THE BIOAVAILABILITY OF SEDIMENT-BOUND CD, CO, AND AG TO THE MUSSEL MYTILUS-EDULIS

Marine sediments, long thought to be a final repository of toxic conta minants in marine ecosystems, may also serve as a source of toxic cont aminants for marine food chains. The influence of physical and chemica l properties of oxidized sediments on the bioavailability of metals fr om sediments to marine filter-feeding invertebrates is largely unknown . We examined the relative importance of specific sedimentary componen ts that may affect the uptake of Cd, Co, and Ag by the mussel Mytilus edulis. Iron and manganese oxides, montmorillonite clay, silica, and n atural sediment particles were radiolabeled with Cd-109, Co-57, and Ag -110m; some particles were also coated with marine fulvic acids to sim ulate the influence of organic coating on metal bioavailability. Musse ls were fed radiolabeled particles and then allowed to depurate by fee ding on nonradioactive particles, following a pulse-chase protocol dev eloped to determine assimilation efficiencies of ingested metals. Meta ls were absorbed by mussels from all sediment particles, but metals as sociated with organic-coated particles were generally absorbed to a gr eater extent than metals associated with uncoated particles; absorptio n efficiencies were as high as 34% (for Co from organic-coated silica particles). Desorption experiments with radiolabeled particles at pH 5 were performed in parallel to simulate the behavior of food-bound met als in the acidic gut of bivalves. High correlations (r > 0.97) betwee n the amount of metal desorbed under these conditions and the assimila tion efficiency for metal bound to particles were noted among organic- coated particles but not uncoated particles (r < 0.6). Differences bet ween coated and uncoated particles were principally due to differences in gut transit times of the ingested particles. These results suggest that suspended sediment particles may be a source of metals for suspe nsion-feeding animals, but the relationship between metal partitioning to sediments and biological availability is not obvious, because orga nic coatings and the acidic gut environment influence metal absorption in mussels.