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Abstract(s)
Na sua definição, toxicologia é o estudo dos efeitos adversos de produtos químicos
sobre organismos vivos. A Daphnia magna é um dos organismos largamente utilizados para
averiguar a toxicidade devido à sua elevada sensibilidade a tóxicos. O principal objetivo deste
trabalho foi averiguar a ecotoxicidade de águas residuais tratadas usando, para o efeito, D.
magna. Foram analisados cinco efluentes, entre os quais um efluente secundário e quatro
efluentes terciários [ultravioleta (UV), ultrafiltração (UF), ozonização e plasma não-térmico].
Foram realizados ensaios agudos e ensaios crónicos. Nos ensaios agudos, as dáfnias
com menos de 24 h ao início do teste, foram expostas à substância a ser testada, numa gama
crescente de concentrações, registando-se a morte das dáfnias ao fim de 24 h e de 48 h. Em
contraste, os ensaios crónicos, implicam a exposição de dáfnias juvenis à substância de teste
por um período aproximado de 21 dias, com o objetivo de monitorizar o seu comportamento
reprodutivo quando expostas a substâncias tóxicas.
Uma parte fulcral deste projeto foi o estudo das condições mais favoráveis à realização
dos ensaios crónicos. Foram testados parâmetros como o local para a realização dos ensaios,
alimentação dos organismos teste (D. magna) e meio de cultura. Por causa do tempo
despendido nesta otimização, foram apenas realizados ensaios crónicos aos efluentes
terciários tratados por UV e UF. Devido a fatores externos não identificados, não foi possível
a realização de um controlo, pelo que foram usados dois controlos disponíveis na literatura
para comparar comportamentos reprodutivos.
Dos ensaios agudos, averiguou-se que o tratamento por ozonização foi o que provocou
maior mortalidade nos organismos de teste, tendo sido possível calcular um EC50 de 85,75%.
Nos restantes efluentes, não foi possível calcular o EC50, uma vez que a mortalidade das
dáfnias não foi significativa, assim, foi oportuna a realização de ensaios crónicos.
Dos ensaios crónicos realizados aos efluentes tratados por UV e UF, verificou-se uma
disparidade notável do número de descendentes produzidos pelas dáfnias submetidas ao
efluente tratado por UV relativamente às submetidas ao efluente tratado por UF, indicando a
presença de algum composto que possa estar a atuar como um disruptor endócrino, levando a
uma alteração reprodutiva das dáfnias.
In its definition, toxicology is the study of the adverse effects of chemical products on living organisms. Daphnia magna is one of the most widely used organisms for ascertaining toxicity due to its high sensitivity to toxicants. The main goal of this work was to assess the ecotoxicity of treated wastewater using D. magna. Five effluents were analysed, including a secondary effluent and four tertiary effluents [ultraviolet (UV), ultrafiltration (UF), ozonation and non-thermal plasma]. Acute tests and chronic tests were performed. In the acute tests, Daphnia less than 24h old at the start of the test were exposed to the test substance at a range of concentrations for a period of 48h, with the death of Daphnia occurring after 24 and 48 hours. In contrast, chronic tests involve exposing juvenile Daphnia to the test substance for a period of approximately 21 days, with the aim of monitoring their reproductive behaviour when exposed to toxic substances. A key part of this project was the study of the most favourable conditions for the chronic tests. Parameters such as test site, feeding of test organisms (D. magna) and culture medium were tested. Because of the time spent on this study, only chronic tests were performed on tertiary effluents treated by UV and UF. Due to unidentified external factors, it was not possible to perform a control test, so a control available in the literature was used to compare reproductive behaviours. From the acute tests, it was found that the ozonation treatment caused the highest mortality in the test organisms, and it was possible to calculate an EC50 of 85.75%. In the remaining effluents, it was not possible to calculate this value since the mortality of Daphnia was not significant. To ascertain the real effect of these effluents on Daphnia, chronic tests were necessary. From the chronic tests performed on UV and UF treated effluents, there was a remarkable disparity in the number of offspring produced by Daphnia submitted to UV treated effluent compared to those submitted to UF treated effluent, indicating the presence of some compound that may be acting as an endocrine disruptor, leading to a reproductive abnormality of Daphnia.
In its definition, toxicology is the study of the adverse effects of chemical products on living organisms. Daphnia magna is one of the most widely used organisms for ascertaining toxicity due to its high sensitivity to toxicants. The main goal of this work was to assess the ecotoxicity of treated wastewater using D. magna. Five effluents were analysed, including a secondary effluent and four tertiary effluents [ultraviolet (UV), ultrafiltration (UF), ozonation and non-thermal plasma]. Acute tests and chronic tests were performed. In the acute tests, Daphnia less than 24h old at the start of the test were exposed to the test substance at a range of concentrations for a period of 48h, with the death of Daphnia occurring after 24 and 48 hours. In contrast, chronic tests involve exposing juvenile Daphnia to the test substance for a period of approximately 21 days, with the aim of monitoring their reproductive behaviour when exposed to toxic substances. A key part of this project was the study of the most favourable conditions for the chronic tests. Parameters such as test site, feeding of test organisms (D. magna) and culture medium were tested. Because of the time spent on this study, only chronic tests were performed on tertiary effluents treated by UV and UF. Due to unidentified external factors, it was not possible to perform a control test, so a control available in the literature was used to compare reproductive behaviours. From the acute tests, it was found that the ozonation treatment caused the highest mortality in the test organisms, and it was possible to calculate an EC50 of 85.75%. In the remaining effluents, it was not possible to calculate this value since the mortality of Daphnia was not significant. To ascertain the real effect of these effluents on Daphnia, chronic tests were necessary. From the chronic tests performed on UV and UF treated effluents, there was a remarkable disparity in the number of offspring produced by Daphnia submitted to UV treated effluent compared to those submitted to UF treated effluent, indicating the presence of some compound that may be acting as an endocrine disruptor, leading to a reproductive abnormality of Daphnia.
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Keywords
D. magna ecotoxicity tertiary treatments acute tests chronic tests