Influence of bioturbating animals on flux of cadmium into estuarine sediment

The role of bioturbation in downward transport of cadmium from the water phase into a sandy marine sediment was investigated in a series of laboratory experiments, where dissolved 109Cd was added to overlying water in sediment cores with and without bioturbating animals. The polychaetes Nereis diversicolor and Arenicola marina and the crustacean Corophium volutator initially stimulated the downward transport of water-phase cadmium into uncontaminated sediments by a factor of 1.5–2 compared to control sediments without benthic macrofauna. N. diversicolor and A. marina transferred cadmium to > 4 and 13 cm depth in the sediment, respectively, whereas in the presence of C. volutator no cadmium was detectable below 1.5–2 cm. Cadmium transported to the deeper layers in N. diversicolor bioturbated sediments was primarily adsorbed to the 0–3-mm radial zone around burrows. It is suggested that the higher downward transport of cadmium from the water-column into sediments with infaunal burrows is driven by adsorption to metal oxides (iron and manganese) and to the mucus cement in burrow linings combined with the increased area of oxidized sediment-water interfaces. In the case of A. marina, percolation of irrigated water through the reduced head-shaft sediment may cause cadmium adsorption to sulfides as well.