Evaluation of produced water toxicity from an oil maritime terminal through Skeletonema costatum toxicity tests

. Abstract: The liquid eftluent from an oil maritime terminal, with produced water as the main component, had its toxicity evaluated through toxicity tests with the diatom Skeletonema costatum. Two previously treated eftluent samples (eftluents A and B), were provided by PETROBRAS for the experiments. Both samples presented high salinity (67%0for eftluent A and 62%0for eftluent B) and low pH values (6.2), whereas total sulphide, phenol and nutrient content, dissolvedldispersed petroleum hydrocarbon concentration, BOD and COD values were quite different from each other. During the toxicity experiment, three replicate flasks with samples for each treatment were exposed to a light radiation of 266).tEm-2S-Iand maintained under a 10 h/l4 h light/dark cycle, at a temperature of 24 :t 2°C. The ECSOvalues could not be accurately estimated for eftluent A: 60 h and 132 h afier starting the experiment they were below 3% and between 3-6% eftluent concentration, respectively. Synergistic effects between eftluent toxicity and salinity on the growth of S. costatum were detected. The eftluent B showed higher toxicity: the ECSOvalues were 0.17% and 0.40% of eftluent concentrations, afier 48 h and 96 h, respectively. These results evidenced the deleterious effects of residual organic compounds contained in the aqueous eftluents from the oil terminal under the present pretreatment on S. costatum. ln the light of the present data, the direct disposal of these eftluents into São Sebastião Channel waters might be very hazardous to its indigenous biota.