CHIANG RAI – Three government agencies shared the latest findings on arsenic monitoring in Chiang Rai. So far, they say arsenic levels found in people and local water sources haven’t reached a point considered dangerous to the public.
The Ministry of Public Health (MOPH) plans to expand health screening to 1,400 more additional residents and continue monitoring for five years. Officials also noted that arsenic found in nails or hair can reflect long-term exposure over several years.
Key points from the update
- Tests from the Kok River and village tap water systems show results within standards and are considered safe.
- Some arsenic findings in a small number of people may relate to occupational exposure, especially farming, not water contamination.
- Agencies will keep a five-year watch plan and expand health checks to more than 1,400 people to track trends over time.
The update follows reports from academics who found arsenic above reference levels in nails and hair among 16 out of 90 residents across four Kok River basin areas (Chiang Mai and Chiang Rai). After that, there were calls for the government, especially MOPH, to list “arsenic poisoning” as a legally monitored disease so that the area has a clear system for prevention and care.
What MOPH and partner agencies reported
On Feb 26, 2026, MOPH met with several agencies, including the Department of Health, the Department of Disease Control, and the Department of Medical Sciences. Regional public health offices and a medical sciences center in Chiang Rai joined the meeting, and the Pollution Control Department provided environmental data.
Dr. Somruek Jungsaman, Permanent Secretary of MOPH, said early results from local agencies show arsenic monitoring in the Kok River and village tap water remains within standards. Because of that, he said residents can continue their normal daily life without expected health impacts from arsenic in the water.
He also thanked researchers and local teams for keeping attention on possible health effects. That attention, he said, helped agencies set clearer plans and preparedness measures. MOPH said it’s ready to support efforts that protect local health.
MOPH also asked residents to contact local public health units right away if they notice unusual conditions or suspect pollution that could affect health. That includes local health centers and community hospitals.
No evidence of arsenic at dangerous levels so far
Officials said environmental arsenic levels still do not exceed standards and remain under ongoing control measures. At the same time, the province continues routine steps to reduce pollution risk factors.
MOPH said it will keep monitoring drinking water quality, checking for contamination in food, and screening at-risk groups. The goal is to protect vulnerable residents and prevent exposure from turning into a bigger problem.
Dr. Somruek said agencies have already instructed Chiang Rai’s provincial public health office to create a five-year monitoring plan. He said the plan should explain the situation from all angles and keep arsenic risks from affecting the public.
Kok River water tests, recent rounds show little to no arsenic
Surin Worakithamrong, Director-General of the Pollution Control Department, said the department has tested water quality since March 2025. So far, it has completed 15 rounds of testing across 27 monitoring points.
He said the most recent five rounds found almost no detectable arsenic. In areas where arsenic still appeared, such as Tha Ton, results were around 0.011 to 0.012 milligrams per liter. He described that as very low compared with the standard benchmark of 0.01 milligrams per liter.
In addition, the overall water assessment showed a pH range of about 6.5 to 7.8. That places the water in “Type 3,” meaning it can be used for consumption after treatment, such as disinfection and filtration. For agriculture, officials said the water can be used as well.
Arsenic is found in people; most results point to non-harmful forms.
Dr. Wichada Jongmeewasana, Director of the Bureau of Food Quality and Safety under the Department of Medical Sciences, said the department has worked with regional teams on monitoring since 2025. They conducted four rounds in 2025 and planned 12 more rounds in 2026. The checks cover village tap water, local produce grown near the basin, and urine testing in people.
She said results through January 2026 show arsenic in water and vegetables remains within standards. For urine results, the department tracked cases and found no sign of ongoing exposure linked to the environment.
Natthapong Laemman from the Department of Disease Control (occupational and environmental diseases unit) said that in 2025, the department monitored 362 residents in areas aligned with water testing sites. Seven people tested positive for a non-harmful arsenic form. One person exceeded the standard, so officials investigated further. In 2026, they plan to collect more background data, including other higher-risk jobs.
He added that agencies will monitor water sources for five years, following World Health Organization guidance. During 2026, they plan to expand screening to more than 1,400 people and include all rivers linked to arsenic concerns. The Department of Disease Control also plans to coordinate with the researchers behind the public reports. It will also include the 19 people reported in the news as having arsenic findings, so officials can confirm results through follow-up testing.
Symptoms that may suggest high exposure
Dr. Amพร Benjapolpitak, Director-General of the Department of Health, said current information indicates the Kok River remains safe, but agencies still won’t take the situation lightly. She said residents should contact public health teams if they have concerns.
She also said people should watch for possible symptoms linked to higher arsenic exposure, such as:
- nausea and vomiting
- stomach pain
- diarrhea
- dizziness
- fatigue
- skin irritation
- rashes
These symptoms can come from many causes. Still, if someone has a known exposure history or an abnormal urine test, they should seek prompt evaluation and follow-up.
The Department of Health also recommended using treated water from the Provincial Waterworks Authority or village systems that meet production standards. Officials said these sources go through checks and improvements. SEhRT teams from the Health Center Region 1 in Chiang Mai continue field work with provincial agencies, including spot checks of water quality and ongoing public education.
Officials suspect farming-related exposure among people with higher results.s
Dr. Somruek said discussions with the research team suggest the highest reported values were slightly above the upper threshold. He added that symptoms reported through questionnaires didn’t clearly match the people with higher measurements, although he said he wouldn’t comment on the research details.
He explained that MOPH testing has two main parts:
- The Department of Medical Sciences tested urine in higher-risk areas. In the third and fourth rounds, one person initially showed a finding, but the sample process wasn’t properly prepared. When officials retested, they did not find elevated levels. He said one possible reason is seafood intake before testing, since some seafood can raise arsenic readings even though the body later clears it.
- The Department of Disease Control found seven cases in earlier screening, with one person showing a very high level. All seven were farmers, and officials linked the risk to pesticide use and other work-related exposures. They did not see a broader pattern across the general community or from food intake.
He said that for residents without clear exposure risks, officials do not see evidence that arsenic in local water is causing harm. He also said the Pollution Control Department continues routine environmental monitoring.
More follow-up checks are planned to confirm the source
Officials said environmental monitoring from the Department of Medical Sciences has not shown high arsenic in water sources. Because the higher readings appeared mainly in farmers, agencies suspect job-related exposure. Even so, the Department of Disease Control will do more field follow-up to provide clearer answers.
Natthapong said field teams visited homes to review how people use pesticides. They also checked information from the Department of Agriculture and found that Thailand uses several pesticide products, including some that still involve arsenic. He said the one person with very high results may still need more scientific evidence to confirm the source, so the agency will expand follow-up among farmers in 2026.
Dr. Somruek explained that arsenic mainly enters the body through food and water, but it isn’t always toxic. For example, arsenic associated with seafood is often in a form considered non-harmful. Because of that, she recommended avoiding seafood for 4 to 5 days before a urine test. That helps clarify whether arsenic, if found, likely came from another source.
She said the body removes arsenic through urine, which is why urine testing is commonly used. If repeated tests stay high over time, it can suggest ongoing exposure or accumulation. If levels drop, it may mean a previous result reflected a recent diet, a temporary exposure, or normal clearance.
Urine vs nails vs hair, what each test reflects
Natthapong said different tests reflect different timeframes. The Department of Disease Control chose urine testing because it’s a standard method that can separate harmful and non-harmful arsenic forms more clearly. Urine results generally reflect exposure in the past 1 to 2 months, which fits the timeline officials want to compare with environmental conditions.
On the other hand, nail and hair tests can reflect exposure over many years. He also noted that hair testing is less preferred because arsenic can cling to the outside of hair from things like hair dye. In addition, hair testing does not separate arsenic types into harmful and non-harmful forms.
