T7 AM Metals in the Environment: Dietary Concerns in Aquatic Systems
Tuesday, 15 November 2005: 8:00 AM - 11:40 AM in 327-329

(CLE-1122-062323) Does bioincorporation of dietary cadmium alter its toxicity to fish?

Clearwater, S.^{1, 3}, M. J. Ellwood, M¹, Wood, C.², ¹ National Institute of Water and Atmospheric Research Ltd., PO Box 11-115, Hamilton, New Zealand.³ Email: s.clearwater@niwa.co.nz² McMaster University, 1280 Main Street West, Hamilton, Ontario, Canada L8S 4K1.

ABSTRACT- Our research is exploring the idea that all cadmium-contaminated diets are not created equal. In particular, we are comparing the bioavailability and toxicity of cadmium (Cd) in live invertebrates exposed acutely to dissolved Cd versus invertebrates exposed chronically to dietary and dissolved Cd. We are developing a laboratory-based food chain using wheatgrass (Triticum sp.), chironomid larvae (Chironomus zealandicus) and zebrafish (Danio rerio). Wheatgrass is grown in soil, or hydroponically, and is contaminated with Cd by only exposing the roots (not the leaves) to Cd-contaminated solutions. The wheatgrass is harvested after 10 or 20 d and fed to chironomid (or midge) larvae in static cultures. This exposes the chironomids to both dissolved (25 and 50 ug/L) as well as dietary cadmium for at least 10 d prior to feeding the chironomids to zebrafish. Our preliminary results show that a 10 d exposure to only 5-7 mg Cd/kg wet weight in Cd-fed chironomids, equivalent to daily doses of 0.4-0.6 mg Cd/kg wet weight/day, caused decreased growth of zebrafish. In previous dietary studies, Cd toxicity has only been observed after fish were fed Cd-contaminated food containing > 37 mg/kd wet weight (or daily doses of 0.7 mg Cd/kg wet weight/day). In these previous studies, the diets were invertebrates or practical fish feeds contaminated with dissolved Cd only. Zebrafish may be particularly sensitive to Cd exposure or, incorporation of Cd into chironomids via dietary as well as dissolved exposure may alter Cd bioavailability and toxicity to zebrafish. Subsequent experiments will compare the effect of feeding zebrafish either chironomids exposed to dissolved Cd only or chironomids exposed to both dissolved and dietary Cd.

Key words: metal, dietary, bioavailability, bioincorporation