Phthalates

Phthalates are a group of endocrine-disrupting chemicals commonly used to render plastics soft and flexible. They are found in soft plastic chew toys marketed for infants and in some varieties of nail polish, perfumes, skin moisturizers, flavorings and solvents. Phthalates have been found in indoor air and dust, in human urine and blood samples. Levels are highest in children ages 6 to 11 and in women.

Phthalates are considered to be endocrine disruptors because of their complex effects on several hormonal systems including the estrogen and androgen hormone systems. The endocrine disrupting properties of this class of chemicals have been well established in the male offspring of mother rats who had been treated with phthalates while pregnant. Abnormalities reported included nipple retention, shortened ano-genital distance and increased cryptorchidism (undescended testes).  Exposure of human mothers to phthalates, as measured by chemical analysis of urine samples, has also recently been associated with shortened ano-genital distances in their newborn sons.

Some phthalates including butyl benzyl phthalate (BBP) and di-n-butyl phthalate (DBP) act as weak estrogens in cell culture systems. They can bind to estrogen receptors (ER), induce estrogenappropriate cellular responses and act additively with estradiol in altering these systems. BBP, DBP and another common phthalate, di-(2- ethylhexyl) phthalate (DEHP) significantly increase cell proliferation in MCF-7 breast cancer cells. In addition, these three phthalates inhibited the anti-tumor action of tamoxifen in MCF-7 breast cancer cells.

In rat studies, phthalates have been shown to disrupt the development and functioning of male and female reproductive systems by interfering with the production of testosterone and estradiol, respectively. Phthalates also bind weakly to the androgen receptor (AR), disrupting the cellular actions ordinarily initiated by the androgens. Those that bind the strongest to the AR, and therefore might be expected to exert the greatest effects through this pathway, include DBP, di-ibutyl phthalate and BBP. The role, if any, this androgenic pathway might play in breast cancer development remains to be explained.

Learn more about phthalates in cosmetics, toys, plastics and household cleaning products.

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See also: Comprehensive chemicals policy reform recommendations »

For references, see State of the Evidence 2008.