Report Heavy Metal Contamination Alarms Northern Thailand: Rivers at Risk

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Picture courtesy of Bangkok Post

 

Authorities in northern Thailand have confirmed alarming levels of arsenic and other heavy metals in the Kok, Sai, and Mekong rivers, as discovered by the Pollution Control Department (PCD). The contamination, traced back to upstream mining operations in Myanmar’s Shan State, poses a significant threat to the region's water quality and public health.

 

Findings from PCD's three rounds of water and sediment sampling, conducted between March 19 and May 16, revealed extensive pollution. The Kok River, particularly from Tha Ton in Chiang Mai's Mae Ai district to Chalerm Phrakiat Bridge in Chiang Rai, exhibited the highest contamination levels. Here, arsenic concentrations were recorded at 0.44 milligrams per litre (mg/l) — over 40 times the safe threshold of 0.01 mg/l.

 

In the vicinity of the Thai–Myanmar border in Chiang Rai, lead levels also exceeded safety standards, peaking at 0.076 mg/l. Although other metals like cadmium, mercury, and manganese were within safe limits, the persistence of arsenic remains a primary concern for health and environmental officials. The PCD emphasizes that arsenic's presence in these waters is a stark indicator of mining activity's impact.

 

“Water quality along the Myanmar border shows elevated turbidity and arsenic due to mining impacts,” noted a PCD official. Historical data from 2014-2015 had not shown such contamination, suggesting a recent escalation. Sediment testing further confirmed that arsenic and lead levels exceeded safety standards for benthic organisms. Experts warn that regular consumption of fish from these waters could pose serious long-term health risks.

 

The PCD warns that chronic exposure to these metals, particularly arsenic, could lead to severe health outcomes over time. Although arsenic levels downstream are within acceptable limits, sedimentation has allowed contaminated particles to settle at certain points, mitigating the spread slightly.

 

However, the situation in the Sai River is more severe, with arsenic levels at all sites surpassing safety guidelines, ranging between 0.044 and 0.049 mg/l. Although lead levels initially exceeded limits, they returned to normal by the third testing round. Meanwhile, the Mekong River showed arsenic concentrations remaining a concern, with variations recorded in the Chiang Saen district.

 

Tributaries such as the Fang, Korn, Lao, and Suai rivers showed sporadic spikes in nickel, arsenic, and chromium. The Korn River registered the highest contamination range. The PCD attributes arsenic in the Mekong to inflows from the Sai and Ruak rivers, which originate in Myanmar.

 

Natural Resources and Environment Minister Chalermchai Sri-on acknowledged Thailand's challenges in addressing cross-border pollution, noting that mining in Shan State, controlled by the United Wa State Army, is the primary source. “We must proceed carefully, using diplomatic channels step by step,” he stated.

 

In response, the ministry has proposed constructing check dams to trap sediments before they travel further downstream, a project estimated to cost over 7 billion baht. Water resources expert Sitang Pilailar from Kasetsart University cautioned that the dams should be well-designed to contain fine sediments and withstand pressure. She also advocated for immediate exploration of clean water sources and investment in reverse osmosis systems to filter heavy metals.

 

"Thailand must not act as though it is powerless in safeguarding its territory," Ms Sitang urged, calling for a decisive national response to protect public health.

 

Locally, Chiang Rai residents plan to rally for an end to Myanmar's mining activities, appealing to embassies for intervention. As the situation unfolds, Thailand’s ability to manage cross-border environmental challenges is put to the test, highlighting urgent needs for policy action and international cooperation.

 

  Adapted by ASEAN Now from Bangkok Post 2025-06-05