Fish Tainting (Off-flavour or smell) – Analytical and Sensory Analysis

Reports have stated that fish caught near the oil sands have an off‐flavour, or taint. This project investigated whether naphthenic acids from oil sands operations are causing fish tainting. Researchers developed and applied advanced analytical methods using GC-MS to detect and quantify free, conjugated, and hydroxy-naphthenic acids in fish exposed to oil sands-affected waters. Both analytical and sensory experiments (using trained human panels) were conducted to assess whether these compounds produced detectable off-odours in fish.

This study faced some limitations and was unable to complete all planned objectives, so further research is recommended. Fish tissues were found to contain free naphthenic acids, with the highest concentrations in gills and livers. The odour detection thresholds for commercial naphthenic acids in steamed fish ranged from 0.6 mg/kg to over 21 mg/kg. A taint becomes noticeable in fish at around 12 mg/kg. Wild fish near the oil sands had much lower levels, suggesting they are unlikely to be tainted. This 12 mg/kg threshold can be used to assess taint risk in reclaimed oil sands lakes. Since fish accumulate only small amounts, tainting would only occur in waters with naphthenic acid levels of 3–6 mg/L or more. Taste tests showed no difference in consumer preference for fish from near the oil sands compared to other Alberta locations.