When you outlaw or discourage the sale of plastic bags, fewer of them end up as litter on beaches.

That’s the intuitive finding of a paper published Thursday in the journal Science, which involved an analysis of policies to restrict plastic bag use across the United States. The study authors found that, in places with plastic bag bans or taxes, volunteers at shoreline cleanups collected 25 to 47 percent fewer plastic bags as a total fraction of items collected, compared to places with no plastic bag policies.

The study adds weight to less formal analyses of plastic bag bans conducted by advocacy organizations and could inform negotiations later this summer over the United Nations’ global plastics treaty. “These are large-scale, robust findings that show that these policies are effective in at least limiting plastic bags in the environment,” said Anna Papp, one of the study’s co-authors and an incoming environmental economics postdoc at MIT.

As litter, plastic bags entangle wildlife and kill more sea turtles, whales, dolphins, and porpoises than any other type of plastic. They also break down into microplastics that have been linked to metabolic disorder, neurotoxicity, and reproductive damage in humans; a study published on Wednesday found that communities living near high concentrations of marine microplastics had an increased risk of Type 2 diabetes, coronary artery disease, and stroke.

In response to these harms, cities and states across the country have passed laws that ban plastic bags from certain retail locations, or impose a small fee on them — usually 5 to 10 cents. At least a dozen states have banned plastic bags, including Delaware, New Jersey, and Vermont. Jurisdictions with plastic bag fees include Alexandria, Virginia; Duluth, Minnesota; and Howard County, Maryland.

Papp and her co-author — Kimberly Oremus, a marine sciences professor at Delaware University — said they got the idea for their study after learning about beach, riverbank, and lakeshore cleanups organized by the nonprofit Ocean Conservancy. These volunteer cleanups go all the way back to 1986, and reports from each year document the number and type of plastic items collected across jurisdictions. In more recent years, participants have logged their item counts and types in a mobile phone app.

Read the full article about plastic bag bans by Joseph Winters at Grist.