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

(AAA-1117-798972) Waterborne vs. dietary Zn exposure of Daphnia magna: molecular, physiological, organismal and population level effects.

De Schamphelaere, K¹, Muyssen, B¹, Soetaert, A², Vandenbrouck, T², Moens, L², Van der Ven, K², Blust, R², De Coen, W², Janssen, C¹, ¹ Ghent University - Laboratory of Environmental Toxicology and Aquatic Ecology, Gent, Belgium² University of Antwerp - Laboratory of Ecophysiology, Biochemistry and Toxicology, Antwerp, Belgium

ABSTRACT- In this study the effects of waterborne and dietary zinc on Daphnia magna were investigated on different levels of biological organization, i.e. gene expression level, organism, and population. Green algae Pseudokirchneriella subcapitata were exposed to a range of dissolved zinc concentrations and a control to obtain Zn-contaminated food with Zn-burdens of about 100 to 1,000 ug Zn/g dry wt. These foods were then used in a number of waterborne (dissolved Zn-concentrations: 100 to 500 ug/L + control food) and dietary (contaminated food) 21-day exposure experiments with D. magna. Mechanistically different toxicity patterns were observed for waterborne vs. dietary exposure. Waterborne exposures resulted in a general stress response, affecting feeding rates and consequently also growth and reproduction. Parallel experiments with Ca-deprived organisms suggested that Zn-induced hypocalcaemia might be at the basis of decreased feeding rates. This suggests a physiological basis for Zn-Ca antagonism in daphnids. Dietary zinc specifically targeted reproduction in D. magna, and did not affect feeding rates or growth. Effects on both brood size and brood quality have been observed and are hypothesized to be mediated by inhibition of vitellogenesis. The above-mentioned suggestions and hypotheses were further investigated using a D. magna-specific micro array cDNA analysis. The expression of reproductive and metabolic genes was determined to discriminate between mechanisms of waterborne vs. dietary exposures. Finally, life-history-table analysis revealed that waterborne exposures are more likely to affect populations than dietary exposures as a direct consequence of their different modes of action. The implications of these findings for water quality criteria and risk assessment of Zn will be discussed.

Key words: Daphnia, Zinc, Dietary exposure, ecotoxicogenomics