RESUMO
Improved endocrine disrupting compound (EDC) removal is desirable in municipal wastewater treatment plants (MWWTPs) although increased removal does not always translate into reduced biological activity. Suitable methods for determining reduction in biological activity of effluents are needed. In order to determine which MWWTPs are the most effective at removing EDC activities, we operated three configurations of pilot sized biological reactors (conventional activated sludge, CAS; nitrifying activated sludge, NAS; and biological nutrient removal, BNR) receiving the same influent under simulated winter and summer conditions. As frogs are model organisms for the study of thyroid hormone (TH) action, we used the North American species Rana catesbeiana in a cultured tadpole tailfin (C-fin) assay to compare the effluents. TH-responsive (thyroid hormone receptors alpha (thra) and beta (thrb)) and stress-responsive (superoxide dismutase, catalase, and heat shock protein 30) mRNA transcript levels were examined. Effluents infrequently perturbed stress-responsive transcript abundance but thra/thrb levels were significantly altered. In winter conditions, CAS caused frequent TH perturbations while BNR caused none. In summer conditions, however, BNR caused substantial TH perturbations while CAS caused few. Our findings contrast other studies of seasonal variations of EDC removal and accentuate the importance of utilizing appropriate biological readouts for assessing EDC activities.
Assuntos
Nadadeiras de Animais/metabolismo , Rana catesbeiana/metabolismo , Estações do Ano , Estresse Fisiológico , Hormônios Tireóideos/metabolismo , Águas Residuárias/química , Purificação da Água , Animais , Biodegradação Ambiental , Disruptores Endócrinos/análise , Nitrificação , Projetos Piloto , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Rana catesbeiana/genética , Receptores dos Hormônios Tireóideos/genética , Receptores dos Hormônios Tireóideos/metabolismo , Esgotos/química , Estresse Fisiológico/genética , Eliminação de Resíduos LíquidosRESUMO
Thyroid hormones (THs), l-thyroxine (T4) and 3,5,3'-triiodothyronine (T3), are essential for vertebrate growth and development. Classically, T4 is 5'-deiodinated to the active hormone, T3, in target tissues which then binds nuclear TH receptors (TRs) and regulates gene transcription. However, it is possible that T4 acts directly on target tissues. Frog metamorphosis is a powerful TR-dependent model for studying TH action. Premetamorphic Rana (Lithobates) catesbeiana tadpoles were injected with 0.1-50 T3 or 0.5-250T4pmol/gbodyweight to account for their 5-fold difference in biological activity and the mRNA profiles in six tissues from well-characterized TH-responsive genes were evaluated after 48h using quantitative real time polymerase chain reaction. 5'-deiodinase-poor tissues should produce superimposable dose-response curves if T4 does not require conversion to T3. This was the case in lung and tail fin; the latter tissue recapitulating these responses in organ culture. 5'-deiodinase-rich tissues should convert T4 to T3. Because T3 has a higher affinity to TRs, a 5-fold higher T4 dose compared to T3 should produce greater transcript induction. This was observed in the brain and for most intestinal transcripts. However, some gene transcripts in the intestine and all transcripts in the back skin produced superimposable response curves suggesting that a direct mode of T4 action is plausible in these tissues. While the liver showed results consistent with its 5'-deiodinase-poor status, we found evidence of an alternate, non-genomic mechanism for two gene transcripts. Therefore, mechanisms not requiring T4 conversion to T3 may play a far greater role than previously thought.
Assuntos
Larva/efeitos dos fármacos , Metamorfose Biológica/efeitos dos fármacos , Rana catesbeiana/genética , Hormônios Tireóideos/farmacologia , Tiroxina/farmacologia , Tri-Iodotironina/farmacologia , Animais , Iodeto Peroxidase/metabolismo , Larva/genética , Larva/metabolismo , Metamorfose Biológica/genética , Técnicas de Cultura de Órgãos , Especificidade de Órgãos , RNA Mensageiro/genética , Rana catesbeiana/metabolismo , Reação em Cadeia da Polimerase em Tempo Real , Receptores dos Hormônios Tireóideos/genética , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Hormônios Tireóideos/genética , Tiroxina/genética , Tri-Iodotironina/genéticaRESUMO
Conventional municipal wastewater treatment plants do not efficiently remove contaminants of emerging concern, and so are primary sources for contaminant release into the aquatic environment. Although these contaminants are present in effluents at ng-µg/L concentrations (i.e. microcontaminants), many compounds can act as endocrine disrupting compounds or stress-inducing agents at these levels. Chemical fate analyses indicate that additional levels of wastewater treatment reduce but do not always completely remove all microcontaminants. The removal of microcontaminants from wastewater does not necessarily correspond to a reduction in biological activity, as contaminant metabolites or byproducts may still be biologically active. To evaluate the efficacy of conventional municipal wastewater treatment plants to remove biological activity, we examined the performance of a full scale conventional activated sludge municipal wastewater treatment plant located in Guelph, Ontario, Canada. We assessed reductions in levels of conventional wastewater parameters and thyroid hormone disrupting and stress-inducing activities in wastewater at three phases along the treatment train using a C-fin assay. Wastewater treatment was effective at reducing total suspended solids, chemical and biochemical oxygen demand, and stress-inducing bioactivity. However, only minimal reduction was observed in thyroid hormone disrupting activities. The present study underscores the importance of examining multiple chemical and biological endpoints in evaluating and monitoring the effectiveness of wastewater treatment for removal of microcontaminants.