PARENT SESSION
3I Metal Availability
9:00 AM to 7:00 PM, Monday, 07 May 2001

(M/EH115) Zinc accumulation and regulation in the crustacean Daphnia magna .

Janssen, Colin¹, Muyssen, Brita¹, ¹

ABSTRACT- In the framework of a larger study on zinc acclimation, regulation and homeostasis, several aspects of zinc accumulation in the crustacean Daphnia magna were investigated. These aspects include zinc uptake and elimination as a function of time, the influence of zinc acclimation on accumulation, internal versus adsorbed zinc concentrations and determination of the zinc uptake route (medium versus food). The results indicate that zinc uptake and elimination are rapid processes. Two to three day fluctuations were observed around a constant level indicating the role of moulting in the regulation and elimination of metals. Determination of total zinc concentrations in D. magna after acclimation to a concentration range of 3 to 800 g Zn/L showed that the body concentration of this essential metal was regulated up to a concentration of 450 g Zn/L in laboratory as well as in field-collected clones. This corresponds well with the previously established optimal concentration range for zinc of which 450 g Zn/L was the toxicity boundary. Adsorbed zinc concentrations (removed by washing the organisms in EDTA) accounted for up to 10 % of the total zinc concentration. Zinc contaminated algae were fed to the daphnids to determine the main uptake route of the metal. Results of chronic (21 day) tests clearly indicate that zinc was mainly taken up via the water (≥80 %) and to a lesser extent via the food. Generally it can be concluded that the results of zinc accumulation make a contribution to unravel the processes of metal regulation, acclimation and adaptation, factors which need to be considered in ecologically-relevant and scientifically based risk assessments.

Key words: zinc, accumulation, homeostasis, Daphnia magna