Effect of Crude Oil Effluent (Produce Water) on Brackish Water Fish and Microbial Growth in Aquarium Environment.

The toxicity of crude oil effluent (produce water) was tested on Tilapia guinensis and mangrove swamp microbial community (bacteria and fungi) in the aquarium environment. One hundred percent mortality occurred in the Tilapia sp exposed to 60 % concentration of produce water within 24 hours. Mortality ranged between 50% and 80 % when the same organism was exposed to 40 % concentration for 96 hours. No mortality was observed below 30 % concentration during 96 hours. Since total hydrocarbon levels in produce water were low with indicated value of ±2.19 part per million (ppm), observed mortalities were attributed to the presence of toxins other than the oil. The bacterial character of the effluent was also confirmed by the marked growth inhibition at 96 hours relative to controls. Inhibition of bacterial growth resulted in competitive advantage to fungi, which show enhancement in growth relative to controls. The effect of produce water on the microbial community clearly showed the extent of ecosystem alteration associated with chronic low-level pollution from oil field produce water. There was no indication that microbial growth affected the toxicity of effluent to fish. In the light of these results, the discharge of crude oil produce water, even if it meets the oil and grease limits, must be considered with caution until comprehensive analysis of effluent characteristics and subsequent treatment has been performed