Who is testing our food for residues?

Testing of food for contamination by pesticides is carried out by a number of organisations in Thailand, such as the Ministry of Agriculture and Cooperatives (Office of Research and Development on Agricultural Production) and the Ministry of Public Health (Department of Medical Sciences). These institutions have special laboratories to conduct detailed tests. Pesticide residues can also be tested on farms, in restaurants and markets using a simple kit, but these tests do not detect all types of pesticides.


Mr. Wittaya Hansuwan is Deputy Manager of the Sri Moom Muang market. This is the largest wholesale market for fruits and vegetables in Thailand, which supplies many of the smaller markets in Bangkok.

“Our market accepts vegetables from the Northern, North-Eastern, Central and Western Regions. In total there are about 5,000 tons of vegetables passing through Sri Moom Muang each day.”

“We test all kinds of vegetables for Maximum Residue Levels (MRLs). We can detect chemical pesticides and other contaminants such as Borax, Formalin, Sulfates and Bleaching agents.”

“We carry out tests on a random basis and on request. The tests are carried out for farmers, middlemen, buyers and export companies. In cases of serious contamination we report back to the original producer, and if we find contamination in three samples from the same trader we ban them from the Sri Moon Muang market.”

“I think the Government is on the right track to improve food safety, but there is always a danger that people will try to improve their image by talking about policy rather than practicing the real thing.”

“Consumers need to realize that they can influence the production methods of the farmers. If they keep demanding vegetables with a perfect appearance, farmers will continue to use a lot of pesticides to protect their vegetables. Farmers are afraid of losing income by producing vegetables which are not attractive.”

Testing pesticide residues

Residues are often tested using a ‘GT-test’ kit, which was developed by Gobthong Thoopom from the Thai Ministry of Public Health.

The GT-test detects whether or not a sample of food contains chemicals that inhibit an enzyme called ‘acetylcholinesterase’. This enzyme plays an important role in the human body, but it does not function if certain types of pesticides are present in the sample, specifically Organophosphates and Carbamates.

The GT-test can be carried out at any location, for example in the market, and the results are obtained within a few hours. The kits are low cost and simple to use; no expensive equipment or laboratories are necessary.

Unfortunately, this method is not very precise. The GT-test will tell you if a sample contains Organophosphates or Carbamates, but cannot identify the specific chemical or the quantity. Comparing the results with the Maximum Residue Levels is not possible. Also, there are some types of pesticides that are not detected. For example, Pyrethroids cannot be detected by the GT-test kit because these pesticides do not inhibit the acetylcholinesterase enzyme.


Organophosphates and Carbamates

Organophosphates and Carbamates are two chemical families of pesticides that affect the central nervous system (brain) and peripheral nervous system (nerves found outside of the brain or spinal cord). These chemicals attach themselves to the enzyme (acetylcholinesterase- AChE) that stops nerve transmission in the body. In this way they suppress the functioning of that enzyme which results in continuous electrical nerve transmission. This particularly affects the muscles and glands that make the body organs function.

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