Many fat-loving (lipophilic) chemicals enter into an organism through the fatty layer of cell membranes more easily than their water-soluble (hydrophilic) counterparts do. Once inside the organism, these fat-soluble chemicals may move through numerous membranes until they are stored in fatty tissues and begin to build up there.

Another factor affecting bioaccumulation is whether or not an organism can break down the chemical that has entered into its cells and tissues. The biological breakdown of chemicals is called metabolism. This ability varies among individual species and also depends on a chemical’s physicochemical properties. For example, natural pyrethrins are insecticides derived from the chrysanthemum plant. They are highly fat-soluble but are easily degraded, and hence do not accumulate in an organism.

In short, when a chemical enters the cells of an organism, it is subject to distribution and then to storage, metabolism, and elimination within the organism. Bioaccumulation thus results from a dynamic equilibrium between exposure to a chemical from the outside environment and its uptake, storage, and degradation within an organism.

In technical terms, bioconcentration and biomagnification are two specific consequences of bioaccumulation. The first refers to the process leading to an increase in concentration of a pollutant from the environment to one of the organisms in a food chain. The second process refers to the increase in concentration of a pollutant from one link (organism) in a food chain to another. In either process, the aforesaid factors still apply.