Biokinetics of zinc and cadmium accumulation and depuration at different stages in the life cycle of the cuttlefish Sepia officinalis

Bioaccumulation of Zn-65 and Cd-109 by the cuttlefish Sepia officinalis L. was studied at different stages of its life cycle, i.e. in embryos, juveniles and adults, following exposures via sea water, sediments and food. Cuttlefish eggs efficiently accumulated both elements from seawater with bioconcentration factors of 79 for Zn-65 and 46 for Cd-109 after 11 d exposure. Most of the radiotracers were found in the capsule membrane of the eggs, demonstrating that the capsule acts as a shield to protect embryos against metals. Juveniles and adults efficiently bioconcentrated both radiotracers from seawater, with the muscular tissues containing 84% of the total Zn-65 and 62% of the total Cd-109. Loss kinetics followed a single exponential function for Zn-65, while for Cd-109 loss was best described by a double exponential model. Biological half-lives for elimination were ca. 2 mo for both elements. After 29 d depuration in uncontaminated seawater, 76 to 87% of the radiotracers were found in the digestive gland. For both elements, the dissolved phase can be considered as a significant source of accumulation. In an experiment with radiolabelled sediments, transfer factors were very low, even after 29 d exposure. Food-chain transfer experiments demonstrated that both juveniles and adults assimilated Zn-65 and Cd-109 very efficiently. Moreover, loss of ingested radiotracers was much slower than elimination of Zn-65 and Cd-109 taken up from seawater, indicating a very strong retention of dietary Cd and Zn by juvenile as well as by adult cuttlefish. As with direct uptake from seawater, ingested radiotracers were mainly found in the digestive gland, with fractions reaching 82% for Zn-65 and 97% for Cd-109 after 29 d depuration. These tracer experiments indicate that (1) food is the likely primary pathway for Zn and Cd bioaccumulation in S. officinalis, and (2) the digestive gland plays a major role in the subsequent storage and presumed detoxification of these elements regardless of the uptake pathway.