What was the black soot that the Malleable Castings company in my neighborhood produced?

My dad told me that when I was little, we lived within 4-5 blocks of a Malleable Castings company that produced so much black soot in my neighborhood that it made it hard to breathe and they had to turn the company into the EPA. What is a Malleable Castings company, and what would have produced the black soot?|||a Malleable Casting is something made from metal. as for the black soot not sure but it could have been they used coal to fire the furnaces