Northern Thai Rivers Face Escalating Arsenic Crisis

Tests by Thailand’s Pollution Control Department have revealed that arsenic concentrations in the Kok River and tributaries now exceed national safety limits by up to five times. Biochemical analysis indicates that these toxic levels are linked to unregulated mining operations in Shan State, Myanmar, particularly within territories controlled by the United Wa State Army.

The Kok River, which begins its 285km course in Myanmar’s Daen Lao Range before entering Thailand through Mae Ai and flowing into Chiang Rai and eventually the Mekong, has become the focus of mounting alarm. Tests conducted between late May and early June demonstrated elevated arsenic at all 15 tested points along the Kok and Sai rivers, with further contamination detected in two Mekong sampling sites.

Local fishermen have reported adverse impacts to aquatic life and livelihoods. Prices for catch in Chiang Rai have dropped by nearly half, as consumer fear surrounding contamination takes hold. Fisherman Sawat Kaewdam told AFP: “They say, ‘There’s arsenic. I don’t want to eat that fish.’”.

Satellite imagery and drone footage show dozens of active mining sites emerging since around 2022, believed to involve both gold and rare earth minerals. These mines operate under minimal environmental safeguards, with tailings and chemical-laden effluent discharged directly into rivers. One environmental campaigner described the situation as Thailand’s “largest-ever case of transboundary pollution”.

Health experts warn that while immediate poisoning symptoms may not materialise, long‑term exposure through contaminated water and fish consumption could lead to chronic arsenic poisoning. Somporn Phengkham of the Community Health Impact Assessment Platform emphasised the risk of gradual accumulation, urging increased scrutiny of wells and irrigation systems.

Communities along the Kok River have experienced unusual water discolouration, persistent skin irritations, and fish deformities. Chiang Rai environmentalists staged protests on 5 June, tying ribbons along the river bridge to demand intervention and mine closure. In Chiang Mai’s Mae Ai district, a monk from Wat Thaton confirmed that the river’s appearance and use had become culturally and practically untenable.

Thailand’s federal government has initiated emergency measures. Deputy Prime Minister Prasert Jantararuangtong has overseen a new response centre, while the Pollution Control Department is conducting enhanced sampling. Officials reassure domestic water supplies are safe, although the contamination source remains external.

Proposals for containment include constructing a dam across the Kok River to trap sediments, dredging heavily polluted sections, and pursuing diplomatic negotiations with Myanmar and China. The Foreign Affairs Committee is engaging Beijing to urge oversight of Chinese mining companies operating within UWSA territories.

Challenges persist as Shan State’s mines lie beyond Myanmar’s central control. With the UWSA exerting autonomy and Chinese-linked firms driving extraction operations, finding a direct negotiating partner proves elusive. Regional analysts warn that building physical barriers without curbing source pollution will yield temporary alleviation at best.

Environmental advocates underscore the urgency of scaling up real-time monitoring and cross-border coordination. They highlight growing concerns that contamination could extend throughout the Mekong basin, threatening agriculture, fisheries, and water security across Southeast Asia.

Experts like Tanapon Phenrat of Naresuan University stress that addressing the problem requires systemic reform: mandated tailings treatment, strict environmental standards, and international cooperation. “We need to act now,” he stated.