The stable isotope ratios of carbon (dC) and nitrogen (dN) of the muscle, ctenidia and viscera of the Sydney rock oyster, Saccostrea glomerata, showed the dilution and assimilation of tertiary treated sewage along an estuarine gradient. The enriched N values of oyster ctenidia and viscera from within 50 m of the sewage outfall indicated the use of N-enriched tertiary treated sewage effluent (16...