W7 AM Acclimation / Adaptation of Animals to Metals: Resistance, Tolerance, and Cost
Wednesday, 16 November 2005: 8:00 AM - 11:40 AM in 327-329

(FRA-1117-851238) Chronic waterborne and dietborne cadmium exposures to juvenile rainbow trout: physiological and molecular endpoints.

Franklin, N¹, Galvez, F¹, Wood, C¹, ¹ McMaster University, Hamilton, Ontario, Canada

ABSTRACT- Previous research has shown that the gill epithelium of freshwater fish undergoes significant alterations in calcium transport during chronic exposure to waterborne cadmium. However, the effects of chronic dietary exposure and possible interactions between waterborne and dietary cadmium uptake have been largely overlooked. The present study uses a novel radiotracer technology to evaluate the relative contribution and potential interaction of each exposure pathway to fish. Juvenile rainbow trout were fed diets containing control (0.1 mg Cd/kg) or elevated dietary Cd (500 mg Cd/kg, radiolabelled with ¹⁰⁹Cd) in combination with either background (0.04 g Cd/L) or moderately elevated waterborne Cd (3g Cd/L) for 28 d. To further investigate the importance of dietary calcium on cadmium exposure via the different routes, each diet was also supplemented with elevated Ca (60 mg/g as CaCO₃; control diet = 15 mg Ca/g). The combined waterborne/dietborne Cd exposure produced significantly greater mortality (13%) than either exposure alone (<2%), and Ca in the diet was shown to protect against short-term Cd toxicity. Dietary Cd uptake contributed the majority (70 – 100%) of the body′s Cd accumulation from a combined exposure, and resulted in a significant gill Cd burden (35 – 65%). Results indicate that tissue accumulation of Cd via each exposure pathway is largely additive with prolonged exposure, and suggests that assumptions of additivity used to model chronic metal accumulation and toxicity may hold true for non-nutrient metals such as Cd. We are currently using quantitative PCR to assess possible changes in the expression of various genes encoding calcium transporters which may be altered by chronic cadmium exposure. (Funded by ILZRO, ICA, CDA, NiPERA, Noranda-Falconbridge, Teck Cominco, and an NSERC CRD grant).

Key words: dietary/waterborne interaction, cadmium, rainbow trout, chronic exposure