Arsenic Contamination in the Kok River Has Become an Environmental Crisis

CHIANG RAI – Although the arsenic contamination problem in the Kok River in Chiang Rai Province has been ongoing for several months, the situation remains unresolved, impacting residents.

Dr. Sonthi Kotchawat, an environmental and health academic from the Thai Environmental Academic Club, has revealed that arsenic contamination in the Kok River, Chiang Rai, has turned into an environmental crisis.

This problem now threatens public health and makes the repeated flooding in the area even worse. Talks with Myanmar have made little progress, so Thailand must urgently put in place measures to reduce the damage at home.

There is also a need to push for clear laws on cross-border pollution within ASEAN as a way to address this issue in the long term.

Water tests from the Myanmar side, taken in June 2025, reinforce the Myanmar government’s position. Arsenic levels at three locations, 0.026, 0.012, and 0.013 milligrams per litre, are within Myanmar’s standard of no more than 0.05 milligrams per litre.

However, these figures go above Thailand’s tighter threshold of 0.01 milligrams per litre. Myanmar insists there is no legal mining in these areas. If any mining does happen, it is seen as illegal and outside government control.

Myanmar has even suggested Thailand should monitor and regulate chemical exports to make sure they do not end up being used in unauthorized mines.

Rare Earth Mines in Myanmar

Thailand faces a major hurdle. Satellite photos from Thai agencies cannot be presented as negotiation evidence because the areas in question sit within Myanmar’s border. Sharing such information could be viewed as spying, which might damage international relations.

This means bilateral talks alone are not enough to fix the problem.

ASEAN could offer a path forward by using the framework set out in the Agreement on Disaster Management and Emergency Response (AADMER). This would allow countries to discuss the matter together.

However, unlike the European Union, ASEAN does not have any laws about cross-border pollution.

This creates a diplomatic dilemma and highlights why ASEAN should speed up work on laws that handle pollution across borders. Such rules would help manage environmental risks that exceed national boundaries.

Meanwhile, Thailand cannot wait for other countries to act. The government must move ahead with urgent local steps, like building several temporary check dams to slow the water and limit the impact on local ecosystems. Safe disposal of arsenic-rich sediments is a must to stop further contamination from spreading.

The arsenic situation in the Kok River is more than just a local environmental problem. It shows the bigger political and legal challenges between countries. Fixing it will take a mix of on-the-ground solutions, policy work, and diplomacy. All of this is needed to protect people’s health and secure clean water for the future.

Although the problem of arsenic contamination in the Kok River, Chiang Rai, has been ongoing for months, the issue remains unresolved and still affects local communities. Thai PBS and Thai PBS Sci & Tech looked into why this situation is so difficult to address.

Dr. Sonti Kotchawat gives five key points on Kok River Contamination:

1. Talks with Myanmar have not led to a solution. The government spokesperson stated that in discussions with Myanmar on 3 July 2024, Myanmar had these viewpoints:
   • Myanmar believes the arsenic contamination may be naturally occurring. Arsenic is already present in the soil, and heavy rainfall in both Myanmar and Thailand, especially in forested and mountainous areas, can wash soil containing arsenic into water sources. Both countries also clear land for farming, which could increase the runoff.
   • There are no registered or licensed mining operations in the Shan State region near the Kok River. Myanmar notes that mining projects must follow strict environmental rules that require Environmental Impact Assessments (EIA), and any legal mines must sit at least 300 metres from rivers. The area is also classed as a conservation zone, which makes mining illegal there. Myanmar has been in talks with Shan State representatives to monitor this issue.
   • Water tests from Myanmar in June 2024 at three points along the river found arsenic levels within Myanmar’s national safety limits of 0.050 milligrams per litre. The readings were 0.026 mg/L near the river’s start, 0.012 mg/L at the second point, and 0.013 mg/L near the Thai border. Myanmar plans to continue these checks. For reference, Thailand’s legal limit is stricter at 0.01 mg/L.
   • Myanmar pointed out that they do not allow mining on the Kok River. If any mines do exist, as Thailand suggests, they would be operating illegally, making it nearly impossible for Myanmar to regulate or monitor them. Myanmar suggested that Thailand restrict chemical exports for mining, so illegal mines on their side cannot get the needed supplies. This, they say, could reduce illegal mining and help stem the problem at its source.
2. Thailand cannot use its own satellite images in talks with Myanmar because suspected mining sites are across the border. Using Thai government satellite data risks diplomatic strain and could be seen as spying, which is a sensitive security issue for Myanmar.
3. Thailand may need to raise the issue at the ASEAN level, using the regional agreement for disaster management and emergency response as a way to discuss the problem collaboratively.
4. ASEAN nations do not yet have laws to address cross-border pollution like the EU does with its own transboundary pollution regulations. This makes regional solutions harder. It would help if ASEAN countries worked together to set up rules for dealing with pollution that travels between countries.
5. While stopping arsenic at the source remains out of reach, Thailand must take practical steps to lessen its impact on Chiang Rai and nearby areas. Temporary measures could include setting up small dams that slow down the river, aimed at minimizing harm to local ecosystems. Contaminated sediment should be collected and disposed of safely to keep arsenic from spreading wider.

Dr. Sonthi said tackling the arsenic issue will demand persistent joint efforts, both within Thailand and with its neighbours, to protect local communities from further harm.