Health Alert: Avoid Eating Shrimp and Shellfish as Third Arsenic Test Shows Contamination Across Mae Saliang-Sob Moei Waterways

The Pollution Control Department (PCD) under the Ministry of Natural Resources and Environment announced on April 30, 2025 that the third round of sediment sampling from the Salween River conducted between March 24-27 showed continued arsenic contamination. Samples were collected from monitoring points SAL08 (Ban Tha Ta Fang) through SAL13 (Ban Sob Moei) in Mae Hong Son Province.

Analysis results revealed that arsenic (As) levels at all six monitoring points exceeded the severe safety standard of 33 mg/kg, with concentrations ranging from 41-82 mg/kg. The highest reading of 82 mg/kg was recorded at SAL09 at the boundary between Sob Moei and Mae Saliang districts, while SAL08 measured 49 mg/kg, SAL10 measured 43 mg/kg, SAL11 measured 55 mg/kg, SAL12 measured 41 mg/kg, and SAL13 measured 50 mg/kg.

Testing of tributary water quality also revealed contamination in certain areas. The Mae Samlab River showed 16 mg/kg of arsenic, the Mae Yuam River contained 17 mg/kg arsenic along with 56 mg/kg chromium and 25 mg/kg nickel, and the Mae Pai River had 11 mg/kg arsenic. The Mae Po and Mae Kong Ka rivers tested within acceptable standards. Other heavy metals including lead, cadmium, copper, zinc, mercury, and manganese remained within safe limits.

Although current aquatic animal samples still fall within safe consumption levels, the PCD warned that arsenic accumulates in the food chain over time. Authorities recommend always cooking food thoroughly, avoiding repeated consumption of the same aquatic species, reducing intake of bottom-dwelling creatures like shrimp and shellfish, and avoiding fish organs, which are primary accumulation sites for contaminants. The department will continue monitoring water quality and coordinating with relevant agencies to protect public health.