Toxicity Assessment of Produced Water Using Microtox Rapid Bioassay

Aim: The study aimed at employing the Microtox test procedure in the current biological monitoring protocol as a reliable, rapid and ecologically relevant bioassay tool for toxicity assessment in environmental compliance monitoring of produced water discharges.

Study Design: Inhibition of bioluminescence by V. fischeri [median effective concentration (EC50)] was employed as the toxicity index.

Place and Duration of Study: Microbiology Department of Halden Laboratories, Port Harcourt, Nigeria / one month.

Methodology: Percent reduction in bioluminescence by V. fischeri after 15-min exposure to the PW samples was recorded as median effective concentration (EC50) values.

Results: The 15 min EC50 values of the untreated and treated produced water samples for V. fischeri was 1.0% and 23.27% respectively. Microtox test indicated the treated and untreated produced water samples were “very toxic” and “extremely toxic” respectively, after 15 min exposure time.

Conclusion: These findings emphasize the need for adequate treatment of produced water to meet standard discharge limits of regulatory agencies in Nigeria, as both physicochemical analysis and bioassay (Microtox) suggested that the treated PW was toxic to V. fischeri. This study thus supports the use of Microtox (bacterial toxicity) system as a sensitive and rapid bioassay tool for biological monitoring protocol in Nigeria's petroleum industry.