Effect of biostimulation treatments on the toxicity of oil-contaminated mangrove sediment

Bioassays with the marine copepod Tisbe biminiensis were used to evaluate the efficiency of three bioremediation treatments on oil contaminated sediments. Two biostimulation treatments (adding NPK and OSMOCOTE fertilizers) and a natural attenuation treatment (experimental control, without fertilizers) were evaluated. The addition of NPK fertilizer had a strong lethal effect on T. biminiensis females probably associated to ammonium compounds, but this effect disappeared after 15 days. The OSMOCOTE releases nutrients in a gradual manner and as such, had no lethal effect on T. biminiensis females. In the natural attenuation treatment, the fecundity of T. biminiensis increased 200% and this indicates that natural attenuation treatment effectively attenuated the sub-lethal toxicity. Biostimulation treatments were not more efficient in obtaining lower toxicity levels of oil contaminated sediment compared to natural attenuation as the recovery of the endpoint affected by contamination (fecundity) increased at the same rate in the 3 treatments over time. In conclusion, adding fertilizers with high ammonium compound concentrations and rapid release is not recommended as a bioremediation treatment in mangroves.