Fungi and other organisms attack wood, breaking down its cellular structure and weakening the wood. Fungi cause decay, sapstains and soft-rot. The rate of fungus growth depends on temperature, available oxygen, wood moisture content, and the nature of the wood itself. Continuously damp wood will not last long. Untreated timbers used in mines may have a life span of less than two years.
Marine borers can destroy an untreated dock piling in less than one year.
Treating wood with chemicals which are toxic to attacking organisms extends the lifetime of wood, but it also necessitates careful administration and control of these chemicals to prevent negative impacts on humans and the environment. The intended use of a wood product, the type of wood treated, the comparative cost, aesthetic effects, safety and properties of the chemical applied, and government regulations determine which pesticide is most appropriate. The chemical must be toxic to the organisms present, be able to penetrate the wood, be chemically stable, safe and economical to use, and not weaken the wood or pose an unreasonable threat to plant, animal or human life. Several other wood protection chemicals are now under review. Creosote railroad ties, marine pilings and timber, other construction timbers.