China finds melamine and milk don't mix

Tech.view

Land of milk and money

Oct 3rd 2008
From Economist.com

China finds melamine and milk don't mix

AS AN industrial chemical, melamine has many genuinely useful applications. But a protein booster for milk is not one of them. How melamine got into baby food in China, killing four infants and sickening 54,000 to date, is a scandalous tale of greed, criminal negligence, political cover-up and shoddy science.

Melamine is used to make durable work-surfaces for kitchen cabinets and bathroom furniture, and is formed into heat-resistant jugs, bowls, dinnerware, and other household items. To be accurate, such products are made not from melamine, but from melamine resin—a thermosetting plastic produced by combining melamine with formaldehyde.

The difference is important. Melamine resin is an especially stable plastic. Though it will decompose under a high enough temperature, the resin barely dissolves in water and is otherwise reasonably inert.

AFPDon't get fooled again

Fabrics containing stiffeners made from melamine resin may be a different matter. There’s some suggestion that, handled badly, they may release traces of formaldehyde, a known carcinogen. But the stability of melamine resin makes it almost impossible to recycle. So don’t worry about melamine entering the body from kitchen utensils or false teeth.

Melamine itself is a different matter. In low doses, it is non-toxic; its so-called LD50 (median lethal dose) is on a par with table salt. But should it be combined with a closely related chemical called cyanuric acid, the resulting compound (melamine cyanurate) can cause fatal kidney disease. Melamine cyanurate is widely used as a fire retardant.

Until recently, however, there was a good deal of scientific confusion over melamine’s toxicity. Many people in the industry were led to believe it was virtually harmless.

Belatedly, we now know that, though a single dose of pure melamine is unlikely to kill you, ingesting even modest amounts over time can cause bladder or kidney damage, leading to renal failure and even cancer and death. The Chinese children who died and were sickened consumed the tainted infant formula daily for six months or more.

What business has melamine in baby food anyway? To understand the reasons, look no further than the compound’s chemical architecture.

A molecule of the stuff comprises three carbon atoms and six each of hydrogen and nitrogen. Forget about the hydrocarbon part—it contributes little to the chemical’s mass. Pound for pound, melamine is two-thirds nitrogen.

Because it contains so much nitrogen, agricultural researchers once thought melamine would make an ideal fertiliser. Unfortunately, they found it took too long to break down in the soil—and ever since, urea has been the fertiliser of choice, even though it contains far less nitrogen.

Clearly, some dairy farmers and milk collectors haven’t forgotten about melamine’s nitrogen wallop—especially those who routinely dilute their milk and need a way to fox the testing gear.

Milk analysers (like the popular Lactoscan machine from Bulgaria) use ultrasound to measure the fat and protein content, as well as the percentages of non-fat solids, lactose and water. If the milk is diluted in any way, the fat and protein levels fall to about half their normal levels. One way to mask illicit adulteration is to add vegetable oil to boost the fat count and melamine to rig the protein figure.

The melamine trick works because the protein content is deduced by measuring the amount of nitrogen in the sample. By adding melamine and water, one litre of milk can apparently be bulked up into four litres—and still pass the protein test.

Melamine was certainly found in the contaminated milk that sparked the recent worldwide recall of Chinese dairy products. Having sat on the evidence for more than a month so as not to mar the Beijing Olympics, the Chinese authorities have now labeled it the official culprit.

But something fishy seems to be going on here. For one thing, melamine is not all that easy to dissolve into milk. For another, there’s been a worldwide shortage of melamine for some time now. Its price has shot up to more than $1,750 per tonne from $1,100 a few years ago.

So why use an expensive industrial chemical that’s in short supply to dilute a dirt cheap product like milk? The answer can only be that either some flaw rendered the melamine industrially worthless, or it wasn’t melamine at all. The first suggestion is scary enough; the second is even more ominous.

The only thing your correspondent can imagine that would render melamine industrially worthless is if it were reclaimed waste from the production process.

Industrially, melamine is usually made by heating urea in the presence of a catalyst. Because large amounts of ammonia and carbon dioxide are given off in the process, most modern plants now combine melamine production with urea production, which uses ammonia and carbon dioxide as feedstocks. As the two processes feed off one another, a combined plant is considerably more efficient than two separate ones.

But the final stage—washing the melamine and turning it into crystal form—produces lots of effluent that needs treating before releasing into the environment. The usual way to do that is to filter the waste water and pipe that away, and then dispose of the concentrated solids separately.

Those accumulated solids are around 70% melamine, with the rest being made up of various by-products, including our old friend cyanuric acid. As mentioned before, a mixture of melamine and cyanuric acid can be a nasty witches’ brew, especially when ingested by infants.

But what if it’s not melamine that’s being used to spike China’s diluted milk? Urea may be not as rich in nitrogen, but it’s certainly a whole lot cheaper (around $650 per tonne). Sprayed into the milk at the temperature used to create a powdered product for baby food and confectionery, enough of the urea would be converted into melamine to show up in tests.

If that’s the case, where does the urea come from? Is it really fertiliser—or something else cattle produce in prodigious quantities? Perhaps that’s why the Chinese authorities are suddenly so keen to blame more hygienic melamine for all their woes.