Coastal acid sulfate soils are soils and sediments containing iron sulfides, the most common being pyrite. When exposed to air after to drainage or disturbance, these soils produce sulfuric acid, often dissolving and releasing iron, aluminum and heavy metals into the environment from the soils. It can be extremely toxic to plants and animals.
When coastal acid sulfate soils are exposed to air for prolonged periods of time, 'soil ripening' occurs. Soil ripening is an irreversible loss of water resulting in physical, chemical and biological changes to the soil.
Coastal acid sulfate soils may be present in most low-lying coastal regions in South Australia and can be disturbed and exposed by developments that involve drainage, dewatering, excavation and filling.
A strategy for dealing with coastal acid sulfate soils was developed in 2003 by the Coast Protection Board, in collaboration with the CSIRO's Coastal Acid Sulfate Soils Program (CASSP).