Investigation of Ag in the king scallop Pecten maximus using field and laboratory approaches

22 23 The bioaccumulation, tissue and subcellular distributions of Ag were investigated in the 24 king scallop Pecten maximus from the Bay of Seine fishery area (France) in laboratory and in 25 field conditions. Experimental investigations with the radiotracer Ag showed that the 26 scallop readily concentrated Ag when exposed via seawater and to a much lower extent when 27 exposed via sediment. Retention of the metal incorporated via all tested contamination 28 pathways was shown to be very strong, but the assimilation efficiency of Ag ingested with 29 food was found to be tightly depending on the phytoplankton strain used to feed the scallops 30 (74 and 33% with Skeletonema costatum and Isochrysis galbana, respectively). The uptake 31 and depuration kinetic parameters determined in the laboratory experiments were used to run 32 a global bioaccumulation model. The latter indicated that the major uptake pathway of Ag in 33 P. maximus was strongly depending on the food quality. Indeed, when fed the diatom S. 34 costatum which was characterised by a high affinity for Ag (high distribution constant Kdf) 35 the relative contribution of the feeding pathway reached 98% of the global Ag 36 bioaccumulation. In contrast, when fed I. galbana which displayed a lower Kdf than S. 37 costatum, dietary Ag was retained to a lesser extent by P. maximus, and seawater appeared as 38 the major contributing uptake pathway. In wild scallops collected from reference and 39 contaminated sites, Ag was mainly concentrated in the digestive gland and secondarily in the 40 gills, and was mainly found associated with the insoluble subcellular fraction in all the scallop 41 tissues. 42 43