Differential bioaccumulation behaviour of Ag and Cd during the early development of the cuttlefish Sepia officinalis

Abstract

Cuttlefish eggs were exposed to background concentrations of dissolved Ag and Cd, using the radiotracers 110mAg and 109Cd. At different time of the embryonic development (50 days), some eggs were placed in non-contaminating conditions. During the experiment, the uptake and depuration kinetics, and distribution of these metals among the egg compartments (i.e. eggshell, vitellus, peri-vitelline fluid and embryo) were assessed. In parallel, experiments were conducted with sub-lethal concentrations of stable Ag and Cd (2 and 1 μg l −1, respectively) to compare the metal behaviour at higher concentrations. From the spawning date up to 1 month of development, both metals were taken up efficiently by the eggs, reaching load/concentration ratio (LCR) of 1059 ± 75 and 239 ± 22 for 110mAg and 109Cd, respectively. From this time onwards, 110mAg activity continued to increase in eggs, whereas 109Cd kinetics displayed a significant decrease. Whatever the developmental stage, Cd was mainly associated with the eggshell all along the exposure experiment. In addition, both stable Cd concentrations and 109Cd LCR remained low in the embryo all along the embryonic development, indicating that the eggshell acted as an efficient shield against the penetration of this metal. In contrast, 110mAg passed through the eggshell from day 30 onwards and was then accumulated in the embryo, which contained more than 40% of the whole egg metal burden at the end of the exposure period. In depuration conditions, it is noteworthy that Ag continued to accumulate in the embryo indicating translocation processes from the eggshell and a high affinity of the metal for the embryo tissues. Overall our results showed that at day 30 of the embryonic development the cuttlefish eggshell becomes permeable to Ag but not to Cd. Exposure to stable metals confirmed the saturation capacities of the eggshell for Cd and the Ag penetration properties.