When Gina McCarthy started her professional life, she was a public health worker in community health centers.

She still considers herself a public health worker, although her job today - administrator for the U.S. Environmental Protection Agency - is vastly different.

What that early community work showed, McCarthy recently told a group of digital health professionals meeting in Philadelphia, was the strong connection between environmental health and public health.

"I was seeing people come in day in and day out with asthma, or the elderly who couldn't breathe," she said. She realized that the problem wasn't access to health care, "it was about them getting access to clean air."

As such, she said, the EPA is "primarily a public health agency. That is our mission."

It always has been, she told the health-care audience. It's just that about 45 years ago, when the agency was formed, "environmental pollution was extraordinarily visible, in terms of black smoke pouring out of every smokestack. You had rivers that were burning, the Love Canals of the world. . . . We recognized very directly that environmental pollution was making people sick."

Now, she said, "It continues to make people sick. The challenge we face today is they can't see it, they can't taste it, they can't feel it."

After the conference, we spoke more about this issue.

Is this a new focus for your agency?

EPA has always been focused on public health. Science tells us that exposure to environmental pollution continues to take lives, and it continues to rob our children's future. As those challenges get a little more difficult to see, we just need to remind people about our mission to protect public health and the environment, and how important that is to them and to their children.

When I was growing up - I grew up in the city of Boston - we had black smoke coming out of smokestacks. We had rivers outside the city in industrial areas that some days were bright green, some days were bright red, some days were bright yellow, because the textile industry was discharging into them.

Now I know, and every mayor of the city will tell you, that the cleanup of Boston Harbor was the most influential thing that ever happened to that city in terms of making it a world-class city. . . .

In this country, our core values are reflected in our environmental mission and what we do to protect public health, and that has been the basis for strong economies. When you don't invest and you don't keep protecting those core values, like safe drinking water and clean air and clean land, that is when the economy will not continue to grow.

How well does this message resonate today, with critics calling for smaller government and industry saying pollution controls are too expensive?

I actually think it resonates very well. If you go and ask people if they care about clean air and clean water and clean land, it's going to be at the top of their agenda every time.

If you look at the work we've done on brownfields, you'll see that when you take a contaminated site and you bring it back to productive use, everything around it is elevated. Not just the community itself and its economic vitality and its ability to attract more business, but also the health of the kids in the community.

Tell us about a major environmental public health issue that needs to be addressed.

We have been trying to communicate the challenge of climate change for many years. I think we turned a corner with the public when we started to actually see the impacts, not just studies modeling the impacts. People now feel that they know it. They know climate change is happening.

The U.S. government put out a report a couple of weeks ago that detailed the impacts it will have on our lives if we don't address it and take action today. It's everything from our kids getting more asthma attacks to our elderly having more cardiac problems as a result of the warmer temperatures and the higher ozone levels that we anticipate.

We see the droughts in California, and people left without access to clean water. We see the floods that are inundating Florida, where saltwater infiltrates the drinking water.

What are some recent air-quality initiatives that also address health issues?

Science is telling us that particulate matter is one of the biggest challenges we face, especially in urban areas. So we are doing work now that actually serves dual purposes. It both lowers carbon pollution that's fueling climate change, and it's taking care of traditional pollutants that are causing us more health problems than we ever knew before.

We're going to finalize a heavy-duty vehicle rule, which is going to require that heavy-duty trucks get cleaner. It's going to drive down carbon pollution, but also, significantly, levels of particulate matter. Also, we've recently finalized our Clean Power Plan. We've done that to reduce carbon pollution, but it also drives down lots of pollutants from the energy sector that are impacting our health today.

You spoke at the conference about better monitoring technology and the links between environmental exposure and health effects.

Let's talk about pharmaceuticals showing up in our rivers and streams and drinking water. Let's talk about perfluorinated compounds - basically, industry chemicals that are now not just in our products and getting in our bodies, but also in our drinking water. Those are opportunities not just for continued diligence, but also for new technologies.

We have to think a lot more about the complexity of the challenges we face today, but also return to the simple message that we knew in the '60s. We have to invest in public health. We have to invest in reducing environmental pollution and we have to modernize to keep our water clean, our air clean, and our land safe - for our children to play and to go to school, and for us to work.