Arsenic Levels Found Above Standard in Salween River, Prompting Cross-National Investigation

Mae hong son: The Pollution Control Department has discovered arsenic levels exceeding acceptable standards in the Salween River, prompting collaboration with Myanmar to identify the source of pollution and explore alternative water sources for local communities. According to Thai News Agency, Mr. Surin Worakithamrong, Director-General of the Pollution Control Department, announced that the department conducted a comprehensive field study, collecting water and sediment samples from the Salween River and its tributaries in Mae Hong Son Province from November 12-13, 2025. These samples were evaluated against both national and international standards for water and wastewater quality. The laboratory analysis revealed arsenic concentrations at all 13 testing points in the Salween River surpassed the acceptable standard of 0.01 mg/l, with actual measurements ranging from 0.023 to 0.029 mg/l. Additionally, elevated lead levels were detected at Ban Tha Ta Fang in the Mae Yuam Subdistrict of Mae Sariang District, me asuring 0.076 mg/l. Conversely, mercury levels remained within normal limits across all testing sites, and the water quality in the five tributary basins met standard requirements. Contaminants were detected in areas stretching from the Thai-Myanmar border in Mae Kong Subdistrict, Mae Sariang District, to Ban Sop Moei in Mae Sam Laep Subdistrict, Sop Moei District, Mae Hong Son Province. The arsenic levels were found to be consistent across all locations. In response, the Ministry of Natural Resources and Environment (MNRE) plans to urgently coordinate with Myanmar through the Ministry of Foreign Affairs to address the inspection findings and collaboratively investigate the pollution sources. The Pollution Control Department will also provide guidance to the public on safe water usage and methods to improve water quality. Despite the contamination, most villagers rely on mountain tap water, which has tested free of arsenic contamination. Continuous monitoring and dissemination of water quality information are underway. Additionally, water resource agencies are actively seeking alternative water sources, such as surface and groundwater, to ensure water supply for consumption and agriculture. This includes drilling artesian wells or arranging backup water resources for residents affected along the Salween River. The Pollution Control Department (PCD) plans to revisit the area next week to engage with villagers. Meanwhile, tests on fish and aquatic plant contamination are being analyzed by relevant agencies, with results to be reported in due course.