Vegetation-Associated Mercury Patterns and Biogeochemical Signals in a Tropical Urban Mining Region

Abstract

Abstract To evaluate vegetation-associated mercury (Hg) loading in tropical regions affected by artisanal and small-scale gold mining (ASGM), we quantified total mercury (HgT) in canopy leaves and leaf litter of Licania tomentosa across an ASGM-impacted urban center, Peixoto de Azevedo (PEI), and two lower-exposure reference sites: Nova Santa Helena (ASH) and a native forest fragment (ANM). Canopy leaves reached up to 543 μg kg–1 near gold-buying shops, with probabilistic modeling identifying a high-concentration subpopulation extending to 607 μg kg–1. Leaf litter consistently exhibited higher HgT than paired canopy leaves (RatioC = 1.39–4.70; mean = 3.15), indicating relative enrichment during senescence. Spatial interpolation suggested sharply localized vegetation-associated Hg hotspots within ∼300 m of gold-trading units, superimposed on a heterogeneous urban baseline. The regional baseline was defined using ASH, where HgT concentrations ranged from 6.82 to 35.31 μg kg–1 after excluding a single transport-related outlier. These results demonstrate that gold-trading corridors are plausible localized contributors to elevated HgT in urban vegetation and may produce Hg-enriched biomass that can enter municipal waste streams. This framework provides a high-resolution, low-cost approach for Hg surveillance in tropical ASGM regions and offers chemically grounded insight into vegetation-associated Hg patterns and biogeochemical partitioning in urban environments.