Transcriptome Profiling in Larval Fathead Minnow Exposed to Commercial Naphthenic Acids and Extracts from Fresh and Aged Oil Sands Process-Affected Water

Surface mining and extraction of oil sands results in the generation of and need for storage of large volumes of oil sands process-affected water (OSPW). More structurally complex than classical naphthenic acids (NAs), naphthenic acid fraction components (NAFCs) are key toxic constituents of OSPW, and changes in the NAFC profile in OSPW over time have been linked to mitigation of OSPW toxicity. Molecular studies targeting individual genes have indicated that NAFC toxicity is likely mediated via oxidative stress, altered cell cycles, ontogenetic differentiation, endocrine disruption, and immunotoxicity. However, the individual-gene approach results in a limited picture of molecular responses. This study shows that NAFCs, from aged or fresh OSPW, have a unique effect on the larval fathead minnow transcriptome and provides initial data to construct adverse outcome pathways for skeletal deformities. All three types of processed NAs (fresh, aged, and commercial) affected the immunome of developing fish. These gene networks included immunity, inflammatory response, B-cell response, platelet adhesion, and T-helper lymphocyte activity. Larvae exposed to both NAFCs and commercial NA developed cardiovascular and bone deformities, and transcriptomic networks reflected these developmental abnormalities. Gene networks found only in NAFC-exposed fish suggest NAFCs may alter fish cardiovascular health through altered calcium ion regulation. This study improves understanding regarding the molecular perturbations underlying developmental deformities following exposure to NAFCs.