As Halloween treats smother supermarket shelves, a new study echoes a lingering pediatric concern: Chocolate can be contaminated with worrisome amounts of lead.

Until now, conventional logic was this: Cocoa-producing countries use leaded gasoline. Leaded gasoline contaminates cocoa plants; cocoa beans are tainted from the start. Look up "chocolate" in the Wikipedia, an estimable online encyclopedia, and that's just the story you'll find.

But a study published in this month's Environmental Health Perspectives suggests otherwise. A team of American and Nigerian researchers found that lead levels in raw cocoa beans were 60 times lower than lead levels observed in processed chocolate products.

"The logical step you can take from here is that most of the contamination isn't coming from the producer," explained Charley Rankin, the paper's lead author and a toxicology researcher at the University of California at Santa Cruz. "It's either coming from the shipping or the manufacturing process."

Regardless of the source of contamination, "there is no excuse for a product that is about to be consumed by children to contain lead, period," said Dr. John Rosen, a pediatrician and lead program director at Montefiore Medical Center in New York City.

The list of permanent developmental deficits due to childhood lead exposure is long. Elevated blood lead levels can harm a child's ability to think, plan, organize and memorize, Rosen explained. "And lower levels of lead may produce intellectual deficits that are with a child forever."

But the National Confectioners Association, which has a vested interest in monitoring kids' love for candy, reports that half of the nation's 36 million trick-or-treaters prefer chocolates on Halloween.

"If it was up to me, it would be no chocolate," Rosen countered. "It's better to be safe than sorry."

Dark chocolate and hot cocoa are often lauded for their high antioxidant value, but these goodies also harbor higher levels of lead. The more raw cocoa there is in the mix, the more lead there is in the final product.

Documented lead content in candy has ranged from a mean concentration of 21 nanograms per gram in milk chocolate bars in an Australian study to an average of 1,920 ng/g in chocolates in India. Not to say chocolate is the only food containing lead. U.S. lead concentration for apples is 20 ng/g, 200 ng/g for dry table wine and 100 ng/g for canned pineapple, according to the study.