The question "how safe is our rice?" has been raised again after rumours spread through social media that the government may have sold overfumigated rice stocks to leading hypermarket operators to be repacked for distribution under their house brands.
Pledged rice at a Chachoengsao warehouse decomposed, emitting a mouldy smell.
The rumours have gone viral on Facebook, as well as LINE, with posts warning consumers not to buy house-brand rice packs from hypermarkets.
The posts claim overfumigated rice is hazardous to health and poses a cancer risk.
A miller based in Sara Buri who asked not to be named said fumigation is a common practice to kill insects for both domestic consumption and exports.
But for state rice stocks which have been kept for a long time, fumigation is repeated several times a year, he said.
In normal practice, millers will fumigate two times a year at most as their grain circulated in accordance with the annual harvests.
The chemical used to fumigate rice is phosphine, a substance promoted by the UN Food and Agriculture Organisation to replace methyl bromide, a more hazardous chemical.
"We don't exactly know how many times a year the government's rice stocks are fumigated, but we think the frequency is high because the rice is relatively old and contains high moisture," he said.
"We also believe overfumigated rice pose certain risks to consumers. Therefore, consumers have to be smart and choose new rice. They should avoid old rice which is normally muddy in colour and contains flakes or dust, and smells mouldy."
However, authorities and rice traders have brushed aside such rumours, alleging they are politically motivated and aimed at discrediting the government.
"We don't know where the rumours came from and there have never been reports that people die from eating the government's rice stocks," replied Pranee Siriphand, director-general of the Foreign Trade Department.
"People should not panick just because of the rumours, and overfumigation is not possible, as frequent fumigation will add expenses to surveyors (which function on behalf of the government)."
According to Ms Pranee, the rumours which have spread for a few days could be aimed at making it harder for the government to clear its existing rice stocks.
"Phosphine is supposed to a safe substance, as normally its residue will gradually be lower or vaporise after 5-7 days of fumigation," she said.
"Rumours that rats fall dead after eating overfumigated rice are also not true. The rats may die because they run into the silos during fumigation."
Somkiat Makkcayathorn, president of the Thai Rice Packers Association, has also played down the rumours, saying phosphine is a food-grade substance used to fumigate weevil without chemical residue.
Mr Somkiat also insisted that there is no addition of anti-fungus chemicals to the packed rice. This is because packed rice is polished and clean before packing and has low moisture of around 12-14% moisture.
The Thai Retailers Association also released a statement yesterday, affirming that all member stores have carefully chosen their rice packers.
The selection process is up to international standards, ranging from factory inspection, storing and rice packaging process to product quality and safety inspection, it said.
The operations and labelling of these packers are also in line with state regulations.
The association also called on consumers to apply discretion in spreading groundless information. Doing so will not only cause panic among the public but also affect creditability of the country's overall produce.
Kudatara Nagaviroj, corporate affairs director of Big C Supercenter Plc, the operator of Big C hypermarkets, said the chain had carefully selected its five packed-rice suppliers for its house brands and they comply strictly with international standards.
"We inspect and audit our rice suppliers on stocking procedures, packing processes and food safety compliance frequently," said Mr Kudatara.