EDCAT 5. A catchment-based study of endocrine disruption in surface waters: multivariate evaluation of the health of a sentinel fish species exposed to sewage treatment works effluent. Annexe to EDCAT Final report – CYP1A gene expression results

Summary: The levels of CYP1A expression vary significantly between sites on the Ray, exhibiting a similar pattern in 2007 and 2008, and these trends seem to be linked with sediment contaminant loading, as reported by EDCAT 3/4, rather than waterborne contamination. If the primary route of exposure to organic chemicals for the fish in the Ray is indeed linked to sediment concentrations (e.g. via sediment-dwelling invertebrates) this may explain the complete absence of effect of remediation on CYP1A expression in fish in the Ray. It also suggests that exposure of the resident fish populations to contaminating chemicals may continue for some time after remediation of the STW effluent. Further chemical and fish monitoring effort would establish how long is required for the system to depurate fully. Relatively high levels of CYP1A expression were detected in fish from sites on the Ock during 2008. This is consistent with data obtained from EROD analyses of fish collected on a different occasion during 2008 and is strongly suggestive of a contaminant episode. The source and nature of this contamination remains unknown.