PCD’s latest tests find arsenic still above standard in Kok, Sai, Mekong rivers
PCD’s 16th round of monitoring found arsenic above the 0.01 mg/L limit at several points in the Kok, Sai and Mekong rivers, while all sampling points on the Ruak River met the standard.
- The Pollution Control Department's (PCD) latest monitoring found arsenic levels exceeding the standard of 0.01 mg/L in several northern rivers.
- Elevated arsenic levels were detected in the Kok River (at four points), the Sai River (at all monitored points), and the Mekong River (at two points).
- The measured arsenic concentrations in the affected rivers ranged from 0.011 to 0.016 mg/L.
- In contrast, tests showed that arsenic levels in the Ruak River were within the acceptable standard at all monitoring locations.
The Pollution Control Department (PCD) under the Ministry of Natural Resources and Environment reported the results of water and sediment monitoring on March 20, 2026, in the Kok River, its tributaries, the Sai River, the Ruak River and the Mekong River, covering areas in Chiang Mai and Chiang Rai provinces, in the 16th round of monitoring conducted between February 24-27, 2026, to continuously monitor turbidity and contaminants.
The results of the 16th water quality analysis under surface water quality standards found that, overall, heavy metal levels were within the standards for surface water sources.
However, arsenic was still found above the standard level, at more than 0.01 milligrams per litre (mg/L), in many areas, with details as follows.
- Kok River: Levels above the standard were found at four points, from Tha Ton Bridge in Chiang Mai to the bridge across the Kok River in Doi Hang Subdistrict, Chiang Rai, with readings ranging from 0.013-0.016 mg/L.
- Sai River: Arsenic levels above the standard were found at every monitoring point, ranging from 0.011-0.015 mg/L.
- Mekong River: Levels above the standard were found at the Golden Triangle permanent border crossing and at the water intake point of the Provincial Waterworks Authority’s Mae Sai branch, ranging from 0.014-0.015 mg/L.
- Ruak River: Arsenic levels were within the standard at every monitoring point.
The PCD will continue to closely and continuously monitor the situation and keep the public informed. It advised people in the area that, if they need to use water continuously, it should first go through a water quality improvement process to ensure health safety.
