Acid sulphate soils (ASS), sediments and rocks contain iron sulfides. The presence of iron sulfides in soils and rocks occurred naturally around 10,000 years ago, after the last major sea level rise. In Australia, these soils were formed predominantly on coastal lowlands with elevations generally below 5m.
If left undisturbed, these soils and rocks are harmless and are called potential acid sulphate soils (PASS). However, if soils and rocks containing iron sulfides are disturbed by actions including, excavation and draining, these soils will rapidly form sulphuric acid by reacting with oxygen in the air. Acid sulphate soils that have been disturbed are called actual acid sulfate soils (AASS), which may result in certain hazards and impacts.
Impact of acid sulphate soils on the use and development of land
The disturbance of potential acid sulphate soils (PASS) can affect the development and use of land. For example, sulphuric acid can leach into surrounding environments, possibly causing damage to concrete, iron and steel structures such as building foundations and swimming pools. Acid sulphate soils can cause bricks and mortar to break down or crack at a more rapid rate. Buried metal pipes may corrode at an accelerated rate due to the presence of acidity in the surrounding soil.
The development of farming and agricultural areas, drainage canals, marinas, golf courses and various other coastal developments similarly can expose acid sulphate soils to air and cause the soils to be very acid and toxic.
The effects of sulphate soils on the use and development of land may lead to increased replacement and maintenance costs of buildings and other constructions. Acid soils can result in the degradation of drainage systems, recreational fisheries and losses in farming and rural productivity. For this reason, environmental investigations and contamination testing for acid sulphate soils need to be considered before land is cleared, drained or construction works commence.
Impact of acid sulphate soils on the environment
Acid sulphate soils can have a destructive effect on plant and fish life and ecosystems for land and aquatic habitats. For instance, increased acidity in aquatic habitats may kill fish or make fish more prone to fungal infections including epizootic ulcerative syndrome or ‘red spot’.
Acid sensitive animal and plant species can become vulnerable to acid-tolerant species. For example, mosquitoes tolerate higher levels of acidity in the water. Furthermore, populations of mosquitoes will thrive in areas affected by acid sulphate soil drainage because of how in the breakdown of the aquatic ecosystem, the natural predators of mosquitoes including fish become displaced by the acid conditions. Therefore, sulphate soil poses a health hazard to humans, animals and the environment because mosquitoes carrying diseases including Ross River Virus (RRV) are attracted to higher levels of acidity in the water.
Based on the hazards that acid sulphate soils pose to the environment, it is important that action is taken to test soil for contamination.
Impact of acid sulphate soils on health and wellbeing
Human health and wellbeing may be affected by acid sulfate soils in a number of ways. Water quality may reduce, so that water becomes unsafe to drink and food may become contaminated.
Construction sites and drying wetlands or draught can be affected by acid sulphate soils, which can increase skin irritation and dermatitis. Dust in the air from acid sulphate soils may result in various eye and throat irritations.
Considering the health risks associated with acid sulphate soils, it is worth conducting investigations of sites suspected to be contaminated.
Benefits of testing for acid sulphate soils
Envirolab Services has NATA Accreditation for the full SPOCAS suite (Suspension Peroxide Oxidation Combined Acidity and Sulphur), SCR suite (chromium reducible sulphur) and the Chip Tray method (pHF/pHox and pHINC). This will provide results for both the 'acid' trail and the 'sulphur' trail allowing comparison of results to guideline values.
How to prepare a sample for the testing of acid sulphate soils
For the testing of acid sulphate soils, a minimum of 200g should be collected in zip-lock bags to minimise contact with air. Large shells, wood, charcoal and stones should be removed in the field, but biological remnants such as roots should not be removed.
Samples should be kept cold in the field and should reach an Envirolab Services lab within 24 hours of sampling. Where this is not possible samples should be either frozen or dried at 85°C and stored in zip lock bags.
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