Can Plastic Chemicals Cause Effeminate Behavior in Boys?

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© Philippe Lissac / GODONG/Godong/Corbis

18 Mar 2009 --- Boy playing with toy cars --- Image by © Philippe Lissac / GODONG/Godong/Corbis

Prenatal exposure to common chemicals used to soften plastics may impact boys’ play behavior later in life, according to new research published in the International Journal of Andrology.

This new study expands on a wealth of previous research in animals showing that exposure in the womb to chemicals known as phthalates was associated with lower testosterone production, and subsequently impaired genital development. (This phenomena, known as the phthalate syndrome, has also been shown to influence sexual development in animals later in life.)

And in addition to animal studies, the lead author of the current research, Shanna H. Swan, director of the Center for Reproductive Epidemiology at the University of Rochester, has also published previous findings demonstrating similar developmental issues in male human infants. This current study suggests that, not only does prenatal exposure to these common chemicals impact testosterone production, but it may also have longer term influence on gender identity and play behaviors as children grow up.

“Play behaviors offer themselves as a test of the hypothesis that phthalate exposures during gestation may alter brain sexual differentiation and its behavioural outcomes,” Swan and colleagues write.

To test this hypothesis, researchers initially began with 334 pregnant women, 150 of whom ultimately participated in all phases of the research. Midway through pregnancy, phthalate levels among the pregnant women were measured using urinalysis. Four to seven years later, when the participants’ children were between the ages of 3.6 to 6.4-years-old, researchers sent out questionnaires to assess the children’s play preferences, and also, how their parents’ attitudes might impact how they chose to play.

To assess behavior, researchers used a slightly modified version of the Pre-School Activities Inventory, a widely used screening tool that measures gender-related play in small children. (Much previous research has shown that there are objectively different play preferences among boys and girls: boys tend to do more play-fighting, for example, girls tend to be more captivated by dolls than toy trucks, etc.)

To determine how parental views might sway behavior, parents completed a survey that included questions such as, “What would you do if you had a boy who preferred toys that girls usually play with?” They were asked to respond with whether they would support or discourage such behavior, and how strongly. The combination of these two assessments was used to measure children’s gender-related play preferences.

What the researchers found was that, while, in girls exposure to phthalates had little significant impact on behavior, in boys, higher levels of exposure were correlated with “less masculine” preferences. What’s more, exposure to specific varieties of phthalates correlated most strongly with behavioral differences — namely, di(2-ethylhexyl) phthalate, or DEHP, and dibutyl phthalate, or DBP. As the authors write, “[t]he two metabolites of DBP, as well as their sum, were associated with a decreased (less masculine) composite score in boys.” Concentrations of DEHP too, the researchers found, “were associated with a decreased masculine score.”

These findings, the researchers say, suggest that phthalates indeed do “possess the potential to modify male behavior, potentially reflecting changes to the developing brain.” And this latest research may add to growing concerns about how common chemicals used in ubiquitous plastics, such as bisphenol A, or BPA, may be impacting our health — for the worse. (A study recently published in the journal Human Reproduction found high exposure levels to BPA among Chinese factory workers were associated with sexual dysfunciton.)

Of course, to substantiate these findings about phthalates, researchers acknowledge that more investigation beyond this relatively small sample population is necessary. But if these results are verified through additional, rigorous research, it may pose some unique and potentially challenging questions, not only about healthy levels of exposure to common plastic chemicals, but about just what factors shape gender identity in childhood, and as we grow older. Or, as the authors put it, “[i]f replicated in a larger sample, it would be a finding with implications that extend far beyond the scope of children’s play preferences…”

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