Impacts of Sediment Particle Grain Size and Mercury Speciation on Mercury Bioavailability Potential

Particle-specific properties, including size and chemical speciation, affect the reactivity of mercury (Hg) in natural systems (e.g., dissolution or methylation). Here, terrestrial, river, and marine sediments were size-fractionated and characterized to correlate particle-specific properties of Hg-bearing solids with their bioavailability potential and measured biomethylation. Marine sediments contained similar to 20-50% of the total Hg in the <0.5 mu m size fraction, compared to only 0.5 and 3.0% in this size fraction for terrestrial and river sediments, respectively. X-ray absorption spectroscopy (XAS) analysis indicated that metacinnabar (beta-HgS) was the main mercury species in a marine sediment, whereas organic Hg-thiol (Hg(SR)(2)) was the main mercury species in a terrestrial sediment. Single-particle inductively coupled plasma time-of-flight mass spectrometry analysis of the marine sediment suggests that half of the Hg in the <0.5 mu m size fraction existed as individual nanoparticles, which were beta-HgS based on XAS analyses. Glutathione-extractable mercury was higher for samples containing Hg(SR)(2) species than beta-HgS species and correlated well with the amount of Hg biomethylation. This particle-scale understanding of how Hg speciation and particle size affect mercury bioavailability potential helps explain the heterogeneity in Hg methylation in natural sediments.

Automated summary

The study found that marine sediments contained 20-50% of total Hg in the <0.5 µm size fraction, while terrestrial and river sediments only contained 0.5-3.0% in this fraction. X-ray absorption spectroscopy revealed that metacinnabar (beta-HgS) was the main mercury species in marine sediment, while organic Hg-thiol (Hg(SR)(2)) was predominant in terrestrial sediment. Single-particle inductively coupled plasma time-of-flight mass spectrometry analysis indicated that half of the Hg in the <0.5 µm size fraction of marine sediment existed as individual nanoparticles.