Toxicity of heavy fuel oil, dispersant, and oil-dispersant mixtures to a marine fish, Pagrus major

This study examines the toxicity of three dispersants and heavy fuel oil to a marine fish, red sea bream (Pagrus major). Also studied was the toxicity of a mixture of heavy fuel oil and the least toxic of the three dispersants. The 24-h LC50 of all three dispersants were at least 1500 mg/L; these dispersants appeared relatively less toxic to marine fish than others studied in the past. The mean lethal oil concentration of the water-accommodated oil fraction was 325 micro g/L Mixtures of oil and dispersant were more toxic than dispersant or oil alone. Large amounts of dispersant decreased the toxicity of the mixture for the marine fish. Use of a dispersant-to-oil percentage of 20%, which is recommended by the manufacturer because of its efficiency in oil emulsification and dispersion, yielded higher 24-h oil concentrations and resulted in a higher mortality rate than did the use of higher percentages of dispersant. The application of dispersant to oil in coastal areas, especially with higher activities of fisheries and aquaculture like Japan, must be considered carefully in the context of the benefits versus environmental cost.