Bivalves have long been used as a bioindicator to assess environmental mercury (Hg) pollution and its potential impacts on ecosystems and human health.However, the mechanisms underlying sediment-water Hg accumulation in bivalves and how they vary with environmental conditions are not yet fully understood.This study investigated the effect of environmental variation on sedimentwater Hg accumulation in bivalves, using Hg stable isotope analysis ( 202 Hg, 199 Hg) and sediment sequential extraction methods (weak acid-soluble, organic-bound, and residual fractions).Asian clams, collected from an uncontaminated area of the Hyeongsan River in Pohang city (sediment THg: 0.025 0.004 mg/kg), were transplanted to the upstream region of the Nakdong River in Bonghwa city, Korea (sediment THg: 0.41 0.05 mg/kg) for a two-month period (clam 0-day 202 Hg: -0.63 0.01, 199 Hg: 0.35 0.02).During the early phase of in situ experiment, when rainfall and suspended particle concentrations were high, the clam Hg isotopes (14-day 202 Hg: -0.61 0.06, 199 Hg: 0.10 0.04) turned over toward the values of sediment ( 199 Hg: 0.02 0.01).The THg concentration in the clams increased by a factor of 2.4 compared to day 0. Weak acid-soluble Hg ( 202 Hg: -0.62 0.01) or organic-bound Hg ( 202 Hg: -0.64 0.03) in sediment may have been preferentially accumulated in the clams.During the later phase of in situ experiment, when rainfall and suspended particle concentrations were lower, the clam Hg isotopes (58-day 199 Hg: 0.16 0.07) were more similar to those of the water column ( 199 Hg: 0.13 0.02).At this point, the clam THg concentration decreased moderately and remained 1.1-fold higher than day 0.This study demonstrates that bivalves are sensitive to environmental changes, which modulate sources, cycling, and fate of Hg bioaccumulation, and suggests that Hg stable isotopes are an effective tool for monitoring these processes.
Kim et al. (2026) studied this question.