RACHEL MARTIN, HOST:
Rats - they have plagued cities for centuries. But as Isaiah Thompson from member station WGBH reports, some cities are turning to an innovative method to help keep the rodents away.
ISAIAH THOMPSON, BYLINE: It's a steamy summer day. John Stellberger is standing by a reeking dumpster, staring at a series of fist-sized holes pockmarking the ground - rat boroughs.
JOHN STELLBERGER: So they come out. They climb up. They climb these. Yeah, it smells the food. There's plenty of fresh stuff in here.
THOMPSON: Stellberger calls himself an environmental health specialist. He doesn't like to use the word exterminator. But part of Stellberger's job is to kill rats.
STELLBERGER: And then they're - so look at all the droppings.
THOMPSON: Oh, yeah.
Stellberger is pouring white, chalky pellets into a borough hole.
I just saw one.
STELLBERGER: Someone come out? Oh, cool.
THOMPSON: Yeah. It just ran under the dumpster.
He's using dry ice, the same you might find chilling a cocktail. Dry ice is just carbon dioxide. Exposed to air, it becomes CO2 gas - and in a tiny, confined space like a rat borough, lethal. The rats asphyxiate.
BOBBY CORRIGAN: Quite frankly, this is the good thing because it's a very humane thing. The rats simply go into a kind of a sleep. And they simply don't wake up.
THOMPSON: Urban rodentologist Bobby Corrigan advises cities on rodent control. He says dry ice is safer than poison. A couple of years ago, Boston, one of the top rodent-infested cities in the country, started using dry ice. So did New York, D.C. and Chicago. But then the Environmental Protection Agency ordered them to stop, saying dry ice wasn't an approved pesticide. Since then, the EPA has approved only one company's product, called Rat Ice. It's just dry ice. But now Stellberger has to drive 20 miles to buy EPA-approved rat ice and pays three times more. Still, he says, it's a step in the right direction. After all, the real solution isn't about killing rats. He says it's about getting humans to be less, well, messy.
STELLBERGER: You know, I've done work for towns where some of the neighbors are blaming the town for something that isn't their fault. It's, you know - it's them. You know, it's their litter.
THOMPSON: Stellberger likes to say that rat problems are really human problems. And dry ice won't solve those. For NPR News, I'm Isaiah Thompson in Boston.
(SOUNDBITE OF ZEROPOSITIVO SONG, "ESTA BIEN") Transcript provided by NPR, Copyright NPR.
