Fate and risks of potentially toxic elements associated with lacustrine groundwater discharge: quantification, modeling, and biogeochemistry

Abstract

• PTE fluxes and fate in lake were quantified using source model and 222 Rn mass balance model. • PTEs correlate with microbial functions, with reduced direct effects in groundwater. • Mineral dissolution, human inputs and redox environment-controlled the sources of PTE. • Lacustrine groundwater discharge and biogeochemical process affected PTE behavior. • PTE in over a half of samples posed human health risks to all populations. 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. Thus, self-organizing maps (SOM) and positive matrix factorization (PMF) were employed in present work to decipher source of selected PTE (Li, V, Mn, Cr, Co, Ni, Cu, Zn, Ba, Pb, U, Sr) in Ulansuhai Lake basin (Inner Mongolia, China). On this basis, multi-isotopic tracers (δD/δ 18 O water , 87 Sr/ 86 Sr, δ 34 S/δ 18 O sulfate , 222 Rn) were used to indicate the geochemical processes related to PTE enrichment and fate. Groundwater exhibited higher PTE concentrations than surface waters, with Mn levels 230-fold higher (0.575 vs. 0.003 mg/L), while Cr, Ni, Zn, and Ba showed 2-, 2.2-, 3-, and 1.5-fold increases, respectively. 68 samples were grouped to four clusters (C1-C4) and characterized by a hazard gradient of 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/m 2 /d) and Sr (8.63 ± 0.23 mg/m 2 /d), substantially influenced lake water quality. Microbial analysis revealed higher diversity (ace index = 1751 ± 577) in groundwater, while surface water PTE had a more pronounced impact on microbial functionality than groundwater ( p < 0.001). Health risk assessment demonstrated elevated hazards in PTE contaminated groundwater, posing higher non-carcinogenic (non-carcinogenic risk-HI: 1.43 vs 1.25) and carcinogenic risks (carcinogenic risk assessment-CR: 0.005 vs 0.003) than surface water, with children being more vulnerable (5, 8 and 7 cases per 1000 children were found at carcinogenic risk). This multi-method investigation elucidates LGD-driven PTE cycling fluxes and mechanisms, providing critical insights for groundwater-lake management.

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