Chiang rai: The Pollution Control Department (PCD) has reported that arsenic levels have exceeded the standard for the 19th consecutive time in a border river in northern Thailand. This revelation is part of the latest water quality test conducted on the Kok, Sai, Ruak, and Mekong rivers.
According to Thai News Agency, the testing results indicated that arsenic levels remained above the standard in several locations along the Kok, Sai, and Ruak rivers. Additionally, the Sai River showed elevated levels of lead and manganese, highlighting a persistent issue of heavy metal contamination in the northern border river basins. In contrast, the water quality of the Mekong River remains within standard limits.
The PCD, under the Ministry of Natural Resources and Environment, carried out the 19th water quality monitoring survey in the provinces of Chiang Mai and Chiang Rai, from May 19-22, 2026. This initiative aims to maintain continuous oversight of heavy metal contamination in these water sources.
Measurements from 22 surface water points revealed that most heavy metals, including cadmium, copper, nickel, chromium, zinc, and mercury, were within acceptable limits. However, arsenic levels surpassed the surface water quality standard of 0.010 milligrams per liter in several areas of the Kok, Sai, and Ruak river basins.
The Mae Sai River is particularly concerning, with arsenic levels exceeding the standard at all three monitoring points in Mae Sai District, Chiang Rai Province. The highest recorded value was 0.041 milligrams per liter near Ban Hua Fai. Lead and manganese levels also exceeded the standards at various monitoring points in Mae Sai District.
In the Kok River, arsenic levels above the standard were found at four locations, spanning from Mae Ai District in Chiang Mai Province to Mueang District in Chiang Rai Province. In the Ruak River, arsenic levels exceeding the standard were detected at two locations, near the Koh Chang pumping station of the Provincial Waterworks Authority and in Wiang Subdistrict, Chiang Saen District, Chiang Rai Province.
For the Mekong River, measurements did not reveal any heavy metal levels exceeding the standard, indicating that the river's water quality remains within the specified limits.
The PCD emphasized the necessity of close monitoring, as this marks the 19th consecutive occurrence of arsenic levels surpassing the standard. This aligns with ongoing monitoring trends that indicate persistent contamination in major rivers within the northern border region.
The PCD has committed to ongoing surveillance of water quality, sharing information with relevant agencies and the public periodically to assess the impact on the environment, public health, and ecosystem in the river basin area.