Bioturbation and bioaccumulation of cadmium by nymphs of the burrowing mayfly Hexagenia bilineata exposed to cadmium-spiked sediment

The authors exposed nymphs of the mayfly Hexagenia bilineata to cadmium-spiked sediment for 21 d and evaluated turbidity as a sublethal indicator of respiratory stress and assessed the bioaccumulation of cadmium. Surficial sediments (uppermost 5 cm) were collected from a relatively uncontaminated (0.98 {micro}g Cd/g dry weight) site in Pool 7 of the upper Mississippi River and spiked with cadmium to achieve target sediment concentrations of 3, 7, and 15 {micro}g Cd/g dry weight. The experimental design was completely randomized, with three cadmium-spiked sediment treatments and a reference-sediment control, with 10 nymphs in each of six replicates per treatment. The effect of cadmium on bioturbation by nymphs, as measured by turbidity, differed significantly among treatments (P = 0.045) and over time within treatments (P = 0.01). Cadmium concentrations in unfiltered, overlying test water ranged from 0.06 to 3.2 {micro}g/L, indicating that nymphs mobilized sediment-associated cadmium into the water column through their burrowing and respiratory activities. Nymphs accumulated significant quantities of cadmium over the exposure period. Mean concentrations of cadmium in nymphs varied from 0.22 to 6.24 {micro}g/g dry weight and were correlated with the cadmium concentration in unfiltered test water and bulk sediment. Cadmium concentrations in bulk sediments from manymore » lakes and rivers are within the range tested here, and mayflies exposed to sediment within this range rapidly accumulate cadmium, which represents a potentially substantial dietary source for the transfer of cadmium to higher trophic levels.« less