Dangerous arsenic levels detected in Thailand’s Mekong mainstream for the first time

BANGKOK — Thai authorities have discovered what they described as harmful levels of arsenic contamination in sediment from the Mekong River and three of its tributaries in the northern provinces of Chiang Mai and Chiang Rai.

Heavy steel air pollution has been reported from key tributaries of the Mekong for greater than a 12 months now, however the assessments carried out in March by Thailand’s Pollution Control Department mark the first time that arsenic contamination has been detected on the mainstream of the Mekong, an important transboundary river that helps 1000’s of plant and wildlife species and the livelihoods of thousands and thousands of individuals.

The check outcomes revealed in mid-April present that sediment taken from three separate monitoring stations alongside the Mekong mainstream contained arsenic concentrations of between 73 and 296 milligrams per kilogram of sediment. According to the Pollution Control Department, concentrations of lower than 10 mg/kg are thought-about usually protected for aquatic life; Levels greater than 33 mg/kg are deemed harmful.

Arsenic levels in sediment taken from numerous factors alongside the Kok, Sai and Ruak rivers, key tributaries of the Mekong, all ranged from under the 33 mg/kg protected restrict as much as 57 mg/kg, the Pollution Control Department stated by way of its official Facebook pagenoting the contamination seems to be spreading by means of the river system.

Heavy steel air pollution in the Mekong Basin has been broadly linked to unregulated mining additional upstream in Myanmar. A rush of mining in search of to extract gold, essential minerals and uncommon earth components has left a swath of destruction in northeastern Myanmar, with US-based think tank the Stimson Center Using satellite tv for pc imagery evaluation to establish 833 unregulated mines throughout the Mekong River Basin. Of these, 86 are considered uncommon earth mines, because of the distinctive blue tarpaulin leaching ponds. More than half of those 86 mines opened between 2024 and 2026.

More than 50 million people throughout the Lower Mekong River Basin depend on the river for water, fish and livelihoods, however the Mekong has additionally lengthy been a biodiversity hotspot, internet hosting some 20,000 species of vegetation, together with a wide selection of aquatic life equivalent to the critically endangered Mekong giant catfish (Pangasianodon gigas) and the endangered Irrawaddy dolphin (Orcaella brevirostris). The Mekong subspecies of Irrawaddy dolphin is taken into account critically endangered, with fewer than 100 individuals thought to stay. the river also supports an estimated 1,200 chicken, 800 reptile and amphibian, and 430 mammal species.

In latest years, the Mekong and its beneficiaries have been strained by the proliferation of hydropower damstogether with unsustainable fishingrampant deforestation, altering land-use and contamination from agricultural chemicals. Now, the latest growth in uncommon earth and important mineral extraction dangers pushing the river to the brink.

Exporting the drawback downstream

Rare earth components are essential to army, aerospace and vehicle industries globally, in addition to fueling the inexperienced vitality transition. But they’re sometimes extracted utilizing an particularly ecologically damaging type of mining. The course of includes injecting a liquid resolution of poisonous chemical compounds into mountaintops, liquefying the contents, draining them out, and separating the uncommon earth components from the liquefied ore in leaching ponds.

The stage of environmental harm attributable to this type of mining, generally known as in situ miningnoticed China, the world’s main producer and processor of uncommon earths, place heavy restrictions on its home mines back in 2009whereas quietly transferring mining operations into different jurisdictions, like Myanmar, Mongolia and Malawi.

While numerous armed factions in Myanmar are mining essential and uncommon earth minerals as a method of financing the ongoing fightinga lot of the uncommon earth mining operations in the Mekong River Basin are centered in the Kengtung, Tachileik and Monghsat districts of Shan state on the nation’s japanese border with Thailand. These elements of the basin are primarily territories held by the United Wa State Army (UWSA) and the allied National Democratic Alliance Army, each of which get pleasure from shut ties to China and agreements with Myanmar’s army guaranteeing a stage of autonomy in trade for neutrality in the ongoing battle.

Mining throughout Shan state can be suspected to the supply of contamination that was detected by Thailand’s Pollution Control Department in the Salween Riverthe place assessments carried out in March 2026 noticed an increase in arsenic levels in comparison with January 2026 and November 2025 outcomes.

Thai authorities have since issued alerts to numerous riverine communities, together with these dwelling alongside the Mekong in Chiang Rai, warning them towards consuming an excessive amount of fish from the rivers. Some communities have been urged to keep away from the water altogether.

Regan Kwan, lead researcher at the Stimson Center, helped devise the suppose tank’s on-line platform monitoring mining throughout mainland Southeast Asia. In an e-mail, he instructed Mongabay that the most up-to-date detections of arsenic contamination in the Mekong might be associated to seasonal modifications, with heavy rainfall rising the probability of leaching ponds at mining websites overflowing and accelerating the movement of rivers, carrying contamination farther downstream. The outcomes, Kwan added, look regarding and critical.

“While government action should be focused on addressing immediate needs for communities who rely on the river for sustenance, income, and cultural reasons, this should raise the call for long-term and consistent water testing throughout the basin,” Kwan stated. “There is now more data than a year ago when the mines on the Kok River were discovered, but it still feels like governments aren’t responding accordingly.”

I’ve famous that there are nonetheless many unknowns relating to the basin-wide impacts of mining air pollution, significantly on plant and animal life, however the lack of regional coordination is not serving to.

Limits to authority and testing

A consultant of the Mekong River Commission, which seeks to manage exercise on the transboundary river community, instructed Mongabay by e-mail that arsenic contamination seems to be domestically concentrated in Chiang Rai and that there is “no indication of immediate basin-wide impacts.”

The Mekong River Commission is working to facilitate cooperation and knowledge exchanges between governments, however would not perform unbiased discipline testing, its consultant stated.

“With the information currently available, there is no confirmed evidence establishing a direct link between the observed conditions in the Mekong River and mining activities in any specific country or area,” the consultant stated. “However, monitoring results indicate that inputs through the Kok–Sai–Ruak river network may be one pathway requiring further assessment.”

They added that the transboundary nature of the Mekong requires monitoring of the total basin and that this monitoring is ongoing all through the fee’s member states: Cambodia, Laos, Thailand and Vietnam. China and Myanmar stay dialogue companions over which the Mekong River Commission has no regulatory authority.

Mongabay contacted the Thai Pollution Control Department, the Lao Ministry of Agriculture and Environment and the Lao National Mekong Committee for touch upon the subject. None had responded by the time this story was revealed. Cambodia’s Ministry of Environment additionally didn’t reply, however Heng Kong, director of the new Cambodian Agricultural Sciences Academyinstructed Mongabay that “We do not have budget to [test for] these heavy metals.”

Mongabay additionally despatched questions on the import of minerals from Myanmar to China’s overseas ministry, however it hasn’t responded.

Information has remained sparse throughout the area, with few particulars supplied on the penalties of publicity to heavy metals polluting river methods.

“Unlike many chemicals, metals do not degrade,” stated Brian Eyler, director of the Stimson Center’s Southeast Asia program. “They persist, accumulate, and proceed to trigger hurt lengthy after mining stops.

“And to be sure,” he added, “the mining has not stopped in the Mekong region.”

Banner picture: Fishermen in the Mekong River close to Chiang Khong, Thailand. Elevated arsenic levels at testing websites in the Mekong point out that contamination could also be spreading into this important waterway. Image by Stefan Lovgren.

Citations:

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