Pyrite is a soil mineral often found in swamps, including peat. Pyrite becomes a toxic compound when exposed to surfaces and in contact with air.
Peat drying accelerates the process of peat decomposition and reduces the peat layer. A decrease in the peat layer exposes the substratum layer to air.
If the peat substratum layer contains pyrite, then oxygen will oxidize the pyrite and produce toxic acids such as sulfuric acid (H2S) or sulfuric acid (H2SO4). The soil will then experience iron and aluminum poisoning which inhibits plant growth and can even cause rust on agricultural equipment. These toxic acids can also flow through canals and contaminate the environment and agriculture of peatland communities.
For instance, the exposure of the pyrite layer to air during the construction of a 187 km canal during the PLG Project caused mass fish deaths in the Mangkatip River and Barito tributaries in 1997.