Immunotoxic effects of oil sands-derived naphthenic acids to rainbow trout

Naphthenicacids are the major organic constituents in waters impacted by oilsands. To investigate their immunotoxicity, rainbowtrout (Oncorhynchus mykiss) were injected with naphthenicacids extracted from aged oilsands tailings water. In two experiments, rainbowtrout were injected intraperitoneally with 0, 10, or 100 mg/kg of naphthenicacids, and sampled after 5 or 21 d. Half of the fish from the 21 d exposure were co-exposed to inactivated Aeromonas salmonicida (A.s.) to induce an immune response. A positive control experiment was conducted using an intraperitoneal injection of 100 mg/kg of benzo[a]pyrene, a known immune suppressing compound. T-lymphocytes, B-lymphocytes, thrombocytes, and myeloid cells were counted in blood and lymphatic tissue using flow cytometry. In the 5 d exposure, there was a reduction in blood leucocytes and spleen thrombocytes at the 100 mg/kg dose. However, at 21 d, leucocyte populations showed no effects of exposure with the exception that spleen thrombocyte populations increase at the 100 mg/kg dose. In the 21 d exposure, B- and T-lymphocytes in blood showed a significant Dose × A.s. interaction, indicating stimulated blood cell proliferation due to naphthenicacids alone as well as due to A.s.Naphthenicacid injections did not result in elevated bile fluorescent metabolites or elevated hepatic EROD activity. In contrast to naphthenicacids exposures, as similar dose of benzo[a]pyrene caused a significant decrease in B- and T-lymphocyte absolute counts in blood and relative B-lymphocyte counts in spleen. Results suggest that the naphthenicacids may act via a generally toxic mechanism rather than by specific toxic effects on immune cells.