From Water to Whale
A trace amount of mercury in lake water — barely detectable at parts per trillion — can become a health crisis in the fish, seals, and humans at the top of the food chain. Bioaccumulation and biomagnification are the processes that transform imperceptible environmental contamination into dangerous tissue concentrations, amplifying chemical exposure by factors of millions through the trophic cascade.
The Bioconcentration Factor
The BCF measures how efficiently an organism concentrates a chemical from its environment. For aquatic organisms, BCF = C_tissue / C_water at steady state. Lipophilic chemicals partition into fatty tissues and resist metabolic breakdown, yielding BCFs of thousands or more. The octanol-water partition coefficient (Kow) predicts BCF — chemicals with log Kow above 4 are generally bioaccumulative.
Trophic Magnification
Biomagnification multiplies the problem at each step of the food chain. When a small fish eats contaminated plankton, it absorbs the chemical but eliminates water and metabolizes the organic matrix. The persistent chemical concentrates in the predator's tissues. A biomagnification factor (BMF) of 5 per trophic level means a four-level food chain amplifies concentrations by 125-fold above the base level — and this compounds on top of the initial bioconcentration.
Legacy Pollutants and Emerging Concerns
The DDT crisis of the 1960s — documented by Rachel Carson in Silent Spring — demonstrated biomagnification's devastating ecological consequences. Despite bans decades ago, PCBs and DDT persist in Arctic food webs. Today, PFAS ('forever chemicals') represent a new generation of bioaccumulative pollutants. Their extreme persistence, widespread use, and resistance to all known degradation pathways make PFAS bioaccumulation a defining environmental challenge of the 21st century.