Cyst-based toxicity tests. XVIII. Application of ostracodtoxkit microbiotest in a bioremediation project of oil-contaminated sediments: sensitivity comparison with Hyalella azteca solid-phase assay.

To further validate the scope of use of the 6-day sediment contact microbiotest conducted with the ostracod Heterocypris incongruens, we compared the sensitivity of this small-scale culture/maintenance-free assay with the 14-day solid-phase Hyalella azteca test. The present study was undertaken within the framework of a Canadian bioremediation project on oil-contaminated freshwater sediments along an intertidal shoreline of the Saint-Lawrence River near the town of Sainte-Croix, Quebec, Canada. Sediment subsamples, collected during three sampling periods over 21 weeks from five plots (each with four replicates) contaminated with different treatments, were analyzed for their toxic effects on the two test species. Sediment samples taken immediately after the plots were spread with oil were very toxic to both crustaceans (mortality between 80% and 100%), but the mortality of the amphipods was substantially lower than that of the ostracods for samples collected after 6 weeks. Fifteen weeks after the onset of the controlled oil spill experiment, the sediments of all plots were still quite toxic to Heterocypris but not to Hyalella. Statistical analysis of the mortality figures was performed by Blaise et at. (2003) and revealed a statistically significant correlation (R = 0.584 at the P = 0.001 level) between data pairs. Analysis of the precision of the two assays showed a substantially higher uniformity (lower variation coefficients between the four replicas) of the ostracod results over that of the amphipod assay. This study corroborated the findings of two previous investigations conducted in Canada and in Belgium with the same test species. All three investigations concur in pointing out the potential of the new ostracod microbiotest as a reliable and sensitive ecotoxicological test for routine and low-cost monitoring of contaminated sediments.