The gradual accumulation of a chemical substance in the tissues of a living organism over time, reaching concentrations that exceed those in the surrounding environment. Bioaccumulation of pollutants in aquatic organisms is a major water quality and human health concern.
Bioaccumulation is the process by which a chemical substance accumulates in an organism's tissues at concentrations higher than those in the surrounding environment, occurring when the rate of intake exceeds the rate of metabolic breakdown and excretion. In aquatic systems, bioaccumulation is particularly significant for persistent, lipophilic (fat-soluble) contaminants including mercury (especially methylmercury), polychlorinated biphenyls (PCBs), organochlorine pesticides (DDT, dieldrin), per- and polyfluoroalkyl substances (PFAS), and some heavy metals. Biomagnification extends this concept across trophic levels, where predators accumulate higher concentrations than their prey, leading to the highest concentrations in top predators such as piscivorous fish, birds of prey, and marine mammals. The bioconcentration factor (BCF), defined as the ratio of chemical concentration in an organism to that in water at steady state, is a key metric used in environmental risk assessment. Bioaccumulation of mercury in fish tissue is the primary reason for thousands of fish consumption advisories across the United States. Water quality criteria and standards often incorporate bioaccumulation factors to set discharge limits that protect both aquatic life and human consumers. Monitoring programs that sample fish tissue provide critical data for assessing the ecological and human health risks of contaminated water bodies.