CHIANG RAI – Associate Professor Dr. Sitang Pilaila, a water resources engineering academic at Kasetsart University and advisor to the Minister of Agriculture and Cooperatives, shared insights during a recent meeting aimed at tackling cross-border pollution from upstream mining.

The event was held at Rai Mae Fah Luang in Chiang Rai on August 17, 2026. Dr. Sitang highlighted several worrisome issues, focusing on heavy metal contamination in the Kok, Sai, Ruak and Mekong rivers. The pollution affects water used for drinking, farming and fishing, as well as sediment that harms bottom-dwelling animals and people. Standards for these impacts differ, and soil contamination is another concern for both homes and crops.

Dr. Sitang explained that recent tests have revealed levels of contamination above the minimum standards. This means there’s an urgent need to find new sources of raw water. But Chiang Rai faces a lack of underground and surface water, so other methods may be necessary, such as reverse osmosis systems.

The government must find solutions regardless of the challenges. Sediment and soil pollution pose real risks because Chiang Rai often floods. Sediments can return to the water’s surface and spread toxins over a wider area during floods.

Groundwater in the area is still safe for now, as pollutants move more easily sideways than downwards. Yet once groundwater becomes contaminated, it’s nearly impossible to fix in our lifetimes. One idea is to build sediment-trapping weirs, since they’re quick and simple to make.

These are only temporary and usually fail during floods, and they cannot trap toxic substances—just sediment. Chiang Rai’s frequent floods can damage these structures, letting toxins escape without effective controls.

The concept of using sediment curtains, like those at Klity Creek, was also mentioned. These curtains are meant for heavy metals in river water and need a sealed system to prevent the spread of contaminants during any clean-up process. This method works in limited cases, but isn’t suitable for Chiang Rai’s rivers, which face strong flows and flooding.

There’s a higher chance of toxins spreading if structures fail. In addition, the presence of sediment curtains could slow water flow and make flooding worse in local communities.

Dr. Sitang also noted that new tests found arsenic in the water, but the specific form isn’t confirmed yet. Arsenic comes in several types, from -3 to +5, ranked by toxicity. The type found in the Kok River is +5, which is the least toxic, while in the Mekong, it is +3, which is more dangerous and dissolves easily in water.

If +3 arsenic is trapped behind weirs in the Kok River or if +5 arsenic sits in low-oxygen water, it can change into the more harmful +3 type. This shows the risk of using sediment barrier methods, as they may worsen toxicity. To fix that, you’d need to add oxygen to the water.

Chromium is another heavy metal found in the area that can cause harm. The levels in sediment are above the warning threshold, even if still below the strictest limits. Unlike arsenic, chromium’s toxicity increases when oxygen is added.

This means using sediment barriers could make things worse rather than better. The complex mix of chemicals and reactions makes it clear that technical fixes alone can’t solve this contamination. Environmental engineering must consider both physical and chemical effects.

Dr. Sitang said the province must face the issue directly and acknowledge it as a crisis. When local leaders admit there’s a problem, other agencies and organizations, like universities, can step in and help.

If the problem isn’t recognized, poisons could reach people and even impact human genes. Without cooperation and acceptance at the local level, progress is impossible.

If Chiang Rai’s authorities are ready to take charge, they need a task force and a clear plan. Each department should send in experts so everyone works together. If the root cause isn’t addressed, the province will continue facing both immediate and long-term problems.

Reporters noted the meeting brought together a wide range of representatives, including Phra Mahanikom, Assistant Abbot at Tha Ton Temple in Chiang Mai, Mr. Prasert Chitphaleechiep, Deputy Governor of Chiang Rai, Mrs. Atitathorn Wanchaitanawong, Provincial Administrative Organization President, Dr. Malee Sithikriangkrai from Chiang Mai University’s Social Science Faculty, Ms. Maneerat Khemawong, Senator, MP Thakorn Yasang from Chiang Rai, MP Songdun Utcharoen and MP Pattarapong Leelapat from Chiang Mai, and Mr. Khongsak Tharanisorn, President of the Upper Northern Chambers of Commerce.

Other attendees included Dr. Suebsakul Kitnukul from Mae Fah Luang University, Associate Professor Dr. Sathian Chantha from Chiang Rai Rajabhat University, Dr. Arissara Lekkam, Deputy Dean of Law at Mae Fah Luang University, Mrs. Tuenjai Deetes from the Community Development and Mountainous Area Foundation, Mr. Niwat Roykaew, chairman of Rak Chiang Khong Group, Mr. Montri Chantawong from the Mekong Liberty Group, Ms. Piyanphorn Deetes representing International Rivers, and Ms. Rakdao Pritchard from the people’s network to protect the Kok, Sai, Ruak, and Mekong.

During the meeting, participants shared many ideas to find solutions. Everyone agreed that the starting point is to stop upstream mining in Shan State from releasing heavy metals into the rivers.

Arsenic Above Safety Levels

Meanwhile, on August 18, the Pollution Control Department under the Ministry of Natural Resources and Environment shared the results of their eighth round of water and sediment quality checks, done from July 21 to 25, 2025. The findings show that several main rivers in northern Thailand have arsenic (As) levels above the set safety standard.

This review is part of the department’s ongoing plan to monitor unusual cloudiness in the Kok River. The scope included not just the Kok River but also nearby branches and main rivers in Chiang Mai and Chiang Rai. Key rivers sampled were the Kok, Sai, Ruak, and Mekong.

Kok River: Arsenic levels were too high at almost every sampling point, from Mae Ai in Chiang Mai through to Chiang Saen in Chiang Rai. Levels ranged from 0.010 to 0.018 milligrams per litre (mg/L), above the standard limit of 0.010 mg/L. While a few spots met guidelines, results across the river remained a worry.
Sai River: Every site checked showed arsenic above the standard, with readings from 0.052 to 0.055 mg/L—over five times the allowed limit.
Ruak River: At one sampling spot, near the Mae Sai water pumping station, arsenic registered at 0.040 mg/L, above the acceptable limit.
Mekong River: At Chiang Saen in Chiang Rai, one location had arsenic at 0.012 mg/L, a level over the safety cut-off.

On a positive note, the branches of the Kok River—including Fang, Lao, Korn, and Sruay Rivers—showed water quality within safe standards.

These results highlight a growing pollution problem in some of Thailand’s key rivers. An urgent investigation is needed to find the sources of arsenic and ways to address this issue. Taking quick action will help protect public health and the environment in the long run.