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(PW271) The use of morphological alterations in microalgal colony structure as an endpoint for effluent toxicity.

Tim-Tim, A. L. S.1, Silvestre, A. J. D.2, Calado, A. J. B. F. M.1, 1 Department of Biology, University of Aveiro, Aveiro, Portugal2 Department of Chemistry, University of Aveiro, Aveiro, Portugal

ABSTRACT- Given the economic importance of the paper industry in Portugal and the frequent debates on the environmental effects of its effluents, especially organochlorine compounds, great efforts have been made to reduce the emission of these compounds to the receiving environment. Imposed restrictions include the replacement of elemental chlorine by chlorine dioxide during the bleaching process, as well as the introduction of other chlorine free oxidizing agents, like oxygen, hydrogen peroxide or ozone. The introduction of these agents has eliminated the presence of highly chlorinated compounds in effluents but has also generated new series of chlorinated compounds of unknown toxicity. The aim of this work was to determine the potential toxicity of effluents from different bleaching processes using as endpoint the morphological alterations in colonial structures of two species of microalgae, Scenedesmus cf. quadricauda and Pediastrum duplex. The organisms were isolated into unialgal cultures and toxicological tests were performed using five different effluents produced in laboratory: i) chlorine dioxide bleaching (D0); ii) followed by a alkaline extraction (E1); iii) oxygen bleaching (O); iv) hydrogen peroxide bleaching (P); and v) ozone bleaching (Z). The results show consistent relationship between effluent concentration and the morphological alterations observed in both species, in all effluents. The use of this sublethal endpoint for evaluating potential toxicity of kraft paper mill effluents seems promising as it presents several advantages to traditional methods like growth, biomass or cellular density. Some advantages are that it minimizes the effect of nutrients present in effluents, which enhance growth (disguising growth reduction from toxic effects), since morphological alterations are not influenced by nutrients; and it reduces counting effort when determining cell density, especially in effluents with particles.

Key words: microalgae, morphological alterations, pulp mill effluents, ecotoxicity


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