In-vitro experiments have been developed to ascertain whether pelotherapy applications involve the transfer of chemical elements from the healing mud to the human body, across the skin. All the materials used for therapy (raw clay, mineral water and healing mud obtained after maturation) have been characterised from different points of view (mineralogy, chemistry, exchange properties, radioactivity, grain size and microbiology) in order to get an accurate knowledge of the natural media used for therapy and to follow the development of maturation in the spa centre.
A polymineralic silty clay with rather a common mineralogical and chemical composition is used; the mud is matured in a very saline mineral water, of marine origin, for 5 months. Under these conditions the maturation process increases the dispersion of clay particles and allows cation exchange between clays and water, whereas neither microbiological nor mineralogical changes are detectable. In absence of the biologic indicators of mud maturity, the equilibration of clay with mineral water represents an objective quantitative criterion.
In-vitro tests have been carried out by using the Franz-type diffusion cells, which show that the transfer of chemical elements across the skin is very well-developed, and also involving many essential or possibly essential elements. The amounts of chemical elements transferred were compared with toxicological guidelines and with world-wide daily requirement models.
No concerns appear from the data, whereas a significant supply of some elements results from a typical application of thermal mud (20 min, full body). The elements which have been considered in order to represent a significant supply are Li, Sr, B, I, Rb, Br, Ba, Na, Cl, Se and Ca, some of these are essential nutrients. The biological effects of the main elements are briefly discussed.