Fate and Risks of Potentially Toxic Elements Associated with Lacustrine Groundwater Discharge: Quantification, Modeling, and Biogeochemistry

Abstract

While potentially toxic elements (PTE) in lake have been widely studied, their enrichment, fate and health risks associated with lacustrine groundwater discharge (LGD) remain poorly understood. This study integrated isotopic tracers (δD/δ18Owater, 87Sr/86Sr, δ34S/δ18Osulfate, 222Rn) and source modeling to assess selected PTE (Li, V, Mn, Cr, Co, Ni, Cu, Zn, Ba, Pb, U, Sr) behavior in Ulansuhai Lake basin (Inner Mongolia, China). Groundwater exhibited markedly higher PTE concentrations than surface water, with Mn levels 230 times higher. Four hydrochemical clusters established a hazard gradient (C4 > C3 > C1 > C2). Quantitative source apportionment identified evaporite dissolution (46.2%) as the dominant PTE contributor, followed by industrial (23.1%) and redox processes (23.9%), with minor agricultural inputs (6.8%). LGD-mediated fluxes, particularly Mn (1.71 ± 0.05 mg/m2/d) and Sr (8.63 ± 0.23 mg/m2/d), substantially influenced lake water quality. Microbial diversity was higher in groundwater, yet surface water PTE exerted stronger functional stress (p < 0.001). Health risks from contaminated groundwater exceeded surface water hazards, with children disproportionately affected (5, 8 and 7 cases per 1000 children were found at carcinogenic risk). This multi-method investigation elucidates LGD-driven PTE cycling fluxes and enrichment mechanisms, providing critical insights for groundwater-lake management.

Keywords: Potentially toxic elements, Environmental isotopes, Positive matrix factorization model, 222Rn mass balance model, Lacustrine groundwater discharge