CHICAGO (CBS) — After halting the use of dry ice to kill rats last winter, city officials said Chicago has been given the green light to start up again, and the Department of Streets and Sanitation also has started trying a new non-lethal method to fight Chicago’s rodent problem.

Chicago is adapting its rodent control strategy to include a method some call more humane and perhaps more effective.

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The city is expected to announce Tuesday that it is beginning to use a fertility-reducing bait called ContraPest. According to a New York City Transit study, after months of eating the bait, rats become unable to breed. The contraceptive is not lethal, does not affect humans or other animals besides rats, and is considered cost-effective.

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The new method will be tested at the city’s garbage transfer station at 34th and Lawndale.

Earlier this year, the city announced rat complaints were on the rise. Complaints from November to February were up 30 percent compared to the same time a year earlier.

Officials said it was largely due to an unusually mild winter, but also might be due in part to expanded pest awareness programs.

In addition, the city had to stop using dry ice to kill rats at the end of last year, because it was not approved on the U.S. Environmental Protection Agency list of rodenticides for any city, yet. Chicago started using this method in August of 2016 and stopped in December of 2016.

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However, city officials said the EPA has now approved using dry ice as a rodenticide, and Chicago will resume using dry ice to kill rats – dropping it into burrows to suffocate rats as it changes from a solid into a gas.