Toxicity identification and evaluation (TIE) of a petroleum refinery wastewater

Petroleum refineries generate large amounts of wastewaters, which can have acute/chronic toxicity toward aquatic organisms. Previous studies have shown that many contaminants can be responsible for this toxicity, among them ammonia, sulfide, cyanide, phenols and hydrocarbons. In the study reported herein, the cause of the chronic toxicity of a biotreated petroleum refinery wastewater was investigated by applying the TIE methodology using the microcrustacean Ceriodaphnia dubia. Five samples were analyzed, and the results suggest that copper is the primary toxicant, showing a strong correlation with wastewater toxicity in Phase III. Other metal contaminants, such as zinc and nickel, are present in the samples at toxic concentrations and these may also contribute (to a lesser degree) toward the toxicity. In the case of one sample, the toxicity was attributed to polycyclic aromatic hydrocarbons (PAHs), possibly benzo(a)pyrene, which was present at a concentration toxic to C. dubia. Although the values for the physicochemical parameters of the samples were below Brazilian environmental regulation limits (CONAMA 430), this was not sufficient to prevent chronic toxicity toward aquatic life, indicating that these limits are relatively high.