What is an example pollutant that demonstrates bioaccumulation and biomagnification in a food chain?

• A. Sodium in drinking water
• B. Calcium in bones
• C. Mercury in fish
• D. Oxygen in air

Answer: (C)

Bioaccumulation happens when a pollutant builds up in an organism faster than it can be eliminated, and biomagnification occurs when these stored levels become higher at each step up the food chain as predators eat contaminated prey. Mercury in fish demonstrates this well. Mercury released into the environment can be converted to methylmercury in aquatic systems, which is highly persistent and binds strongly to tissues. Small organisms absorb it, and as they are eaten by larger fish, mercury concentrations accumulate still further, leading to high levels in top predators that humans may consume. This is why mercury in fish is a classic example of how pollutants can bioaccumulate and biomagnify. Sodium in drinking water, calcium in bones, and oxygen in air do not exhibit this pattern: sodium and calcium are nutrients or ions regulated by the body, and oxygen cycles without building up in organisms to higher concentrations through the food chain.