Countries Tried to Curb Trade in Plastic Waste. The U.S. Is Shipping More.

One reason for the rise in plastic scrap from the United States, she said, could be the manufacturing of personal protective equipment that has been booming in Asia during the pandemic.

“I can say with confidence that there is compliant material’’ being shipped, she said.

But illicit material, once it arrives by ship, can be difficult to turn away. The worry, advocates say, is that the difficulty of getting American plastic scrap exporters to take the shipments back will mean they slip through customs around the world, or get shipped off again to an alternative destination.

“There’s going to be a bit of chaos,” Mr. Puckett said. “If a shipment does get returned, the question is, where is it going to go next? It could just end up on another ship, or in some other country that brokers are going to find is the next weak link out there.”

If the United States were to ratify the Basel agreement — which would require Congress to pass legislation — traders found to be shipping plastic waste overseas could be prosecuted. But short of that, the United States government is limited in its ability to stop plastic waste exports.

Still, growing awareness could start to change things, said David Azoulay, a Geneva-based lawyer with the Center for International Environmental Law, a nonprofit environmental law firm.

Even ardent opponents of the agreement may be shifting their position. The Institute of Scrap Recycling Industries has opposed the United States joining the Basel agreement, arguing that it hampers legitimate trade of plastic scrap that can be recycled. This week, Ms. Adler said that the trade group’s position on Basel was under an internal review.

“You’re starting to see an outcry in countries being flooded with waste. And we are already seeing more countries starting to put their foot down,” Mr. Azoulay said. And the more Americans “learn that their waste ends up in fields in Malaysia, or openly burned in Indonesia or Vietnam, it’s not going to sit very well.”

“I do think that we’re in a pivotal moment,” he said. “Is illegal trade of waste going to continue to happen? Yes, without a doubt. But can it continue at the scale that it is currently happening? I don’t think so.”