Mercury in chemical fractions of recent pelagic sediments of the sea of Japan

Abstract

The distribution of mercury (Hg) in chemical fractions (H₂O, 0.05 M Na₂-EDTA pH 3, 1 M HCl, humic and fulvic acids, and non-hydrolysing residue) of recent pelagic sediment cores of the Sea of Japan (East Sea) was studied. Total Hg content in the sediments was rather low: 83 ± 30 (21–173) ηg g⁻¹, indicating the absence of substantial specific sources of the element in the deep part of the sea. Hg content within the sediment core varied by a factor of 1.3–1.8, showing peaks that coincide with the near-surface and buried sediment slices of light brown and brown “oxidized” colours and evidencing Hg redox-sensitive diagenetic redistribution. Hg exerted its maximum mobility in the near-surface sediment strata as a component of water-soluble organic matter. Despite the predominance of fulvic acids in extracted humus fractions, humic acids were a much more efficient concentrator for Hg (0–79 vs. 188–233 µg Hg g⁻¹ C_org, respectively). Nevertheless, the most refractory non-hydrolyzing residue (humin) fraction contained the principal Hg pool in the sediments. Hg content in all the extracted fractions decreased with core depth, thus indicating Hg immobilization as a principal tendency in Hg fate during post-depositional diagenesis.