Nothing says "lunch time" to an American kid quite like a peanut butter and jelly sandwich. Slices of deli meat might be a close second. Unbeknownst to most parents who pack school lunch boxes, however, both of these favorites could expose kids to toxic chemicals.

In a new study of popular products purchased from grocery stores in Dallas, Texas, researchers found that nearly half of the sampled peanut butter and cold cuts, as well as turkey, fish, beef and other fatty foods, contained traces of a flame retardant commonly used in the foam insulation of building walls.

"This is not good news. Here's yet another toxic chemical that can be found in many of the foods we buy at our supermarkets," said Dr. Arnold Schecter of the University of Texas School of Public Health and an author of the study published on Thursday. "Food does not need to have flame retardants."

The particular flame retardant Schecter's team investigated, hexabromocyclododecane (HBCD), is just the latest in a string of manmade chemicals that researchers are discovering in popular foods. Previous research has turned up DDT, polychlorinated biphenyls (PCBs), mercury, dioxins and other flame retardants. And this is in addition to the chemicals purposefully added to products during processing, or that leach into food from packaging.

Each of the uncovered chemicals poses health concerns, from diabetes to cancer, and HBCD is no exception. According to the U.S. Environmental Protection Agency, the flame retardant is "highly toxic" to marine life and may disrupt the proper function of human hormones and reproduction. Most worrisome are the chemical's potentially damaging effects to a young child, even before it's born.

Sonya Lunder, a senior analyst with the Environmental Working Group, noted that the chemical has been discovered in umbilical cord blood. "The prenatal period is an incredibly sensitive time," she said, adding that breastfeeding and toddlers' penchant for putting their hands (and other objects) in their mouths is likely to add to a body's early burden of the chemical. "Exposure starts before birth and may continue on in the diet for their entire life."

The chemical industry, however, offers a different interpretation of the new study. "Based on these findings, the real story is that HBCD was not detected in the majority of the samples and in those where it was, it was well below levels where one might see adverse health effects," Bryan Goodman, a spokesperson for the lobbying group North American Flame Retardant Alliance of the American Chemistry Council, said in a statement. "These results should not pose a concern for human health."

The study did not specify which particular brands were tested, but Schecter noted that all were "conventional" brands and not brands that market themselves as organic.

While the amount of HBCDs found in the food samples studied were relatively small -- below what the government considers dangerous -- Lunder still expressed concern. The chemical isn't acting alone, she explained. Rather, it is just one of multiple chemicals to which consumers are frequently exposed, which, when combined, could prove more harmful than any one acting alone. Small quantities of HBCDs can add up to a much more significant chemical presence over time. Once in the human body, the same fat-loving disposition that attracted the chemical to fatty foods like meat and nuts can help it bind to human fat, where it can stick around for years.

"We can expect levels to slowly increase over a lifetime," said Lunder.

So, how does a chemical meant for use behind a thick wall end up in our lunch bags and on our dinner plates? Experts suggest that HBCDs make their way into the food chain via the air, water and soil. "They could migrate out of products into dust and end up in sewage sludge," suggested Arlene Blum, executive director of the Green Science Policy Institute, an environmental health watchdog and research group. "The chemical may then end up in the marine food supply, or the sewage sludge could get put on fields," where peanuts crops might be grown or on which livestock might graze.

The dangers of HBCDs are receiving increased attention around the world. In fact, Blum expects them to be the next class of toxic chemicals banned globally through the Stockholm Convention.

Blum highlighted the problem of simply replacing one toxic chemical with a related one. When Congress banned PCBs in the 1970s, for example, the chemical industry began employing an alternative flame retardant called polybrominated diphenyl ether (PBDE) for use in furniture and other products. When PBDE was found to be equally as harmful, the industry looked again among its related chemical cousins, including chlorinated Tris, which has itself been declared a carcinogen by a California state science panel. Meanwhile, HBCDs have remained a go-to for reducing flammability in home insulation despite growing evidence of harm.

"After 30-some years of doing this, I have yet to see a case of a halogenated flame retardant that didn't have problems," said Blum, whose research contributed to the removal of chlorinated Tris from children's pajamas in the 1970s. (PCBs, PBDEs, chlorinated Tris and HBCDs are all considered halogenated chemicals.)

Lunder, too, has been paying attention to the science and policy surrounding flame retardants, including HBCDs, for many years. "It's difficult to watch," she said. "The tragic story here is that people have been talking about this family of chemicals for 10 years and slowly amassing a body of data on how toxic it is to people, and how it's found in the food chain."

"It's a common story, with unintended effects on the environment and human health," she added. "But I'm not seeing a system that is very rational or preventative, or that is learning from prior experiences. Right now, the system is very reactive. No one has a clear mandate to look for problems or ban chemicals, when it comes to that."

Environmental health advocates and experts have been urging Congress to retire the 1976 Toxic Substances Control Act and replace it with the more rigorous and precautionary Safe Chemicals Act, which currently awaits a Senate vote.

In the meantime, Lunder and Schecter suggest that people can reduce their own exposures to HBCDs by eating fewer fatty foods, such as peanut butter and meat. Parents can consider filling lunch boxes with more fruits and vegetables.

"However, we can't prevent the problem completely," Lunder said. "It's going to take more than shopping tips to really reduce exposures."