A Biomonitor for Tracking Changes in the Availability of Lakewater Cadmium over Space and Time

ABSTRACT

Determining the exposure of organisms to contaminants is a key component of Ecological Risk Assessments (ERAs). Effective estimates of exposure consider not only the total concentrations of contaminants in an organism's surroundings but also the availability of the contaminants to organisms. Contaminant availability can be inferred from mechanistic models and verified by measurements of contaminant concentrations in organisms. We evaluated the widespread lake-dwelling insect Chaoborus as a potential biomonitor for use in exposure assessments for three metals: cadmium (Cd), copper (Cu), and zinc (Zn). We show that larvae of this midge maintain constant their concentrations of the essential metals Cu and Zn and thus cannot be used to monitor them. In contrast, larval Cd concentrations varied widely both among lakes and in a given lake over time. We were able to relate these variations in biomonitor Cd to changes in lakewater Cd and pH using the Free Ion Activity Model (FIAM). Our results suggest that Chaoborus larvae could be used as an effective tool for estimating the Cd exposure of organisms in lakes for the purposes of ERAs.

Key Words:

• metal
• Cd
• bioaccumulation
• biomonitor
• ERA
• lakes

ACKNOWLEDGMENTS

We acknowledge comments by D. Buchwalter, D. Cain, and D. Ponton as well as funding from the Metals in the Environment Research Network, the Mining Association of Canada, Ontario Power Generation, the National Sciences and Engineering Research Council of Canada, and the Québec Fonds de Recherche sur la Nature et les Technologies.