>Much of the thousands of tons of debris resulting from the collapse of the Twin Towers was pulverized concrete, which is known to cause silicosis upon inhalation. The remainder consisted of more than 2,500 contaminants, more specifically: 50% non-fibrous material and construction debris; 40% glass and other fibers; 9.2% cellulose; and 0.8% of the extremely toxic carcinogen asbestos, as well as detectable amounts of lead and mercury.

https://en.wikipedia.org/wiki/Health_effects_arising_from_th...

In April 1970, the New York City Department of Air Resources established asbestos spray insulation regulations. As a result, the Department ordered contractors to stop the use of asbestos in the World Trade Center. The upper levels of the north tower and the entirety of the south tower contained asbestos alternatives.

It's estimated that the north tower contained 300 – 400 tons of asbestos.