A recent study conducted on monkeys indicates that the ovary of the foetal primate is sensitive to BPA. This chemical appears to adversely affect egg cell formation: this may in turn influence the chances of conceiving later, the reproductive lifespan and may even cause birth defects.
What is Bisphenol A?
BPA, discovered in 1891, is a synthetic chemical that has been extensively utilised in the manufacture of plastics and epoxy resins since the 1950s. The plastics are used to make common commercial plastic containers such as water bottles, cups, plastic utensils, microwavable plastic food holders and food packaging. They can also be found in toys, thermal papers (such as receipts and tickets), dental sealants, laminations and CDs. The resins are used to coat the interior of cans, metal cups, electronic appliances and water supply pipes. BPA is also added to fertilisers and other chemicals.
The bonds that make up BPA are unstable, causing the chemical to leech into substances with which it is in contact; for instance food or beverages. BPA’s chemical structure is similar to the hormone oestrogen and mounting evidence suggests that BPA can disrupt hormonal balance and cause several diseases. On the other hand, some scientists have claimed that BPA is only harmful if taken in very large doses.
‘The concern is exposure to this chemical that we’re all exposed to could increase the risk of miscarriages and the risk of babies born with birth defects like Down Syndrome’, said Patricia Hunt, one of the study authors.
Scientists from the Washington State University exposed two groups of gestating rhesus monkeys (a species whose reproductive physiology is similar to ours) to single daily doses of BPA and low-level continuous doses. They discovered that chromosomal damage occurs at maternal levels of BPA analogous to the levels to which humans are routinely exposed.
BPA appears to disturb egg cell development at two crucial stages. Exposure to BPA during meiotic prophase (early stage of cell division which involves exchange of genetic material between parental chromosomes) augments the risks of formation of a genetically defective egg. Without a specific number of chromosomes, a fertilised egg cannot come to term; this can cause spontaneous abortion or birth defects.
During the third trimester of gestation, the monkeys who were continuously exposed showed abnormally formed follicles; structures in which foetal eggs develop. For eggs to develop and mature healthily, they need to be properly ‘packaged’ in these follicles. Otherwise, this would reduce the number of viable eggs, thus impairing fertility.
The implications of this study are worrying because at least three generations are affected by BPA and it might be difficult to establish direct links with the chemical. Exposure of a pregnant female implies that not only can the developing foetus be affected, but if the foetus is a female, the eggs developing in her ovaries (which will give rise to the grandchildren of the pregnant female) are less likely to develop normally due to BPA exposure.
This research has been published in the Proceedings of the National Academy of Sciences.
Hunt et al (2012) Bisphenol A alters early oogenesis and follicle formation in the fetal ovary of the rhesus monkey. Proc Natl Acad Sci U S A. 109(43):17525-17530.