Cadmium dynamics in estuarine sediments: Effects of salinity and lugworm bioturbation

Abstract We investigated the effects of lugworm bioturbation on the fate of Cd added either to a thin layer at the sediment surface or homogeneously mixed throughout the sediment. In both situations, the Cd release to the overlying water was highest when lugworms were not present, most likely because bioturbation transported Cd-contaminated sediment away from the sediment surface. Also, irrigation transported water-borne Cd back into the sediment. When Cd was added to the sediment surface, a Cd peak emerged at the feeding depth of the worm within 1 d because of the transport of water-borne Cd down into the sediment by lugworm irrigation. In addition, the conveyor-belt feeding mode of the worm caused both burial of Cd by fecal casts and a gradual spreading of the Cd distribution within the sediment column. When Cd was added to the entire sediment column, bioturbation caused a net transport of Cd upwards, resulting in the surface layers having higher Cd concentrations than the deeper layers, indicating a net release of Cd from deeper sediments. The distribution of Cd in lugworms depended on the Cd exposure situation and suggested that worms were exposed mainly to water-borne Cd when Cd was added to the top of the sediment, whereas worms were exposed mainly by ingesting Cd-labeled sediment when Cd was mixed homogeneously throughout the sediment.