Which scenario best illustrates bioaccumulation?

• A. A fish gradually accumulates mercury in its tissues over its lifetime
• B. A fish consumes contaminated water and releases mercury
• C. Mercury is evenly distributed in water
• D. Mercury evaporates from water

Answer: (A)

Bioaccumulation happens when a living thing takes in a contaminant faster than it can remove or metabolize it, so the level inside the organism builds up over time. In the fish example, mercury enters the fish from water and its diet and is stored in tissues, continuing to accumulate as the fish lives. Because mercury can be persistent and not easily excreted, the concentration inside the fish rises, which is the essence of bioaccumulation. The other scenarios don’t show this buildup inside the organism: taking in mercury from water and then releasing it reflects uptake with rapid elimination, mercury evenly distributed in water is a distribution issue in the environment rather than inside an organism, and evaporation removes mercury from water rather than causing it to accumulate in an organism.