Bangkok, Thailand – A surge in rare earth mining in rebel-held pockets of Myanmar supplying Chinese processing plants is being blamed for toxic levels of heavy metals in Thai waterways, including the Mekong River.

China dominates the global refining of rare earth metals – key inputs in everything from wind turbines to advanced missile systems – but imports much of its raw material from neighbouring Myanmar, where the mines have been blamed for poisoning local communities.

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Recent satellite images and water sample testing suggest the mines are spreading, along with the environmental damage they cause.

“Since the mining operation started, there is no protection for the local people,” Sai Hor Hseng, a spokesman at the Shan Human Rights Foundation, a local advocacy group based in eastern Myanmar’s Shan state, told Al Jazeera.

“They don’t care what happens to the environment,” he said, or those living downstream of the mines in Thailand.

An estimated 1,500 people rallied in northern Thailand’s Chiang Rai province in June, urging the Thai government and China to pressure the mining operators in Myanmar to stop polluting their rivers.

Villagers in Chiang Rai first noticed an odd orange-yellow tint to the Kok River – a tributary of the Mekong that enters Thailand from Myanmar – before the start of this year’s rainy season in May.

Repeated rounds of testing by Thai authorities since then have found levels of arsenic and lead in the river several times higher than what the World Health Organization (WHO) deems safe.

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Thai authorities advised locals living along the Kok to not even touch the water, while tests have also found excess arsenic levels in the Sai River, another tributary of the Mekong that flows from Myanmar into Thailand, as well as in the Mekong’s mainstream.

Locals are now worried about the harm that contaminated water could do to their crops, their livestock and themselves.

Arsenic is infamously toxic.

Medical studies have linked long-term human exposure to high levels of the chemical to neurological disorders, organ failure and cancer.

“This needs to be solved right now; it cannot wait until the next generation, for the babies to be deformed or whatever,” Pianporn Deetes, Southeast Asia campaign director at the advocacy group International Rivers, told Al Jazeera.

“People are concerned also about the irrigation, because … [they are] now using the rivers – the water from the Kok River and the Sai River – for their rice paddies, and it’s an important crop for the population here,” Pianporn said.

“We learned from other areas already … that this kind of activity should not happen in the upstream of the water source of a million people,” she said.

‘A very good correlation’

Thai authorities blame upstream mining in Myanmar for the toxic rivers, but they have been vague about the exact source or sources.

Rights groups and environmental activists say the mine sites are nestled in pockets of Shan state under the control of the United Wa State Army (UWSA), a well-armed, secretive rebel group that runs two semi-autonomous enclaves in the area, one bordering China and the other Thailand.

That makes the sites hard to access. Not even Myanmar’s military regime dares to send troops into UWSA-held territory.

While some have blamed the recent river pollution on the UWSA’s gold mines, the latest tests in Thailand lay most of the fault on the mining of rare earth minerals.

In a study commissioned by the Thai government, Tanapon Phenrat, an associate professor of civil engineering at Naresuan University, took seven water samples from the Kok and surrounding rivers in early June.

Tanapon told Al Jazeera that the samples collected closest to the border with Myanmar showed the highest levels of heavy metals and confirmed that the source of the contamination lay upstream of Thailand in Shan state.

Significantly, Tanapon said, the water samples contained the same “fingerprint” of heavy metals, and in roughly the same concentrations, as had earlier water samples from Myanmar’s Kachin State, north of Shan, where rare earth mining has been thriving for the past decade.

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“We compared that with the concentrations we found in the Kok River, and we found that it has a very good correlation,” Tanapon said.

“Concentrations in the Kok River can be attributed about 60 to 70 percent … [to] rare earth mining,” he added.

The presence of rare earth mines along the Kok River in Myanmar was first exposed by the Shan Human Rights Foundation in May.

Satellite images available on Google Earth showed two new mine sites inside the UWSA’s enclave on the Thai border developed over the past one to two years – one on the western slope of the river, another on the east.

The foundation also used satellite images to identify what it said are another 26 rare earth mines inside the UWSA’s enclave next to China.

All but three of those mines were built over the past few years, and many are located at the headwaters of the Loei River, yet another tributary of the Mekong.

Researchers who have studied Myanmar’s rare earth mining industry say the large, round mineral collection pools visible in the satellite images give the sites away as rare earth mines.

The Shan Human Rights Foundation says villagers living near the new mines in Shan state have also told how workers there are scooping up a pasty white powder from the collection pools, just as they have seen in online videos of the rare earth mines further north in Kachin.

‘Zero environmental monitoring’

Patrick Meehan, a lecturer at the University of Manchester in the UK who has studied Myanmar’s rare earth mines, said reports emerging from Shan state fit with what he knows of similar operations in Kachin.

“The way companies tend to operate in Myanmar is that there is zero pre-mining environmental assessment, zero environmental monitoring, and there are none of those sorts of regulations or protections in place,” Meehan said.

The leaching process being used involves pumping chemicals into the hillsides to draw the rare earth metals out of the rock. That watery mixture of chemicals and minerals is then pumped out of the ground and into the collection pools, where the rare earths are then separated and gathered up.

Without careful attention to keeping everything contained at a mine, said Meehan, the risks of contaminating local rivers and groundwater could be high.

Rare earth mines are situated close to rivers because of the large volumes of water needed for pumping the extractive chemicals into the hills, he said.

The contaminated water is then often pumped back into the river, he added, while the groundwater polluted by the leaching can end up in the river as well.

“There is definitely scope for that,” said Meehan.

He and others have tracked the effect such mines have already had in Kachin – where hundreds of mining sites now dot the state’s border with China – from once-teeming streams now barren of fish to rice stalks yielding fewer grains and livestock falling ill and dying after drinking from local creeks.

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In a 2024 report, the environmental group Global Witness called the fallout from Kachin’s mining boom “devastating”.

Ben Hardman, Mekong legal director for the US advocacy group EarthRights International, said locals in Kachin have also told his team about mineworkers dying in unusually high numbers.

The worry now, he adds, is that Shan state and the neighbouring countries into which Myanmar’s rivers flow will suffer the same fate as has Kachin, especially if the mine sites continue to multiply as global demand for rare earth minerals grows.

“There’s a long history of rare earth mining causing serious environmental harms that are very long-term, and with pretty egregious health implications for communities,” Hardman said.

“That was the case in China in the 2010s, and is the case in Kachin now. And it’s the same situation now evolving in Shan state, and so we can expect to see the same harms,” he added.

‘You need to stop it at the source’

Most, if not all, of the rare earths mined in Myanmar are sent to China to be refined, processed, and either exported or put to use in a range of green-energy and, increasingly, military hardware.

But, unlike China, neither Myanmar, Laos nor Thailand have the sophisticated processing plants that can transform raw ore into valuable material, according to SFA (Oxford), a critical minerals and metals consulting firm.

The Institute for Strategy and Policy-Myanmar, a local think tank, says Chinese customs data also show that Myanmar has been China’s main source of rare earths from abroad since at least 2017, including a record $1.4bn-worth in 2023.

Myanmar’s exports of rare earth minerals were growing at the same time as China was placing tough new curbs on mining them at home, after witnessing the environmental damage it was doing to its own communities. Buying the minerals from Myanmar has allowed China to outsource much of the problem.

That is why many are blaming not only the mine operators and the UWSA for the environmental fallout from Myanmar’s mines, but China.

The UWSA could not be reached for comment, and neither China’s Ministry of Foreign Affairs nor its embassy in Myanmar replied to Al Jazeera’s emails seeking a response.

In a June 8 Facebook post, reacting to reports of Chinese-run mines in Myanmar allegedly polluting Thai rivers, the Chinese embassy in Thailand said all Chinese companies operating abroad had to follow local laws and regulations.

The embassy also said China was open to cooperating with Mekong River countries to protect the local environment, but gave no details on what that might entail.

Thailand has said it is working with both China and Myanmar to solve the problem.

In a bid to tackle the problem, though, the Thai government has proposed building dams along the affected rivers in Chiang Rai province to filter their waters for pollutants.

Local politicians and environmentalists question whether such dams would work.

International Rivers’ Pianporn Deetes said there was no known precedent of dams working in such a manner in rivers on the scale of the Mekong and its tributaries.

“If it’s [a] limited area, a small creek or in a faraway standalone mining area, it could work. It’s not going to work with this international river,” she said.

Naresuan University’s Tanapon said he was building computer models to study whether a series of cascading weirs – small, dam-like barriers that are built across a river to control water flow – could help.

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But he, too, said such efforts would only mitigate the problem at best.

Dams and weirs, Tanapon said, “can just slow down or reduce the impact”.

“You need to stop it at the source,” he added.