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Abstract
<p class="first" id="P1">The largest bioconcentration step of most metals, including
methylmercury (MeHg),
in aquatic biota is from water to phytoplankton, but the extent to which dissolved
organic matter (DOM) affects this process for MeHg largely remains unexplored in marine
systems. This study investigated the influence of specific sulfur-containing organic
compounds and naturally occurring DOM on the accumulation of MeHg in a marine diatom
<i>Thalassiosira pseudonana</i>. Initial uptake rate constants and volume concentration
factors (VCFs) of MeHg were
calculated to evaluate MeHg enrichment in algal cells in the presence of a range of
organic compound concentrations. At environmentally realistic and higher concentrations,
the addition of glycine and methionine had no effect on algal MeHg uptake, but thiol-containing
compounds such as cysteine and thioglycolic acid reduced MeHg accumulation in algal
cells at high added concentrations (> 100 times higher than naturally occurring
concentrations).
However, environmentally realistic concentrations of glutathione, another thiol-containing
compound as low as 10 nM, resulted in a decline of ~ 30% in VCFs, suggesting its possible
importance in natural waters. Humic acid additions of 0.1 and 0.5 mg C/L also reduced
MeHg VCFs by ~ 15% and ~ 25%, respectively. The bioaccumulation of MeHg for
<i>T. pseudonana</i> in coastal waters with varying levels of dissolved organic carbon
(DOC) was inversely
correlated with bulk DOC concentrations. Generally, naturally occurring DOM, particularly
certain thiol-containing compounds, can reduce MeHg uptake by phytoplankton.
</p>