Evaluating the efficiency of oil spill countermeasures by monitoring changes in the bioavailability and toxicity to fish of PAH from wetland sediments

The impact that oil spills have on fish can be assessed most accurately by using biological responses that reflect the flux of hydrocarbons through fish, rather than absolute concentrations. In this study, the exposure and toxicity to fish of oiled sediments was assessed in a freshwater semidiurnal tidal area of the St. Lawrence River in Quebec and at a tidal salt marsh at Petpeswick Inlet in Nova Scotia. The effectiveness of wetland bioremediation strategies was assessed by monitoring the bioavailability and toxicity of oil-derived polycyclic aromatic hydrocarbons (PAH) to early life stages of fish. The study involved the application of weathered MESA oil to experimental plots on vegetated beaches with different combinations of fertilizer, plant removal and sediment aeration. Sediments sampled over 1.5 years were tested by bioassays of mixed function oxygenase enzyme activity in livers of trout as an index of PAH exposure. The study revealed that oil alone, oil mixed with sediments in the lab, and oiled sediments from the experimental plots, caused enzyme induction relative to un-oiled controls. This suggested the presence and bioavailability of PAH. It was also shown that induction did not vary significantly between treatments, but declined slowly with time. The observations were supported by chemical analysis. It was concluded that PAH most likely depletes through weathering or sediment dispersion instead of by bioremediation treatment. The increased rate of deformities and mortality among trout and medaka indicated that oiled sediments are chronically toxic to developing stages fish. 19 refs., 1 tab., 7 figs