Does Microbial Biodegradation of Water-Soluble Components of Oil Reduce the Toxicity to Early Life Stages of Fish?

Microbial degradation following oil spills results in metabolites from the original oil. Metabolites are expected to display lower bioaccumulation potential and acute toxicity to marine organisms due to microbial-facilitated incorporation of chemical functional groups and a general decrease in lipophilicity. The toxicity and characterization of metabolites are poorly studied. The purpose of the present work was to evaluate the toxicity of degraded (0–21 days) water-soluble oil components. Low-energy water accommodated fraction (LE-WAF) of a weathered crude oil was prepared with nutrient amended seawater at 5 °C, kept in the dark, and sampled at 0, 10, 14, and 21 days. Samples were extracted with dichloromethane and toxicity experiments were conducted with reconstituted extracts. Toxicity experiments were conducted for 4 days on developing cod (Gadus morhua) embryos during a critical period of their heart development. After exposure, embryos were kept in clean seawater and observed until 5 days post hatch. Survival, hatching, morphometric aberrations, and cardiac function was studied. The expected decrease in sublethal toxicity during the biodegradation period was not found, indicating that metabolites formed during biodegradation likely contributed to larvae toxicity.