Bioconcentration as a key driver of Hg bioaccumulation in high trophic level fish
Abstract. The ability of monomethylmercury (MMHg+) to bioaccumulate in seafood is of concern due to its neurotoxic properties. Understanding the bioaccumulation of MMHg+ is challenging because the MMHg+ content at higher trophic levels depends on both bioconcentration and biomagnification. Furthermore, Hg can occur in several chemical species, including Hg2+ and MMHg+, which both bioaccumulate. Although the dominant pathway for MMHg+ bioaccumulation into seafood is the bioconcentration of MMHg+ in primary producers and the subsequent biomagnification to higher trophic levels, other pathways can contribute to MMHg+ bioaccumulation. In this study, we quantify the importance of the bioaccumulation of Hg2+ and the bioconcentration of MMHg+ in higher trophic levels in the bioaccumulation of MMHg+ in high trophic level fish by running a fully coupled 1D water column Hg bioaccumulation model under 3 hydrodynamic regimes typical for the North and Baltic Seas. We find that Hg2+ bioaccumulation does not influence the bioaccumulation of MMHg+ but the bioconcentration of MMHg+ plays an important role. Although direct bioconcentration accounts for < 15 % of MMHg+ bioaccumulation in cod, the cumulative effect of bioconcentration on all trophic levels increases the MMHg+ content of cod by 28–48 %. We show that up to the highest trophic level modeled (TL = 3.7), the percentage of MMHg+ that originates from consumer bioconcentration increases with an average of 15 % per trophic level. These results demonstrate that bioconcentration in consumers is essential to accurately model the bioaccumulation of MMHg+ at higher trophic levels.