Arsenic crisis on Salween and Mekong tied to Myanmar mining threatens Thai communities

Arsenic alarms on the Salween spur urgent calls in Thailand

Recent lab tests in Mae Hong Son province have detected arsenic levels in the Salween River far above national safety limits, forcing local authorities in Sop Moei district to ban residents from using river water or consuming fish caught from it. The emergency measure underscores a growing crisis that stretches beyond the Thai border. Pollution linked to mining in Myanmar is spreading through shared river systems that support drinking water, fisheries, irrigation, and daily life for villages on both sides.

Thai agencies are retesting water and fish from multiple sites to verify the scale of contamination and to rule out seasonal spikes. Early findings from researchers at Chiang Mai University showed arsenic readings up to five times the standard at locations in Mae Sariang, while other heavy metals were approaching unsafe thresholds. That pattern points to a chronic source upstream rather than a single spill.

Associate Professor Surasak Boonrueang, an environmental law scholar at Thammasat University, argues that Thailand will need stronger and sustained diplomacy with Myanmar and with authorities in territories run by ethnic armed groups to reduce risk at the source. He has urged the government to create a formal process for cross border environmental assessment and early warning, together with short term relief for affected families.

Thai officials have begun to coordinate a broader response. The Pollution Control Department and the Department of Water Resources are conducting confirmatory sampling, with guidance from the Geo Informatics and Space Technology Development Agency to help trace likely sources. Local leaders say many households rely on the Salween for agriculture, livestock, fishing, and washing, and floating communities are most exposed because they depend directly on river water.

Why contamination is rising now

Mining inside Myanmar has expanded rapidly in recent years, especially extraction of rare earth minerals used in smartphones, electric vehicles, and wind turbines. A surge in demand and stricter environmental enforcement inside China has pushed more production across the border. In Myanmar, the 2021 coup weakened oversight and emboldened operations in frontier areas where the central military has limited control. Many mines use a chemical method known as in situ leaching. Operators pump acidic solutions into hillsides to dissolve rare earths, then pipe the liquid to circular ponds for processing. Heavy rain frequently overtops these ponds, flushing toxic mixtures into streams that feed the Salween and the Mekong.

New satellite analysis from researchers at the Stimson Center identified 513 rare earth mining sites across tributaries of the Mekong, Salween, and Irrawaddy in Myanmar over the past decade, with at least 40 new sites opening this year. Activity has shifted from Kachin to Shan state, closer to the Thai border. Thai communities downstream report sticky mud and discolored water during high flow periods, and local groups estimate losses to farming, fishing, and tourism of about 1.3 billion baht, or roughly 40 million dollars. The Kok, Sai, and Ruak rivers, along with stretches of the Mekong and the Salween, are all at risk.

How pollution moves from Myanmar hills to Thai taps

The mining belt straddles watersheds. Wastewater and leachate flow west through small streams such as the Kar River into the Salween, and east through channels like the Lwai into the Mekong. In northern Thailand, contamination has tracked through the Sai and Kok rivers before merging with the Mekong, carrying a mixture of acids, arsenic, and other metals that attach to sediment. Rivers do not respect borders, and fine particles travel far during monsoon surges.

Arsenic occurs naturally in ore bodies, but mining accelerates its release. Acid mine drainage pulls metals from rocks and soils, creating water that can be both acidic and loaded with dissolved contaminants. As the plume moves, some metals bind to mud that settles in calmer reaches or on floodplains, while dissolved forms can stay in the water column. Fish and shellfish accumulate these substances over time and can transfer them to people who rely on river catch for protein.

Flood events magnify the spread. During Typhoon Yagi in 2024, floodwaters rushed through rare earth zones in Shan state and inundated nearby towns, then drained back into the river network. Each flush mobilizes pollutants that can linger in riverbed sediment or seep into shallow aquifers, creating a problem that persists long after the rain recedes.

What arsenic and heavy metals mean for health and food

Arsenic is a potent toxin. Chronic exposure is linked to skin lesions, cancers of the skin and internal organs, cardiovascular disease, and neurological problems. Infants and children are especially vulnerable because metals can impair development. Pregnant women face added risks from exposure through water and food. When arsenic levels are several times the drinking water standard, both ingestion and food chain exposure become key concerns.

The danger extends to crops and livestock. Irrigation with contaminated water can leave residues in soils and in produce, depending on soil chemistry and the form of the metal. Fish and mollusks concentrate arsenic and other metals such as lead, antimony, and nickel. Communities that depend on fishing often face the hardest choices, since switching to new livelihoods or buying food from outside the basin can be costly.

Who is responsible and how can accountability work

The sources sit in a patchwork of authority. Parts of northern Shan state are controlled by the United Wa State Army and other ethnic armed organizations, and some areas fall under the Myanmar military or its allies. Reports from the Shan Human Rights Foundation show an eightfold increase in mining sites around Mong Bawk since 2015, including new operations only a few kilometers from towns and farms. The group has documented in situ leaching ponds and suspected contamination of streams such as the Pai that run directly through residential areas. Floods in late 2024 washed waste from mine slopes into streets and fields before the water drained back to rivers.

Debate over responsibility is intensifying. Community activists and Thai commentators often single out ethnic armies for enabling the mining boom. Regional analysts counter that Chinese backed firms and financiers sit behind much of the expansion, using proxies and informal joint ventures that blur lines of accountability. A fair assessment requires field sampling and hydrological tracing that can connect specific mining clusters to contamination seen downstream. Without transparent data and access to sites, blame will only shift without reducing risk.

What Thai authorities are doing now

Thailand has started to move on several tracks. In Mae Hong Son, district officials have ordered temporary bans on using river water or eating fish from affected stretches of the Salween. The Pollution Control Department and the Department of Water Resources are retesting water and fish samples from multiple locations, with results expected within a week. Agencies are coordinating with the national space agency to use satellite and land use data to pinpoint likely sources on the Myanmar side.

Associate Professor Surasak Boonrueang says emergency relief should be paired with structural fixes, including a single public alert system, a central database, and a legal framework to assess and disclose environmental risk before mining concessions are approved. He wants the Pollution Control Department to lead water quality monitoring and to share data in a way that communities can easily use.

After calling for a binding process, he highlighted the need for shared standards across borders. He framed the aim in simple terms.

Transboundary impact assessments are essential to protect public health and shared ecosystems.

What a cross border framework could look like

A transboundary environmental impact assessment, or TEIA, is a formal process that requires project developers to analyze risks that cross borders and to share the results with neighboring governments and the public. If Thailand and Myanmar adopt a TEIA for mining, operators would have to disclose who is investing, where chemicals are stored, how waste ponds are lined, what baseline water quality looks like, and what monitoring will continue during and after operations. Agencies on the Thai side would gain an avenue to review plans, issue warnings, and request mitigation before damage spreads downstream.

International examples offer a guide. In Central Asia, agencies from Kyrgyzstan and Kazakhstan tested a TEIA process for a copper and gold project near their border. The pilot created a shared platform for collecting baseline data, consulting communities, and designing emergency communication protocols. The details differ from Southeast Asia, yet the principle is the same. Neighboring states have legitimate interests in projects that could contaminate their rivers.

Thailand also has a regional tool to build on. The Mekong River Agreement sets out rules for notifying other members about activities that may affect the river, such as dam operations and major diversions. Extending that spirit to mining would mean regular disclosure, joint monitoring stations on shared tributaries, and agreed steps for emergency alerts when dust, acid, or heavy metals surge after storms. Dialogue with Myanmar and China would need to be practical and focused on information sharing even when politics are strained.

What communities and experts say is needed now

Grassroots networks in northern Thailand have filled gaps left by slow official action. They have pushed for continuous testing of water, soil, and fish, mobile clinics to screen for heavy metal exposure, alternative water supplies for villages that rely on river intakes, and financial support for fishers and farmers who have lost income. Some groups want a temporary halt to imports of rare earth concentrates from Myanmar until mines comply with credible environmental standards.

Pianporn Deetes, Southeast Asia program director at International Rivers, has monitored the issue and reviewed satellite evidence of rare earth mining near the Thai border. She argues that the extraction method and waste management are fundamentally unsafe and that communities bear the costs while exporters profit. In her view, nothing will change without coordinated action by Thailand and neighboring states to restrict illegal shipments and to raise standards at the source.

These mining methods are the epitome of irresponsibility. They use harsh chemicals to dissolve the ore and store it in toxic blue ponds, before burning it to extract the minerals. The result is devastating, leaving behind dangerous contaminants in the soil, water, and air.

Local health workers report growing anxiety about food safety. Residents in Chiang Rai and Chiang Mai have asked for frequent updates in plain language, clearer guidance on which stretches are safe for fishing and bathing, and a map of clean water points. Community leaders also want compensation mechanisms that move quickly and that are triggered by measured contamination, not long legal battles.

The Salween at a turning point

The Salween is one of Asia’s last great free flowing rivers. It runs more than 3,200 kilometers from the Tibetan Plateau through Yunnan and Myanmar and along the Thai border, supporting more than ten million people and a remarkable diversity of fish, birds, and mammals. Its upper reaches are a World Heritage Site, and the river’s seasonal rhythm moves sediment and nutrients that sustain floodplain farming and fisheries.

That heritage faces multiple pressures. Plans for large hydropower projects have long sparked conflict and displacement. Since Myanmar’s coup, illegal logging and mining have expanded in remote areas and conservation zones. Rare earth extraction has added a new layer of risk by releasing acids and metals into headwater streams that feed the Salween, the Mekong, and the Irrawaddy. The problem does not stop at a border line on a map. Countries as far downstream as Cambodia and Vietnam are being urged by researchers to test for acids and metals linked to mining, because the same contaminants can travel through the connected river network.

Key Points

• Arsenic well above safety limits was detected in the Salween in Mae Hong Son, prompting bans on river water use and fish consumption.
• Thai agencies are retesting water and fish while using satellite data to trace sources, and local leaders warn that floating households are most exposed.
• Rare earth mining in Myanmar has surged to more than 500 sites across the Salween, Mekong, and Irrawaddy basins, many using in situ leaching that leaks chemicals.
• Satellite and field reports point to rapid expansion in United Wa State Army territory near Mong Bawk, with operations close to towns and farms.
• Stimson Center researchers estimate about 1.3 billion baht in losses to farming, fishing, and tourism in northern Thailand from river pollution.
• Debate over responsibility spans ethnic armed groups, Myanmar authorities, and Chinese backed investors, highlighting the need for transparent data and joint monitoring.
• Experts urge a transboundary environmental impact assessment between Thailand and Myanmar, along with a single public alert system and a central database.
• Grassroots networks call for continuous testing, alternative water supplies, compensation, and tighter controls on imports of rare earth concentrates.
• The Salween remains a vital free flowing river, yet illegal mining and other pressures are putting shared ecosystems and livelihoods at risk.