William Ruckelshaus was the first director of the U.S. Environmental Protection Agency (EPA). In a recent interview he reflected on what’s changed during the 43 years since the agency was established — and in particular since the passing of landmark legislation on clean air and water in the 1970s (full interview here).

Interviewer: Take me back to the time of the creation of the Clean Water Act – what was the feeling at the time that made the EPA and made the Clean Water Act necessary?

Well, the sentiment was an explosion of public concern about the environment. It was caused by a number of factors. Rachel Carson’s book [Silent Spring], which was written in 1962, had a cumulative effect that was quite pronounced in the country at the time. We had flammable rivers — you already mentioned the Cuyahoga River in Cleveland. We had people in Denver wanting to see the mountains and people in Los Angeles wanting to see one another….

The difference today from where we were 40 years ago is where public opinion is. If public opinion were as intolerant of what’s happening to our environment and our public health today as they were 40 years ago, you wouldn’t have a partisan split on this issue. There was almost unanimity that something be done about it.

Interviewer: So, what changed?

I think a number of things changed. Maybe the most important thing is success. The EPA may well be a victim of its own success. We don’t see the same kinds of visible pollution problems today that we did. We don’t have flammable rivers anymore and we don’t have smog that’s so awful that you can’t even see one another. That was the situation back in the ’60s when the public’s concern began to express itself.

We still have problems today; they tend to be more invisible. They tend to be things that you can’t smell, touch and feel the way you could 40 years ago. And that just doesn’t get public attention.

In the developing world there are still plenty of “smelly” problems. But it may be that the invisible, odorless ones are ultimately the most perilous.

How do we mobilise concern over invisible threats?

If the nudge units of the world aren’t working on this already, they ought to be.