The start of the suburban sprawl changed the US into a nation of voracious consumers, and the chemical industry responded by creating products to meet those demands

• Read our entire Toxic America series

My students sometimes ask me why in the United States there are cancer-causing ingredients in their cosmetics, or neurotoxins in their mattresses. Or hormone disruptors, and prescription drugs, in their drinking water.

I always answer by chalking out a map of the country, and its grid of 48,000 miles of interstate highways that were constructed after the second world war. The roads were initially conceived as a defense against foreign invasion, I tell them. But the unintended consequences include a host of major environmental and health problems we are only now beginning to understand, from climate change and species extinction to cancer.