SLIGHT anatomical oddities in infant boys are being heralded as the first evidence that gender-bending chemicals are affecting humans.
A number of synthetic chemicals can activate the same receptors in the body as the female hormone oestrogen. There is no doubt that many of these chemicals can affect animals such as fish, most dramatically triggering the development of female-like organs and behaviour in males living in heavily polluted habitats. There has been considerable concern about their effects on people, but no direct evidence of a link.
In the latest study, Shanna Swan鈥檚 team at the University of Rochester in New York state measured the levels of chemicals called phthalates in the urine of 85 women pregnant with boys. Phthalates are added to many plastics, including cling film and PVC, to make them more flexible, and can leach into food and water.
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The team examined the boys after birth. In boys whose mothers had the highest phthalate levels, the anogenital distance along the perineum between the anus and the base of the penis was shorter. The anogenital distance is normally twice as long in boys as in girls. The boys also had slightly smaller penises.
These differences match those seen when animals are exposed to low doses of the same chemicals. At higher exposures, animals suffer from graver abnormalities, including undescended testicles and misplaced urethral openings in the penis, known collectively as testicular dysgenesis syndrome. 鈥淲e鈥檙e not exactly seeing testicular dysgenesis syndrome, but a cluster of end points consistent with it,鈥� Swan told a press conference last week.
鈥淚f you see this, you鈥檙e very likely to see every other aspect of masculinisation changed too,鈥� claims Frederick vom Saal of the University of Missouri-Columbia. He says this might include behavioural changes such as decreased aggressiveness.
鈥淚f you see this, you鈥檙e very likely to see every other aspect of masculinisation changed too, including behaviour鈥�
Swan screened the mothers鈥� urine for nine common breakdown products of phthalates, and found four that correlated with the genital oddities. The strongest link was with mono-n-butylphthalate (MBP), most probably a metabolite of di-n-butylphthalate (DNBP). The quarter of women with the highest levels of MBP in their urine were 10 times as likely to have boys with small anogenital distances as the quarter of mothers who had the lowest levels. The corresponding increases for the other three products, which probably came from diethylphthalate (DEP), benzylbutylphthalate (BBP) and di-i-butylphthalate (DIBP), were 5, 4 and 7 times respectively.
鈥淭his research highlights the need for tougher controls on gender-bending chemicals,鈥� says Gwynne Lyons, toxics adviser to WWF UK. The European Union is considering a ban on three phthalates, including BBP, but only from children鈥檚 toys.
Makers of phthalates have criticised the study design. The measurements of anogenital distances were made at a range of ages up to 24 months, and so had to be corrected to allow comparisons. And mothers gave only one urine sample, so the team could not check for variations in phthalate levels over time.
