Toxic found in Kok River; Chiang Mai-Chiang Rai warned off

Chiang Mai’s Office of Environment and Pollution Control Region 1 inspected water quality in the Kok River, which flows from upstream in Myanmar into Mae Ai District, Chiang Mai Province, after the water appeared unusually muddy and sediment-laden. 

Typically, the Kok River remains clear during the dry season, unlike in the rainy season when sediment is more common. 

Additionally, several people reported skin rashes after entering the water. The office has since collected water samples from various points along the river for testing.

Aweera Phakamat, Director of the Office of Environment and Pollution Control Region 1, revealed that preliminary tests showed water turbidity levels nearly 10 times higher than normal.

More importantly, lab analysis detected arsenic, a toxic substance, at levels more than double the standard limit. While the safe standard is 0.01 mg/L, samples taken near Kaeng Tume village in Mae Ai District — the first point where the Kok River enters Thailand — showed arsenic levels at 0.026 mg/L.

This contamination has caused allergic reactions among people who swam in the river, with symptoms including skin irritation and rashes. Long-term exposure could increase the risk of cancer. 

If consumed, arsenic-contaminated water can disrupt the body's biochemical processes — even small amounts may cause diarrhea or gastrointestinal distress. Prolonged accumulation could also lead to cancer.

Additional water samples from other points in the Kok River revealed arsenic levels exceeding safety standards as well — 0.012 mg/L near Ban Tha Ton and 0.013 mg/L near Ban Pha Tai. 

Authorities are still awaiting results from sediment analysis, as heavy metals are believed to have settled at the riverbed.

In addition, three more water samples were collected from the Kok River in Chiang Rai city to test for contamination. The results are expected within two weeks. 

Authorities are urging the public to avoid swimming in the river or consuming untreated river water. There are also concerns about rural water supply systems that use the Kok River as a raw water source, as their filtration systems may not meet safety standards.

It is suspected that the arsenic contamination may be linked to upstream gold mining activities in Myanmar. Gold ore often contains arsenic as a byproduct, known in chemistry as a “gangue mineral.” When gold is extracted, arsenic is separated in the process — and improper handling could lead to environmentalcontamination.