Plastic shopping bags, made from petroleum, usually used once, are often left to spend a generation floating in the ocean, breaking down into microplastics or becoming deadly food for sea life. The Ocean Conservancy estimates 11 million metric tons of plastic end up in the ocean every year. However, a new study shows that, in places where plastic shopping bags are banned, the problem is greatly mitigated.
Researchers Anna Papp of the School of International and Public Affairs, Columbia University and Kimberly L. Oremus of the School of Marine Science and Policy, University of Delaware wanted to investigate how effective plastic bag bans had been in reducing the amount of waste plastic in the environment. Though more than 100 countries have some form of plastic bag bans, no studies had tested their efficacy in reducing plastic litter in the environment. Their study, published in the journal Science, undertook to answer the question.
Whether a plastic bag policy succeeds in reducing shoreline litter depends on how it affects both consumption and waste management, the researchers said. For instance, a partial ban could fail to reduce plastic consumption but still reduce litter if customers substitute thin bags for thicker ones that are less likely to blow away. Or it could reduce consumption but not litter if the bags most likely to become litter are exempted from the ban. To directly measure the impacts of policies on plastic litter in the environment they leveraged the patchwork of hundreds of state and local plastic bag policies that were adopted across the United States between 2017 and 2023. They combined this with crowdsourced citizen-science data from more than 45,000 shoreline cleanups, in which participants counted and categorized the items they found.
Their design allowed them to control for the share of plastic bag litter in shoreline cleanups before and after each policy’s implementation, as well as plastic bag litter trends from places that do not have a policy.
Over the study period, plastic bags’ share of cleanup items increased overall. But in places with plastic bag bans there was a 25-to-47% decrease in plastic bags as a share of total items collected relative to areas without policies.
This difference increased over time with no evidence of rebound or spillover effects. They concluded that both plastic bag bans and fees reduce plastic litter. The least effective strategy, though were partial bans, likely owing to exemptions for thicker plastic bags. They said state-level policies are the most robust but policies at all geographic scales are effective. Bag policies yield similar effects along coasts and rivers, with evidence for larger effects along lakes. And they have the greatest impact in places where plastic bag litter is most prevalent.
The researchers also found an imprecise reduction of animals entangled in plastic in areas with plastic bag policies of 30 to 37% reduction in the presence of entangled animals in areas with plastic bag policies.
Their conclusions are timely as 175 countries are currently weighing options for a Global Plastics Treaty.
