Copper regulation and homeostasis of Daphnia magna and Pseudokirchneriella subcapitata: influence of acclimation Bart T.A. Bossuyt * , Colin R. Janssen Laboratory of Environmental Toxicology and Aquatic Ecology, Ghent University, J. Plateaustraat 22, B-9000 Ghent, Belgium Received 12 March 2004; accepted 22 November 2004 A freshwater alga and zooplankter maintained copper homeostasis, particularly when acclimated to high copper levels. Abstract This study aimed to evaluate (1) the capacity of the green alga Pseudokirchneriella subcapitata and the waterflea Daphnia magna to regulate copper when exposed to environmentally realistic copper concentrations and (2) the influence of multi-generation acclimation to these copper concentrations on copper bioaccumulation and homeostasis. Based on bioconcentration factors, active copper regulation was observed in algae up to 5 mg Cu L ÿ1 and in daphnids up to 35 mg Cu L ÿ1 . Constant body copper concentrations (13 G 4 mg Cu g DW ÿ1 ) were observed in algae exposed to 1 through 5 mg Cu L ÿ1 and in daphnids exposed to 1 through 12 mg Cu L ÿ1 . At higher exposure concentrations, there was an increase in internal body copper concentration, while no increase was observed in bioconcentration factors, suggesting the presence of a storage mechanism. At copper concentrations of 100 mg Cu L ÿ1 (P. subcapitata) and 150 mg Cu L ÿ1 (D. magna), the significant increases observed in body copper concentrations and in bioconcentration factors may be related to a failure of this regulation mechanism. For both organisms, internal body copper concentrations lower than 13 mg Cu g DW ÿ1 may result in copper deficiency. For P. subcapitata acclimated to 0.5 and 100 mg Cu L ÿ1 , body copper concentrations ranged (mean G standard deviation) between 5 G 2 mg Cu g DW ÿ1 and 1300 G 197 mg Cu g DW ÿ1 , respectively. For D. magna, this value ranged between 9 G 2 mg Cu g DW ÿ1 and 175 G 17 mg Cu g DW ÿ1 for daphnids acclimated to 0.5 and 150 mg Cu L ÿ1 . Multi-generation acclimation to copper concentrations R12 mg Cu L ÿ1 resulted in a decrease (up to 40%) in body copper concentrations for both organisms compared to the body copper concentration of the first generation. It can be concluded that there is an indication that P. subcapitata and D. magna can regulate their whole body copper concentration to maintain copper homeostasis within their optimal copper range and acclimation enhances these mechanisms. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Daphnia magna; Pseudokirchneriella subcapitata; Copper; Body concentrations; Bioconcentration factor 1. Introduction Copper is a co-factor in a wide range of biochemical redox reactions involving intracellular enzymes/proteins such as cytochrome oxidase, superoxide dismutase, dopamine-hydroxylase, lysyl oxidase, and extracellular ceruloplasmin (Harris and Gitlin, 1996). The redox nature of copper which makes it essential to processes such as cellular respiration, free-radical defence, and cellular iron metabolism, also makes copper a very potent toxicant. Consequently, for each species a bell-shaped concen- tration-effect curve can be observed, with deficiency symptoms occurring at low concentrations, toxic effects occurring at high concentrations and the optimal concentration range or OCEE in between (Van Assche et al., 1997; Hopkin, 1989; Bossuyt and Janssen, 2003). Given that copper is essential but potentially toxic, it is not surprising that this metal is highly regulated in some * Corresponding author. Tel.: C32 9 264 7932; fax: C32 9 264 3766. E-mail address: bart.bossuyt@ugent.be (B.T.A. Bossuyt). 0269-7491/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2004.11.024 Environmental Pollution 136 (2005) 135e144 www.elsevier.com/locate/envpol