Melamine

The recent food scare involving the addition of melamine to milk has really affected each one of us greatly, so I thought I would post some facts related to melamine so that everyone can have a broader picture of what's happening!

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Picture showing the resonant forms of melamine

Melamine is an organic base chemical most commonly found in the form of white crystals rich in nitrogen, with a 1,3,5-triazine skeleton. It is an aromatic compound consisting of carbon, nitrogen and hydrogen, and is a trimer of cyanamide (CN₂H₂), containing 66% nitrogen by mass. It is also a metabolite of cyromazine, a pesticide, and is formed through dealkylation of ingested cyromazine.

Melamine is most often produced using urea in an industrial process. First, urea decomposes into cyanic acid and ammonia in an endothermic reaction:

6 (NH₂)₂CO → 6 HCNO + 6 NH₃

Then, cyanic acid polymerizes to form melamine and carbon dioxide:

6 HCNO → C₃H₆N₆ + 3 CO₂

This is exothermic, but the overall process is endothermic.

Melamine is widely used industrially to manufacture plastics, adhesives, countertops, dishware and whiteboards. It is prized for its durability and is used to produce brightly-coloured dishware most popular in the 1950s. As a component of plastics and laminates (in wood, dishware etc.), melamine is used to form a melamine formaldehyde resin that is a hard, thermosetting plastic material made from melamine and formaldehyde by polymerization.

Picture of melamine plates

Melamine resin is known for its fire resistance and heat tolerance. In contact with heat, it decomposes, thus acting as a heat sink; furthermore it releases inert nitrogen gases upon combustion thus limiting the access to oxygen and flammable gases; and the resin also chemically and physically inhibits burning through char formation.

However, melamine has numerous biological side effects which have grabbed the world’s attention through the recent China milk contamination debacle. Where adulteration of the milk took place, water was added to raw milk to increase its volume, but this lowered its nutritional and protein content, which was checked by distributors by measuring nitrogen content. This prompted farmers to add melamine to increase the apparent protein content due to the high amount of nitrogen present.

There have been no studies on melamine on human health, but it can be extrapolated from other studies involving small mammals and other animals. Exposure to melamine has resulted in the irritation of eyes, skin and mucous membranes; dermatitis; chronic inflammation of kidneys and the ulceration of urinary bladder epithelium in mice; urolithiasis (kidney stone formation, at the centre of the recent scandal); and bladder cancer. Melamine’s effects are most serious in the kidneys and urinary tract, with ingestion of melamine in animals resulting in acute renal failure. Bladder tumours found through animal studies were secondary to the development of calculi (kidney stones) and uroliths (urinary bladder stones), caused by chronic physical injury by such stones.

Picture showing kidney stones formed
from mineral deposits in the kidney

The main constituents of the stones in the urinary bladders of rats given melamine in the diet were found to be unchanged melamine and uric acid in a 1:1 molar ratio. Melamine complexes with cyanuric acid to form melamine cyanurate, precipitating as stones in the bladder and kidneys. This crystalline complex is held together by hydrogen bonds similar to DNA base pairing, and is repeated throughout to form an extensive network of hydrogen bonds and a lattice-like structure. The formation of this complex vastly increases its toxicity over melamine and cyanuric acid individually.

Extensive hydrogen bonding between melamine (in blue) and cyanuric acid (in red)

The tolerable Daily Intake (TDI) of melamine as established by the US Food and Drug Administration (FDA) is 0.63 mg/kg of body weight. This means that an adult weighing 60 kg or a child weighing 30 kg can ingest 37.8 mg of melamine and 18.9 mg of melamine respectively every day over a lifetime without any appreciable health risk.

But even if officials say these safety figures are already a reduced estimate, who really knows about melamine’s true effects? Meanwhile what we can do is to be judicious in selecting our groceries and food intake, avoiding those suspected dairy products from China.

Picture of polyunsaturated fatty acids, including
omega-3 (n-3) and omega-6 (n-6) fatty acids

Here’s something that has not been reported in the news so far though: scientific studies show that dietary PUFA (polyunsaturated fatty acids) modulate differentially normal and pre-neoplastic (preceding the formation of an abnormal growth of tissue, which can be benign or malignant) urothelial proliferation induced by melamine. Fish oil, rich in omega-3 fatty acids, have shown a strong protective effect against the formation of such uroliths.

A toast to salmon!