Researchers at the University of Illinois (UI) have found that giving female mice oral doses of the phthalate DiNP for 10 days disrupted their reproductive cycles, decreasing their ability to become pregnant for up to nine months afterward.
Phthalates, which are added to plastic and vinyl to make them softer, flexible and more durable, are found in many types of consumer goods, including food and beverage packaging, vinyl flooring, medical devices and cosmetics.
To investigate phthalates' effects on female fertility, the researchers fed female mice corn oil solutions containing environmentally relevant concentrations of DEHP or DiNP ranging from 20 micrograms to 200 milligrams per kilogram of body weight, which are comparable to the levels of exposure that people may experience during their daily living and work activities.
After the 10-day dosing period ended, the phthalate-treated female mice and their counterparts in the control group were paired with untreated male partners twice for breeding.
"At three months post-dosing, a third of the females that were treated with the lowest doses of DEHP and DiNP were unable to conceive after mating, while 95 percent of the females in the control group became pregnant," said graduate student Katie Chiang, a co-author of the current study.
"The thing that was really concerning was that these females' fertility was impaired long after their exposure to the chemicals stopped," said Jodi Flaws, a professor of comparative biosciences at UI.
In examining the mice immediately after the 10-day dosing period, the researchers also found that the treated females' uteruses weighed significantly less than those of the females in the control group. However, they found no such differences at the three-month and nine-month intervals.
Among the females treated with the lowest doses of DEHP or DiNP, there was a significant reduction in the number that became pregnant and produced pups compared with the control group.
The researchers hypothesized that dysregulation of the mice's steroidal hormones made their uterine linings less receptive to embryo implantation, or, perhaps phthalate exposure accelerated the end of the female mice's reproductive lifespans, reducing their chances of becoming pregnant.
The study is yet to be replicated in humans.
The findings have been published in a recent issue of the journal Toxicological Sciences.