Fig. 7: Conceptual framework for sulfate (SO₄^2‒) and dissolved organic matter (DOM) effects on methylmercury (MeHg) risk in subtropical wetlands.

Low risk is observed at high (~>15 mg/L) and low (<1 mg/L) SO₄^2‒ that facilitate unfavorable conditions for MeHg formation, due to geochemical bioavailability of Hg(II), wetland redox status, and hgcAB abundance of microbial community¹⁹. High risk is observed at intermediate SO₄^2‒ (2–12 mg/L) that facilitates a suitable redox status, Hg(II) bioavailability (due to DOM aromaticity^36,40 and thiol content)^34,41, and hgcAB abundance¹⁹ that collectively promote MeHg formation in proximity to the aquatic food web.