Earlier quoted context omitted.
> formaldehyde As a metabolic intermediate, formaldehyde is present at low levels in most living organisms. Formaldehyde can be found naturally in food up to the levels of 300 to 400 mg/kg, including fruits and vegetables (e.g. pear, apple, green onion), meats, fish, crustacean and dried mushroom, etc. Ingestion of a small amount of formaldehyde is unlikely to cause any acute effect. The main health concern of formal…
Well, sure. Here's the thing: with anything , the dose makes the poison -- and "low levels" and "small amount" are pretty important phrases in those claims, right? ( https://wwwn.cdc.gov/TSP/MMG/MMGDetails.aspx?mmgid=216&toxid... ) People aren't talking about the amounts in apples when they're referring to e.g. https://en.wikipedia.org/wiki/2005_Indonesia_food_scare
But selecting formaldehyde for your scary example mostly just sounds scary because of it’s relation with embalming fluid. As you say, anything can be poisonous: the LD50 of many substances is surprisingly high https://en.wikipedia.org/wiki/Median_lethal_dose#Examples
From https://www.smithsonianmag.com/science-nature/19th-century-f...
In 1896, desperately concerned about diseases linked to pathogens in milk, he even endorsed formaldehyde as a good preservative. The recommended dose of two drops of formalin (a mix of 40 percent formaldehyde and 60 percent water) could preserve a pint of milk for several days. It was a tiny amount, Hurty said, and he thought it might make the product safer.
But the amounts were often far from tiny. Thanks to Hurty, Indiana passed the Pure Food Law in 1899 but the state provided no money for enforcement or testing. So dairymen began increasing the dose of formaldehyde, seeking to keep their product “fresh” for as long as possible. Chemical companies came up with new formaldehyde mixtures with innocuous names such as Iceline or Preservaline. (The latter was said to keep a pint of milk fresh for up to 10 days.) And as the dairy industry increased the amount of preservatives, the milk became more and more toxic.
Hurty was alarmed enough that by 1899, he was urging that formaldehyde use be stopped, citing “increasing knowledge” that the compound could be dangerous even in small doses, especially to children. But the industry did not heed the warning.
In the summer of 1900, The Indianapolis News reported on the deaths of three infants in the city’s orphanage due to formaldehyde poisoning. A further investigation indicated that at least 30 children had died two years prior due to use of the preservative, and in 1901, Hurty himself referenced the deaths of more than 400 children due to a combination of formaldehyde, dirt, and bacteria in milk.
Following that outbreak, the state began prosecuting dairymen for using formaldehyde and, at least briefly, reduced the practice. But it wasn’t until Harvey Wiley and his allies helped secure the federal Pure Food and Drug Act in 1906 that the compound was at last banned from the food supply.