Arch. Environ. Contam. Toxicol. 17, 345-354 (1988) EArchfv• of nvir'on~! con, r..amir~cior~ 9 1988 Springer-Verlag New YorkInc. Cadmium and Zinc Interactions in Fish: Effects of Zinc on the Uptake, Organ Distribution, and Elimination of l~ in the Zebrafish, Brachydanio rerio Anders Wicklund*, Per Runn*, and Leif Norrgren** *Department of Zoology, Uppsala University, Box 561, S-751 22 Uppsala, Sweden and **Department of Pathology, Faculty of Veterinary Medicine, Swedish University of Agricultural Sciences, S-750 07 Uppsala, Sweden Abstract. The fate of equal nondietarian "pulses" of t~ was studied in the zebrafish, Brachydanio rerio, at two Cd water concentrations (<0.05 ~xg/L and 1 Ixg/L) during Zn (10 fxg/L) exposure periods of various duration. This approach was used to in- vestigate Cd-Zn interactions at subacute toxicity levels. There was no effect of Zn on the l~ up- take by the whole body and gills. An antagonistic effect of Zn, on the l~ uptake, was revealed in the intestine. Zn tended to increase the l~ elimi- nation rate in the gills at the higher Cd level, while retarding the elimination from the gastro-intestinal tract. Zn also increased the amount of 1~ re- tained in the liver and, under certain conditions, in the kidney. A simple mathematical description of l~ elimination and accumulation for the various organs is presented. Proposed mechanisms for metal-metal interactions are discussed in an at- tempt to explain the, present results. Hill and Matrone (1970) claimed that elements re- sembling each other in physical and chemical prop- erties interact antagonistically. From metal toxicity tests on chickens they concluded that zinc, cad- mium, and silver act as copper antagonists, and that cadmium acts as a zinc antagonist. Metal-metal interactions can be influenced by chemical associa- tion between metals, competition for carriers, met- abolic changes, induced production of binding pro- teins, and membrane alterations (Magos and Webb 1978). Two mechanisms have been extensively studied regarding heavy-metal interactions: compe- tition for carriers (Foulkes 1985) and induced pro- duction of metal-binding proteins. A group of metal-binding ligands in fish, called metallothionein (MT), has received much attention (Noel-Lambot etal. 1978; Bradley et al. 1985; Kito etaI. 1986; Olsson et al. 1987). MT synthesis is induced by heavy-metal ions, and these ligands have a high af- finity for ions such as Cu z+ , Zn 2+ , and Cd z+ (Karin 1985). A positive association between increased tissue levels of MT and increased metal tolerance in fish has been suggested (Klaverkamp et aL !984). According to current theories, the binding of a metal to MT would prevent the metal from inter- acting with sensitive biological molecules, e.g., en- zymes (Petering and Fowler 1986). Since heavy-metals often occur together in pol- luted areas, it is of vital importance to study metal- metal interactions in fish. Few detailed investiga- tions have been made concerning the effects of one heavy-metal on the accumulation, turnover, and elimination of another metal in fish at metal con- centrations representative of polluted water systems. We have studied the effect of zinc expo- sure on cadmium uptake, turnover, and elimination in the zebrafish, Brachydanio rerio. An equal non- dietarian "pulse" of 1~ (8000 cpm/ml, <0.05 l.~g Cd/L) was studied at two cadmium water concen- trations and for each of two zinc treatments. Materials and Methods Animals and Experimental Design The zebrafish (150-600 rag) were purchased at a local pet shop. They were divided into 6 groups (55 fish/group). Each groap was exposed to the metals in the water during a pre-exposure period of 30 days, a pulse period of 3 days, and an elimination period of 53 days. Three groups of fish were exposed to background levels of Cd (<0.05 txg Cd/L) throughout the experimental period (Exp. 0), and the other three to a nominal concentration of 1 ~xg Cd/L from the start of the pulse period and thereafter (Exp. 1).