Which of the following could be a munitions constituent that might be monitored?

Heavy metals such as lead or mercury are common munitions constituents that require monitoring due to their potential environmental and health impacts. These metals can leach into soil and groundwater from munitions sources, especially in areas where the military has conducted operations or where munitions have been disposed of improperly. Monitoring these heavy metals is crucial when assessing contamination risks, as they can be toxic to both human health and ecosystems, accumulating in organisms and potentially causing long-term damage.

The other options, while they may have environmental significance, do not represent munitions constituents. Common soil minerals are typically naturally occurring and are not related to munitions. Plant nutrients like potassium are essential for plant growth; they are not harmful munitions constituents. Building materials, although they can pose risks if they contain hazardous substances, are not classified under munitions constituents that specifically require monitoring in the context of military operations or munitions disposal.