Science says plastic bag bans really do work

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.

That standardized data could help fill an important research gap, Oremus said, on the connection between plastic bag restrictions and shoreline pollution. Prior scientific analyses had tended to focus on consumer behavior — for example, by counting the number of shoppers who emerge from a supermarket with plastic versus reusable bags. Some studies had focused on plastic bags clogging storm drains, since this can create a flooding hazard. “What we were missing was a direct measurement of the litter in the environment,” Oremus said. 

A small number of analyses looking at this had come from nonprofits, including the Ocean Conservancy, and had not undergone peer review, she added.

Papp and Oremus combined eight years of Ocean Conservancy’s data — constituting more than 45,000 cleanups across the U.S. from between 2016 and 2023 — with information on roughly 180 plastic bag bans and fees implemented between 2017 and 2023. They analyzed plastic bag collection in ZIP codes with and without plastic bag restrictions, and took into account differences in the bag policies, including whether they banned all bags or only certain kinds. 

According to the analysis, plastic bags’ share of collected items increased over the study period: They represented a larger and larger fraction of all the pieces of plastic that volunteers picked up. But this increase was much slower in places covered by a plastic bag restriction, where volunteers collected 25 to 47 percent fewer plastic bags as a fraction of their total haul. The study showed the highest impact from state-level policies compared to local ones, and found that decreases in the share of plastic bags grew over time after bag policies went into effect. 

The study looked at bags as a fraction of plastic items collected rather than the total number of plastic bags because this helped make the measurements more comparable between jurisdictions. “This measure is not sensitive to the size and frequency of cleanups, fluctuations in overall litter, and other factors,” Papp said.

The study also suggested that taxes — like a 10-cent charge per plastic bag — cause a greater reduction in shoreline litter than outright bans, though the researchers said this finding was inconclusive. Not a lot of jurisdictions have fees, Oremus said, so the sample size is small. And there could be explanations that extend beyond the fee itself: Washington, D.C., for example, uses revenue from its plastic bag fee to fund river and shoreline cleanups that might reduce the number of bags found by Ocean Conservancy volunteers. Oremus said it’s also possible that fees have greater coverage than bans — the latter sometimes apply to grocery stores but not to restaurants, for example — or that supermarkets and restaurants are less likely to flout a fee than a ban.

What is clearer, according to Papp, is that “partial bans” aren’t as effective. These policies outlaw plastic bags below a certain thickness, on the basis that thicker bags can count as “reusable” or “recyclable” and are less likely to become litter. Papp and Oremus’ study showed that jurisdictions covered by partial bag bans had the “smallest and least precise” effect on reducing plastic bag litter, potentially because consumers treated the thicker bags just like they had the thin ones. 

Other analyses have shown that California’s partial bag ban led to an increase in the weight of plastic bags used per person between 2014 and 2021. The state closed this loophole last year by banning plastic bags outright, and Oregon followed suit with its own bag ban earlier this month. Lawmakers in other states, however, oppose bag bans altogether — at least 17 states have passed “preemption” laws preventing their cities and counties from restricting the sale of plastic bags.

Susanne Brander, an ecotoxicologist and associate professor at Oregon State University, applauded the research, though she said it’s unfortunate that plastic bag bans have become so politicized that a scientific study is needed to back their effectiveness. “We knew they were working, but this gives hard data to support that,” she said. 

Brander is also a member of the Scientists’ Coalition for an Effective Plastics Treaty, which is advocating for the international agreement — which will enter its sixth round of negotiations in August — to include legally binding limits on plastic production and the use of some types of plastic. One of the articles in the current draft of the treaty proposes restrictions on individual items like balloon sticks, plastic drink stirrers, and “plastic-stemmed cotton bud sticks.” Brander said the new study makes “a strong argument” in favor of broader bans.

“Rather than asking scientists to go and say you need to study Styrofoam containers separately, and study plastic takeaway containers separately, I think we should be able to apply these findings broadly to other bans of harmful products,” she said.

Martin Wagner, a biology professor at the Norwegian University of Science and Technology who is also a member of the Scientists’ Coalition for an Effective Plastics Treaty, agreed with Brander. He also said the study could be used by U.N. member states to craft their own plastic reduction policies: “These political measures are often discussed in the absence of data — they just say, ‘Let’s ban some items,’” he said. Having concrete evidence that policies can reduce pollution will be “really helpful.”

Celeste Meiffren-Swango, state director of the nonprofit Environment Oregon, said the study in Science reinforces the recommendations of a report she co-authored last year. That report, “Plastic Bag Bans Work,” estimated that five U.S. policies in New Jersey; Vermont; Philadelphia; Portland, Oregon; and Santa Barbara, California, had prevented the use of 6 billion bags per year. Presumably, many of those avoided bags would have become litter.

“There are proven environmental benefits to passing plastic bag laws,” she said. “It’s not just that we want people to change their shopping habits.”