Cadmium bioaccumulation and distribution in the freshwater bivalve Anodonta woodiana exposed to environmentally relevant Cd levels.

Anodonta woodiana is a globally distributed freshwater bivalve, which is a unique bioindicator in the "Freshwater Mussel Watch" project. Numerous countries have used A. woodiana for biomonitoring the aqueous cadmium (Cd) contamination. However, the bioaccumulation and distribution characteristics of environmentally relevant Cd concentrations in the bivalve were unknown. In this study, A. woodiana was exposed to aqueous Cd concentrations (1.1, 2.6, and 5.5 μg/L) for 30 days. The concentrations of Cd in the whole soft tissues were linearly and positively correlated with the aqueous Cd concentrations and exposure time (P < 0.05). Analysis of the organic bioaccumulation and distribution showed that Cd concentrations and proportions in the gills and mantle were linearly and positively correlated with aqueous Cd concentrations and with the Cd concentrations in the whole soft tissues (P < 0.05). Analyses of the subcellular fractions showed that Cd concentrations and proportions in the metal-rich granule (MRG) were linearly and positively correlated with aqueous Cd concentrations and with the Cd concentrations in the whole soft tissues (P < 0.05). This suggests that the gills and mantle could be the main target organs for Cd bioaccumulation, and that the MRG could be the major site for Cd bioaccumulation and distribution. These results improve our understanding of the bioaccumulation and distribution mechanisms of Cd in bivalves.