A biocie is a chemical substance capable of killing living organisms , usually in a selective way and commonly used in fields such as medicine, agriculture and forestry. Large quantities are also used in industrial applications preventing fouling in water and oil pipelines. The distinction between a biocide and an anti fouling agent or a disinfectant is often vague. As an example, chlorine is used as a short-life biocide in industrial water system, but a a disinfectant in swimming pools.