Nearly two-thirds of the samples of hydroponically-grown vegetables tested were found to be contaminated with pesticides in excess of the maximum residue limit, according to the Thailand Pesticide Alert Network (Thai-PAN).
The non-governmental organisation working on food safety recently tested 30 samples of vegetables marked as hydroponic and sold at fresh markets and supermarkets in Bangkok and other provinces.
Nineteen of them, or 63.3%, contained pesticides at levels above the maximum residue limit. Three others were found to have residue but not exceeding the limit, while the other eight samples were free of residue.
The tests were made exclusively on vegetables grown at hydroponic farms - where crops are grown in a water-based, nutrient-rich medium, without the use of soil.
Thai-PAN coordinator Prokchon Usap told a news conference the findings suggested that hydroponic vegetables were not as safe as some consumers might have thought.
Thai-PAN conducted a similar test on fruits and vegetables grown in soil late last year and found that 54.4% of the samples were contaminated with pesticides exceeding the limit.
"Some people understand that hydroponic vegetables are safe and use less pesticides or are even free of them. That’s not true," she said.
Ms Prokchon said the tests found 25 types of toxic chemicals such as Ametryn (herbicide), Azoxystrobin (fungicide), Carbofuran and Methomyl (insecticide and acaricide).
She said the findings would be presented to the farm operators to encourage them to better regulate the use of toxic chemicals in hydroponic vegetables.
She urged the consumers to check the details of the test at the Thai-PAN website.