Males exposed to high doses in the womb went on to be less likely to play with boys' toys like cars or to join in rough and tumble games, they found. The University of Rochester team's latest work adds to concerns about the safety of phthalates, found in vinyl flooring and PVC shower curtains.
The findings are reported in the International Journal of Andrology.
Phthalates have the ability to disrupt hormones, and have been banned in toys in the EU for some years. However, they are still widely used in many different household items, including plastic furniture and packaging. There are many different types and some mimic the female hormone oestrogen.
The same researchers have already shown that this can mean boys are born with genital abnormalities. Now they say certain phthalates also impact on the developing brain, by knocking out the action of the male hormone testosterone.
Dr Shanna Swan and her team tested urine samples from mothers over midway through pregnancy for traces of phthalates. The women, who gave birth to 74 boys and 71 girls, were followed up when their children were aged four to seven and asked about the toys the youngsters played with and the games they enjoyed.