What is Melamine?
Melamine is used in a variety of manufacturing processes. It is used in glue, ink and plastic colorants and it can be polymerized into a lightweight, fire-retardant resin that is used in making housewares, countertops and dry-erase boards. How does it find its way into food products? The tests used to measure protein in food actually use nitrogen content as a proxy for protein content. Because melamine is nitrogen rich (see picture), it can fool these tests giving a higher readout. This means unscrupulous companies can dilute their product (milk, for example), spike it with melamine, and tests will show that it's still protein-rich, saving money on production costs and stretching supply (a little milk ends up going a long way). The only problem is the milk is watered down. And toxic.
Or is it? Melamine itself has a low toxicity. In rats the LD50 is over 3g/kg (acute dose) and they can consume lower doses long term with no adverse effects (63mg/kg/day for 13 weeks up to 417 mg/kg/day for 14 days) [source] Of course rats aren't humans, but low toxicity doesn't explain why so many children - over 50000 at last count - have fallen ill with the milk scandal. While malnourishment due to consuming nutrient-poor milk and formula is likely a factor, most of the victims suffered from kidney problems which is likely due to the contaminant itself rather than poor quality food. When combined with its sister compound, cyanuric acid, they form an insoluble salt which can from crystals in the kidney and lead to the kind of renal problems seen in the tainted milk scandal.
Cyanuric acid is a chemical used to stabilize chlorine in outdoor pools and as a precursor to chlorine compounds used to disinfect water. It can also be found as a non-protein nitrogen source in animal feed and, similar to melamine, used to fake out protein assays. Cyanuric acid can be synthesized by hydrolysis of melamine and is also a known metabolite (in bacteria). Like melamine, cyanuric acid has low toxicity on its own - people swallow pool water all the time - but the two in combination can have serious effects.
Cyanuric acid and melamine readily form hydrogen bonds, making an insoluble crystal lattice. In fact, the analytical test for cyanuric acid is precipitation with melamine. When this reaction occurs in the body, can lead to kidney stones and renal damage. Of course, the people thinning their milk with melamine had no idea that it would have such broad, devastating effects other than cheap, low-quality milk, right?
Wrong. The Chinese food industry had a massive clue that adding melamine to food products could be disastrous a year ago when people's pets started dying and the huge pet food recall that followed. As now, melamine was the culprit. It was being added to pet food to improve results on protein assays. But that giant heads up that cheating quality assurance with melamine might not be safe wasn't enough to discourage its use in milk products. It wasn't even enough to make the Chinese government keep a closer eye on food manufacturers. Sanlu and other companies involved in the scandal were enjoying inspection-free status.
This is another in a line of recent Chinese manufacturing issues (eg. the pet food recall, tainted toothpaste, lead toy recall). Cheap products are nice, but clearly there are larger costs to be paid. Poisoning children? WTF, China