Sean Lema, Northwest Fisheries Science Center
Polybrominated diphenyl ethers (PBDEs) are flame retardant chemicals added to plastics, polyurethane foams and textiles. While PBDEs have helped reduce the loss of human life from fires, concern about the ecological and health risks of PBDEs has been heightened recently by evidence that levels of these chemicals are increasing in wildlife and humans. Although several studies have shown rising levels of PBDEs in a variety of marine mammal, bird and fish species, little is known about potential impacts of PBDEs for wildlife or human health. We have been examining the endocrine disrupting and developmental toxicity effects of the PBDE congener 2,2',4,4'-tetrabromodiphenyl ether (PBDE 47) in several teleost fish models. PBDEs share a structural similarity with polychlorinated biphenyls (PCBs), and there is evidence from rodent studies that PBDEs may disrupt the thyroid system. We therefore have been examining the influence of PBDE 47 exposure on the hypothalamic-pituitary-thyroid axis, a key endocrine regulator of brain development, growth and metabolism. We found that adult fathead minnows (Pimephales promelas) given oral doses of PBDE 47 showed depressed plasma levels of the thyroid hormone thyroxine (T4) and altered expression of genes for thyroid-stimulating hormone b subunit (TSH²) in the pituitary and thyroid hormone receptors ± and ² in the brain. Male minnows also showed a reduction in brain gene expression of basic transcription element binding protein (BTEB) a thyroid hormone induced transcription factor that regulates neurite outgrowth suggesting possible impacts of PBDE 47 exposure for thyroid hormone mediated neurogenesis. From these studies with adult minnows, it also became clear that PBDEs can be transferred maternally to offspring through the lipid stores of eggs. We have therefore also been exploring the early developmental impacts of PBDE 47 using zebrafish (Danio rerio) as an ontogenetic model. Zebrafish embryos exposed to PBDE 47 developed a suite of morphological and physiological defects that included an abnormal dorsal spinal curvature with flexion at the hindbrain and a tachycardia that progressed into atrioventricular block arrhythmia. This arrhythmia likely contributed to the elevated mortality seen in zebrafish exposed to highest levels of PBDE 47. While the exposure concentration required to cause this acute developmental toxicity is considerably higher than current environmental exposure levels, our findings provide evidence that PBDE 47 can disrupt the thyroid system and cause developmental abnormalities in fish and serves as an important first step toward informing concerns about the health risks of environmental PBDE contamination.
University of Washington
The Old Fisheries Center Auditorium (rm 201)
Date and Time:
January 18, 2007,
11:00 am - 12:30 pm