HA4 Metals and Bioaccumulation
Room 16A/B, Level 4
8:00 AM - 12:00 PM, Thursday, 13 November 2003
Chair: Paquin, Paul ,
Co-chair: Schlekat, Chris ,
(516) Exchange rates of metals between a burrowing mayfly and its surroundings in nature.
Michaud, A1, Hare, L1, Campbell, P.G.C.1, 1 INRS-Eau, Terre et Environnement (ETE), Université du Québec, Québec, Québec, Canada
ABSTRACT- Biomonitors are used to estimate bioavailable metal concentrations in aquatic environments. Nymphs of the burrowing mayfly Hexagenia are well suited as trace metal biomonitors in lakes and slow-flowing rivers because they are large insects that tend to be abundant, widespread and tolerant of metals. To determine the scale of time over which this biomonitor would respond to changes in metal concentrations in nature, we transferred nymphs of Hexagenia limbata between metal-rich and metal-poor rivers. The rates of metal uptake and loss were measured in two animal compartments that were obtained by dissecting nymphs into gut and remaining body parts. Furthermore, we measured changes in metal partitioning at the sub-cellular level by separating both compartments into various fractions using differential centrifugation. That is, we compared metal concentrations among: a first pellet comprising intact cells, the exoskeleton and granules; a second pellet containing heat-denatured proteins and a supernatant comprising heat stable proteins such as metallothionein. Larvae transplanted from the low-metal to the high-metal river showed an increase in their cadmium concentration over time up to steady-state values similar to those in indigenous nymphs after about a month. The Cd accumulated by nymphs was located mainly in the gut compartment associated with a metallothionein-like protein. Our results suggest that H. limbata Cd concentrations respond rapidly to those in their surroundings and that nymphs take up most of their Cd from food (sediment). Furthermore, nymphs appear to have the capacity to synthesize metal-binding proteins rapidly thereby mitigating any negative effects that could be caused by this metal. Our results for Cd will be compared with those for several other metals.
Key words: metals, Hexagenia limbata, rivers, transplantation