Rich Western nations have been sending tens of millions of tons of plastic waste to developing Southeast Asian countries for decades.

It is not clear how much of it got there. Western companies pay for disposal of trash, contracts that can be accepted by overseas companies that import the waste.

This is legal, but authorities allege that the trash often isn't what the senders say it is and that illegal operators are taking the waste to burn or bury it without permission.

A lot of plastics end up being burned in illegal incinerators, which releases highly toxic fumes and causes respiratory illnesses and water-contamination issues.

Malaysia and the Philippines have recently decided to act, and they have sent large shipments of trash back to the West.

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Countries in Southeast Asia, long the recipients of huge consignments of Western trash, have decided to take a stand and send tons of the waste back to where it came from.

The world's richer nations have been exporting waste for at least 25 years, particularly plastic waste that is sorted for recycling, Channel News Asia reported.

Countries like the US, the UK, Germany, Canada, and Australia are among those to send large consignments to Asian countries including China, Malaysia, the Philippines, and Vietnam.

Many of those countries lack environmental regulations as stringent as those in Western nations, making them an attractive place to dispose of plastics, according to The Guardian.

It is difficult to track exactly how the global waste trade works. But, broadly, Western companies are prepared to pay to dispose of trash, and companies in poorer nations have been accepting the contracts.

Officials in the affected nations, however, say the trash they receive is often incorrectly labeled (for instance, shipments meant to contain plastic sometimes include household waste like soiled diapers).

They also say unscrupulous operators in their countries have been illegally incinerating or burying the trash.

China had for years been the largest dumping ground for plastics, receiving some 600,000 tons of imported plastic waste a month at its height in 2016, Greenpeace said in a report published in April.

Plastic waste piled outside an illegal recycling factory in Jenjarom, in Malaysia's Kuala Langat district, on October 14. Lai Seng Sin/Reuters

For many years, China took much of it and processed it into higher-quality material that could be reused by manufacturers, the South China Morning Post reported.

It banned the process last year, however, diverting vast amounts of trash to other countries still prepared to take it.

Unrecycled plastics tend to end up rotting in landfills or being burned in illegal incinerators, a process that releases highly toxic fumes that come with an acrid smell, according to The Guardian and the BBC. Only 9% of the world's plastic end up being recycled, National Geographic reported in 2017.

The illegal dumping and burning has caused respiratory illnesses among nearby residents, water contamination, and crop deaths, Greenpeace said.

Read more: Staggering photos show one small town covered in 19,000 tons of plastic waste

A worker sorting recyclable plastic waste at the Prabkaya Recycle Factory in Pathum Thani outside Bangkok in June 2017. Athit Perawongmetha/Reuters

When China banned imports of plastic, Malaysia took up most of the slack.

A HuffPost investigation last year found wrappers and packages from distinctly American companies, like Walmart, sticking out from trash heaps in Malaysia.

An article from China's state-owned CGTN channel said last month that after Beijing's ban, Western trash had turned Southeast Asia into a "global dumpyard."

Many Southeast Asian countries quickly followed in China's footsteps and imposed their own ban on foreign plastic waste starting in mid-2018, which contributed to a drop but ultimately did not stop the waste from flowing into their borders, according to Greenpeace statistics.

Now, those countries are taking their rejection of Western plastic a step further by sending the trash back where it came from.

Containers filled with plastic waste seen Tuesday in Port Klang, Malaysia, before being sent back to the country of origin. Adli Ghazali/Anadolu Agency/Getty

'Treated as trash'

Malaysia, which became the world's largest importer of plastic waste after China's 2018 ban, on Tuesday said it would send 3,000 metric tons back to the exporting countries.

Those countries include the US, Japan, France, Canada, Australia, and the UK, Reuters reported.

Yeo Bee Yin, Malaysia's environment minister, said her country would ship 60 containers of trash back, saying they had been "illegally brought into the country under false declaration," according to Reuters.

"If you ship to Malaysia, we will return it back without mercy," she said.

Yeo argued that the citizens of wealthy nations were largely unaware that their plastic trash was being dumped in Malaysia, where it is destroyed in ways harmful to the environment.

Dozens of mostly illegal recycling factories have cropped up in Malaysia amid the influx of rubbish. Many of those factories have been operating without licenses and have been ruining the surrounding environment by burning plastics.

Philippine President Rodrigo Duterte in Manila on July 24, 2017. NOEL CELIS/AFP/Getty Images

Malaysia's move comes weeks after Rodrigo Duterte, the strongman president of the Philippines, threatened to "declare war" on Canada last month if it did not take back 1,500 metric tons (1,650 tons) of garbage that had been shipped there in 2013 and 2014, the BBC and The Guardian reported.

Canada agreed to take back the rubbish but missed a May 15 deadline to take back the shipment. Last week, Duterte's government sent 69 containers of the trash to Canada, instructing the shipping company to leave them in Canada's territorial waters if the country refused to accept them.

"The Philippines as an independent sovereign nation must not be treated as trash by other foreign nation," Duterte's spokesman Salvador Panelo told reporters, as cited by Reuters.

Workers pushing a bundle of crushed plastic bottles at a recycling factory in Ahmedabad, India, in November. Amit Dave/Reuters

Greenpeace has accused Western countries of exploiting poorer, developing nations with inadequate regulatory framework.

"Instead of taking responsibility for their own waste, US companies are exploiting developing countries that lack the regulation to protect themselves," John Hocevar, a campaign director for Greenpeace USA, told The Guardian.

"It's a problem for the US and other developed countries to produce, often, toxic material which they can't or won't take care of themselves."

Beau Baconguis, a plastics campaigner at the Global Alliance for Incinerator Alternatives, also told the Thomson Reuters Foundation last month: "For the first world, it makes them feel good about their waste supposedly being recycled, but in reality it ends up in countries that cannot deal with the waste."

The world's 21 largest plastic exporters — with the three largest being the US, Japan, and Germany — produced 12.5 million tons of plastic in 2016, Greenpeace reported.

That number dropped to 9.99 million tons in 2017 and dramatically to 5.8 million tons in 2018. The new Chinese and Southeast Asian plastic import restrictions most likely contributed to the decrease, Greenpeace said.