In a simple aquatic food chain, which organism is most likely to have the highest contaminant concentration due to biomagnification?

• A. Phytoplankton
• B. Small zooplankton
• C. Large predatory fish
• D. Benthic bacteria

Answer: (C)

Biomagnification causes contaminants to build up as you move up a food chain because each predator accumulates the pollutants from its prey, and persistent substances are not easily excreted. In an aquatic chain, phytoplankton may take in contaminants from water, but the amounts are relatively low. Small zooplankton accumulate more because they feed on contaminated phytoplankton, yet the highest concentrations appear in top predators who eat many contaminated prey over time and often have long lifespans and fat-rich tissues that store these chemicals. Benthic bacteria act mainly as decomposers and don’t sit at the top of the energy transfer, so they don’t reach the highest biomagnified levels like the large predatory fish do. So the organism most likely to have the highest contaminant concentration is the top predator, the large predatory fish.