Measurements of Residual Toxicity During Crude Oil Degradation
Microtox® toxicity assay was used to evaluate the residual toxicity. The method is based on the analysis of light emission reduction of luminescent bacteria (Vibrio fischeri) under toxic stress. All materials were purchased from SDI Europe. The tests were carried out in a Microtox M500 analyzer according to the Microtox Manual (1992). The samples were centrifuged (11,000 x g) for 5 min. Results of toxicity are presented as a percent of luminescence reduction. If luminescence reduction is ± 20%, the samples are not found to be toxic to Vibrio fischeri; if luminescence reduction is between 20–50%, the samples have low toxicity; if luminescence reduction reaches above 50%, the samples are toxic, and EC50 should be calculated.