Microtox Toxicity in Sediments. Modified Method for the Direct Contact test with Luminiscent Bacteria

Effects on bacterial bioluminescence of pore waters, elutriates with aqueous solutions and organic solvent extracts have earlier been used to characterize chemical contamination of marine and limnic sediments. Recently, a toxicity test method with bacteria in direct contact with sediment was described. We found that the luminometric measurements in this test were severely hampered by the light scattering of residual sediment particles. Modifications were introduced to decrease and to compensate for this contribution. The test strategy was changed to a preliminary test to choose concentration level and a main test in triplicate. A correction procedure for the light scattering contribution was included. The remaining effect was measured as 65 to 78000 toxic units/g dry sediment for sediments from various sources and with a varying degree of antropogenic contamination. The bacterial bioluminescence was positively correlated with the acute toxicity with the marine crustacean Nitocra spinipes