Bioavailability of sediment-bound metals for Vallisneria americana Michx, a submerged aquatic plant, in the St. Lawrence River

We have assessed the bioavailability of sediment-bound metals (Cd, Cr, Cu, Ni, Pb, and Zn) in the St. Lawrence River using a rooted aquatic plant, Val lisneria americana Michx, as the biomonitor species. The host sediments wer e subjected to a sequential leaching procedure to determine the partitionin g of the metals present in the surficial oxic stratum; previously published equations were then used to estimate the free metal ion concentrations at the root-sediment interface. Suspected metal accumulation in foliage from p oint-source pollution of the water column obscured sediment-plant relations hips at several sampling stations, but in general, plant metal concentratio ns could be predicted on the basis of sediment geochemistry (including sedi ment metal concentrations). Metal concentrations in Vallisneria tissues cor related more closely with estimates of bioavailable sediment-bound metal th an with total metal concentrations in sediments, particularly for Cd, Pb, a nd Zn. Roots proved to be better bioindicator organs than shoots for monito ring sediment contamination. Overall, the results demonstrate that Vallisne ria would be a useful biomonitor species of metal contamination in the St. Lawrence River.