Calcium EDTA is primarily indicated for the treatment of:

Calcium EDTA is specifically indicated for the treatment of lead poisoning. This chelating agent works by binding to lead in the bloodstream, allowing it to be excreted through the kidneys, thereby reducing lead levels in the body. Lead toxicity can affect multiple organ systems in both humans and animals, leading to serious health issues.

The action of Calcium EDTA is particularly effective in cases of lead exposure because it can effectively reduce lead concentrations and alleviate the toxic effects associated with lead poisoning. The mechanism involves the formation of a stable complex between lead and Calcium EDTA, facilitating the removal of lead from the body.

In the context of the other possible answers, while Calcium EDTA is a chelator, it is not the first-line treatment for mercury poisoning, copper toxicity, or iron overload, each of which may require different agents for effective treatment. For instance, mercury poisoning is typically treated with agents like dimercaprol or DMSA, while copper toxicity treatment might involve the use of penicillamine. Iron overload is managed through chelators such as deferoxamine. Thus, the specific indication of Calcium EDTA for lead poisoning underscores its role in the management of this particular type of heavy metal toxicity.