CHIANG MAI, THAILAND – Arsenic levels in parts of the Kok River and its tributary Sai were measured above Thailand’s national water quality limit, while other rivers in the region remained within standards for heavy metals.
Tests Follow Reports of Unusual Water Discoloration
The Thai Pollution Control Department (PCD) collected water and sediment samples between 13 and 16 January in the provinces of Chiang Mai and Chiang Rai after reports of unusual turbidity and possible contamination. The agency’s 15th report on water and sediment quality documented for the first time exceedances of the national arsenic limit of 0.01 milligrams per liter (mg/l) in certain stretches of the river system.
Arsenic Exceedances in Kok River
In the Kok River, arsenic concentrations of 0.011–0.012 mg/l were recorded between the Tha Ton Bridge in Mae Ai district and the Mae Nawao–Tha Ton Friendship Bridge, slightly above the permitted value. These findings led authorities to focus their monitoring on this specific section of the Kok River, where levels narrowly surpassed the 0.01 mg/l threshold.
Elevated Values Along the Sai River
All monitoring stations along the Sai River also registered increased arsenic levels, averaging between 0.011 and 0.014 mg/l, according to the PCD report. This meant the entire observed course of the Sai River showed values above the national standard for arsenic in surface water.
Other Heavy Metals Within Standards
According to the PCD, concentrations of other tested heavy metals such as cadmium, copper, nickel, chromium, zinc and mercury in the samples remained within national quality standards. The agency underlined that the exceedance applied specifically to arsenic, and that no limit violations for the other metals were identified on the basis of the current sampling.
Tributaries and Major Rivers Deemed Compliant
The Fang, Korn and Lao tributaries, as well as the Ruak and Mekong rivers, met the applicable safety standards for arsenic content in the latest measurements, the PCD reported. As a result, official attention was currently concentrated on the affected sections of Kok and Sai, while other monitored waterways in the region were classified as unremarkable for the time being.
Public Concerns Over Health Risks
Rising arsenic readings drew public attention and raised questions about long-term water safety in northern Thailand.
“Increased arsenic levels are causing concern and raising questions about water quality,”
said the agency, adding that fears over potential health risks persisted even though many other heavy metals remained within limits.