Mercury in Fish Mercury Is a Highly Toxic Metal Found in Neon Signs

Mercury in Fish
Mercury is a highly toxic metal found in neon signs, fluorescent lights, older thermometers, and certain kinds of telescopes. It can also be found in something that many people eat on a regular basis: fish. The mercury we might find in a can of tuna is most likely an indirect result of the coal industry. Mercury, which is naturally found in coal, is released into the air when coal is burned. It finds its way into waterways via mercury-laced rain.
Mercury accumulates in certain kinds of fish through a process called biomagnification. Biomagnification occurs when a substance enters the food chain in small amounts at the very bottom and then increases in concentration in animals higher up on the food chain. Once a fish eats another creature containing mercury, the mercury does not leave that fish's body but instead is stored in fat. Therefore, the mercury continually accumulates as more mercury-contaminated fish are eaten.
Despite the toxicity of mercury and the widespread nature of fish contamination, there is no need for the public to be overly apprehensive. Many popular fish, such as salmon, catfish, or tilapia, are generally safe to eat. Other fish, especially tuna and grouper, should only be eaten in moderation. Young children and pregnant women should be especially cautious about how many servings of mercury-contaminated fish they have per week. It is recommended that people in these groups not eat more than 2 servings of mercury-contaminated fish per week. Fish with the highest levels of mercury include shark, swordfish, and king mackerel. All people should avoid eating large amounts of these kinds of fish, and no one should eat these fish more frequently than once a month.
Question: Which detail is NOT included in the passage regarding biomagnification?

A) The process explains how mercury can accumulate in various fish.
B) The process involves an increase in concentration in animals higher on the food chain.
C) The process occurs when something enters the food chain in large amounts.
D) The process involves the introduction of a substance at the bottom of the food chain.