Answer:
B. Mercury.
Explanation:
Mercury enters the environment naturally and through industrial pollution, mostly from coal-fired power plants. Mercury concentrations in the air are of little concern, but when mercury enters water, microorganisms transform it to a highly toxic form methylmercury that builds up in fish.
These species of fish that are long-lived and high on the food chain, such as marlin, tuna, shark, swordfish and king mackerel contain higher concentrations of mercury than others.
Size is the best predictor of increased levels of accumulated mercury. This is because of its hierarchy on the food chain that is, once this mercury gets into the marine food chain, it accumulates in the larger predators. That’s why larger fish are generally riskier to eat than smaller ones.