Role of atmospheric sulfate from industrial gypsum emissions in shaping soil solution chemistry and aluminum speciation along the soil profile.

Atmospheric deposition of sulfate-rich particles derived from gypsum mining and industrial processing can significantly alter soil solution chemistry in tropical environments. This study aimed to evaluate the effects of continuous sulfate deposition on soil solution chemical speciation along the soil profile in areas influenced by a gypsum dust plume. The Grajaú gypsum production hub has maintained structured industrial activity for at least 20 years, with accelerated growth occurring between 2005 and 2015. Soil samples were collected across distinct landscape units and depths (0.0-0.2, 0.4-0.6, and 1.0-1.2 m), and soil solution chemistry was modeled using Visual MINTEQ to quantify the distribution of major ionic species. Principal component analysis (PCA) was applied to identify the dominant geochemical gradients associated with ion mobility. The results revealed a marked increase in sulfate species, particularly SO42- and AlSO4+, especially in plume-affected areas. Elevated sulfate availability was associated with the downward co-mobility of Ca2+ and Mg2+, indicating vertical redistribution driven by water fluxes. PCA identified sulfate as the primary variable governing the organization of soil solution chemistry along the soil profile. Overall, these findings demonstrate that continuous atmospheric sulfate deposition from industrial activities can induce processes analogous to those observed in soils amended with high rates of agricultural gypsum, with important implications for nutrient dynamics, aluminum availability, and the environmental quality of tropical soils.