Exposure of zebrafish to brominated environmental chemicals : studies on reproduction, maternal transfer and early life-stage development

Abstract: Fish reproduction and embryonic development may be sensitive to environmental chemicals. This thesis investigated effects of brominated flame retardants (BFRs) and polybrominated dibenzo-p-dioxins (PBDDs) on reproduction and early life-stage development in zebrafish (Danio rerio). Most of these compounds are highly hydrophobic, hence it was hypothesized that important routes of exposure are dietary uptake and maternal transfer. Adult zebrafish were exposed to feed spiked with a mixture of structurally diverse BFRs to investigate accumulation from feed, maternal transfer, and effects on reproduction and early life-stage development. One of the compounds in the BFR mixture, i.e. 2,4,6-tribromophenol, was tested separately. The BFRs were also tested individually in an embryo toxicity test, to screen for effects of waterborne BFRs on early life stages. To investigate effects of PBDDs on reproduction, early life-stage development, and on the aryl hydrocarbon receptor (AHR) pathway, adult zebrafish were exposed to feed spiked with 2,3,7,8-tetraBDD (TBDD), or a mixture of PBDDs that was designed to reflect relative concentrations found in Baltic Sea biota. Most brominated chemicals exposed via feed were detected in females and in their offspring. Ovarian morphology was altered in all studies, and the PBDDs induced AHR-regulated genes and ethoxyresorufin-O-deethylase activity. Effects on early life-stage development were seen after parental and water exposure, although at concentrations generally higher than in the environment. However, compared to several other fish species, zebrafish have a relatively low sensitivity to AHR agonists regarding effects on early life stages. To be able to evaluate the risk of PBDDs for fish in the Baltic Sea, future studies should focus on fish species native in the Baltic Sea. Overall, the results suggest that maternal transfer is an important exposure route for several brominated environmental chemicals, and that these compounds may interfere with reproduction and early life-stage development in fish.