The destruction of the twin towers was a site that became the definition of terror. It was an onslaught that killed nearly three thousand people - but a decade later, the attack isn't over. The dust that overwhelmed the streets of Lower Manhattan became a weapon. The clouds contained particles of pulverized concrete, asbestos, lead from fifty thousand computers, mercury from countless light bulbs -- a million tons of poisonous fallout. Now nearly 20,000 people are receiving treatment for a range of illnesses, many of them serious. And more than 60,000 are registered as at risk. The BBC Our World team is the first to break the story globally.
—Linda Sills