HARTFORD, Conn. — As curbside recycling has grown, environmentalists around the United States find themselves fighting to protect decades-old bottle recycling programs that critics say are becoming obsolete.

Connecticut, Massachusetts and Iowa are among the states where bills have been proposed to replace the bottle deposits with a tax. Supporters say the tax revenue could support recycling efforts that did not exist when the bottle redemption systems were introduced.

The so-called “bottle bills” remain in place in 10 states. Typically, consumers pay an extra few cents when they buy certain beverages, a deposit they get back when they bring their cans or bottles to a redemption center or grocery store.

Some fear people will be more likely to toss their empties if they’re no longer worth cash.

“This is the most effective, proven way that we have to guarantee that these containers do not end up on our streets and do not end up on our beaches and open spaces as litter,” said Louis Burch, the Connecticut program director for Citizens Campaign for the Environment.

In 1971, Oregon became the first state to pass a bottle bill. It was seen as a way to address a growing litter problem along the state’s beaches and highways. Since then, Hawaii, California, Iowa, Michigan, New York, Vermont, Maine, Connecticut and Massachusetts have passed similar legislation. The types of beverage containers and the deposit amounts can vary by state.