Which of the following is NOT considered a heavy metal that affects health?

Iron is not classified as a heavy metal in the context of environmental and health concerns. Heavy metals typically refer to elements with high atomic weights that can be toxic at low concentrations, such as lead, copper, and mercury. These heavy metals often pose significant health risks due to their ability to accumulate in biological systems and cause various health issues ranging from neurological disorders to organ damage.

Copper and lead are well-known for their toxic effects, while mercury is infamous for its severe impacts on both human and environmental health. In contrast, although iron is essential for human health and plays a crucial role in various biological functions, excess iron can result in toxicity, but it is not categorized among the heavy metals that commonly create risks at lower exposure levels. Thus, it is correctly identified as the option that does not belong in this classification group.