Co-Investigators:
A. Tessier, INRS-Eau
Email: atessier@inrs-eau.uquebec.ca
Tel. 418-654-2538

N. Yan, York University.
Tel: 416-736-2100

To improve our ability to predict the impact of trace metals we need a better understanding of the chemical and biological processes involved in metal bioaccumulation. We conducted experiments to determine: 1. whether aquatic animals take up the majority of their metal from water or from their food, and 2. the influence of food-related variables on consumer metal content.

We determined in the laboratory that food was a much more important Cd source to the aquatic predator Sialis velata (alder fly, Megaloptera) than was water. We accomplished this by measuring Cd accumulation by this predator from either water alone or from chironomid prey (Cryptochironomus sp.) in the laboratory. Both the predator and its prey were exposed to the same free Cd ion concentration, as would occur in nature. The efficiency with which Cd was assimilated by the predator from its prey was high (50%) and comparable to values reported for several other insects. Cadmium taken up by the predator from food was largely stored in its gut tissues (as is the case for larvae in nature) whereas a greater proportion of the metal taken up from water was stored in other animal parts. These results suggest that models designed to predict metal bioaccumulation or toxicity should include food as a potential metal source.

To test the influence of prey-related variables on predator metal concentrations we avoided the standard practice of culturing prey and exposing them to metal in the laboratory because: 1. previous experience had shown us that maintaining cultures of aquatic animals is very time consuming; and 2. metal taken up by prey in the laboratory may be more bioavailable to the predator than metal accumulated by prey in nature. We collected Cd-poor predators from a low-Cd lake and fed them prey contaminated with Cd from a high-Cd lake. We conducted our experiments at Rouyn-Noranda, close to a source of Cd-rich prey (calanoid copepods from Lake Marlon). We determined that various species of Chaoborus (phantom midge, Diptera) exposed to the same Cd-rich prey exposure regime will differ in their Cd concentrations. These differences appear to be due in part to the temperature regime and the length of time that species are exposed to prey, both of which are consequences of the species migratory behaviour. These observations suggest that the life habits of the various Chaoborus species influence their Cd concentrations in nature and could be used to explain the observed differences in Cd among the species in nature.