TOXICITY AND TOXICOKINETICS OF CADMIUM IN CAPITELLA SP. I - RELATIVE IMPORTANCE OF WATER AND SEDIMENT AS ROUTES OF CADMIUM UPTAKE

The importance of dissolved versus sediment-bound cadmium as uptake ro utes for the deposit-feeding polychaete Capitella species I and the to xicity and toxicokinetics of cadmium from these exposure routes were i nvestigated. Effects were reported as changes in worm growth rate, ege stion rate and allometry. Radioactive cadmium (Cd-109) was used as a t racer to examine the uptake (5 d) and subsequent depuration (6 d) of c admium. Both effects and kinetics were investigated in systems with an d without sediment. Individual Capitella sp. I were exposed to (1) dis solved (i.e. <0.45 pm) cadmium (water-only treatment), (2) sediment-bo und cadmium (sediment-bound only treatment), or (3) both dissolved and sediment-bound cadmium (porewater & sediment treatment). The porewate r concentration of dissolved cadmium in porewater & sediment treatment s was set approximately equal to the dissolved concentration in water- only treatments (0, 25, 50 mu g Cd l(-1)). Worms in water-only treatme nts showed negative growth rates, which decreased linearly from -5 to -10% d(-1) with increasing cadmium concentration. Cadmium had no detec table effect on egestion rate or growth in the presence of sediment in either sediment-bound only (ca 36% d(-1)) or porewater & sediment (ca 30% d(-1)) treatments. Cadmium exposure had no detectable effect on t he allometric exponent (i.e. area-length relation) in any of the treat ments; however, worms in water-only treatments were relatively thinner than in the 2 treatments with sediment. Worms in porewater & sediment treatments took up ca 50-fold more cadmium (ca 195 ng Cd worm(-1)) th an worms in water-only treatments (3.9 ng Cd worm(-1)) during 5 d of e xposure. Sediment-bound cadmium was calculated to contribute 95 % of t he total amount taken up by feeding worms. Starving worms retained all of the cadmium during the subsequent depuration period (6 d), and exh ibited an increased weight-specific body burden (mu g Cd g(-1) dry wt worm) due to shrinkage. In feeding worms, the decrease in weight-speci fic body burden was faster (T-1/2 = 3 d) than the decrease in total bo dy burden (mu g Cd worm(-1); T-1/2 = 11 d), indicating that both activ e excretion and dilution of cadmium body burden as a result of growth contributed to the change in cadmium tissue concentration during the d epuration period. Thus, our results indicate that in Capitella sp. I s ediment-bound cadmium is the major route of uptake. We found that cadm ium affects starving but not fed worms, despite the fact that fed worm s took up considerably more cadmium than starving worms. Our results s uggest that stress associated with food limitation increases the susce ptibility of worms to cadmium stress.