The Euganean thermal district (NE Italy) represents a unique reference for therapies based on the topical use of clay materials matured in thermal waters (pelotherapy, mud therapy, mud-pack therapy): approximately one hundred therapeutic spa centers are concentrated within a small area and share the same virgin clays and the same hypersaline hyperthermal groundwater. The therapeutic mud produced in this district is therefore an ideal test bench for assessing the application of scientific procedures aimed to check and improve the quality of spa products. The measurement of chlorophyll a content was previously suggested as a reliable, easy to acquire, economic and reproducible indicator of the "maturation" process; the new data acquired (>650 samples across two years), associated with mineralogical and geochemical data on approximately 30 therapeutic centers, show instead a more complex and different result. By comparing the analytical data of virgin clays (Della Costa lake sediments), therapeutic mud and mud stored excluding photosynthetic activity, chlorophyll a and its derivatives can be considered better indicators of maturation and recycling procedures than the proliferation of photosynthetic microorganisms in maturation ponds. Some mineralogical and geochemical parameters, as well as the content of chlorophyll a and its derivatives, proved to be distinctive of the virgin clays and therapeutic mud; the latter shows gradual variations, in agreement with progressive departure from pristine composition after repeated use and recycling of the therapeutic mud. Minerals and chemical elements concentrated in the fine-grained fractions (such as illite, kaolinite and Rb, among others) are mechanically depleted compared to virgin clays, whereas for pyrite and organic components (including chlorophyll a and its derivatives), spontaneous degradation can be considered. The rather high frequency of sampling (approximately 1 sample/month) over a long time period (two years) also enabled us to learn that the concentration of chlorophyll a and its derivatives is unique to different therapeutic centers: a few of them show dispersed values and are difficult to fit into a linear trend, whereas in several cases the low dispersion points to a reference value of the center and, in this instance, the degradation rate also turns out to be a characterizing feature of the center. Mineralogical and chemical parameters that discriminate virgin clays and therapeutic mud can be therefore used to monitor the maturation procedures. In addition, for chlorophyll a and its derivatives a double effect can be observed: i) spontaneous degradation with the same rate of mud deprived of possible photosynthetic effects, and ii) possible attenuation or balance of decay after appropriate management of the recycling and replenishment of mud.
