A vendor wearing a face mask and gloves as a preventive measure against the spread of the COVID-19 coronavirus sells vegetables at a market in Bangkok on March 27, 2020. (AFP / Romeo Gacad)

Old hoax about washing fruit and vegetables with salt water resurfaces in Thailand

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Multiple Facebook and Twitter posts shared thousands of times claim that washing fruits and vegetables with salt water will cause insecticide residue to “become more long-lasting”. The claim is misleading; experts maintain that salt water does not cause insecticide residue to become more durable.

The claim was published on Facebook here on December 26, 2016. It has been shared more than 200 times.

The post's Thai-language caption translates in part as: “Don’t use salt water to clean vegetables and fruits!!!

“Many people misunderstood that washing vegetables with salt water will make vegetables become clean. But in reality, salt is Sodium Chloride which will make the residue such as insecticide become more long-lasting in the vegetables and fruits.

“When you want to clean fruits and vegetables properly, you should wash them with water and then put them in the wheat flour mixed with a little bit of water. Because it will make the toxin from insecticide go away.”

A similar claim has circulated on Facebook since at least 2015, for example here. It was also shared in recent years on Facebook here, here, here, here, here and here.

But the claim is misleading, according to experts.

“Salt water doesn’t make the chemical residues left in vegetables and fruits become more long-lasting,” Dr. Tirayut Vilaivan, a professor at Chulalongkorn University’s Department of Chemistry, told AFP by phone on May 18, 2020. “However, I would say it is only 30-40% effective because most insecticides can’t be diluted in water.”

Dr. Vilaivan added that using vegetable washing liquid is the most effective way to clean produce.

“Vegetable washing liquid has the surface-active agent which can help get rid of the chemical residues in fruit and vegetables,” he said. “But you also need to wash the washing liquid thoroughly before eating them.”

Dr. Jessada Denduangboripant of Chulalongkorn University, said “salt water can be used to wash fruit and vegetables” on his Facebook page here on December 17, 2014, adding that it could potentially help to remove insecticides.

"Most insecticides come in oil form so salt will make the oil compound separate from each other," he said.

Below is a screenshot of Dr. Jessada's Facebook post:

Screenshot of Dr.Jessada's Facebook post

Voice TV, a Thai television network, also debunked the claim in December 2014 here.