Exposures in the womb to a ubiquitous family of industrial chemicals can subtly perturb preferences of boys for certain types of child’s play thought to be hardwired in the brain, a new study suggests. Phthalates are widely used solvents and plastics softeners. In this study, the greater a boy’s fetal exposure to certain phthalates, the less often he tended to engage in typically masculine play.
Girls’ play was unaffected, according to the study, set to be published in an upcoming International Journal of Andrology.
The reason boys like trucks and girls like dolls relates to fetal differences in brain development, explains Heather Patisaul, a neuroendocrinologist at North Carolina State University in Raleigh. Males develop differently from females — physically and behaviorally — only through programming by androgens, male sex hormones such as testosterone, she says In animals, anything that dampens the testosterone signal during fetal development, such as a chemical or genetic defect, can trigger a subtle demasculinization in males.
Because phthalates can exhibit anti-androgenic activity (SN: 9/2/2000, p. 152), Shanna Swan of the University of Rochester School of Medicine and Dentistry in Rochester, N.Y., and her colleagues investigated whether testosterone-programmed behaviors in young children might be undermined by fetal exposure to the pollutants.
Researchers measured phthalates during the last trimester of pregnancy in women participating in a four-state project in the United States called the Study for Future Families. Three to six years later, Swan’s group asked these women to answer questions about play by their children — 74 boys and 71 girls.
On a one-to-five scale, with one being “never” and five being “very often,” each mom rated how frequently in the past month her child had done such things as play house, play at fighting, climb, play with dolls, dress up in girls’ clothes or show interest in wheeled cars.
Boys with the highest fetal exposures to phthalates — particularly to diethylhexyl phthalate, or DEHP, and dibutyl phthalate, or DBP — tended to exhibit lower scores on typical male play (such as playing with toy guns or pretending to play with guns) and higher on gender-neutral play (such as puzzles or sports). DEHP is in plastic tubing, including types used widely in food processing, Swan notes. DBP is a solvent in many cosmetics, including nail polish and hair sprays.
The results stood out even after accounting for potentially confounding factors, including parents’ age and education as well as parents’ attitudes about gender-typical play.
Play in the most highly phthalate-exposed boys wasn’t “feminized,” Swan explains, since these kids didn’t preferentially play with dolls or don dresses. Rather, she says, “we’d describe their play as less masculine.”
The new study is not the first to link pollutants with alterations in gender-typical play, but it does appear to be the strongest, says David Carpenter of the University of Albany in Rensselaer N.Y. Bolstering confidence that the new findings are not a fluke, he adds, is earlier research by Swan’s group: It showed fetal exposure to phthalates could alter the genital tracts of infants — again, only in boys.
Kimberly Yolton of Cincinnati Children’s Hospital considers the new findings “a potentially big deal — primarily because we all have exposure to phthalates.” The Pre-School Activities Inventory test used to assess these children “is not super sophisticated,” the developmental psychologist says. Then again, for this age group, she says, “it really is the only means out there.”
Even if socialization or other factors cause affected children to later assume gender-typical play, “their brains will still be a little different,” Patisaul says. “And it’s not clear how that will play out when they get a little older.”
Indeed, Yolton says, “There’s a significant difference here [in gender-typical play] but we don’t know yet that this is bad. Who knows,” she adds, affected boys “might be less violent.” Clearly, more research is needed, she says, in part because this study was so small.
Swan agrees. She’s just beginning a bigger follow-up study, with 800 children whose mothers will be recruited during pregnancy from four regions of the country. These children, like those in the current study, will be followed into school age. “We’ll be looking at lots of physiological factors that are shaped by testosterone,” she says — from size and body build to sexually dimorphic differences in mental processing.