Foods that were contaminated in Michigan in 1973, when a fire retardant containing the chemical polybrominated biphenyl PBB was accidentally mixed with animal feed, have been associated with an early onset of menstruation and pubic hair in some daughters of the women exposed, scientists reported in the journal Epidemiology (Nov. 2000, Vol. 11, No. 6.)
The daughters of the most highly exposed women began menstruation, on average, before they reached their twelfth birthdays.
The study by scientists at Emory University and the Centers for Disease Control and Prevention in Atlanta, and the Michigan Department of Community Health, was funded by the National Institute of Environmental Health Sciences, part of the National Institutes of Health, and by the U.S. Environmental Protection Agency's Office of Research and Development.
In 1973, a fire retardant containing PBBs, was mistakenly mixed with cattle feed in place of a feed additive. The contamination was eventually discovered when milk production went down and calves were stillborn or born with hoof deformities. By the time the source of the PBBs was identified, at least 4,000 people had been exposed through contaminated meat and dairy products. PBB accumulates in fatty tissue in the body and is stored for years.
In the current study, researchers contacted female offspring, 5 to 24 years of age, born after the Michigan PBB incident to mothers listed as exposed to PBB in the Michigan PBB registry. Those with earliest menstruation were daughters of mothers with the highest estimated serum levels of PBBs during pregnancy, who had also nursed their infant daughters, giving them both prenatal and breast milk exposures. In the PBB study, the most highly exposed girls were a year ahead in starting their periods, at 11.6 years compared to 12.7 years for less-exposed girls.
"This study lends support to the hypothesis that events associated with puberty may be affected by pre- and postnatal exposure to PBB's," Michele Marcus, Ph.D., principal investigator of the study.
This is the second study to associate early puberty with exposure to a specific chemical. The first study, by Ivelisse Colon and co-authors, appearing in the NIEHS journal Environmental Health Perspectives in September (Vol. 108, Number 9) associated precocious puberty in young girls in Puerto Rico with the plasticizer chemicals called phthalates.
The largest study to date to determine the incidence of precocious puberty in the United States was published by Marcia Herman-Giddens in the journal Pediatrics in 1997, and with a sample size of 17,000 showed that 1 in every 7 Caucasian girls and 1 out of every 2 African American girls develop breasts or pubic hair before the age of 8. In the current study, the girls who were most highly exposed to PBBs had pubic hair at an earlier age than less-exposed girls. However there were no differences found in timing of breast development.