Evaluation of Common Use Brominated Flame Retardant (BFR) Toxicity Using a Zebrafish Embryo Model

Abstract

Brominated flame retardants (BFRs) are used to reduce the flammability of plastics, textiles, and electronics. BFRs vary in their chemical properties and structures, and it is expected that these differences alter their biological interactions and toxicity. Zebrafish were used as the model organism for assessing the toxicity of nine structurally-diverse BFRs. In addition to monitoring for overt toxicity, the rate of spontaneous movement, and acetylcholinesterase and glutathione-S-transferase (GST) activities were assessed following exposure. The toxicities of BFRs tested can be ranked by LC50 as tetrabromobisphenol A (TBBPA) < 4,4'-isopropylidenebis[2-(2,6-dibromophenoxyl)ethanol] (TBBPA-OHEE) < Pentabromochlorocyclohexane (PBCH) < 2-ethylhexyl 2,3,4,5-tetrabromobenzoate (TBB) < hexabromocyclododecane (HBCD) < hexabromobenzene (HBB) < Tetrabromophthalic anhydride (PHT4). No adverse effect was observed in di(2-ethylhexyl) tetrabromophthalate (TBPH) or dibromoneopentyl glycol (DBNPG)-treated embryos. The rate of spontaneous movement was decreased in a concentration-dependent manner following exposure to four of the nine compounds. GST activity was elevated following treatment with PBCH, TBBPA, HBCD, and HBB. The results indicate that exposure to several BFRs may activate an antioxidant response and alter behavior during early development. Some of the BFRs, such as TBBPA and TBBPA-OHEE, induced adverse effects at concentrations lower than chemicals that are currently banned. These results suggest that zebrafish are sensitive to exposure to BFRs and can be used as a comparative screening model, as well as to determine alterations in behavior following exposure and probe mechanisms of action.

Keywords: brominated flame retardant; oxidative stress; zebrafish.

Figure 1

Concentration-response curves of the nine selected Brominated flame retardants (BFRs). Exposure to most BFRs resulted in a concentration-dependent increase in rate of mortality over 168 h of exposure. Exposure to TBBPA, PBCH, TBBPA-OHEE, and TBB induced the highest rate of mortality at the lowest concentration. * p < 0.05, N = 12.

Figure 2

Malformations induced by BFR exposure as observed daily until 168 hpf. (A) HBCD and HBB induced curved body malformations; (B) Fin malformations were also observed in TBBPA and TBBPA-OHEE exposed embryos; (C) TBBPA, TBBPA-OHEE, and PBCH induced pericardial edema. Representative images of 120 hpf larvae from studies shown in panels A–C; (D) control, normal morphology (E) 2.5 ppm TBBPA, FM = fin malformation; (F) 5 ppm PBCH, PE = pericardial edema; and (G) 5 ppm HBCD, curved body malformation.

Figure 3

Alterations of spontaneous movement behavior at 24 hpf. Exposure to TBBPA, TBBPA-OHEE, HBCD, and PBCH decreased rates of spontaneous movement in a concentration-dependent manner. Significance is noted by * p < 0.05, N = 12. Data for chemicals that did not alter rates of spontaneous movement are not shown.

Figure 4

Acetylcholinesterase activity at 120 hpf. Embryos were exposed to BFRs at the indicated concentrations and AChE activity was measured at 120 hpf. Only exposure to 1.25 ppm TBBPA increased AChE activity (N = 4). No compounds tested suppressed AChE activity below control.

Figure 5

The activity of glutathione-S-transferase (GST) was measured at 120 hpf following exposure. Exposure to TBBPA, HBB, HBCD, and PBCH significantly increased GST activity as compared to the control. * p < 0.05, N = 4.