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Feds put freeze on Boston’s rat-killing experiment

The EPA is temporarily shutting down Boston’s program for killing rats with dry ice.
The EPA is temporarily shutting down Boston’s program for killing rats with dry ice.

Federal officials have put a freeze on Boston’s new tactic of killing rats by using dry ice.

City workers began using the super-cold substance to exterminate rats earlier this year by packing it into rat burrow exits and letting it melt. Dry ice, which is frozen carbon dioxide, reverts to being a gas as it melts, filling the burrows and suffocating any rats inside.

Boston officials said the method is effective, more humane, and significantly cheaper than using rat poison.

“We were using it with great success,” said William Christopher, commissioner of the city’s Inspectional Services Department, adding that the city had not run into any problems during the new campaign. “It’s such an effective process.”


But the US Environmental Protection Agency has ordered Boston to stop the practice — at least for now.

The EPA said that Boston must first register carbon dioxide as a pesticide used for rodent control with both federal and state agencies.

The EPA’s ruling came after state officials asked the federal agency for guidance.

“When a product is being used as a pesticide, it must first be registered through the Environmental Protection Agency under the Federal Insecticide, Fungicide, [and] Rodenticide Act,” the Massachusetts Department of Agricultural Resources said in a letter to Boston officials, relaying the EPA ruling.

After registering the product with the EPA, the city must also register it with the state, the letter added.

Christopher said city officials have since stopped using the dry ice and are working now to fulfill the registration requirements.

He said he is not sure how long the process will take but hopes to get the green light to resume using dry ice by the spring, when he said rat activity tends to pick up.

“Luckily, right now, it’s during the winter season, so it’s slow in terms of rodent activity,” he said.


In the meantime, Boston officials have resorted to using their “old standbys” for rat control: traps and poison, Christopher said.

Carbon dioxide is a colorless naturally occurring compound that is produced, for example, by humans and other animals exhaling and carbon-containing materials being burned.

The shutdown of Boston’s dry ice program was reported on previously by NECN.

Matt Rocheleau can be reached at matthew.rocheleau@globe.com. Follow him on Twitter @mrochele