Long Term Exposure of Freshwater Mussels to a Municipal Effluent Plume Leads to Feminisation

The purpose of this study was to verify the hypothesis of feminisation of the freshwater mussel Elliptio complanata exposed for one complete reproductive cycle (1 year) to a municipal effluent plume. Mussels were harvested from a reference lake and placed in specially-designed cages adapted for long-term exposure to a suspended matter-rich river environment. After exposure, mussels were collected to measure growth-related indices, vitellogenin-like proteins and sex ratio. Results showed that mussels from the downstream sites had increased condition factor and gonado-somatic index. They also displayed significantly more vitellogenin related proteins in their gonads and the proportion of females was increased from 41 % (upstream site) to a high of 66 % (farthest downstream site). This high proportion of females is not usually observed in natural populations of Elliptio complanata and indicates a feminisation effect on freshwater bivalves by estrogenic compounds continually discharged into the receiving environment.