Dynamic modeling of copper bioaccumulation by Mytilus edulis in the presence of humic acid aggregates

• Cu accumulation by mussels was enhanced in the presence of humic acids.
• Accumulation kinetics were different in the gills than in the rest of the tissues.
• Two-compartmental modeling of Cu bioaccumulation was performed.
• It is demonstrated that Cu-HA aggregates contribute to Cu uptake via the gut.

Copper (Cu) complexation by humic acids (HA) is expected to decrease Cu bioavailability for aquatic organisms as predicted by metal bioavailability models, such as the biotic ligand model (BLM). This has been confirmed for non-feeding organisms such as marine invertebrate embryos or microalgae, but for filter-feeding organisms such as the mussel Mytilus edulis, Cu bioaccumulation was higher in the presence of HA, suggesting that part of the Cu-HA complexes were available for uptake. This study shows the dynamic modeling of Cu accumulation kinetics in the gills and rest of the soft-body of M. edulis in the absence and presence of HA. Assuming that truly dissolved Cu is taken in the body via the gills following BLM premises, and including uptake of Cu-HA aggregates via the gut into the rest compartment, this two-compartmental model could successfully explain the observed bioaccumulation data. This modeling approach gives strong evidence to the hypothesis that Cu-HA aggregates can be ingested by mussels leading to Cu absorption in the digestive system.