Laboratory experiments employing gamma-emitting radiotracers assessed the retention efficiency of ingested metals in the calanoid copepod Anomalocera patersoni and the retention of excreted metals in fecal pellets. Adult copepods ingested the haptophyte Isochrysis galbana labeled with Io9cd , "Z n, 2 0 3~g , " Â ¥ ' "~ and '-"Pu at a rate of 3.79 mg algal C g-I ammal dry wt h-I. Average retention efficiencies were 30 % for Cd, 48 % for Zn, 21 O/O for Hg, 4.5 % for Am, and 0.8 % for Pu. Algal cells resuspended into unlabeled seawater retained metals to varying extents, with depuration curves conforming to a 2-compartment model; Cd was lost most rapidly. The fecal pellets produced by animals feeding on radioactive I. galbana lost essentially all of their l o g c d , "~n , ~m , and 2 3 7~u to unlabeled seawater within 1 d. ^Hg was lost most slowly, again conforming to a 2-compartment model; its retention half time was about 25 d in the slowly exchanging pool. Bacterial activity did not appear to have an effect on metal retention in the fecal pellets. The retention efficiencies suggest that Cd, Zn, and Hg should be recycled by copepods in surface waters as part of the organic cycle in the sea, while the transuranic elements should be defecated and removed from surface waters by sinking biogemc debris.

ABSTRACT:We describe comparative studies, using double-radiolabelling techniques, on the uptake and retention of cobalt species in a simple marine food chain which includes phytoplankton (Dunaliella tertiolecta and Chaetoceros pseudocurviseturn), mixed copepods (mainly Centropages sp.), and fish (the sea perch Serranus scnba). Retention of cobalt from the diet was also studied for the latter 2 organisms. Phytoplankton accumulated more than 60 times as much Co-cobalarnine as CoC12 from the water, and retained the metal for a significantly longer period (a retention half-time of 4.4 vs 0.6 d). Accumulation of CoC12 after ingestion of radiolabelled phytoplankton by copepods was not measurable, whereas retention of Co-cobalamine reached 42 % of the quantities ingested. Fish accumulated Co-cobalamine 21 times more rapidly from seawater than CoClz and retained ingested Co-cobalamine 20 times more efficiently (100 %) than ingested CoC12 (5 %). Two thirds of the ingested Co-cobalamine was retained in the fish with a retenhon half-time of 8 d. The remaining one third of the organic form was retained with a half-time of 54 d, a value which was not significantly different from that of CoClz (47 d). The results of other experiments indicated that the Co-cobalamine complex was stable in freshwater and in both 0.22 and 10 &m filtered seawater for at least several weeks. Potential size effects on cobalt intake in the diet are discussed, as are size effects on long-term loss rates of the metal. The application of the measured parameters in a simple biokinetic model shows that preferential accumulation of the Co-cobalamine con~plex over inorganic cobalt species In the food web could explain the cobalt concentrations measured in marine organisms.