DYNAMICS OF CADMIUM, LEAD, AND ZINC EXCHANGE BETWEEN NYMPHS OF THE BURROWING MAYFLY HEXAGENIA-RIGIDA (EPHEMEROPTERA) AND THE ENVIRONMENT

Radioisotopes of cadmium, lead, and zinc added in trace amounts to lake sediments were used to measure the uptake and efflux of these metals from various body parts of nymphs of the burrowing mayfly Hexagenia rigida (Ephemeroptera). Total metal concentrations in Hexagenia and its environment were held constant. A simple model permitted the estimation of rate constants that were used to generate model curves which corresponded closely to the measured trends in trace metal uptake and efflux. There was no measurable accumulation of radioisotopes in gill tissues, suggesting that the gills were not the major organ of metal uptake in Hexagenia in this experiment. On the other hand, net uptake of Cd-109 and Zn-65 the gut exceeded that by all other body parts in both quantity and concentration terms, suggesting that the primary source of these metals to Hexagenia is sediment consumed as food. The rate of exchange of Zn-65 was slower than that of Cd-109. Pb-210 differed from the other two metals in that it was not detected in the gut, but was found mainly on the body surface.