Infant formulas purchased from stores in Canada show widespread tainting with traces of melamine, a toxic constituent of plastics and other materials. In China, the fraudulent use of melamine as a protein replacement in infant formulas resulted in the poisoning of more than 1,200 babies last year, six of whom died. Canada’s widespread contamination, however, appears unintentional and to stem from a very different source.

Chemists with Health Canada in Ottawa report they have yet to identify the source of the pollutant they’ve just turned up in 71 of 94 samples of infant formula. In a report of their findings, however, just published online ahead of print in the Journal of Agricultural and Food Chemistry, Sheryl Tittlemier and her colleagues do finger one key suspect: the insecticide cyromazine. It’s legal for use on food crops and animal forage — and melamine is one of its breakdown products.

“In all instances in which melamine was detected, concentrations observed were below the standard of 0.5 micrograms per gram set by Health Canada for infant formula,” the researchers note. Indeed, levels ranged from 4 to 346 nanograms per gram (or parts per billion) of assayed formula. Based on the concentration present in even the most contaminated product, Tittlemier’s group calculates that a baby’s likely intake of the kidney-toxic chemical would only come to about 1 percent of the allowable intake.

The peak tainting found, 346 ppb, is in the same ballpark that the U.S. Food and Drug Administration reported finding in a single domestic infant formula — one of 74 samples it tested last year. In November, Stephen Sundlof, director of FDA’s Center for Food Safety and Applied Nutrition, noted that at such concentrations U.S. infant formulas are “safe” for continued use as a sole source of nutrition for babies.

The real question is how melamine has been making its way into North American infant formulas. At a press briefing last fall, Sundlof posited that it might be from melamine-based plasticware or food packaging. He noted that some foodware and plastic-laminate counter materials are made from melamine, which studies have shown can leach into foods.

But clearly, no one believes manufacturers are storing their wholesale supplies of baby formula in melamine vats. It also would appear, Tittlemier’s group says, that the melamine it found did not come from packaging. These chemists tested the material lining the can from which the most tainted formula had come — and found no melamine. Most reassuring: Melamine concentrations in North American products are far lower than those linked with the deliberate adulteration of dairy products in China.

Which brings Tittlemier's group back to cyromazine, an insecticide used on Canadian and U.S. produce. The pesticide’s manufacturer has published data showing that when goats had been dosed with a radioactively labeled form of the insecticide, five to nine percent of the residues turned up as radiolabeled melamine in the milk. “It appears plausible,” Tittlemier and her colleagues now conclude, “that milk from cattle exposed to cyromazine may contain melamine,” explaining how the chemical could end up in milk-based infant formula.

Of course, melamine also turned up in most of the 19 samples of soy-based formula that Health Canada tested — products with no milk. I’m guessing the pesticide is also used on soybean fields, although a quick scan of FDA’s pesticide-tolerance data sheet doesn’t identify allowable levels for soy as it does for onions, potatoes, corn, radishes and lima beans.

Bottom line: Even our salads and casseroles may have a little something in common with the laminate counter tops on which so many are prepared: melamine.

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