Crude oil bioremediation in sub-Antarctic intertidal sediments: chemistry and toxicity of oiled residues

The effectiveness of fertilizers for crude oil bioremediation in sub-Antarctic intertidal sediments was tested over a one-year period in a series of ten (10) experimental enclosures. Chemical, microbial and toxicological parameters demonstrated the effectiveness of various fertilizers in a pristine environment where hydrocarbon degrading bacteria (HDB) had not been stimulated by previous accidental spills or human activities. The low temperature of seawater (3–4 °C) had no obvious effects on the HDB community and the bioremediation process. Over 90% of n-alkanes were degraded in the first six months and most light aromatics (2–3 rings) disappeared during the first year of observation. The toxicity of oiled residues (Microtox® SP) was significantly reduced in the first 6 months of the process, but it increased again in the last months of the experiment. One of the fertilizers containing fishbone compost enriched with urea, inorganic phosphorus and a lipidic surfactant reduced significantly the toxicity of oil residues in the last 3 months of the experiment. Interstitial waters collected below the oil slicks during the remediation showed no toxicity, and even stimulated Vibrio fischeri. When comparing all fertilizers to the control plots, a good correlation (r2=0.82) was found between the growth rate of HDB and the degradation rate of n-alkanes in the first 90 days of the experiment only indicating that fertilizers were efficient for at least 3 months but their beneficial effects were lost after 6 months.