Cyst-based toxicity tests XIV--application of the ostracod solid-phase microbiotest for toxicity monitoring of river sediments in Flanders (Belgium).

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.