High-throughput transcriptome sequencing reveals the combined effects of key e-waste contaminants, decabromodiphenyl ether (BDE-209) and lead, in zebrafish larvae

- Zebrafish larvae were co-exposed to BDE-209 and Pb, major e-waste contaminants.
- Their transcriptional profiles and phenotypic endpoints were examined 6 dpf.
- The steroidogenic pathway and vitellogenesis were stimulated by BDE-209.
- Pb exposure caused cardiac dysfunction and affected neuroendocrine regulation.
- Co-exposure led to synergistic and antagonistic effects on gene transcriptions.

PBDEs and heavy metals are two major contaminants at e-waste disposal sites, but their combined effects remain largely unexplored. In the present study, the transcriptomic profiles of zebrafish larvae were examined after acute exposure of embryos to 200 μg/L BDE-209, 20 μg/L lead (Pb) or their mixture (Mix). Stimulation of steroidogenic pathway and vitellogenesis in the BDE-209 and Mix treatments indicated the estrogenic activities of BDE-209, while Pb antagonized those estrogenic effects in the Mix treatment. Increased heart rates were observed in zebrafish exposed to the Pb and Mix treatments. The cardiac dysfunction probably resulted from the promotion of angiogenesis, increased adrenergic drive and induction of the formation of blood clot. Furthermore, the Pb and Mix treatments activated neuroendocrine regulation of the pituitary in a positive feedback loop, via the thyrotropin-releasing hormone receptor, thus increasing thyroid hormone production self-adaptively. Overall, the interaction between BDE-209 and Pb led to synergistic and antagonistic effects on gene transcriptions, with concerted contribution from their individual toxicological properties.