Thyroid Hormone Disrupting Effects of Municipal Wastewater
Date
2013-12-10
Authors
Wojnarowicz, Pola
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Abstract
Current municipal wastewater treatment plants (MWWTP) technologies are insufficiently removing emerging contaminants of concern. These emerging contaminants are an issue as many are known endocrine disrupting compounds (EDCs). EDCs are contaminants that can have severe and irreversible impacts on highly conserved endocrine systems that are critical during developmental periods in vertebrates as well as during adult life. Many EDCs have non-monotonic dose-response curves yet they are not often tested at low, environmentally relevant concentrations. EDC research to date has focused heavily on xenoestrogenic compounds whereas thyroid hormone (TH) disruption has been largely overlooked.
TH is conserved in all vertebrates and plays crucial roles in neural development, basal metabolism, and thermoregulation. TH is comprised of thyroxine (T4), often known as the transport form of TH, and triiodothyronine (T3), the more bioactive form of TH. A TH spike occurs in the perinatal period of humans, and when disrupted, this spike can cause severe developmental defects. An analogous, but perhaps more overt, TH spike occurs in amphibians. TH is the sole hormone that drives amphibian metamorphosis, thus providing an excellent model for TH action. Our lab has previously developed the cultured tailfin (C-fin) assay, which uses biopsies from premetamorphic Rana catesbeiana tadpole tailfins cultured in the presence of an exogenous chemical of concern to assess perturbations to TH- and stress-responsive gene transcript levels by QPCR.
This thesis uses the C-fin assay to assess the efficacy of removal of biological TH- and stress-altering activity in conventional municipal wastewater treatment systems. We first assess the successive levels of a full-scale conventional activated sludge (CAS) MWWTP in its ability to reduce perturbations of mRNA transcript levels of the critical TH receptors alpha (thra) and beta (thrb), and stress responsive gene transcripts superoxide dismutase (sod), catalase (cat) and heat shock protein 30 (hsp30). Secondary treatment of wastewater effluents removes cellular stress perturbations when compared to influents, but thr disruptions remain after conventional secondary wastewater treatment. We then assess three pilot-sized conventional secondary MWWTP configurations run at two operational conditions. The C-fin assay results suggest that the current understanding of operational conditions and the efficiency of complex MWWTP configurations is not clear-cut when assessed by biological endpoints such as the transcript abundance perturbations in the C-fin assay.
Finally, the C-fin assay is used to investigate transcript profiles of genes of interest when the tissues are treated with the endogenous hormones T3, T4, and estradiol (E2). Our results indicate that T4 acts as more than solely a T3-prohormone and that gene expression levels in response to the two different forms of TH can be T3 or T4 specific. E2 effects, although implicated in altering TH-mediated responses in other contexts, do not affect TH-responsive gene transcripts in the C-fin. The data presented use the novel C-fin assay to challenge and advance the currently accepted views of TH-action, as well as develop necessary yet practical biological knowledge for management of emerging contaminant release from MWWTPs.
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Keywords
Thyroid Hormone, Amphibian, Rana catesbeiana, Endocrine Disruption, Municipal Wastewater