Chronic toxicity of oil sands tailings pond sediments to early life stages of fathead minnow (Pimephales promelas)

In this study fathead minnow (Pimephales promelas) embryo-larval stages were exposed to two oil sands tailings pond sediments which had previously been shown to decrease the survival of embryo-larval larval stages of walleye (Sander vitreus) and northern pike (Esox lucius). Fathead minnow are standard test species and we wanted to compare their sensitivity to the other two species. Fathead minnow larvae were exposed for 20 days (5 days in the egg stage and 15 days in the larval stage) with daily renewal of sediments and waters. Sediments contained polycyclic aromatic hydrocarbons (PAHs) and alkylated PAHs (APAHs). Results from an earlier study showed that Sediment 1 contained 173 μg/g total PAHs + APAHs (97 % alkylated), and sediment 2 contained 401 μg/g total PAHs + APAHs (95 % alkylated). Fathead minnow larvae exposed to oil sands tailings pond sediments had decreased survival, decreased weight, and increased deformities. Fathead minnow survival was unaffected at the embryo stage and at hatch. Most deaths occurred at the larval stages 1–8 days after hatching, showing the importance of exposing the fish for at least a week after hatch. Toxicity was seen at 0.2 g/L of sediment, which was equivalent to the addition of 35 and 80 μg total PAHs + APAHs to 1 L of overlying water for sediment 1 and 2, respectively. When compared to embryo-larval northern pike and walleye results from previous studies, all three species of fish responded more strongly to sediment 2 compared to sediment 1. For effects on lethality, fathead minnow were equally sensitive to pike, but walleye were 5–28 times more sensitive to the lethal effects of the sediments compared to both fathead minnow and pike. The study (and comparisons to our previous studies) shows the difference in sensitivity between a model laboratory species (fathead minnow) and some species of wild fish that are highly relevant to the oil sands area of Alberta.