Which two metals are most likely to leach out in the EPA TCLP test?

The reason Cadmium and Lead are the correct choices in this context relies on their known environmental behavior and toxicity when subjected to leaching tests such as the Toxicity Characteristic Leaching Procedure (TCLP) mandated by the EPA.

Cadmium is a heavy metal that, due to its solubility in acidic conditions, can readily leach from contaminated soil or waste materials, becoming a concern for groundwater contamination. Its toxicological profile makes it an important metal to monitor in waste disposal scenarios.

Lead, similar to cadmium, is another heavy metal often found in various waste forms, including batteries and electronic waste. It is also prone to leaching, especially in environments with acidic conditions or in the presence of certain complexing agents. Lead's widespread usage and its toxicity have led to rigorous testing protocols to evaluate risks associated with leaching.

In contrast, while other metals mentioned like mercury have significant toxicological concerns, their leaching potential under TCLP conditions may not be as prominent as that of cadmium and lead. Zinc and copper are generally more abundant and less toxic than cadmium and lead, and cobalt and iron tend to have stronger adsorption characteristics, thus are less likely to leach compared to the heavy metals in focus. The TCLP