Which statement best describes mercury's movement and danger in aquatic ecosystems?

• A. Mercury is released from industrial sources, converted to methylmercury in water, bioaccumulates in organisms and biomagnifies up the food chain, harming nervous systems.
• B. Mercury is released from industrial sources and remains harmless.
• C. Mercury is not persistent in water.
• D. Mercury only affects soil.

Answer: (A)

Mercury in aquatic systems moves from releases into water as inorganic mercury, then bacteria convert much of it into methylmercury, a highly toxic form. This methylmercury stays in organisms and becomes more concentrated as predators eat prey, a process called bioaccumulation and biomagnification. Because methylmercury accumulates up the food chain, top predators like larger fish can have very high levels, and people can be exposed by eating contaminated fish. The main danger is to the nervous system, especially developing brains in fetuses and children, where mercury can cause serious effects. The idea that mercury remains harmless or isn’t persistent isn’t accurate—mercury can linger in water and sediments, and it can affect more than just soil, moving through aquatic ecosystems and posing risks to wildlife and humans.