Acute toxicity of an effluent and two oil spill dispersants to Vibrio fischeri

Contamination of aquatic systems due to different anthropogenic activities including discharge of industrial wastes (effluent) and application of mitigation chemicals (oilspill dispersants) is a major issue in Nigeria as the effect could be detrimental to important organisms of various trophic levels in marine environments. This study aimed at evaluating the acute toxicity of Vibrio fischeri to a treated effluent and two dispersants- Corexit 9527 and Finasol OSR. The Omni model 500 Microtox Analyzer for bacterial bioluminescence inhibition, a rapid and ecologically relevant bioassay tool for ecotoxicity assessment during Biological Monitoring Studies was employed. The oil spill dispersants were obtained from licensed oil field chemical stores in Port Harcourt, Rivers State while the treated effluent was sourced from a natural gas production industry that discharges its treated effluent into Bonny Estuary, Rivers State, Nigeria. The experimental procedure involved exposure of reconstituted freeze-dried cells of the marine bioluminescent Vibrio fischeri to various dilutions of the toxicants, reference chemical (KCl), including instruments reference chemical for 5minutes and 15 minutes. The percentage reductions in bioluminescence by Vibrio fischeri after 5minutes and 15minutes exposure to the toxicants (Treated Effluent, Corexit 9527, and Finasol OSR) was recorded as median effective concentration value (EC50). The 5 minutes-EC50 values of Treated Effluent, Corexit 9527, and Finasol OSR for Vibrio fischeri were 27.54%, 18.61% and 4.35% respectively while the 15minutes-EC50 values of Treated Effluent, Corexit 9527, and Finasol OSR were 13.75%, 15.18% and 4.21% respectively. The test indicated that Vibrio fischeri was sensitive to the treated effluent and the two oil spill dispersants. Finasol OSR was more toxic to Vibrio fischeri than Corexit 9527. The continuous discharge of effluents (treated and untreated) and the application of oil spill chemicals offshore can lead to inhibition of bioluminescence by marine bacteria an important organism in marine environments.