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

However, it can be difficult to avert illegal material once it arrives on the ship. The concern, proponents say, is that the difficulty getting American scrap plastic exporters to take back the shipments means they will slip through customs around the world or be re-shipped to an alternate destination.

“There will be a bit of chaos,” said Mr. Puckett. “When a shipment is returned, the question is where will it go next? It could just end up on another ship or in another country brokers will find is the next weak link out there. “

If the United States ratified the Basel Convention, which would require Congress to pass laws, traders found to be shipping plastic waste overseas could face prosecution. That being said, the United States government has limited ability to stop the export of plastic waste.

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

Even ardent opponents of the agreement could change their position. The Institute for the Scrap Recycling Industry has spoken out against the United States joining the Basel Accords, arguing that this hinders the legitimate trade in plastic scrap that can be recycled. This week, Ms. Adler said the trading group’s position on Basel was undergoing an internal review.

“In countries flooded with rubbish, there is gradually an outcry. And we are already seeing more countries starting to gain a foothold, ”said Azoulay. And the more Americans “learn that their waste ends up in fields in Malaysia or is openly incinerated in Indonesia or Vietnam, the better it gets.”

“I think we are at a crucial moment,” he said. “Will the illegal waste trade continue? Yes, without a doubt. But can it continue to the extent that it is happening? I do not believe that. “