The tests with the porewaters were valid according to the validity criteria in the ISO standard used for testing liquid samples. No 30 min-IC50 value could be determined for the sediment porewater and thus all samples were classified as non-toxic according to this criterion (Table 2). However, four of the sediments showed a low toxicity when 30 min-IC20 values were calculated but no trend with reduced toxicity with distance from the inlet was observed (Table 2).