PCD reveals heavy metal levels in northern rivers

Govt urges cautious approach to dealing with neighbouring Myanmar, writes Apinya Wipatayotin

- Apinya Wipatayotin

The Department of Pollution Control (PCD) has confirmed unsafe levels of arsenic and other heavy metals in the Kok, Sai, and Mekong rivers in the North, with the contamination traced to upstream mining operations across the border in Myanmar's Shan State.

The PCD released its findings from three rounds of water and sediment sampling conducted between March 19 and May 16, revealing widespread pollution in northern waterways.

The highest levels of contamination were detected in the Kok River, particularly from Tha Ton in Chiang Mai’s Mae Ai district, to Chalerm Phrakiat Bridge in Chiang Rai’s Mueang district. In some locations, arsenic concentrations reached 0.44 milligrams per litre (mg/l) — more than 40 times above the safety threshold of 0.01 mg/l.

Lead levels also exceeded safe standards, peaking at 0.076 mg/l near the Thai-Myanmar border in Chiang Rai. While other metals such as cadmium, mercury, and manganese were found within safe limits, the persistence of arsenic is raising concerns among health and environmental authorities.

"Water quality along the Myanmar border shows elevated turbidity and arsenic, a clear indicator of mining impacts," a PCD source said. Officials said historical monitoring from 2014 to 2015 had shown no such contamination, suggesting a recent and worsening trend.