Bioaccumulation of essential metals (Co, Mn and Zn) in the king scallop Pecten maximus: seawater, food and sediment exposures

In order to understand the bioaccumulation of essential metals in filter-feeding mollusks living in soft sediments, the uptake and depuration kinetics of three elements (Co, Mn and Zn) were investigated in the king scallop Pecten maximus exposed via seawater, food, or sediment, using radiotracer techniques. The scallops were collected in April 2005 in the Pertuis Breton, France and acclimated to laboratory conditions for eight weeks prior to the experimental exposures. Dissolved metals were efficiently bioconcentrated with mean concentration factors (CFs) ranging from 65 (Co) to 94 (Mn) after 7 days of exposure. Feeding experiments using microalgae Skeletonema costatum (diatom) or Isochrysis galbana (flagellate) showed that metal assimilation efficiency (AE) and retention (Tb1/2) were strongly influenced by food source. For Co, AE was higher when ingested with I. galbana (29 vs 4%), whereas Mn and Zn AE was higher for S. costatum (82 vs 44% and 86 vs 68%, respectively). Transfer Factors (TFs) in P. maximus exposed to radiolabelled sediment were 3 to 4 orders of magnitude lower than CFs. Nevertheless, the fraction of sediment-bound metals that was taken up was efficiently absorbed in scallop tissues (> 85%). Whatever the exposure pathway, metals were strongly retained in the kidneys of P. maximus. Due to poor determination of Mn biokinetics (and related parameters) in scallops exposed through sediment, the relative contribution of the three different pathways could be determined only for Co and Zn using a biodynamic model. The particulate pathway (i.e. food or sediment) appeared to be the main route for bioaccumulation of both metals in this scallop. In addition, even though P. maximus displayed different AEs for Co and Zn according to the food, results of the model were only slightly affected, if any, by change in the dietary parameters (AE and depuration rate constant, ke).