Mineralogy and geochemistry of herbalist's clays for internal use: simulation of the digestive process

Abstract

The laboratory simulation of the digestive process has been carried out considering 14 different herbalist's clays for internal use found on the Italian market. The digestion has approximately used a two-stage experiment: the first one involving acidic solutions (matching the stomach environment), the other one reproducing bile–pancreas juices. The clay composition of a few samples is rather selected (mainly kaolinite and illite) and several are poly-mineralic clays, mainly with phyllosilicates, calcite, dolomite and quartz. One effect of the clay digestion is the dissolution of carbonates, developing a complete transfer of Ca and Mg from the solid to the digestive solutions and an increase of the pH values. The relationship between carbonates and pH can be obtained considering the buffer exerted by carbonates, which results in a bimodal distribution of pH, from about 1 to 3 and from about 5 to 6. The concentration of several chemical elements occurring into the final digestive solution is pH-dependent (the lower the pH, the higher the concentration; for example Al, P, Be, Sc, V, Fe, Cu, Zn, Ga, Ba, La, Nb, REE); on the other hand, chemical elements hosted into carbonates (for example Ca, Sr, Mg) are larger in higher pH solutions. To verify possible hazardous effects on human health, the chemical element concentration into the final solution has been compared to the maximum daily dose available from the drinking water regulation. Among elements not hosted into the carbonates, Al relatively shows high concentration, which can be justified by the occurrence of abundant clay minerals into the solids. Since the toxic effects of Al have been recently stressed, the silicate mineral digestion (and clays in particular) should be considered with caution, especially if the clay is carbonate-free. In this case, the pH stays at low values, increasing the Al solubility. Other hazardous chemical elements reach rather low levels, except for Ba, which is considered very toxic in soluble form. Additional precautionary advice arise from the recognition of serpentine minerals and free silica, due to the relationship between these minerals and human pathologies. Taking into account that hazardous chemical elements have been detected with solutions and that mineralogical risk is far from being excluded, it appears that a regulation will be necessary, if we consider the natural remedy market growing.