That's due to Prop 65, which was a law created on good intentions but extremely poorly implemented. As the law is written, there is no threshold under which something is declared safe, so even the most minuscule quantity of some substance gets it flagged as being there.
Most regulations related to food content define specific allowable amounts of a huge range of weird things. People are grossed out by these regulations. "You're allowed to have fly wings in food products!". Well, its not encouraged, but zero is not something one can test weekly in a lab for compliance.
That's quite right, but not what james was talking about exactly.
He was precisely pointing out that no threshold at all was defined, and as I take it, expressing that the result was to flag absolutely anything detectable. Which in turn is arguably counter-productive as the inability to determine what's a problem and what isn't that comes with it makes it pretty much useless.
I would just reply to james with the following: 1. For many susbtances, we actually don't have a clue what the safe level is. If regulation states that some given level is safe, and it turns out that it isn't, then it has misled people, potentially with very bad consequences, 2. Although a minority, there are some people with very weird allergies that can get triggered even from just traces of some substance. If a company fails to mention its presence, even in insignificant amounts, while it provably has the ability to detect it, then affected people can sue for not having been informed.
So as to the "zero", that's a slightly different matter.
While there is no "zero" in the physical world indeed and having zero as a target for some known value is absurd, here we are talkiing about the presence or absence of some substances inside a product.
That's related, but a bit different: obviously current, state-of-the-art lab equipment can't detect given substances under a certain concentration, and not detecting them doesn't mean there isn't any.
So to be completely rigorous, we should list all possible known substances in the universe (or at least on Earth) and put a '< xxx' (with xxx the limit of detectability with current equipment) rather than omitting them altogether, but obviously it would not be practical.
So when a given substance is not listed, it should just be assumed that it means "below the threshold of detectability with current equipment", if a higher acceptable threshoid has not been defined.
All obvious, but just to say that from a regulatory POV, as long as a minimum safe threshold hasn't been defined, you either list the substance if it's detectable (with the currently used equipment with performance defined by said regulation), or omit listing it altogether.