3.2 We live in an environment full of toxic substances.

Toxic substances are substances that cause damage to living organisms through immediate or long-term exposure. They fall into two broad categories: synthetic and natural. Natural toxins are not to be taken lightly: arsenic, a basic element that sometimes leaches into groundwater, can cause cancer and nervous system damage in humans.

But synthetic substances are a particular problem because there are quite a lot of them and many are persistent chemicals, meaning they don’t readily degrade over time. According to Environment Canada, the agency that protects Canada’s environment and natural heritage, 23 000 chemicals were in common commercial use in Canada in 1986; since then, some 800–1000 new chemicals have entered the Canadian marketplace each year.

The debate over how to regulate these substances—how to determine what quantity of any particular compound is safe for humans, and then how to ensure that our exposure levels stay well below those quantities—began in 1962 with a book called Silent Spring.

In this book, legendary environmental activist Rachel Carson asked her readers to imagine a world without the sounds of spring, a world in which the birds, frogs, and crickets had all been poisoned by toxic chemicals. Just 20 years had passed since the widespread introduction of herbicides and pesticides like DDT, she explained, but in that relatively short time, they had thoroughly permeated our society. These chemicals were obviously great for killing off weeds and pests; they had done an amazing job conquering mosquito-borne diseases like malaria during World War II, and combating world hunger by boosting global food production. But no one seemed terribly concerned about the effects they might have on nontarget species, or on ecosystems. After all, they were designed to kill living things. Wasn’t it at least possible that what killed one organism might also harm or kill others?

Carson went on to identify three specific concerns that were being overlooked at the time: some chemicals can have large effects at small doses; certain stages of human development are especially vulnerable to these effects; and mixtures of different chemicals can have unexpected impacts. The book created an uproar, which led to much stricter regulations for chemical pesticides in general, and, in Canada and the United States, a complete ban on DDT in particular. But half a century later, we are still struggling to effectively regulate the chemicals in our world.