Mr. Siegler said the researchers had evaluated waste-disposal practices in countries around the world and used their “best professional judgment” to determine the lowest and highest amounts of plastic waste likely to escape into the environment. They settled on a range of 25 percent to 75 percent.
Tony Walker, an associate professor at the Dalhousie University School for Resource and Environmental Studies in Halifax, Nova Scotia, said that analyzing waste data can amount to a “data minefield” because there are no data standards across municipalities. Moreover, once plastic waste is shipped overseas, he said, data is often not recorded at all.
Nonetheless, Dr. Walker, who was not involved in the study, said it could offer a more accurate accounting of plastic pollution than the previous study, which likely underestimated the United States’ contribution. “They’ve put their best estimate, as accurate as they can be with this data,” he said, and used ranges, which underscores that the figures are estimates.
Of the plastics that go into the United States recycling system, about 9 percent of the country’s total plastic waste, there is no guarantee that they’ll be remade into new consumer goods. New plastic is so inexpensive to manufacture that only certain expensive, high-grade plastics are profitable to recycle within the United States, which is why roughly half of the country’s plastic waste was shipped abroad in 2016, the most recent year for which data is available.
Since 2016, however, the recycling landscape has changed. China and many countries in Southeast Asia have stopped accepting plastic waste imports. And lower oil prices have further reduced the market for recycled plastic.
“What the new study really underscores is we have to get a handle on source reduction at home,” Mr. Mallos said. “That starts with eliminating unnecessary and problematic single-use plastics.”