Anytime you see an article that starts off with the heading “The Truth About….,” it’s a pretty safe bet that you will not get the truth. And so it is with an article circulating about almonds. “The Truth About Almonds: Almost No One Knows This Dirty Secret.” What is the “dirty secret?” That the almonds are treated with the fumigant propylene oxide to prevent contamination by salmonella bacteria. Salmonella infection is not pleasant to say the least. But people mostly associate it with contaminated eggs, not almonds. Where do the bacteria come from? Mostly fecal matter. Easy to see how eggs can be contaminated as they are laid. But almonds? Birds and insects can spread the bacterium after contacting fecal matter, but exposure may also be indirect through contaminated irrigation water. Salmonella bacteria can survive a long time even in dry conditions and dry heat treatment is not very effective at killing them. But fumigation with propylene oxide is. The nuts are placed in a chamber with liquid propylene oxide and the pressure is then reduced to allow quick evaporation of the liquid. The vapour destroys bacteria very effectively, preventing the possibility of food poisoning. There is no secret here. And nothing dirty is going on.
So what is the alarm all about? That propylene oxide is an animal carcinogen. That does not mean it is known to cause cancer in humans. And even if a substance is a human carcinogen, dosage still matters. While “carcinogen” is a frightening term, all it means is that the substance is capable of causing cancer in some animal at some dose. But there is a threshold effect. In rats no cancer can be found at any dose less than nine milligrams per kilogram of body weight, which has been established as the No Observed Adverse Effect Level (NOAEL). In other words at that dosage there is absolutely no problem detected.
Canada does not grow almonds so there has not been an application to allow the use of propylene oxide. This is not the same as it having been banned, as some alarmists claim. However, since Canada does import almonds that may have been treated with the chemical, the Pest Management Regulatory Agency has looked at the animal data and concluded that the maximum permissible residue is 300 parts per million. That is way below the NOAEL. And how much are almond eaters actually exposed to? The only way to know is to test for residues. That’s why the Canadian Food Inspection Agency tested over a thousand samples of spices, herbs, cocoa powder and nuts, including almonds. Guess what they found? No residue at all! So there is no reason to be concerned about propylene oxide in almonds because it isn’t there. And that is the truth.