1) The accumulation of pollutants in living organisms by direct adsorption or through food chains.
2) Accumulation by an organism of materials that are not an essential component or nutrient of that organism. Usually it refers to the accumulation of metals, but it can apply to bioaccumulation of persistent synthetic substances such as organochlorine compounds. Many organisms, such as plants, fungi and bacteria, will accumulate metals when grown in solutions containing them. The process can be employed usefully as a purification process to remove toxic heavy metals from waste water and contaminated land.