Genetically-modified maize has been found at a local farm near agribusiness giant Monsanto's maize farm in Phitsanulok province, bringing the leakage of transgenic crops in the country to three.
The GM maize contamination was exposed yesterday by Biothai, a non-government organisation working on organic farming.
The group collected 19 samples of maize, soybean and cotton from local plantations and farm shops in Phitsanulok, Nakhon Sawan and Sukhothai late last month and sent them for testing at Chulalongkorn University's food research and testing laboratory.
Test results of the first two samples, collected from a deserted farm in Phitsanulok's Wang Thong district, confirmed they are genetically-engineered maize, said Biothai director Witoon Lianchamroon.
Results of tests on the remaining samples were expected to arrive soon, he added.
Commercial planting of transgenic crops is banned in Thailand. Experimental cultivation is allowed at laboratory and contained greenhouse levels.
Mr Witoon said the contaminated maize farm was located only a few hundred metres from Monsanto's plantations. However, it could not be confirmed at the moment if the GM maize spread from the firm's plantation.
According to the Agriculture Department's records, Monsanto obtained permission to import five kilogrammes of the maize from the United States in 1999 to plant on an isolated farm for experimental purposes.
''Clean up and containment operations are urgently needed to prevent the GM crop spreading further,'' said Mr Witoon.
''This case is much more serious than the previous two GM crop leakages because corn is one of the country's top export produce while its pollen can spread very far and easily breed with conventional corn varieties.''
He recalled the spread of GM cotton in Loei province in 1999 and the leakage of GM papaya from the Agriculture Department's experimental field in Khon Kaen in 2004.
Once the GM maize spreads to sweet corn and baby corn farms, the country's corn exports, which generate about five billion baht in revenue per year, would be badly affected as Thai corn might be banned by the European Union (EU) and Japan, where consumers are strongly against GMOs, Mr Witoon said.
The detection of GM maize in a local farm came as farmers groups and biodiversity advocates are protesting against the Agriculture and Cooperatives Ministry's push to lift a ban on field trials of GM crops.
''[The spread of GM maize] reflects flaws in the government's control of transgenic crop plantations, therefore the ban should be maintained,'' said Mr Witoon.
The group yesterday petitioned Prime Minister Surayud Chulanont to instruct the Agriculture Department to investigate the GM maize leakage and contain the contamination immediately.
Jirakorn Kosaisawe, deputy chief of the Agriculture Department, said he would send officials to collect maize samples from the area soon to verify the group's findings.
Director of Monsanto's commercial acceptance for Southeast Asia, Shanti Shamdasani, said in a statement the company would cooperate fully with Thai authorities to determine the circumstances of the matter.