The problem of melamine in the food chain continues to be discussed, so we thought we’d do a follow-up of our earlier post. The mechanism whereby melamine, or melamine plus some other factor, or something else entirely is the cause of pet deaths remains unclear. The latest theory is that a co-precipitate of melamine and cyanuric acid might be the cause of the apparent renal failure in cats and dogs who ate pet food contaminated with melamine and like compounds. Here’s what I have been able to make out at this point.
To recap, melamine is a nitrogen-rich chemical added surreptitiously to animal foodstuffs to make them look higher in protein than they really are. Exactly what form the melamine is in when it is added isn’t exactly clear. Melanime is polymerized with formaldehyde to make melamine resin (melamine formaldehyde, also frequently called melamine, although it is not the same). When melamine, proper, is synthesized it can produce a significant amount of wastewater:
Crystallization and washing of melamine generates a considerable amount of waste water, which is a pollutant if discharged directly into the environment. The waste water may be concentrated into a solid (1.5-5% of the weight) for easier disposal. The solid may contain approximately 70% melamine, 23% oxytriazines (ammeline, ammelide and cyanuric acid), 0.7% polycondensates (melem, melam and melon). (Wikipedia entry on melamine and SM Lahalih, M Absi-Halabi, “Recovery of solids from melamine waste effluents and their conversion to useful products”, Industrial & Engineering Chemistry Research, vol.28, 500-504 (1989))
It is my impression that this solid waste by-product of melamine synthesis is what is referred to in the news stories as “melamine scrap” and is the melamine rich substance added to the Chinese wheat gluten that wound up in pet food. This scrap is mainly melamine (70%) but contains a significant amount of the oxytriazines, among them, cyanuric acid. One of the leading theories of how pets are being harmed is related to this combination of melamine and cyanuric acid. It has been known for some time that there is a strong tendency for the two to form large hydrogen-bonded complexes (melamine is green, cyanuric acid is red; from the Wikipedia entry on Melamine):
Characteristic spoke-like crystals have been reported in both contaminated wheat gluten concentrate and tissues and urine of afflicted animals. The potential connection strengthened when researchers at the University of Guelph announced they could make similar crystals by combining melamine and cyanuric acid in solutions with the acidity of animal kidneys. This suggested that these two relatively non-toxic materials when combined can interfere sufficiently with kidney function (we don’t know how) to produce the pet deaths. While plausible, most of this is currently speculation.
What about human health? Melamine doesn’t accumulate in the body, since it is water soluble and has a half life reported to be only three hours. That means it is mostly excreted through the kidney, so the main question would be whether there is enough there at any one time to combine with whatever else it needs to combine with (e.g., by speculation, one of the oxytriazines) to cause damage in humans. Since the concentrations in humans are likely orders of magnitude less than for pets, my speculation would be, “no.” This doesn’t mean that we shouldn’t worry about very small amounts of chemical. I have already discussed why we are worried about small amounts when they produce damage that can be biologically amplified (see here, here and here). It means I don’t think melamine contamination is one of those instances.
However it still has major public health significance because it shows how easily potentially harmful contamination can travel undetected through the food chain from distant sources.
Melamine may not be a skull and crossbones but it is certainly a red flag.