The government is being urged to issue urgent health advisories to communities living along the Salween River after Chiang Mai University (CMU) researchers found alarmingly high levels of toxic contamination. Academics have warned residents to avoid consuming freshwater snails and to take precautions as livestock may be exposed to contaminated vegetation, while conservationists point to the absence of mechanisms to regulate transboundary impacts.
On Feb 12, Asst Prof Wan Wiriya, deputy head of the Environmental Science Research Centre at CMU’s Faculty of Science, said water quality assessments conducted along the Salween River — from Karenni State in Myanmar to the Thai-Myanmar border and down to Sob Moei district in Mae Hong Son — revealed elevated concentrations of heavy metals in several areas.
He described the situation as concerning, particularly findings from clay sediments deposited during major flooding in 2024. These sediments showed heavy metal concentrations comparable to samples collected from mining sites in Karenni State. Arsenic levels in water there were recorded at 0.55 milligrams per litre, far exceeding the standard of 0.01 mg/l, while arsenic in soil reached 70 mg/kg, more than double the standard of 33 mg/kg.
By contrast, sandy soils along the riverbanks showed lower contamination levels.
Dr. Wan said authorities should urgently advise residents against using contaminated clay sediments for growing crops and to avoid direct contact. If contact is unavoidable, thorough washing is recommended. Cultivation in existing sandy soils may pose lower risks than in newly deposited sediments.
He also raised concerns about free-grazing livestock — including cattle, buffaloes and goats — which may ingest contaminated grasses along the riverbanks. Aquatic plants, which serve as habitats for fish, were also found to contain heavy metals.
Another major concern is freshwater snails, a seasonal food source for local communities. As bottom feeders, snails are likely to accumulate toxins from contaminated sediments and may no longer be safe for consumption.
Mr Wan said preliminary assumptions suggest that the contaminated sediments may have originated from older mining sites in Karenni State. He noted that some lead mines in the area have recently shifted to chemical-intensive processing methods, including acid leaching, replacing earlier techniques that relied on sediment separation without chemicals. This change may have increased the volume of contaminated waste entering the river system.
“As a result, contamination appears to affect the entire stretch of the Salween in this area,” he said.
However, he noted that samples collected upstream of mining areas also showed traces of heavy metals, albeit at lower levels, indicating that other sources of contamination cannot yet be ruled out.
Previous satellite imagery analyses by several institutions have identified at least 26 rare earth mining sites in areas under the control of the United Wa State Army (UWSA) in the upper Salween basin near the Chinese border. These operations have expanded rapidly in recent years.
According to CMU’s findings, water samples collected upstream in Karenni State showed arsenic levels ranging from 0.042 to 0.096 mg/l — all exceeding the standard limit of 0.01 mg/l. Soil samples from the Thai-Myanmar border area in Mae Sam Laep, Sob Moei district, showed arsenic levels between 15 and 66 mg/kg, compared with the standard of 33 mg/kg.
Pianporn Deetes, executive director of Rivers and Rights, said the Mekong, Salween and Irrawaddy basins are facing an unprecedented environmental emergency.
Limited sources of clean water are increasingly contaminated by toxic substances from unregulated mining, she said, adding that the situation is likely to worsen due to the lack of effective regulatory mechanisms, particularly for transboundary impacts and cross-border investments.
“Global demand for rare earth elements and critical minerals, coupled with high prices, is driving rapid expansion of mining without adequate regional regulations,” she said. “Chinese investment is deeply embedded in these areas, with Thailand often used as a transit route, and there are indications of joint investments.”
She added that while Asean’s Minerals Development Vision promotes small-scale mining, the Salween case demonstrates that such activities can result in severe environmental damage.
“This devastation is only just beginning,” she said.
This is a translation of original Thai news article https://transbordernews.in.th/home/?p=45125
