Toxicity of sediments contaminated with fractions of creosote

Creosote, a mixture of polycyclic aromatic hydrocarbons (PAH), typically becomes depleted of low molecular weight compounds once in the environment. Previous studies indicated that PAH toxicity increased with increasing molecular weight up to phenanthrene; heavier compounds were less toxic than phenanthrene, possibly due to their limited solubility. A high molecular weight fraction (HMWF) of creosote, with a composition similar to environmentally weathered creosote, and a low molecular weight fraction (LMWF) were obtained by distillation. Fish were exposed to suspended sediments contaminated with each fraction for 10 days. Samples of fish were removed on days 2, 4, 7 and 10, observed for gross pathological abnormalities, weighed, measured, and the livers analyzed for ethoxyresorufin O-de-ethylase (EROD) activity. Mortality, epidermal lesions, fin erosion, and temporary induction of EROD activity occurred in fish exposed to the HMWF. No mortality, fin erosion, or induction of EROD activity occurred in fish exposed to the LMWF or uncontaminated sediment. Fish exposed to the LMWF did develop lesions, but only in the area surrounding the mouth, nares, and opercula. These results suggest that the environmental toxicity of creosote is due to the high molecular weight compounds.