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Among the biggest culprits of plastic pollution in the ocean and along shorelines are thin plastic shopping bags, which have low recycling rates and often become litter when they blow away in the wind. Once there, they can entangle animals and break down into harmful microplastics. As awareness of this problem has grown, more than 100 countries have instituted bans or fees on plastic bags. But what effect those policies are having on the amount of plastic litter in the marine environment has not been systematically evaluated until now.

A new study from the University of Delaware and Columbia University has taken a thorough look at plastic bag bans and fees in jurisdictions across the United States to gauge their effectiveness. The researchers found that plastic bag policies led to a 25% to 47% decrease in plastic bags as a share of total items collected in shoreline cleanups relative to areas without policies. This decrease grows in magnitude over time, with no evidence of the rates rebounding.

The study, in the journal Science, was authored by Kimberly Oremus, associate professor in UD's School of Marine Science and Policy; and Anna Papp, an environmental economist who received her Ph.D. in sustainable development from Columbia University's School of International and Public Affairs in 2025.

Oremus got the idea for the study when she learned that volunteers at coastal beach cleanups in Delaware were using an app called Clean Swell to track the litter collected. The data goes into the Ocean Conservancy's Trash Information and Data for Education and Solutions (TIDES) database, which keeps crowdsourced records from thousands of cleanups around the world each year.

"When we found the database that had information on different shoreline cleanups, we realized we could look at the composition of litter before and after a policy to see what effect it had," Oremus said. "And then we could compare that to places that never got a plastic bag policy."

Papp, the study's lead author, said the plastic collected in shoreline cleanups can serve as a proxy for the total amount of plastic litter in the local marine or aquatic environment.

"A lot of the previous economics literature on plastic bag policies has used checkout data at the store level," Papp said. "So we were excited to add to that a direct measurement of plastic litter on these shorelines."

"We always remind volunteers and our partner organizations that the data they collect is used to make real change, and these findings are a great example of that," said Allison Schutes, senior director of conservation cleanups at Ocean Conservancy.

To conduct their study, the researchers looked at tens of thousands of shoreline cleanups and hundreds of local policies to determine how the policies worked in terms of reducing plastic litter in the environment. They focused on the United States because it has no federal plastic bag policy, allowing them to compare the effects of different types of policies at the town, county and state level within a single country.

While it might not seem surprising that banning or taxing plastic bags would reduce litter, Oremus said the results were more robust than she had expected.

"There are so many pathways a bag can take from the checkout line at the store," Oremus said. "It's great to see a policy that works in such a clearly measurable way."

Papp added that looking into the plastic bag policies, she was surprised to find that roughly one-third of Americans are living in an area with some sort of plastic bag policy in place.

"It was interesting to quantify the reach of the policies," said Papp. "We compiled over 600 policies for 2007–2023, with a lot of variation in their scope and geographic scale."

The study also found that some types of policies seemed to be more effective than others in reducing plastic litter. For instance, they found more robust impacts from state-level policies than town-level policies, with fees appearing to reduce litter even more than bans, though more study is needed to understand why. Another finding was that the bag bans and fees were most effective in places where the plastic bag litter problem was more severe to begin with.

An important caveat of the research is that despite these policies working to reduce the percentage of plastic bags on the shorelines, the overall percentage of plastic bags is increasing in both places with and without the policies. It's just increasing less in places with these policies than those without. That's because plastic pollution is growing in general, and bag policies can only mitigate some of its impacts.

"We're still getting more plastic bags on shorelines as a percentage of all the cleanup items over time," said Oremus. "It's not eliminating the problem, it's just making it grow more slowly."

With the United Nations Environment Program announcing the next round of negotiations on an international plastic treaty will happen in August 2025, Oremus and Papp said their study highlights the opportunity for a more comprehensive approach to the problem.

"Overall, our findings do show that plastic bag policies are broadly effective in limiting litter along shorelines," said Papp. "Ours is the first large-scale study to use hundreds of policies and tens of thousands of cleanups to look at their effects. But it is important to keep in mind that this is a relative decrease in affected areas compared to areas without policies."