Italy and Sicily

Low pH environments

Acidity develops from the oxidation, either spontaneous or by action of chemiotrophic bacteria, of sulphur and sulphides to sulphuric acid (Brock , 1978). In Italy three main low pH environments can be found:

1) Sulphur mines
The geological formation of Messinian age, called "gessoso solfifera" is typical of Sicily. This formation is characterized by large amounts of gypsum, potassium salts, sodium chlorates and other compounds. Sulfur can be present at the surface of this formation, where is oxidized to sulphuric acid.
In almost all the sites the soils surrounding the springs and fumaroles showed very low pH values (between 0.0 and 1.0), due to water evaporation, which led to high concentrations of sulphuric acid. In soils at pH 1.0, where temperature was between 45 and 35 °C large algal mats mainly composed by Cyanidium caldarium, (formerly C. caldarium forma A), Galdieria sulphuraria (formerly C. caldarium forma B) and Cyanidioschyzon merolae, were found. Similar Cyanidiales assemblages were found also in sulfur mines of Sicily (DeLuca et al. 1974. Nuove stazioni di “Cyanidium caldarium nell’Italia meridionale ed in Sicilia. Delpinoa, 14-15:49-60; Pinto and Taddei 1975. Nuove stazioni italiane di “Cyanidium caldarium”. Delpinoa 14-15, 125-139).

2) Sulphur springs
Springs whose hot water is brought to the surface together with sulfurous gases. In sulphur hot springs, temperature may reach also 100°C near the source, but water and soils dramatically cool few meter far from the source. Sulphides are constantly liberated from the spring and oxidated to sulphuric acid.

3) Fumaroles
Fumaroles are fissures of rocks or soils emitting gases, due to the presence of volcanic magma or hot igneous rocks located near to the earth surface. Fumaroles emitting sulfurous vapors form surface deposits of sulfur-rich minerals which can be oxidized to sulfuric acid, leading to very low pH values.