2.4. Assessment of sediment toxicity with Aliivibrio fischeri (Vibrio fischeri)
The test procedure for the porewater fraction adhered to the standard protocol ISO 11348-3. Porewater was obtained from the sediments by centrifugation at 3000g for 10 min. Tests were performed with filtered (0.2 μm filters) porewater, with NaCl added to adjust sample osmolarity to 20 ppm. The procedure for the sediment fraction followed the Canadian method EPS 1/RM/42 ( Environment Canada, 2002). The highest sample concentration tested was 80 percent in the test with porewater and 19.6 percent (i.e. 196 g wet sediment/l) in the test with the intact sediment. Light emission was measured in a SDI Model 500 Microtox Analyzer at time zero to determine the base line emission and after 30 min of contact. A log-linear model was used to calculate the Inhibitory Concentration 50 percent (IC50) and 20 percent (IC20) with 95 percent confidence limits using the software MicrotoxOmni™ (Azur Environmentals Inc., USA). The validity of the tests was assessed according to the criteria stipulated in the respective standard method.