Elevated levels of two plastic-softening chemicals in pregnant women's urine are linked to less-masculine play behavior by their sons several years later, according to a study published in the International Journal of Andrology.

Phthalates, which are used in everything from vinyl floors to plastic tubing and soaps and lotions, are pervasive in the environment and have increasingly become associated with changes in development of the male brain as well as with genital defects, metabolic abnormalities and reduced testosterone in babies and adults.

A team of U.S. and British researchers posed a standard play questionnaire to the parents of 145 preschool-age children. Then they ranked the types of play on a scale from most masculine (such as play fighting or using trucks) to most feminine.

An effect was identified among the sons of women with higher concentrations of di(2-ethylhexyl) phthalate (DEHP) and dibutyl phthalate (DBP) in their prenatal urine. On average, those boys scored 8 percent further away from the masculine end of the scale than other boys.