Characterization of toxic elements in clays for human healing use

Abstract

The clay samples available in herbalist's shops, in pharmacies and a natural metal-rich clay have been studied from a mineralogical and a chemical point of view and the toxic elements present in the urine of rats fed with selected clays have been determined. The mineralogical data suggest that the pharmaceutical clay is mostly composed of smectite and organic matter, whereas the natural and the commercial herbalist clay show a more heterogenous composition containing various clay minerals, quartz, feldspars and accessories. The commercial herbalist clay contain also calcite and the natural clay sulphides. The concentration of the trace elements of the commercial herbalist clay is generally similar to crustal abundance; differences are present for Sr, Mo and Ga. The pharmaceutical clay shows an appreciable depletion of elements as Zn, V, Ga, Cr, Cd, Fe, Mo, Ni, Cu, Sb, S and Rb. Instead, the natural clay is characterised by high quantities of U, V, Cd, Mo, Tl, Ag, Ni, Cu, Sb, As, S, Se and Br, likely because of sulphide occurrence. The amount of these elements is several times higher then that of average shale. Considerable quantities of Se and As are present in the rats' urine. As and Se are always detectable, Ni, Cd, Sb and Tl show lower values, whereas Te, Pb and Hg are below the detection limits. The presence of toxic elements in the urine indicates that the absorptive processes occurs after clay ingestion, which causes a progressive increase of metals in the urine and in the blood. Despite the deep mineralogical and chemical differences among clay samples, the metal concentration in the urine is rather similar. Such behaviour can have toxicological significance, because of the increased metal levels in blood. The ingestion of unchecked clays could be hazardous.