Abstract

The interaction between Cd and Zn in aquatic organisms is known to be highly variable. The purpose of this study was to use a subcellular compartmentalization approach to examine Cd and Zn interactions in the deposit-feeding polychaete Capitella capitata (sp. 1). Laboratory-reared C. capitata were co-exposed to Cd (background or 50 mu g Cd l(-1)) and Zn (background or 86 mu g Zn l(-1)) with Cd-109 and 65 Zn as radiotracers for I week. After the 1-week uptake period, subsets of worms were allowed to depurate accumulated metals for an additional I week. Worms from both phases (uptake and loss) were then subjected to subcellular fractionation to determine the compartmentalization of metals as metal-sensitive fractions [MSF - organelles and heat-denaturable proteins (HDP)] and biologically detoxified metals [BDM - heat-stable proteins (HSP) and metal-rich granules (MRG)]. Uptake and loss of Cd and Zn in C. capitata at the whole body level were similar at bkgd-Cd/bkgd-Zn, with worms depurating the majority of accumulated metal (similar to 75% Cd and similar to 64% Zn). When exposure of Zn or Cd was increased (bkgd-Cd/86-Zn; bkgd-Zn/50-Cd), uptake of background levels of Cd or Zn, respectively, was suppressed by similar to 50%. These accumulated metals, however, were retained during the loss phase resulting in similar to 40-50% greater Cd and Zn whole body tissue burdens than those of bkgd-Cdibkgd-Zn worms. Beyond exhibiting similar patterns of uptake and loss at the whole body level, Cd and Zn behaved similarly at the subeellular level. Under background levels (bkgd-Cd/bkgd-Zn), after uptake, worms partitioned a majority of Cd (similar to 65%) and Zn (similar to 55%) to the HSP and organelles fractions. The HDP and MRG fractions contained less than similar to 6% of both metals. Following depuration, at bkgd-Cd/bkgd-Zn, Cd and Zn were lost from all subeellular fractions; loss from HSP was the greatest contributor to whole body loss. When exposed to elevated concentrations of Zn or Cd, the suppression in uptake of bkgd-Cd or bkgd-Zn observed in whole body uptake was largely due to suppressions in the storage of Cd and Zn to HSP. These results suggest that Cd-Zn interactions reduce partitioning of both Cd and Zn to HSP, indicating that metal-binding proteins such as metallothioneins play a key role in these interactions. (c) 2007 Elsevier B.V. All rights reserved.

Keywords

Capitella capitata; Cd; detoxification; interaction; subcellular; Zn

Published in

Journal of Experimental Marine Biology and Ecology
2007, volume: 352, number: 1, pages: 65-77

Authors' information