• Last updated:
  • 16 Aug 2018

Learning about acid sulfate soils

Recently staff from Sunshine Coast Council, Moreton Bay Regional Council, Noosa Council and Unity Water were invited to take part in acid sulfate soils training provided by Department of Natural Resources, Mines and Energy.

This workshop will assist staff in identification, sampling and management of acid sulphate soil across the region. 

What are acid sulfate soils?

Common in many parts of the world, acid sulfate soils are saturated with water, almost oxygen-free and contain microscopic crystals of iron sulfide minerals, commonly called pyrite.

Acid sulfate soils are safe and harmless when not disturbed. However, if acid sulfate soils are dug up or drained they come into contact with oxygen. The oxygen can then react with the pyrite in the soil causing the pyrite to break down and produce sulphuric acid, which can cause damage to the environment, buildings, roads and other structures. The acid also attacks soil minerals, releasing metals like aluminium and iron. Rainfall can then wash the acid and metals from the disturbed soil into the surrounding environment.

Undisturbed acid sulfate soils look quite distinctive. They are always wet, usually entirely saturated, and may not be easy to walk on. Their anaerobic state gives them a steely blue-grey colour, which can range from pale to dark shades. They can even be greenish in some cases. Marine sediments will often contain seashells and similar carbonate materials such as crab shells. Organic materials may be present, particularly the remnants of plants and grasses. If the soil has been consistently anaerobic, they may be well-preserved.

A strong smell of rotten eggs may come from the soil—this is hydrogen sulfide (H2S) gas, produced by the breakdown of sulfur and organic materials. Prolonged exposure to high levels of this gas can be life-threatening. Caution is needed when working in soil pits and confined spaces (e.g. during marine construction works) as the gas is heavier than air and can accumulate fast.