Biomagnification, also known as bioamplification or biological magnification, occurs when the concentration of a substance, such as DDT or mercury, in an organism exceeds the background concentration of the substance in its diet. This increase can occur as a result of:

• Persistence – where the substance can't be broken down by environmental processes
• Food chain energetics – where the substance concentration increases progressively as it moves up a food chain
• Low or non-existent rate of internal degradation or excretion of the substance – often due to water-insolubility