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The performance of four microscale toxicity bioassays conducted on whole sediments was evaluated during a bioremediation project undertaken in 1999-2000 on a crude oil-contaminated freshwater shoreline of the St. Lawrence River, Quebec, Canada. The toxicity tests assessed included: (1) the Microtox solid-phase assay (MSPT), (2) the Biotox Flash solid-phase test (Flash), (3) the algal solid-phase assay (ASPA), and 4) the Ostracodtoxkit solid-phase assay. Data generated with these assays were compared with those obtained using the standard endobenthic amphipod (Hyalella azteca) bioassay. Bioanalytical comparisons indicated that all five solid-phase tests were useful in detecting the toxicity of oiled sediments; however, statistical analyses distinguished a difference in response between the invertebrate (amphipod and Ostracodtoxkit) and bacterial luminescence tests (MSPT and Flash). Based on these results, it is recommended that careful selection of biotests be made in the design of the test battery for assessment of residual oil sediment toxicity. Time-series toxicity data generated with ASPA indicated that oiled sediments in the freshwater wetlands of the St. Lawrence River remained toxic to phytoplankton for at least 65 weeks and that remediation treatment was able to accelerate detoxification by 16 weeks., (Copyright 2004 Wiley Periodicals, Inc.)

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., (Copyright 2003 Wiley Periodicals, Inc.)

In view of the complexity and costs of "traditional" whole sediment assays, a "culture/maintenance free" direct contact microbiotest has been developed with the freshwater ostracod Heterocypris incongruens. The new Toxkit assay (named Ostracodtoxkit) has been applied to 33 sediment samples from Peninsula Harbour, located in Lake Superior of the Great Lakes water basin in Ontario, Canada. The microbiotest was applied in parallel to direct contact tests with the amphipod Hyalella azteca and the midge larva Chironomus riparius, to compare its relative sensitivity with that of the two "conventional" assays. The study was undertaken in the framework of remediation action plans for specific areas of concern, to enable decision making by the Canadian authorities for the restoration of impacted aquatic environments. Most sediments were found non-toxic (<20% mortality) to both the conventional test species and the ostracod. For the large majority of samples, a very good correspondence was found between the two crustacean test species for the intensity of the toxic signal "mortality", as reflected by a 0.71 (p<0.05) correlation coefficient. Growth inhibition, which is determined in the ostracod microbiotest as a sublethal effect criterion, allowed the earmarking of some sediment samples, which were apparently more toxic for the amphipod than to the ostracod. For 20% of the samples, substantially higher mortality scores were noted with the ostracod assay than with the midge larvae tests and the overall correlation coefficient between these two tests was lower (r=0.60,p<0.05). The results obtained in the present study corroborate those of previous research on sediments collected from various rivers in Flanders, Belgium, and confirm the potential of the new ostracod microbiotest as a reliable and sensitive low cost alternative for traditional whole sediment assays.

In view of the need for rapid and low-cost solid-phase assays for contaminated sediments, a new 6-day "culture/maintenance-free" microbiotest has been developed with the freshwater ostracod crustacean Heterocypris incongruens at the Laboratory for Biological Research in Aquatic Pollution at the Ghent University in Belgium. The sensitivity of the Ostracodtoxkit F has been compared with that of the 10-day sediment contact test with the amphipod crustacean Hyalella azteca and the two pore water assays (on the anostracan crustacean Thamnocephalus platyurus and the microalgae Raphidocelis subcapitata) selected by the Flemish Environmental Agency for initial hazard assessment of contaminated sediments. The exercise was performed on 26 sediments collected at random from various rivers of the Flemish hydrographic basin in Belgium. The toxicity data ranged from nontoxic to highly toxic for the solid-phase assays and showed that the mortality of the two test biota varied from "nearly identical" to "substantially different," depending on the sediment. The correlation coefficient for the data pairs was weakly positive (r = 0.60), mainly because of 5 samples for which a low mortality had been noted with the ostracod versus a much higher mortality for the amphipod. However, for 4 out of the 5 samples of concern, a substantial growth inhibition was recorded for H. incongruens, showing that this assay eventually performed as did the amphipod test in detecting the toxic character of the sediments. The comparison of toxicity data of the two solid-phase assays with those of the two pore water tests again confirmed that both types of bioassay provided complementary (nonredundant) information. On the basis of its various advantages (independence of stock culturing/maintenance, user-friendliness, precision, and time and cost savings) the new ostracod microbiotest appears to be a promising tool for routine toxicity assessment of contaminated sediments., (Copyright 2002 Wiley Periodicals, Inc.)

Experiments were carried out with neonates of the freshwater ostracod Heterocypris incongruens to verify and complete previous choices of test parameters for a new culture/maintenance-free solid-phase microbiotest for freshwater sediments. From trials with increasing volumes of reference sediment, it was concluded that 300 microL was the most appropriate amount of substrate to be put in 12-cup multiwell plates with 2 mL of standard freshwater. Tests in 3-9 replicates eventually showed that six parallels were needed to have good assay precision (repeatability). Application of the final test protocol to oil-contaminated sediments from the St. Lawrence River in Canada revealed that the 6-day chronic ostracod microbiotest had less variation in repeated tests than did the 10-day contact assay with Hyalella azteca and hence can be considered more precise. Based on the 95% confidence intervals for mortality and growth of the ostracods in the controls (reference sediment) of the 56 tests carried out for the Canadian project, a validity threshold of 20% for mortality was eventually selected, in analogy with the acceptability limits applied in many chronic bioassays. A minimum length of 600 microm in the control sediment after 6 days' exposure was also taken as the threshold for good health of the test organisms and for reliable test conditions. The new microbiotest has been tailored in a handy and user-friendly new toxkit, the Ostracodtoxkit, which is particularly suited for cost-effective routine monitoring., (Copyright 2002 Wiley Periodicals, Inc.)

Experiments were carried out with neonates of the freshwater ostracod Heterocypris incongruens hatched from cysts in order to develop a new culture/maintenance-free solid-phase microbiotest for the toxicity assessment of contaminated sediments. Based on preliminary investigations, a number of test parameters were investigated for a short-chronic assay: hatching time, size of the cups of the multiwell test plates, feeding of the test organisms prior to the test, amount of supplemental algal food, volume of sediment, and duration of the test. On the basis of the findings, a test protocol was formulated for a 6-day assay in 12-cup multiwell plates with 10 organisms per cup and 3 replicates. The test organisms were collected 52 h after the start of the incubation of the cysts in standard freshwater at 25 degrees C under continuous illumination after a 4-h prefeeding with 1.3 mg/mL Spirulina. The test biota in the cups were exposed to 300 microL of test sediment in 2 mL of standard freshwater with 3 x 10(7) live algal cells (Raphidocelis subcapitata) as food supplement. Calibrated sand was used as a reference sediment. Mortality and growth of the ostracods were determined after 6 days' incubation at 25 degrees C in darkness. The selected test parameters for the new microbiotest were found adequate for toxicity determination of natural sediments compared with the 10-day contact test with the amphipod Hyalella azteca., (Copyright 2002 Wiley Periodicals, Inc.)