Toxicity of creosote water-soluble fractions generated from contaminated sediments to the bay mysid

The effect of creosote on the growth of an axenic culture of Myriophyllum spicatum L

Due to the importance of submersed, rooted macrophytes to the aquatic ecosystem and the use of creosote impregnated structures adjacent to or within water bodies, a study was conducted using an axenic culture of Myriophyllum spicatum to determine the effect of creosote on this aquatic macrophyte. Four plants were cloned and exposed to nominal creosote concentrations ranging from 0.16 to 200 mg/l for 14 days. A variety of response parameters were assessed, including shoot and root length, number of roots and nodes, and dry weight biomass, as well as visual observations on plant colouring and morphology. Regression and ANOVA analyses were conducted to determine EC50s and significant differences. Biphasic responses were observed for shoot length, node production and biomass, with shoot length showing statistically significant stimulation (hormesis) at creosote concentrations below 13.3 mg/l. EC50 values of 55.1 (CI 40-60) mg/l, 33.4 (CI 26-48) mg/l and 86 (CI 70-120) mg/l were determined for shoot length, dry weight and node production, respectively. Root number was significantly higher at 3.6 mg/l and root length was significantly reduced at 4.5 mg/l creosote, within the concentration range that stimulated shoot growth. Visual changes, including an increase in pink colouration and changes in the location of root initiation, were also observed in the same creosote concentration range that affected root length and numbers. Therefore, it appears that changes in root growth and location of root initiation may be the most sensitive endpoints for creosote effects on Myriophyllum.

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 Jämsänvesi, 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 PAH-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.