High Mercury Levels Found in Northern Thai Rivers
A Thai pollution survey found dangerously high mercury levels in sediment across northern rivers, with the Mekong River showing the worst contamination at up to 80 mg/kg—eight times safe limits—while the Kok, Sai, and Ruak rivers also excee
On August 21, 2025, the Pollution Control Department under the Ministry of Natural Resources and Environment released the findings of its 12th sediment quality monitoring survey in the Kok River, its tributaries, the Sai River, the Ruak River, and the Mekong River. Samples were collected between July 7-10, 2025, to track unusual turbidity in the Kok River in Chiang Mai and Chiang Rai provinces. Testing was conducted at 21 locations across all rivers.
Kok River: Six locations exceeded safe sediment quality standards (10 mg/kg maximum) for terrestrial wildlife. The worst case was site KK01 at the Thai-Myanmar border with 23 mg/kg mercury. Site KK05 at the Mae Yao-Doi Hang Friendship Bridge recorded 11 mg/kg mercury and 0.21 mg/kg mercury, exceeding the 0.2 mg/kg safety standard. Other sites (KK07, KK10, KK11, KK12) ranged from 13 to 16 mg/kg. One location, KK09 near the Chiang Rai King's Memorial Bridge, reached severely hazardous levels with 45 mg/kg mercury, plus elevated nickel (26 mg/kg, standard 23), lead (46 mg/kg, standard 36), and chromium (66 mg/kg, standard 43.4).
Kok River tributaries: The Fang and Laao tributaries met standards. The Korn tributary recorded 38 mg/kg nickel, exceeding safe levels.
Sai River: Two locations exceeded safe mercury standards—site SA01 at Ban Hua Fai with 25 mg/kg and site SA03 at Ban Pa Sang Ngam with 13 mg/kg.
Ruak River: Both sampling points showed severely hazardous mercury levels. Site RU01 at the Koh Chang water pumping station recorded 49 mg/kg mercury, 0.24 mg/kg mercury (standard 0.2), and 45 mg/kg chromium. Site RU02 at Tambon Wiang near the river mouth recorded 55 mg/kg mercury, 46 mg/kg nickel, and 61 mg/kg chromium, all at severely hazardous levels.
Mekong River: All four sampling locations showed severely hazardous mercury concentrations. Site NK01 at the Golden Triangle border checkpoint recorded 66 mg/kg. Site NK02 in Wiang, Chiang Saen recorded 80 mg/kg. Site NK03 at Ban Sop Kok recorded 50 mg/kg mercury, 0.22 mg/kg mercury, and 45 mg/kg chromium. Site NK04 at Ban Hua Wiang recorded 68 mg/kg mercury.
