Temporal variation of mercury and methyl mercury in water and accumulation by phytoplankton in the eutrophic estuary, northern Taiwan

Three surveys were carried out to study the phytoplankton role in influencing the Hg distribution in a poorly eutrophic estuary by measuring the total Hg (THg) and methylHg (MeHg) concentrations in waters and four-size fractions of phytoplankton. The THg and MeHg concentrations in waters and phytoplankton varied markedly temporal during the three surveys. The total concentrations of THg and MeHg in the four-size fractions of phytoplankton ranged between 0.62 and 28.15 mg/kg and 0.022–4.411 mg/kg, respectively. The dominance of THg and MeHg phytoplankton concentrations differed from different size fractions and varied with the various surveys. The huge uptake of Hg by abundant phytoplankton decreased both Hg concentrations in waters and phytoplankton, which was attributed to the biomass dilution effect during the July survey. The Hg partition between water and phytoplankton provided substantial evidence to illustrate the huge uptake of Hg by the abundant phytoplankton. •The total Hg and MeHg concentrations in phytoplankton of the estuary were mg/kg level.•The Hg partition reflects huge uptake of dissolved Hg by phytoplankton.•The Hg and MeHg concentrations in phytoplankton varied with different size fractions.•The BCF values of Hg and MeHg of phytoplankton in the estuary exceed 105 and 104.