Chiang Mai University researchers say arsenic and mercury levels in the Salween River remain above safety standards, raising fresh concern for communities along the Thai-Myanmar border.
Assistant Prof Wan Wiriya, deputy head of CMU’s Environmental Science Research Centre, said on November 21,2025 that a joint test of Salween water samples collected by the Office of Environment and Pollution Control Region 1 (Chiang Mai) found two hazardous pollutants — arsenic and mercury — at levels exceeding Thailand’s national limits.
The samples were split and analysed using both field test kits and laboratory methods (ICP-OES). The latest results showed arsenic above the 0.01 ppm standard at nearly all sites, ranging from 0.0195 to 0.0321 mg/l. Mercury exceeded the 0.002 mg/l standard at every site, with readings between 0.0026 and 0.0063 mg/l.
Prof Wan said risk areas cover stretches of the Salween flowing through Mae Sariang and Sop Moei districts in Mae Hong Son. This area is on Thailand-Myanmar border. He urged residents to seek medical attention if they notice abnormal symptoms, and to report concerns through village health volunteers.
Seven sampling points recorded exceedances, including Ban Jor Tha, Ban Sop Ngae, Ban Mae Sakeub, Ban Tha Ta Fang, the Mae Sariang–Sop Moei boundary, Mae Sam Laep, and Ban Sop Moei.
Prof Wan said the most likely source of arsenic and mercury is small-scale gold mining, particularly the use of chemicals and mercury in ore extraction. He noted there have been reports of mercury use in mining areas across the border in Myanmar.
Pianporn Deetes, Executive Director of Rivers and Rights and secretary of the Hill Area and Community Development Foundation called the findings “deeply tragic,” warning that another major regional river system is now contaminated. She said the pollution, from unregulated mines, threatens ecosystems and public health for millions of people downstream, with toxins spreading along the river toward the Andaman Sea, and urged governments in the region to respond seriously and immediately.
Phattarapong Leelaphat, an MP of the People’s Party said the contamination is alarming for local livelihoods. Although the Salween runs along Thai territory for only about 127 kilometres, he said more than 800 Thai households depend on its water, and at least 330 households rely on fishing both for food and income.
He cautioned that mercury can bioaccumulate in fish, meaning concentrations in flesh may rise far above levels measured in water. He called on the government to urgently announce a temporary ban on fishing and consumption of Salween fish until laboratory tests on fish samples are completed.
“The transboundary water pollution crisis is worsening, yet the government response does not match its severity,” MP Phattrapong said, citing earlier arsenic problems in the Kok, Sai, Ruak and Mekong rivers, and now the Salween. He urged Prime Minister Anutin Charnvirakul and Deputy Prime Minister Suchart Chomklin to raise the issue to a higher level, launch multilateral talks involving Thailand, China, Myanmar and Laos, and set out a clear action plan with adequate funding for water, fish, soil and crop testing, alternative water supplies, and support for local businesses hit by the crisis, especially tourism.
“Thai people gain nothing from this supply chain, but they bear the full impact,” he said. “If the government truly cares about quality of life, this problem cannot continue to be neglected.”
This is a translation of original Thai article https://transbordernews.in.th/home/?p=44500
