Screening an alternative flame retardant using biological and transcriptomic endpoints in fish embryos

Although alternative Flame Retardant (FR) chemicals are expected to be safer than the legacy FRs they replace, their risks to human health and the environment are often poorly characterized. This study used a small volume, fish embryo system to reveal potential mechanisms of action and diagnostic exposure patterns for TBPH (bis (2-ethylhexyl)-tetrabromophthalate), a component of several widely-used commercial products. By design, environmentally-high exposures of TBPH were applied to sensitive early life stages of an ecologically important test species, Fundulus heteroclitus (Atlantic killifish), with a well-annotated genome. Exposed fish embryos were sampled for transcriptomics or chemical analysis of parent compound and primary metabolite, or observed for development and survival through larval stage. Global transcript profiling, which requires no a priori information, was applied using a large number of embryos (16) per treatment to provide a non-targeted and statistically robust approach to characterize TBPH gene expression patterns. Transcriptomic analysis revealed a dose-response in the expression of genes associated with a surprisingly limited number of biological pathways, but included the aryl hydrocarbon receptor signal transduction pathway, which is known to respond to several toxicologically-important chemical classes. These results suggest that TBPH has a relatively low potential for developmental toxicity (at least in fishes), despite concerns related to its structural similarities to endocrine disrupting chemicals, and does not present a unique gene expression pattern. More broadly, this study advances the usefulness of a biological testing and analysis system that complements current screening methods to characterize chemicals of ecological and human health concern one control and two treatment groups: low and high concentration, each with 16 biological replicates