The idea that a 5-digit PLU beginning with “8” is a reliable guide to the genetic characteristics of a piece of produce has spread around the internet like wildfire.
Trouble is, it’s false. Now, it’s a falsehood rooted in fact: the numeral “8” (in the 1st position of a 5-digit code) has in fact been set aside, (by the International Federation for Produce Standards) to designate GM foods. But the code is entirely voluntary, and no one is actually using it.
So, in theory, a 5-digit PLU starting with 8 (if you ever saw one) would imply that the product in your hand is genetically-modified. But the absence of that 8 tells you absolutely nothing at all.
(For a longer version of the explanation, see PLU Codes Do Not Indicate Genetically Modified Produce, by Jeffrey Smith.)
I have just a couple of things to add.
First is that this kind of thing just adds to my concerns about the power of labelling to inform consumers. (See my blog entries, Does it Matter if Consumers Understand Food Labels? and Are Labels the Answer (to Everything)?) But now we see even more reason for concern, if labels that are not aimed at consumers (and that don’t tell them much of anything) are liable to be taken up and misinterpreted.
Second is that the confusion over PLU codes suggests that advocates who are concerned to inform the public should be very careful, not just in gathering facts but also in thinking through the logic of what they’re saying. Part of the problem, here, is that most people are bad at conditional reasoning. The fact that an 8 implies GMO does not logically mean that the absence of an 8 implies non-GMO. Advice for consumers needs to be framed in a way that minimizes both false positives and false negatives!