Arsenic Exceeds Standards at All Sai River Test Sites
Arsenic exceeded safety standards at every Sai River testing site in late September, matching a rising trend on the Mekong; authorities plan a joint investigation
The Pollution Control Department detected arsenic contamination exceeding standards at every testing point on the Sai River in its latest measurements, mirroring a rising arsenic trend on the Mekong River. On November 1, 2026, the department released results from its 23rd round of cross-border water pollution monitoring in Chiang Mai and Chiang Rai, conducted in late September across 23 stations on the Kok, Ruak, Mekong, and Sai rivers. Results showed arsenic levels above standard thresholds at all Sai River stations, while other rivers remained within limits. However, the Mekong is exhibiting an upward arsenic trend, which the department associates with transboundary water situations from neighboring countries. Regarding pollution sources, area inspections in the north have not identified any Thai-origin sources causing the problem. Authorities are preparing to cooperate with Myanmar to investigate causes and determine joint solutions, with a meeting scheduled for late November and coordination through the Mekong River Commission (MRC). The department emphasized that these findings pertain to surface water quality and do not confirm arsenic exceedance in tap water. Relevant agencies must continue monitoring water quality for consumption and agricultural impacts. This situation makes cross-border pollution resolution a critical mission for Chiang Rai, concerning water source safety, agriculture, and ecosystems, requiring cooperation from upstream countries alongside domestic vigilance.
