Influence of exposure time on the distribution of cadmium within the cladoceran Ceriodaphnia dubia

The internal distribution of a trace metal can be useful in determining in which body organ toxic effects are most likely to occur and the animal func tion most likely to be affected. In addition, because a metal's distributio n within an organism is likely to influence the rate and efficiency with wh ich it is transferred to a higher trophic level, laboratory measurements of trophic transfer could be influenced by exposure duration. We compared the internal distribution of cadmium (Cd) in a cladoceran crustacean (Ceriodap hnia dubia) destined as food for a predatory insect (Chaoborus) after eithe r a I day or a lifetime of exposure of prey to the trace metal. Prey were e xposed to Cd112+109 in both water (10 nM) and their food (algae), as might occur in nature. The internal distribution of Cd-109 in the cladoceran was determined by whole-animal autoradiography. Both the amount and the tissue distribution of Cd in prey were the same after the short and the long term exposures, suggesting that metal accumulation parameters measured after sho rt-term metal exposures can be valid for this animal. Cadmium was mainly ac cumulated in diverticula of the anterior midgut, a region reported to be re sponsible for nutrient absorption. We hypothesize that Cd is accumulated in the diverticula because of their purported role as sites of calcium uptake . (C) 1999 Elsevier Science B.V. All rights reserved.