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A. Quintela, GeoBioTec Research Unit (Portugal)
S. F. P. Almeida, GeoBioTec Research Unit (Portugal)
F. Rocha, GeoBioTec Research Unit (Portugal)
E. Ferreira da Silva, GeoBioTec Research Unit (Portugal)
V. Forjaz, GeoBioTec Research Unit (Portugal)
D. Terroso, GeoBioTec Research Unit (Portugal)
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Azores Archipelago (Portugal) sits astride the Mid-Atlantic Ridge and is composed by nine volcanic islands, one of them, S. Miguel Island.
Vale das Furnas, in S. Miguel Island, is a particular case of a very restricted area where small ponds and rock cavities can be found with hot whitish smokes being emitted and profuse bubbling coming out from the hot mud that fill those ponds. Numerous thermal and mineral springs located in active volcanic regions frequently developed as spas, improving social and economic well-being.
The empirical application of muds for therapeutic purposes is known all over the world. This is called pelotherapy and consists in the local or generalized application of a mixture of a solid phase and a liquid phase (thermal mud) for recovering rheumatism, arthritis, bone- muscle traumatic damages and psoríasis. During the time of mixture (maturation process) the mud is progressively colonized by thermophilic microorganisms. Several studies report the diatoms as the main agent of thermal muds, capable of producing anti-inflammatory sulfoglycolipid which renders the mud the suitable use. The effect of the temperature is also considered important for therapeutic purposes.
Recent studies assessed physical, chemical and technological properties of S. Miguel Island mud samples. They were considered suitable for pelotherapy application when involved in cloths; however for topical application they should be beneficiated in order to improve some technological properties.
S. Miguel mud samples have high temperature and are "in situ" naturally matured. The aim of this investigation is to characterize diatom communities of these muds for topical application due to their role on therapeutic properties already recognised.
Four mud samples (8B, 16, 19 and 23) were collected in April and November 2007. These samples reveal very low pH (<3) and high temperature (>70°C). Samples were stored in dark glass bottles and preserved with formalin (8%). Samples were cleaned using HNO3 for 24 hours at room temperature and diatom slides were mounted with Naphrax for light microscopy observation. Metal stubs were prepared for SEM studies for identification. Diatom identification was based on Floras commonly used for Freshwater diatom studies. When present, the dominant diatom taxa were: Pinnularia cf. subgibba Kram., Achnanthes lanceolata (Bréb.) Grunow and Nitzschia hantzschiana Rabenh. (sample 16); Gomphonema cf. pumilum (Grunow) Reich. & Lange-Bert., Nitzschia cf. thermalis var. minor Hilse, Pinnularia cf. acoricola Hust. and Cocconeis placentula Ehrenb. (sample 19). Several studies report the presence of these genera in acidic environments while Pinnularia Ehrenb. and Nitzschia Hass. were also found in hot springs. There was a decrease in diversity from Spring to Autumn samples.
This study in volcanic muds from S. Miguel Island provides new data on diatoms from extreme environments and their application for therapeutic purposes.
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