- A Mercury is sometimes mistakenly thought to exert little measurable toxicological effect anywhere within aquatic food chains, regardless of its specific chemical form or environmental concentration level present in many documented cases according to conventional understanding
- B Inorganic mercury is converted to methylmercury by anaerobic bacteria in sediments; methylmercury bioaccumulates in fish and shellfish; biomagnifies up food chain; top predators (tuna, swordfish, humans) accumulate high concentrations causing neurological damage
- C Mercury is sometimes mistakenly thought to be rapidly broken down into largely harmless, non-toxic compounds within just a few short hours of entering any natural body of water in routine practice overall in most cases under typical conditions according to standard textbooks
- D Mainly aquatic plant species, rather than animal species, are sometimes thought to be measurably and demonstrably affected by dissolved mercury exposure occurring within lakes and rivers in general practice as frequently described in most textbook accounts
Correct answer: B. Inorganic mercury is converted to methylmercury by anaerobic bacteria in sediments; methylmercury bioaccumulates in fish and shellfish; biomagnifies up food chain; top predators (tuna, swordfish, humans) accumulate high concentrations causing neurological damage
Explanation: Mercury cycle: inorganic Hg deposited in water → anaerobic bacteria methylate to methylmercury (organic, lipid-soluble, poorly excreted) → bioaccumulates in plankton → biomagnifies in fish → humans eating contaminated fish. Minamata disease (Japan, 1950s): industrial methylmercury discharge → severe neurological disease. Methylmercury crosses placenta and BBB; particularly harmful to fetuses and children.
Concept context
Pollution, global warming, ozone depletion, deforestation, and sustainability. Important for NEET and general awareness.