A rat forages on a city street.

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Boston's use of dry ice to control the city's rat population has proved successful, but federal officials are shutting it down.

The city received a cease and desist letter because it was using dry ice, which is frozen carbon dioxide, as a pesticide, which the letter says violates federal law.

A statement by the Environmental Protection Agency said the product would need to be registered for its use as a pesticide, which it has not been.

The program has been so successful in curtailing rat populations that other cities are considering similar measures, Boston Inspectional Services Commissioner Buddy Christopher told NECN.


The department uses dry ice to suffocate rats living in underground burrows. Workers put dry ice into the holes and cover the exits with dirt. This fills the burrows with carbon dioxide, effectively asphyxiating the rats.

"We have done dozens of locations. We have had no problems,” Christopher said. “It's cheaper than poison — less likely a child or animal will ingest this.”

Christopher said that although the city doesn't agree with this classification, it would comply.

Because of the winter cold, he doesn't expect the temporary halt in the program to allow rat populations to rebound. Areas like Boston Common and Back Bay are known to house large populations of rats.

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