Interactive effects of nitrite and bifenthrin on bioaccumulation, oxidative stress and immune responses of Haliotis discus hannai

Nitrite (NO2−) and bifenthrin (BF), common environmental pollutant, have been proven to perform toxic effects on marine organisms. To have a better understanding of their effects on marine organism, Haliotis discus hannai was exposed to 0.1 mg/L NO2− and/or 10 μg/L BF for 28 days. The results showed that the gills in direct contact with the water environment exhibited the highest levels of BF bioaccumulation (89.37–142.36 μg/kg), especially after NO2− exposure (P < 0.05). Transcriptome analysis of gills showed that significant enrichments were observed in metabolic, signaling and immune pathways after exposure, such as cGMP-PKG signaling pathway. Additionally, superoxide dismutase (SOD) activity was decreased in gills after exposure to NO2− and/or BF, parallel with the increase in catalase (CAT) activity, malondialdehyde (MDA) content, and total antioxidant capacity (AOC). Regarding genes related to immune, the expression of Defensin was significantly decreased while the expressions of B-cell lymphoma-2 (Bcl-2), Tumor Necrosis Factor-α (TNF-α) and Caspase3 were increased. These results suggested that NO2− and BF exposure disrupted metabolic processes, impaired immune function, and dysregulated antioxidant defenses in the gills of abalone. Particularly, significant alterations were observed under the combined stress of NO2− and BF. In hemocytes, the ROS production could be induced by NO2− and/or BF stress, and the number of hemocytes and phagocytosis decreased significantly, especially in NO2− and BF groups. Integrated biomarker response (IBR) analysis proved that NO2− and/or BF exposure detrimentally affected the overall fitness of abalone, and combined NO2− and BF stress was the most stressful condition. This study emphasizes the impact of NO2− and/or BF on the abalone to better elucidate the risk of environmental pollution on abalone.