Effects of cadmium-spiked sediment on cadmium accumulation and bioturbation by nymphs of the burrowing mayfly Hexagenia bilineata

We assessed accumulation of cadmium (Cd) and bioturbation by nymphs of the burrowing mayfly Hexagenia bilineata as indicators of exposure to Cd-spiked sediment in a 21-d test. Surficial sediments (top 5 cm) from Pool 7 of the Upper Mississippi River were spiked with Cd to concentrations of 3, 7, and 15 mu g Cd g(-1) dry weight. The experimental design was completely random ized, with three Cd-spiked sediment treatments plus an unspiked sediment co ntrol (1 mu g Cd g(-1) dry weight), and 10 nymphs in each of six replicates per treatment. Nymphs accumulated Cd during the 21-d exposure; mean concen trations varied from 0.22 to 6.24 mu g g(-1) dry weight, and tissue concent rations were correlated with Cd concentration in unfiltered test water (r = 0.93, P <0.01) and rest sediment (r = 0.93, P <0.01). The effect of Cd on bioturbation by nymphs, as indicated by turbidity, differed significantly a mong treatments (P = 0.045) and over time within treatments (P = 0.01). Tur bidity progressively decreased as Cd concentration in the sediment increase d, up to 7 mu g g(-1); however, turbidity in the 15 mu g g(-1) treatment (o ur greatest exposure concentration) did not differ significantly from the c ontrol. Concentrations of Cd in unfiltered, overlying test water increased significantly within treatments during the test, indicating that nymphs mob ilized sediment-associated Cd into the overlying water, presumably through burrowing and respiratory activities.