An investigation of the uptake of estradiol in the bivalve Mytilus spp. corresponding biological implications and the effect of the addition of Sporopollenin on bioavailability

Harley, Margaret A.

Biological sciences
May 2019

Thesis or dissertation

© 2019 Margaret A Harley. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.

There has been concern over the past two decades over estrogenic hormones such as 17 α-ethinylestradiol and 17 β-estradiol (E2) in fresh water and marine ecosystems and the risk to aquatic organisms even with low exposure levels. This study is to access whether there is any bioaccumulation in mantle tissue of Mytilus edulis exposed to a known concentration of E2 in a controlled experiment and whether the introduction of sporopollenin, exposed to the same concentration of E2, has a similar effect with bioaccumulation in regard to the use of sporopollenin exine capsules (SECs) as a sequestering agent to remove estrogens from water systems.

This study involved an experiment using M. edulis exposed over a week with a regular dose of 200 ng/L E2, SECs treated with the 200 ng/L of E2 and with untreated SECs and untreated Mytilus as controls. At the end of the experiment, tissue was preserved for histology purposes to ascertain the sex and stage of gametogenesis and to detect any presence of SECs. Portions of the mantle and digestive tract and gills were frozen for chemical analysis to ascertain if either free or conjugated E2 had been bioaccumulated. A portion of the mantle was frozen in RNAlater™ for qPCR determination of mRNA ER expression in either of the exposure groups. In parallel, analytical chemistry and extraction methods were optimised to determine the levels of E2 in tissues.

Histological preparations of gonad tissue from all Mytilus indicated the presence of SECs in the gonad tissues of the Mytilus exposed to SECs only. The water filtrates from the tanks of those animals also indicated the presence of SECs in the water throughout the exposure experiment. Chemical analysis of the water indicated that E2 dissolved in the water was present. The Mytilus in the exposure experiment were in the mid to late development stage of gametogenesis. The results of mRNA ER 2 gene expression indicated no significant difference in ER gene expression in the E2 exposed Mytilus compared to the controls but there was a significant difference in ER gene expression compared to mussels that were exposed to SECs and SECs plus E2. There was no statistical significance in the ER gene expression between the SECs and E2 treated SECs. The chemical analysis of the gonad tissue from the exposure experiment was not undertaken due to time constraints but free E2 was extracted from gonad tissue and from the E2 treated SECs, in a similar experiment. As there is such a notable difference in fold change between both of the SECs treatments and the control, there is an unknown biological influence on the mRNA ER gene expression.

In terms of wider implications of this work, the data shows that the SECs are very efficient at adsorbing or absorbing E2 and this property could be applied as a method to remove E2 from WWTPs. But it is not known if the SECs could be applied for this purpose until there is sufficient evidence of bioavailability.

Department of Biological Sciences, The University of Hull
Rotchell, Jeanette M.; Welham, Kevin
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