Retention of Mercury Sulfide Nanoparticles in Natural Soils

Growing evidence has indicated that mercury sulfide nanoparticles (HgS NPs) are the potential precursors for neurotoxic methylmercury. But how and which soil components affect HgS NP retention remains unclear. Here, we examined the retention of uncoated and humic acid coated HgS NPs in 18 natural soils with varied properties. Our results suggested that the K_r values (retention coefficients) for uncoated and humic acid HgS NPs were 2.46 × 10³ to 8.32 × 10⁵ L kg^{- 1} and 3.00 × 10³ to 2.73 × 10⁵ L kg^- 1, respectively. Soil properties (i.e., electrical conductivity, organic matter (OM), oxalate-extractable Fe and Mn) significantly affected the uncoated HgS NP retention, accounting for 69% of the variability in the K_r values. Meanwhile, OM exhibited a tendency to reduce coated HgS NP retention. Importantly, HgS NPs exhibited significant dissolution in representative soil porewaters. These findings highlight the soil property-dependent retention of HgS NPs in realistic environment.