This study evaluated toxicity level of produced water effluent on indigenous organisms in Delta state, Nigeria. Four test organisms, Vibrio fischeri, Palaemonetes africanus, Tympanosomas fuscatus, and Tilapia guineensis, were selected for toxicity assessment using effluent streams from treated produced water and water from the produced water recipient environment. Representative samples of treated produced water effluent were collected from the bulk header within the oil terminal and within the discharge environment. Acute toxicity tests were carried out using the Microtox® Model 500. The results of the acute toxicity tests on V. fischeri revealed that the average inhibitive concentration (IC50) for treated produced water at 5 min and 15 min was 22.20% and 31.17% and the no effect concentration (NOEC) and low effect concentration (LOEC) at 5 min and 15 min was 5.63% and 5.63%, respectively. In the recipient water, at 5 min and 15 min, IC50 estimate was of 33.57% and 47.02% while the NOEC and LOEC were 5.63% and 5.63%, respectively. The average IC50, NOEC, LOEC, toxicity unit-acute (TUa), toxicity unit-chronic (TUc), and toxicity factor (TF) toxicity values for P. africanus were 80.606%, 66.990%, and 73.13%; 1.24, 1.49, and 2066.82; 42.24%, 6.165%, and 11.936%; 2.37, 16.21, and 25.54 in treated and recipient water, respectively. In T. guineensis, average IC50, LOEC, NOEC, TUa, TUc, and TF were 4.86%, 1.786%, 1.059%, 20.60, 94.34, and 269.72 and 5.090%, 1.828%, 1.070%, 19.65, 93.46, and 282.78 for treated produced water and recipient environment, respectively. There was no mortality in T. fuscatus var radula exposed to both treated produced water and recipient water.
Keywords: Assessment; Concentration; Effluents; Microtex; Produced water; Toxicity.