A stick of butter purchased at a Dallas grocery story contained high levels of a flame retardant used in electronics, according to environmental scientists at the University of Texas School of Public Health.

The butter was contaminated with a chemical called polybrominated diphenyl ether, or PBDE.

"To the best of our knowledge, this is the first report of U.S. butter contaminated with PBDEs," said lead research Arnold Schecter, whose study was published Tuesday in the journal Environmental Health Perspectives.

The butter was purchased last year as part of a small research project to test for contaminates. The butter stick's wrapper contained even higher amounts of PBDEs. The source of the contamination remains a mystery.

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