Petroleum-derived hydrocarbon wastes are one of the most dangerous aquatic environmental pollutants, the production and export of oil are regarded as the main sources of these wastes. Discharging of the oil refinery wastes to the aquatic ecosystems can cause hazardous and harmful effects to its food chain levels especially algae, depending on the released concentrations. The present study experiments were conducted with axenic culture of the green algae Chlorella vulgaris and Scenedesmus dimorphus. Different concentrations of the oil wastes (25, 50, 75 and 100 %) from three selected locations (SO1, SO8 and SO12) at the refinery treatment unit of Al-Dura refinery were prepared.
Decreasing in the algal growth rates associated with increasing in the doubling time of the cells were detected for the both strains when treated with tested concentrations of the oil refinery during the exposure period that took 96 hr. The reduction was clear with C. vulgaris, but it was gradual in the case of S. dimorphus. An accelerating increasing in the algal growth inhibition averages accompanied with increasing in the wastes concentrations as well as time of exposure. The differences in the calculated EC50 values for both strains indicate differences in the toxic effects of the oil wastes in addition to their sensitivity towards such pollutants.