Uptake of Hg(II) and methylmercury by the green mussel Perna viridis under different organic carbon conditions

Abstract

The bioavailability and toxicity of mercury to aquatic organisms are greatly dependent on its chemical species, such as inorganic and methylated mercury. We examined the influences of various physico-chemical parameters (metal concentration, salinity, dissolved organic carbon (DOC) and colloidal organic carbon (COC) on the bioavailability of inorganic mercury (Hg(II)) and mono- methylmercury (MeHg) to the green mussel Perna viridis. The uptake rate constant of MeHg was about 8.5x higher than that of Hg(II). The uptake increased by 75% for Hg(II) and 117% for MeHg with decreasing salinity from 30 psu to 15 psu. Biogenic DOC derived from diatom decomposition decreased the uptake of Hg(II), consistent with the results of DOC originating from natural seawater. In contrast, the uptake of Hg(II) was enhanced considerably in the presence of humic acid. The bioavailability of MeHg was only weakly influenced by differences in DOC quality or quantity, but it was significantly decreased by estuarine DOC. The influence of COC on Hg bioavailability was also dependent on the colloidal structural properties and the colloid-metal complexation. Binding with colloidal nanoparticles increased the uptake of Hg(II) by 3.3 to 7.3 times compared to low molecular weight-complexed Hg, but decreased the uptake of MeHg by 42 to 73%. For both Hg(II) and MeHg, the uptake of the 9 d aged radiolabeled metals was lower than the uptake of the 2 d aged radiola- beled forms. Our study suggests that various mechanisms, such as facilitated transport and direct col- loidal ingestion, are involved in the uptake of Hg(II) and MeHg under different dissolved and col- loidal organic carbon conditions. COC and DOC need to be separately considered, given their different influences on mercury uptake.