The discrepancy in concentration of metals (Cu, Pb and Zn) in oyster tissue (Saccostrea glomerata) and ambient bottom sediment (Sydney estuary, Australia)

- Sediments of Sydney estuary are highly enriched in Cu, Pb and Zn over extensive areas.
- Cu oyster tissue concentrations exceed human consumption guidelines in all of the estuary.
- Sediment quality guidelines are not predictive of oyster distribution, weight/size, tissue metals.
- Oyster tissue metal concentrations vary greatly over temporal scales of years at a single locality.
- Oysters cannot be used in Sydney estuary as a valid biomonitor due to overriding regulation.

The current study aimed to examine the relationship between metals in sediments and metal bioaccumulation in oyster tissue in a highly-modified estuary (Sydney estuary, Australia). While extensive metal contamination was observed in surficial sediments, suspended particulate matter and oyster tissue, a significant relationship between these media could not be established. No relationship was determined between sediment quality guidelines and oyster size or weight, nor with human consumption levels for metals in oyster tissue. Moreover, oyster tissue metal concentrations varied greatly at a single locality over temporal scales of years. Oyster tissue at all 19 study sites exceeded consumptions levels for Cu. Bioaccumulation of metals in oyster tissue is a useful dynamic indicator of anthropogenic influence within estuaries, however oysters cannot be used in Sydney estuary as a valid biomonitor due to overriding internal regulation (homoestasis) by the animal, or by external natural (sediment resuspension) and anthropogenic (sewer/stormwater discharges) pressures, or both.