Researchers from the University of Texas, School of Public Health sampled 36 foods, including peanut butter, between 2009 and 2010.
They found that nearly half of their samples had detectable levels of the commercial flame retardant mixture, HBCD.
Researchers also sampled other foods, like deli meat, poultry and canned sardines. They said those foods could be behind elevated HBCD levels in humans and that a larger and more representative sampling should be done.
The study is published in the journal Environmental Health Perspectives.