New insights into the metal partitioning in different microphases of human gallstones

Abstract

Chronic metal exposure, e.g. from metal mining, may cause accumulation of metals in soft and hard tissues, and in developing biomineralizations in the human body. Gallstones are biomineralizations formed in the gallbladder which are able to trap trace elements from the bile. Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) was used to analyze gallstone cross-sections to trace the elemental abundances and correlate them with the principal phases constituting gallstones, namely cholesterol, Ca bilirubinate salts, Ca carbonate, and Ca phosphate. Five different types of gallstones (pure, mixed, and composite cholesterol stones, pigment stone, and carbonate stone) were chosen according to a previous classification based on phase characterization by different spectroscopic and microscopic techniques. These data were combined with bulk solution ICP-MS/OES analyses for total elemental concentrations. The results indicated that cholesterol has a zero capacity to retain elements except for Ca. Hence, pure cholesterol stones contained the lowest bulk metal concentrations, and the metals were found in the scarce carbonate and phosphate phases in these calculi. Calcium and trace element concentrations increased in other types of gallstones along with increasing amount of bilirubinate, carbonates and phosphates; pigment stones being the most enriched in metals. Phosphates were the principal carriers of Ca, P, Na, Mg, Mn, Fe, Pb, and Cd, whereas carbonate phases were enriched in Ca, Mg, Na, and Mn in order of decreasing abundance. Bilirubinate on the other hand was enriched in Ca, Cu, Ag, and Ni. The higher trace metal affinities of bilirubinate and phosphate explain the elevated metal concentrations observed in the pigment stones. These results give new insight to the trace metal behavior in the gallstone formation and the metal accumulation in the human body, validating the possible use of these biomineralizations as a proxy for exposure to metal pollution.