Micro-elemental analysis and characterization of major heavy metals and trace elements in the urinary stones collected from patients living in diverse geographical regions

In the process of urinary stone formation, several heavy metals and trace elements (HMTE) have been identified among the major constituents of the calculi. The micro-elements within the stones cannot be identified by ordinary laboratory analytical techniques, the latter can only detect the major crystalline component. The objective of the present study was to evaluate the different types of HMTE (no. 22) and their concentrations within the urinary stones. The stone samples were obtained from patients living in different geographical locations (10 countries: 5 Western and 5 non-Western). The number of retrieved stones after open or endoscopic procedures was 1177. The concentrations of the 22 HMTE in the stones were assessed by inductively coupled plasma optical emission spectrometry (ICP-OES). The statistical data were analyzed using Kruskal–Wallis, one-way ANOVA, and SPSS software (version 20). The biochemical stone analysis showed that calcium oxalate was present as a major component in 650 patients (55.2%), calcium phosphate in 317 (26.9%), and uric acid and cystine stones in 210 (17.8%). The analyzed stones showed the presence of HMTE in different concentrations. Significantly higher concentrations of 17 elements (Al, As, Ba, B, Ca, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, S, Se, Sr, and Zn) were noted in all stones. Seven elements (Al, As, Se, Sr, Fe, Zn, and Ni) were present in higher concentrations in calcium-based stones. In comparison, eight elements (Mg, B, Ba, Cd, Se, Pb, Sr, and Zn) in higher concentrations were associated with phosphate-based stones. Both uric acid and cystine stones had a higher concentration of sulfur. The concentrations of HMTE in calcium phosphate stones were higher than in calcium oxalate and uric acid stones. Calculi obtained from patients living in western countries contained higher levels of 13 HMTE (B, Ba, Ca, Cd, Co, Cu, Fe, K, Mg, Mo, P, Pb, and Se) than those in non-western countries. The age of calculi-forming patients from non-western countries was younger than those living in western countries. These results may indicate the role of many significant heavy metals and trace elements in the pathogenesis of urinary stone formation. The types and contents of HMTE within urinary stones differ from one country to another. The conventional stone analysis techniques cannot either identify the stone micro-elements or the concentrations of HMTE, so a specific and additional instrument such as the ICP-OES is necessary. Further research work on the urinary stone micro-elemental structure could lead to a new strategy for the prevention of stone formation and recurrence.