Impact of co-exposure with lead and decabromodiphenyl ether (BDE-209) on thyroid function in zebrafish larvae

• PBDEs and metals are the main contaminants at e-waste recycling sites.
• Combined effects of Pb/BDE-209 on thyroid function in zebrafish larvae were studied.
• Co-exposure of Pb and BDE-209 elicited synergistic effects on T3 and T4 levels.
• BDE-209 enhanced Pb uptake, and Pb decreased bioconcentration/metabolism of BDE-209.
• Mixtures of Pb and BDE-209 probably result in an increase in toxicological effects.

Polybrominated diphenyl ethers (PBDEs) and metals are the main contaminants at waste electrical and electronic equipment (“e-waste”) recycling sites. However, the potential environmental health effects of mixtures of PBDEs and metals are not known. We investigated co-exposure of lead (Pb) with decabromodiphenyl ether (BDE-209) on thyroid function in zebrafish larvae. Seven groups of embryos/larvae of zebrafish were treated with Pb (0, 2, 5, 10, 15, 20, and 30 μg/L), six groups were exposed to BDE-209 (0, 50, 100, 200, 400, and 800 μg/L), and nine groups of zebrafish larvae were treated with Pb and BDE-209 (5, 10, and 20 μg/L Pb; 50, 100, and 200 μg/L BDE-209). Embryos/larvae were exposed from 2 h post-fertilization (hpf) until 144 hpf, and thyroid hormone (TH) content measured. Pb exposure significantly decreased whole-body TH contents (triiodothyroxine (T3) and thyroxine (T4)) but BDE-209 exposure significantly increased T3 and T4 levels. Pb or BDE-209 treatment alone caused a predicted downregulation of TH transport (i.e., expression of the mRNA or proteins of transthyretin). Chemical analyses showed Pb uptake to be increased by BDE-209, but BDE-209 bioconcentration was decreased and the ability to metabolize BDE-209 was reduced in the presence of Pb. We also found that a mixture of the two chemicals had a synergistic effect on TH levels in zebrafish.