On October 28, 2025, Assoc. Prof. Dr. Wan Wiriya, Assistant Head of the Environmental Science Research Center at Chiang Mai University (CMU), revealed that samples collected from the Salween River in early September — at three locations in Mae Sariang District, Mae Hong Son Province — showed dangerously high levels of arsenic contamination.
The tests found:
0.05 mg/L of arsenic in samples from the upper Salween River, slightly above Ban Tha Ta Fang (standard limit: 0.01 mg/L),
0.05 mg/L again at a downstream point near Tha Ta Fang, and
0.04 mg/L at Ban Mae Sam Laep.
Dr. Wan said this was not the first such finding. Earlier tests from the Salween also showed arsenic levels exceeding safe standards, along with other heavy metals approaching dangerous concentrations. “This poses a high risk,” he warned. “Authorities should urgently conduct further tests and issue public warnings.”
“There should be an official alert process to tell people to avoid contact with the water for now,” Dr. Wan said. “I’m not sure if the Pollution Control Department has conducted any water quality checks there yet.”
The Salween River, stretching about 2,800 km, originates from the Himalayas, China, flows through Myanmar’s Shan, Karenni, Karen, and Mon States, and forms a 127-kilometer stretch along the Thai border in Mae Hong Son Province before reaching the Gulf of Martaban and Andaman Sea.
When asked about possible causes of the contamination, Dr. Wan referred to data from the Stimson Center, which has documented extensive rare earth and other mining operations in the upper Salween basin. “Those sites are very far from where our samples were taken,” he noted, “so we can’t yet confirm the link. There are also large rubber plantations in some areas, and heavy runoff may contribute to river turbidity — we can’t say for sure yet what caused it.”
Regarding the recent U.S.–Thailand MOU on diversifying global critical minerals supply chains, Dr. Wan expressed strong opposition.
“Personally, I disagree with the signing,” he said. “It’s not worth the environmental cost. If Thailand wants to strengthen its economy, there are many other ways to do it — not by trading public health for profit. Even if they say no rare earth mines will be built, or that it would take years to develop, accidents can always happen, no matter how advanced the technology.”
“We still can’t solve the environmental problems caused by rare earth mining in neighboring countries that are already affecting us,” he added. “Why would we start the same problem here at home? It’s simply not worth the risk. Thailand has so many strengths in innovation — we shouldn’t sacrifice health for short-term gain.”
This is a translation of original Thai article https://transbordernews.in.th/home/?p=44290
