Nano-geo interfaces in urinary stone formation: linking drinking water geochemistry to calcium oxalate...

Drinking water geochemistry is recognized as an important environmental factor influencing urinary stone formation, yet the underlying mechanisms remain unclear. This study aims to explore the relationship between the geochemical characteristics of drinking water and the urinary microenvironment, and their impact on calcium oxalate crystallization dynamics. Urine samples were collected from 30 recurrent calcium oxalate stone formers and 30 age- and sex-matched healthy controls, along with drinking water samples from their respective residential areas, which were analyzed for major ions and trace metals.The results revealed that compared to controls, drinking water from stone formers exhibited significantly higher total hardness (295.0 ± 40.1 mg/L vs. 75.0 ± 30.2 mg/L, p < 0.01), higher calcium concentration (25.3 ± 5.6 mg/L vs. 18.4 ± 4.1 mg/L, p < 0.001), and higher electrical conductivity (375.2 ± 40.1 µS/cm vs. 320.4 ± 30.2 µS/cm, p < 0.05). In contrast, magnesium concentration was significantly lower in stone formers (15.0 ± 3.2 mg/L vs. 20.0 ± 2.5 mg/L, p < 0.01). These differences were associated with a significantly shortened calcium oxalate nucleation induction time in stone formers (95 ± 12 min vs. 120 ± 15 min, p < 0.01) and promoted crystal aggregation. Urine from stone formers showed elevated calcium (2.50 ± 0.15 mmol/L vs. 1.40 ± 0.10 mmol/L) and oxalate (0.25 ± 0.03 mmol/L vs. 0.13 ± 0.02 mmol/L), reduced citrate (1.00 ± 0.10 mmol/L vs. 1.65 ± 0.10 mmol/L) and magnesium (1.35 ± 0.10 mmol/L vs. 1.85 ± 0.10 mmol/L), and lower pH (6.8 ± 0.2 vs. 7.2 ± 0.3), collectively increasing calcium oxalate supersaturation and favoring crystallization.By examining crystallization kinetics and crystal aggregation behavior, we found that water geochemistry influences calcium oxalate crystallization by reshaping the urinary nano-geo interface. This study provides new insights into the environmental geochemical mechanisms driving kidney stone formation and highlights the importance of nano-geochemistry in environmental health research.