Scientists have long suspected that children may be especially vulnerable to the endocrine-disrupting effects of polybrominated diphenyl ether (PBDE) flame retardants because the main route of exposure to the chemicals is through consumer products in the home. A new study by Katharina Maria Main of Rigshospitalet [2.8 Mbyte PDF], part of the Copenhagen University Hospital, is the first to link elevated PBDE levels with a human birth defect.

The study, published online May 31 in Environmental Health Perspectives, associates cryptorchidism, a condition in which one or both testicles fail to descend into the scrotum, with higher concentrations of PBDEs in breast milk. The incidence of cryptorchidism is increasing rapidly in some countries, which suggests that environmental factors may be involved, according to the paper. Main and her colleagues found that PBDE concentrations in the breast milk of Danish and Finnish mothers of sons born with undescended testicles were significantly higher than those in the breast milk of mothers of sons with normal testicles.

Because testicular descent is strongly androgen-dependent, the researchers say that the new findings are in line with a 2005 study showing that PBDEs are antiandrogenic in mice. They also point out that testicular cancer is the most severe symptom of testicular dysgenesis syndrome, which also includes cryptorchidism. In 2006, Swedish researchers linked early-onset testicular cancer with higher levels of maternal PBDEs.

The new findings aren't clear-cut, because researchers saw no correlation between PBDE levels in the cord blood of infants in the study and the incidence of cryptorchidism. Why this is the case is not clear, the researchers write. They posit that the combined exposure to multiple environmental factors may be responsible for the link they observed between PBDE concentrations in mother's milk and cryptorchidism.