Here is a piece of text: Less than 15 percent of spent foundry sand is recycled annually.
3 What Is Good for Compost & What Isn't?
4 How Do I Start a Composting Bin?
Mix equal parts compost and recycled foundry sand in a wheelbarrow or on a large tarp.
Recycle sand from aluminum, iron or steel foundries.
Have the recycled sand delivered. The average homeowners' truck was not built to carry tons of sand.
Use second-growth sustainable redwood or cedar boards to build garden beds.
Wear gloves, safety glasses and a dust mask when working with compost, sand and soil.
Don't use sand from brass or bronze foundries; it may carry hazardous chemicals.
Plant and Soil Journal; Characterization of Physical and Chemical Properties of Spent Foundry Sands Pertinent to Beneficial Use in Manufactured Soils; E.A. Dayton, et al.
de, Ruth. "How to Recycle Old Sand in the Garden for Compost." Home Guides | SF Gate, http://homeguides.sfgate.com/recycle-old-sand-garden-compost-78540.html. Accessed 24 April 2019.

Based on the text material above, generate the response to the following quesion or instruction: Why shouldn't sand from brass or bronze foundries be used in gardening?
This prompt doesn't seem malicious.