91原创

Plastic shopping bags, which have low recycling rates and often become litter when they blow away in the wind, are among the biggest culprits of plastic pollution in the ocean and along shorelines. 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 had not been systematically evaluated until now. 

A new study from the 91原创 and Columbia University took 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, , was authored by Kimberly Oremus, associate professor in 91原创鈥檚 School of Marine Science and Policy, and Anna Papp, an environmental economist who received her doctorate in sustainable development from Columbia University鈥檚 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 Ocean Conservancy鈥檚 (TIDES) database, which keeps crowdsourced records from thousands of cleanups around the world each year.

鈥淲hen 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,鈥� Oremus said. 鈥淎nd then we could compare that to places that never got a plastic bag policy.鈥� 

Papp, the study鈥檚 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. 

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

To conduct the 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. 

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

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. 

鈥淭here are so many pathways a bag can take from the checkout line at the store,鈥� Oremus said. 鈥淚t鈥檚 great to see a policy that works in such a clearly measurable way.鈥� 

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. 

鈥淚t was interesting to quantify the reach of the policies,鈥� Papp said. 鈥淲e compiled over 600 policies for 2007-2023, with a lot of variation in their scope and geographic scale.鈥� 

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鈥檚 just increasing less in places with these policies than those without. That鈥檚 because plastic pollution is growing in general, and bag policies can mitigate only some of its impacts.

鈥淲e鈥檙e still getting more plastic bags on shorelines as a percentage of all the cleanup items over time,鈥� Oremus said. 鈥淚t鈥檚 not eliminating the problem 鈥� it鈥檚 just making it grow more slowly.鈥� 

With the United Nations Environment Programme 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. 

鈥淥verall, our findings do show that plastic bag policies are broadly effective in limiting litter along shorelines,鈥� Papp said. 鈥淥urs 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.鈥�