Padronização de um teste de toxicidade crônica com a bactéria luminescente Vibrio fischeri para análise de qualidade de águas superficiais

AUTOR(ES)

Veridiana Chapiewsky Harmel

DATA DE PUBLICAÇÃO

2004

RESUMO

Biotoxicity assays are experiments, in which living organisms are put into several samples and their reactions are observed. The luminescent bacteria Vibrio fischeri is known and used in acute toxicity tests. Its handling is practical and safe, being fast and efficient. The main objective of this work was to standardize the reactivation solution used for the chronic assay as well as the test itself, with reference substances. The reference substances used were chromium VI in the form of K2Cr2O7, 3,5 dichlorophenol and samples of surface water to observe the behavior of the assay. For comparison reasons, the acute toxicity test was carried out in parallel using the same samples. The analysis of the relative growth of the bacteria was accomplished photometrically. Acute and chronic assays with Daphnia magna were also carried out for methods comparison. The chronic assay showed instability according to the references substances, based on bacterial growth. The composition of the reactivation solution varied during the assays, taking into consideration the availability of the carbon source, to minimize the growth of the bacteria in the test tubes. In an altered reactivation solution the light-emission was kept constant during the necessary period for the test. The assays were repeated, but the instability of the test system continued. Depending on the way, the reaction vials were carried from the incubation block to the measuring instrument, the light-emission suffered alterations, leaving to greatly varying results of luminescence readings. As a consequence, after the 24 hours incubation period, the vials were agitated for 30 seconds in a shaker at 156 rpm, and a new reading were performed. The luminescence values increased due to oxygen availability in the reactivation solution, but, the results showed to be more coherent, if compared with the 24 hours without previous shaking reading, where there had been great variation. This observation shows a possible need of the test to be kept in agitation during the entire incubation period, so that formation of stratification zones in avoided and the suspension kept it homogeneous. The method used to measure the chronic assay with Vibrio fischeri did not show satisfactory results, with great readings variations. However, using samples of surface water, a significant difference was verified among the results of the chronic assay, being compared with the acute assay with V. fischeri, and also if compared with Daphnia magna.

ASSUNTO(S)

reactivation solution ensaio crônico chronic assay vibrio fischeri toxicidade - testes; bioluminescência; bactérias luminosas; Água - análise vibrio fischeri toxicidade - testes; bioluminescência; bactérias luminosas; Água - análise meio de reconstituição controle da poluicao toxicidade

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