Thailand is preparing to formally request Myanmar to curb pollution from Chinese-operated mining activities in Shan State, following the detection of hazardous heavy metals in the Kok and Sai rivers, authorities announced on 21 May 2025.
Laboratory tests conducted by Thailand’s Pollution Control Department and the Ministry of Public Health revealed that water samples from several sites along the Kok and Sai rivers, flowing through Chiang Rai and parts of Chiang Mai, contain arsenic levels exceeding safety thresholds. The contamination is suspected to originate from unregulated mining operations in eastern Myanmar.
In response, the Thai government has directed the Army, the Ministry of Natural Resources and Environment, and the Foreign Ministry to address the issue through diplomatic and environmental channels. The matter will be officially raised during the upcoming Regional Border Committee meeting, set for 17 to 20 June in Kengtung, Shan State.
Efforts to mitigate immediate risks include plans by the army’s engineering corps to remove sediment from a stretch of the Kok River in Chiang Rai’s Muang district. This is seen as a temporary measure while diplomatic discussions proceed.
Additional testing of water and sediment conducted by the Pollution Control Department in early May detected elevated levels of both arsenic and lead in the Kok, Sai, and Khong rivers. Health officials have advised the public to avoid consuming fish from the contaminated waterways and to thoroughly clean vegetables before consumption.
Although preliminary urine tests from local residents did not indicate dangerous levels of heavy metals, authorities are maintaining precautionary measures. The Thai Foreign Ministry has also engaged Myanmar’s Embassy in Bangkok, sharing data sourced from national agencies including the Geomatics and Space Technology Development Agency and the Department of Health.
A broader delegation of Thai officials will present their findings and concerns at the border meeting, where the focus will be on preventing further transboundary environmental harm.
