Final answer:
Power plants emit mercury into water sources, which is absorbed by fish and can lead to health problems. This mercury can biomagnify, which means its concentration increases up the food chain.
Step-by-step explanation:
Power plants, particularly those using coal, are known to emit mercury into water sources, which is then absorbed by fish. When mercury enters water bodies, it can be transformed into methylmercury through biological processes. This highly toxic form of mercury accumulates in fish and subsequently in other organisms including humans that consume the fish. The accumulation and increasing concentration of mercury and other toxic substances in organisms at higher trophic levels is known as biomagnification.
Mercury exposure is associated with neurological and developmental issues, and a famous incident of mercury poisoning occurred in Minamata, Japan, where high levels of methylmercury in fish led to severe health problems for the local population. Hence, among the options given, (b) Mercury is the correct answer.