Plastic bag fees and bans are effective in limiting debris on U.S. shorelines, a new study reports, but even places with bag policies are seeing a greater prevalence of plastic bags on beaches and riverbanks.

The study, published Thursday in the peer-reviewed journal Science, analyzed the relationship between policies on plastic bags and the litter collected in more than 45,000 shoreline cleanups. In communities with policies in place, the prevalence of plastic bags in the trash was 25 percent to 47 percent lower than in places without regulations.

But plastic bags increased as a share of litter both in communities with policies and those without, the researchers noted. The policies appeared to contain that growth but not stop or reverse it.

Measures targeting plastic bags aren’t eliminating the problem, just slowing its growth, said Kimberly Oremus, one of the study’s authors and an associate professor at the University of Delaware’s School of Marine Science and Policy.

The impact of the policies has been somewhat limited, Oremus said, because they can be patchy in what they regulate and are themselves a patchwork, with rules and enforcement varying from place to place.

“Most of these bans and fees don’t cover every type of plastic bag,” she said. “There’s a lot of exceptions to them. It really depends on the state.”

The goal of all these policies is the same: to limit the use of plastic bags, which can take centuries to decompose and, in the interim, can entangle wildlife and release microplastics and toxic chemicals into waterways.

Some places have imposed “bag taxes” or fees on customers using plastic bags. Other places have experimented with bans — though they might prohibit thin plastic bags (which are most likely to blow away and become trash) while allowing thicker ones, or they might leave restaurant takeout bags unregulated.

Erin Murphy, manager of ocean plastics research at Ocean Conservancy, said the new report was “the first large-scale study to systematically assess how plastic bag policies reduce the amount of plastic bag pollution in our environment.”

Murphy was not involved in the analysis, but the researchers used her nonprofit group’s data from shoreline cleanups between 2016 and 2023. That data provided a way to measure litter before and after policies were enacted and conduct comparisons with measurements in places without any regulations.

Lead author and environmental economist Anna Papp said one of the key findings was the difference between broad policies, which appeared to limit plastic litter, versus partial bans, which resulted in the smallest and least precise effects.

There was also some evidence that bag fees could have a greater effect than bans. But the researchers said that fees are also much less common than bans and that more research is needed to assess their relative effectiveness.

The study also found that state-level policies had a greater impact than town-level measures, Oremus said. Larger-scale policies tend to be more robust, she said, because “litter can travel between borders.”

The analysis also showed that the largest reductions in trash occurred in places with high amounts of plastic bag pollution.

“Are you a place that struggles with litter?” Oremus said. “Then, this might be a policy to consider.”

Erin Hass, senior director of strategic alliances with the Plastics Industry Association, noted that plastic bags represent a fairly small portion of litter that winds up along U.S. shorelines.

“Even the study itself acknowledges that the top sources of beach litter are cigarette butts, food wrappers, bottle caps and beverage bottles — not plastic bags,” Hass said. “Why are regulators isolating a single product while overlooking far more prominent contributors?”

Bans could “create unintended consequences,” Hass said. She noted that after the implementation of a bag ban in New Jersey, for example, thin plastic bags disappeared, but overall plastic consumption appeared to increase because of a switch to heavier reusable bags, which tended to be tossed after minimal use.

“If the goal is reducing marine debris and advancing sustainability, the smarter approach is to invest in scalable recycling systems, not sweeping bans that shift the problem rather than solve it,” she said.