The impact of sediment bioturbation by secondary organisms on metal bioavailability, bioaccumulation and toxicity to target organisms in benthic bioassays: Implications for sediment quality assessment.

Bioturbation alters the properties of sediments and modifies contaminant bioavailability to benthic organisms. These naturally occurring disturbances are seldom considered during the assessment of sediment quality. We investigated how the presence (High bioturbation) and absence (Low bioturbation) of a strongly bioturbating amphipod within three different sediments influenced metal bioavailability, survival and bioaccumulation of metals to the bivalve Tellina deltoidalis. The concentrations of dissolved copper decreased and manganese increased with increased bioturbation. For copper a strong correlation was observed between increased bivalve survival (53-100%) and dissolved concentrations in the overlying water. Increased bioturbation intensity resulted in greater tissue concentrations for chromium and zinc in some test sediments. Overall, the results highlight the strong influence that the natural bioturbation activities from one organism may have on the risk contaminants pose to other organisms within the local environment. The characterisation of field-based exposure conditions concerning the biotic or abiotic resuspension of sediments and the rate of attenuation of released contaminants through dilution or readsorption may enable laboratory-based bioassay designs to be adapted to better match those of the assessed environment.