Phthalates impair female reproduction, too, finds fish study.

Carnevali, O, L Tosti, C Speciale, C Peng, Y Zhu and F Maradonna. 2010. DEHP impairs zebrafish reproduction by affecting critical factors in oogenesis. PLoS ONE http://dx.doi.org/10.1371/journal.pone.0010201.

Reproductive problems leading to infertility were seen in female fish exposed to phthalates at levels generally found in the environment. The results are some of the first to show the plasticizers can affect females as well as males, report researchers in the online journal PLoSOne.

Many of the effects found in the study depended on the doses of DEHP administered to the fish, which were environmentally relevant, that is, within a range the people and wildlife might experience. This preliminary evidence of the effects of DEHP on the female reproductive system suggests that further study on females is warranted in other species, including humans.

Evidence has increasingly implicated phthalates, a group of environmental chemicals commonly used to soften plastics, in a wide range of health issues from obesity to attention deficit hyperactivity disorder. Because phthalates are so pervasive in the environment, nearly all humans are exposed to these chemicals, making their health effects a particular concern.

Phthalates typically act as anti-androgens, reducing testosterone production, and one particularly potent phthalate, DEHP, has gained notoriety for its negative effects on the development of the male reproductive system. In animal models (and, to a lesser extent, humans), DEHP exposure has been linked to decreased sperm counts and altered development of the external genitals in males. To date, however, few studies have shown that female reproductive function may be at risk as well.

Using a zebrafish model, Oliana Carnevale and colleagues find that exposure to DEHP does impair female reproductive function in a number of ways. In zebrafish and in humans, similar reproductive hormones and proteins – called growth factors – control the growth, maturing and release of eggs. Many of the genes that control these processes are highly similar across species. This allows researchers to use zebrafish as a starting point for understanding how chemicals such as DEHP might affect people.

In the study, adult female zebrafish were exposed to DEHP for a three-week period, after which the researchers examined various aspects of their reproductive function. The researchers compared the DEHP-exposed fish to fish exposed to environmental estrogens and to unexposed fish acting as controls.

They found that much like the environmental estrogens, DEHP exposure increased levels of a protein that forms the basis for the nutrients in a developing egg. DEHP, then, may act as an estrogen – at least in female zebrafish.

The fish exposed to DEHP showed a number of other changes in their reproductive systems compared to unexposed control fish. After mating, DEHP-exposed females produced far fewer embryos than control fish did, which suggests their fertility had been impaired in some way. In fact, the group exposed to the highest level of DEHP produced only 1 percent of the embryos that controls did.

When developing eggs from zebrafish females were exposed to DEHP in a test tube, the maturation process halted. Additional tests showed that this was due to changes in levels of three important proteins that control the final egg maturation process. DEHP also inhibited the production of a protein necessary for ovulation to occur, particularly at high doses.