Evaluation of ecotoxicity of water produced from oil before and after different treatments in aquatic organisms (Danio rerio, Vibrio fischeri, Daphnia similis, Daphnia magna, Chironomus riparius and Dugesia tigrina)

Produced water (PW) by oil companies is a highly impacting waste for ecosystems. When discarded in aquatic environments, it can contaminate the biota present there, in addition to causing often irreversible damage to the affected ecosystems. Its toxicity is due to the variety of compounds that constitute it, such as metals and a variety of organic and inorganic compounds. Considering the polluting potential of this waste, PW needs effective treatments for its subsequent disposal in the environment. The conventional treatments used are often not efficient to remove the toxicity of this type of waste, requiring the development and standardization of alternative treatments. Within this context, the advanced oxidative processes (POAs) stand out, such as photocatalysis, photoelectrocatalysis, ozonization and photoelectrocatalytic ozonation, and treatment with adsorbent materials such as magnetized vermiculite (VMT-mag), techniques used in this work for the treatment of PW. Thus, the objective of the present work was to evaluate the efficiency of these treatments in reducing the toxicity induced by two samples of PW, identified as petroleum water 1 (AP1) and petroleum water 2 (AP2), in aquatic organisms. The AP1 sample was treated by means of POAs (photocatalysis, photoelectrocatalysis, ozonation and photoelectrocatalytic ozonation) and toxicity was evaluated before and after treatments using the organisms Danio rerio (zebrafish), Daphnia similis and Vibrio fischeri. The AP2 sample was treated with VMT-mag and toxicity was evaluated before and after treatment with Vibrio fischeri, Daphnia similis, Daphnia magna, Chironomus riparius and Dugesia tigrina. The following techniques were used for the organisms: with Danio rerio, the Embryo Acute Toxicity (FET) technique was applied and lethality and subletality were evaluated in embryo-larval stages; with Daphnia similis and Vibrio fischeri acute toxicity test; with Daphnia magna effects on reproduction and intrinsic population growth rate (r); with Chironomus riparius assessment of mortality, growth and emergence; with Dugesia tigrina the evaluation of mortality, locomotion, food and regeneration after beheading. Our tests indicate toxicity for all evaluated organisms: effects (mortality, scoliosis, failure of inflation of the swimming bladder) in the embio-larval stage of Danio rerio; acute toxicity to Daphnia similis and Vibrio fischeri; effects on the emergence of male and female Chironomus riparius organisms, reduction in head and body size of larvae in the untreated sample; in addition to behavioral effects on locomotor activity and head regeneration of planar Dugesia tigrina exposed to AP without treatment; effects on reproduction and intrinsic population growth rate (r) of Daphnia magna microcrustaceans with greater intensity to the untreated sample. This study reveals a reduction in the toxicity of the treated PW, demonstrating the importance of its treatment for disposal in aquatic environments. Our data show that the exposure of different organisms to PW affects lethal and sublethal parameters and, therefore, must be treated before being released into bodies of water. In addition, our data shows that the proposed treatments must be improved in order to achieve efficiency in removing all tested effects. (AU)