Assessment of toxicity hazards of dredged lake sediment contaminated by creosote

In order to predict the potential toxicity hazards of sediment remediation by dredging, an experimental laboratory simulation was made by investigating seven ratios of creosote-contaminated sediment (Lake Jamsanvesi, central Finland) and artificial lake water mixtures. Sediment was suspended in water at the ratios of 1:1, 1:2, 1:4, 1:8, 1:16, 1:32, 1:64, 1:128 v/v. The elutriates were analysed for the acute toxicity by photoluminescence bacterial and waterflea (Daphnia magna Straus) tests. The concentrations of polycyclic aromatic hydrocarbons (PAHs) are determined by gas chromatography (GC/FID). The elutriate of ratio 1:2 was most toxic to bacteria (EC50 = 4.5%), whereas the ratio 1:4 was most toxic to waterfleas (EC50 = 21%). The elutriate of 1:1 contained the highest total PAM-concentration (1.67 mg/l) and total organic carbon (TOC) content (39.4 mg/l). When compared to the 1:1 ratio, taken as unity, the relative toxic emission yield (RTE) for bacteria was 307 for the ratio 1:128, so the high mixing ratio may cause a considerable ecotoxicological hazard. The highest amounts of PAHs were desorbed from sediment to water layer when the sediment was mixed with water at the ratios 1:1, 1:2 and 1:4 (v/v). It is assumed that dredging of creosote-contaminated sediment can potentially cause an ecotoxicological risk for a lake system at wide range of suspension ratios. We recommended that basic knowledge for these risks can be produced by simple laboratory simulation. (C) 1999 Elsevier Science B.V. All rights reserved.