Transcriptomic and functional effects from a chemical mixture based on the exposure profile in Baltic Sea salmon, on...

The Baltic Sea is one of the world's most contaminated seas with long-standing adverse health status of its wildlife such as the Baltic Sea salmon, resulting in reduced fecundity and increased mortality. While adverse health effects have been reported among wild fish from the Baltic Sea, the toxicity mechanisms underlying these adversities, and the chemical effect drivers mediating them are poorly understood. To address this knowledge gap, we utilized the zebrafish (Danio rerio) embryo model to determine molecular and functional effects brought on by exposure to a technical mixture including 9 organohalogen compounds detected in serum from wild-caught Baltic Sea salmon. To align with the salmon exposure scenario, an internal dose regimen was opted to establish same relative proportions of the compounds in the zebrafish (whole body) as observed in the salmon serum. Through transcriptomic profiling, we identified dose-dependent effects on immune system and metabolism as two critical functions overlapping with adverse effects observed in wild fish from the Baltic Sea. We then determined likely effect drivers by comparing gene responses of the mixture with those of individual mixture components. Aligned with our transcriptome results, the number of total macrophages was reduced and the zebrafish's ability to respond to a tissue damage suppressed in a dose-dependent manner. This study brings forth a key advancement in delineating the impact of chemical pollutants on the health of wild fish in the Baltic Sea.