Cadmium accumulation by invertebrates living at the sediment-water interface

Benthic animals can take up trace metals both from the sediment compartment in which they burrow and from the water column compartment above their bur rows (we define both compartments as containing water and particles). If cr iteria for the protection of benthic animals are based on metal concentrati ons in one of these two compartments, then it should first be demonstrated that the majority of the metal taken up by these animals comes from the giv en compartment. To determine whether benthic animals take up the majority o f their cadmium (Cd) from the sediment compartment, we created a Cd gradien t in lake sediment and compared Cd accumulation by the invertebrates coloni zing these sediments with Cd concentrations in the sediment compartment. On the basis of this relationship and using a bioaccumulation model, we estim ate that indigenous benthic invertebrates take up the majority of their Cd from the water column compartment. The results of our experiment are simila r to those from a previous study conducted on a different benthic community in a larger lake. Taxa common to both lakes obtained similar proportions o f their Cd from the water column compartment, suggesting that Cd accumulati on by the same species will be constant across lakes of differing size and chemistry. Our results strengthen the argument that the protection of benth ic communities from metal pollution should consider metal in both the water column and sediment compartments. In this regard, the AVS model, which con siders only sedimentary metals, was more effective in predicting Cd concent rations in pore waters than those in most animal taxa. We suggest that meas urements of vertical chemical heterogeneity in sediments and of animal beha vior would aid in predicting the bioaccumulation and effects of sedimentary pollutants.