On July 8, 2025, Thailand’s Pollution Control Department (PCD) released the results of its 6th round of water quality testing in the Kok, Sai, Ruak, and Mekong Rivers—based on water samples collected between June 23–27, 2025. The sampling took place after periods of heavy rain followed, with high water flow and ongoing dredging activities observed in the Kok River (in Chiang Rai city), Sai River, and Ruak River. The water was fast-flowing and reddish-brown in color.
In the Kok River, arsenic concentrations exceeded the standard (0.01 mg/L) at all sampling sites—from the Thai-Myanmar border at Tha Ton Subdistrict, Chiang Mai, to the river’s mouth in Chiang Saen. The readings ranged from 0.012 to 0.038 mg/L.
In the Sai River, all testing points also exceeded the standard, with arsenic levels ranging between 0.017 and 0.049 mg/L. In the Ruak River, concentrations ranged from 0.014 to 0.017 mg/L, while in the Mekong River they were found to be between 0.020 and 0.025 mg/L—also above the safety line.
Aweera Pakkamart, Director of Regional Environmental and Pollution Control Office 1 (Chiang Mai), spoke at a recent academic seminar at Chiang Mai University’s Faculty of Social Sciences. He shared that, having previously served in Lampang and Chonburi where she handled multiple chemical spill cases, the current situation in Chiang Mai and Chiang Rai is especially troubling. “The test results show irregularities. The water is visibly turbid, and scientific data confirms the contamination,” he said.
Aweera noted that during this dry season (March–April), when irrigation dam in Chiang Rao was closed and water was stored upstream, arsenic was not detected downstream at the Chiang Rai weir. But during the rainy season, when the irrigation gates are open, sediment and arsenic are washed downstream. Currently, the contamination has spread along a 151-kilometer stretch of the Kok River in Thailand. The Sai River, in particular, is in worse condition, though its impact is less severe due to limited usage as a border river between Thailand and Myanmar.
He further explained that the sixth round of official water quality tests showed high turbidity due to stormwater stirring up sediments, which can be alarming. “We tested for all parameters required under surface water quality standards. Arsenic and lead were both detected, but we focus here on arsenic. While the Kok River showed high arsenic levels, the Sai and Ruak rivers had even higher levels, which in turn elevated the levels in the Mekong River.”
“Just days ago, people from the lower Mekong called us asking for clarity. This is no longer a local issue—it’s a regional, cross-border, environmental crisis. The pollutants could reach the South China Sea. The scale is massive. Sediment levels affect benthic (bottom-dwelling) animals: levels above 10 create stress, and above 33 pose serious risks as toxins accumulate in stomachs and tissues,” Aweera said.
He added, “In scientific terms, we can clearly confirm contamination. I’ve been working on this case since the beginning. Communication has been confused—some see it as a minor issue, fearing that addressing it would hurt tourism. Others argue the contamination is severe and impacts public health. The effects might unfold over 5 to 20 years. Understanding the exposure pathway of arsenic—how long one must be exposed to develop health effects—is vital. Vulnerable individuals, especially those with poor health, are at even greater risk.”
See original Thai article https://transbordernews.in.th/home/?p=43239
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