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 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.
2. 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.
3. 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.