The comparative toxicity of rainfall overflows and a municipal effluent plume in Elliptio complanata using a novel qPCR array approach.

Municipal effluents have the potential to disrupt the endocrine system involved in reproduction in aquatic organisms. The purpose of this study was to develop a novel a quantitative polymerase chain reaction (qPCR) array for the freshwater mussel Elliptio complanata to compare the toxic properties of municipal effluents and rainfall overflows. Mussels were caged for 3 months at upstream and downstream sites of a municipal effluent discharge point and 2 rainfall overflow sites in the Saint-Lawrence River. The data revealed that exposure to municipal effluents and overflow sites lead to increased expression of vitellogenin (VTG) in male mussels, altered sexual differentiation in females, gene expression involved in oxidative stress (superoxide dismutase, glutathione S-transferase) and DNA damage (chromosome mismatch and repair of covalently-bound DNA adducts). Mussels at the downstream site accumulated also large amounts of heterotrophic bacteria but not at the overflow sites. However, mussels at the overflow sites had decreased expression in ABC transporter gene expression. Scaling analysis revealed that the following gene expression were related to effects at higher level of biological organization such as total RNA levels, gonad mass and gonad somatic index: DNA repair of covalent DNA adducts, mistmach chromosomal recombination during meiosis and undifferentiated cells in gonads. In conclusion, exposure to rainfall overflow sites have similar effects to municipal effluents based on VTG and oxidative stress responses at the transcriptomic levels only but the effects at the DNA integrity and sexual differentiation were involved in adverse outcome pathways of urban pollution in Elliptio complanata mussels.