An investigation into the effect of microplastic and sporopollenin upon 17β Estradiol uptake in the marine bivalve Mytilus eduli

This project involved an investigation into the effect of microplastics and sporopollenins upon 17β Estradiol (E2) uptake in the bivalve mollusc Mytilus edulis. Microplastics are found in ever increasing quantities in the marine environment and as they degrade they break down into fragments known as microplastics. These microplastics have lipophilic estrogenic properties which leads to the accumulation of Endocrine Disrupting Compounds (EDCs) such as E₂ (Cole et al. 2011; Wright et al. 2013). Furthermore, their small size means that microplastics are often ingested by marine organisms where they cause biological responses (Browne et al. 2008; Wright et al. 2013). Mytilus Estrogen Receptor (MER) or Vitellogenin (VTG) have been proposed as biomarkers indicating a response to E₂ exposure (Matozzo et al. 2008; Puinean & Rotchell 2006). Sporopollenins are naturally occurring polymers derived from plant spores and pollen grains which exhibit similar hydrophobic and lipophilic properties to microplastics (Barrier 2008). Because of their biological stability and inert properties (Archibald et al. 2013; Binks et al. 2005) sporopollenins are proposed as a tool for removing EDCs from polluted aquatic environments.The mussels were harvested from Filey Brigg, N. Yorks and were acclimatised in artificial seawater for 3 days. Following acclimatisation they were exposed to one of 5 exposure regimes, artificial seawater only (control), microplastic only, microplastic with E₂, sporopollenin with E₂, or E₂ only. Following exposure the gonads of each individual were harvested and one half was used for histology and the other half for molecular studies. PCR and qPCR techniques were used to determine if the expression of mRNA for the genes MER or VTG were affected by either microplastic or sporopollenin presence in the water column. The molecular study did not find a significant effect of either microplastic or sporopollenin upon MER or VTG expression in either males or females. The histology revealed that the harvested individuals were in late stage gametogenesis. At this stage the oocytes and spermatocytes are mature and ready for release, therefore, expression of both MER and VTG is down-regulated and the expression levels are not detectable.