Internal handling, shell accumulation and effects of cobalt on the gastropod Ampullaceana balthica

Cobalt (Co) is central to the development of new low-carbon energies, becoming an element of emerging concern for the environment. Gastropods are widely distributed in aquatic ecosystems and represent the largest group of the phylum Mollusca. However very few studies have focused on Co impacts on gastropods. We thus aimed to examine the internal handling of Co in gastropods and its excretion into the shell in order to better understand its toxic actions and how these organisms cope with Co stress. To that end, Ampullaceana balthica was exposed to increasing Co concentrations (6, 30 and 60 μg·L^-1) using outdoor flow-through mesocosms for 28 days in June and October. They were analyzed for their growth, reproduction and Co accumulation in the soft bodies and the outer shell part every week. Cobalt distribution in soft tissues and its subcellular distribution were further examined. Cobalt induced a decrease in the egg mass number and a delay in their hatching. Its accumulation in the soft tissue and the outer shell exhibited distinct seasonal patterns. Linear relationships with the ambient Co concentrations were only evident in the soft tissues in June and in the shell in October. For both periods, Co was mainly distributed in the hepatopancreas and the mantle, particularly in their mitochondria and granules fractions. We thus discussed the possible pathways of Co from the soft tissues to the shell involving granules. The present results demonstrate that using shells as bioindicators of metal exposure has certain limitations, depending on the organism life cycle.