Maternal transfer and toxicity pathways of hexabromocyclododecane in the fathead minnow (Pimephales promelas)

Abstract

Hexabromocyclododecane (HBCD) is a persistent organic pollutant (POP) that undergoes maternal transfer and hinders development and growth of early-life stages of fish. However, there is limited understanding of the maternal transfer kinetics and subsequent molecular mechanisms that drive the embryotoxicity of HBCD. The purpose of this study was to (1) characterize the accumulation of dietary HBCD (11.5, 36.4, 106 mg/kg, ww [wet weight]) in adult fathead minnows (FHM) and the subsequent maternal transfer kinetics to eggs, and (2) link transcriptomics responses to apical and physiological effects in larvae exposed through maternal transfer at seven- and 14-days post-fertilization (dpf), respectively. Maternal transfer kinetics displayed similar egg-to-muscle ratios (EMR) in the low and medium treatment groups (1.65 and 1.27, respectively). However, the high treatment group deviated from other treatments with an EMR of 4.2, potentially due to reaching diffusion and/or lipid saturation limits. A positive correlation was observed between egg HBCD concentration and time of exposure. Larvae sampled at 7dpf revealed dysregulation of pathways involved in membrane integrity (inhibition of calcium channel) and metabolic processes (downregulation of amino acid, glucose, and lipid biosynthesis), while the larvae reared for 14 days exhibited a significant decrease in survival at the highest treatment condition. These results indicate that maternal transfer of HBCD is of concern in fish, which may act through indirect mechanisms involving the inhibition of membrane transport leading to disruption in metabolic processes, collectively resulting in energy depletion and subsequently mortality. This study is part of the EcoToxChip project (www.ecotoxchip.ca). The data derived will be used to inform the development of EcoToxChips, which are qPCR arrays that aim to predict apical endpoints of ecological and regulatory relevance for three model species and three native species for eight model chemicals.