Heavy elements in urinary stones

The presence and role of heavy metals in urinary stones is debated. We investigated the distribution of trace heavy metals in 78 calculi of well-defined composition by means of microfluorescence X analysis using synchrotron radiation. Seven elements were identified, the most abundant being Zn and Sr which together accounted for 91% of the heavy metal content of stones. The other heavy metals were Fe, Cu, Rb, Pb and Se. Zn and Sr were virtually confined to calcium-containing stones, whereas only trace amounts were found in uric acid or cystine stones. Among calcium stones, Zn and Sr were more abundant in calcium phosphate than in calcium oxalate stones and, in the latter, in weddellite than in whewellite stones. Fe, Cu and Rb were much less abundant and also found mainly in calcium stones. Pb was significantly less abundant than in previous studies, thus suggesting a rarefaction of Pb in the environment, and appreciable amounts of Se were found only in cystine stones. In conclusion, the preponderance of Zn and Sr, both bivalent ions, in calcium-containing stones suggests a substitution process of calcium by metal ions with similar charge and radius rather than a contribution of the metals to stone formation. Further studies are needed to examine the relationships between urine concentration in calcium or other solutes and the amount of Zn and Sr in calcium stones.