Couples with high blood concentrations of PCBs (polychlorinated biphenyls) experience greater difficulties to conceive compared to those exposed to lower doses of the environmental chemical, according to a preliminary study by researchers at the National Institute of Health (NIH).
Regular contact with environmental pollutants are known to affect fertility by accumulating in semen, altering the menstrual cycle, inhibiting ovulation and reducing follicle number — small sacs in which the eggs develop and mature.
The basics about polychlorinated biphenyls
Before being banned, PCBs were used as dielectric and coolant fluids in electrical equipment; in plasticisers, fire retardants, de-dusting agents, adhesives, oil-based paints, plastics and floor finishes. Also found in pesticides and industrial chemicals, or formed as chemical by-products, PCBs are persistent organochlorine pollutants resistant to decomposition. Hence, they accumulate in the soil and water; lingering in the environment for decades and eventually reaching the food chain.
Animal and human studies have linked long-term exposure to PCBs to a suppressed immune system, increased cancer risks, and several other adverse health conditions. However, PCB’s effects on fertility were not comprehensively investigated until now.
In order to explore the association between selected persistent pollutants, lifestyle and time-to-pregnancy, the researchers designed the Longitudinal Investigation of Fertility and the Environment (LIFE) Study. The LIFE study comprised of couples residing in specific counties in Michigan and Texas, with identified exposure to persistent environmental chemicals.
501 couples from the LIFE study were recruited between 2005 and 2007 for this research published in Environmental Health Perspectives. The women were aged between 18 and 44 years and all the male subjects were older than 18. None of the participants were sterile and the women all reported a menstrual cycle between 21 to 42 days. Blood samples were analysed for PCBs and other environmental pollutants. The couples were given journals to document sexual activity and the women also had to record their menstrual cycle and home pregnancy tests results. Follow-up lasted either a year after conception trials or until the couples achieved pregnancy.
Using the fecundability odds ratio (FOR), a statistical measure, the scientists evaluated the probability that a couple would successfully conceive based on their blood levels of the pollutants. A ratio below one implied that the couples would need longer to conceive.
Assessment of PCB congeners — single, unique, well-defined chemical compounds in the PCB class — revealed consistently lowered fertility in women exposed to PCB congener 167 and men exposed to PCB congener 138, evidenced by lowest FORs values of 0.79 and 0.71 respectively.
For each standardised increase in blood levels of PCB congeners 118, 167, 209 and perfluorinated compounds — chemicals found in non-stick cookware, fast-food wrappers, stain-resistant carpet, paint and impermeable clothing — women experienced an 18 to 21% decline in chances to conceive.
Regarding male subjects, increased exposure to PCB congeners 138, 156, 157, 167, 170, 172, 209 and DDE (dichlorodiphenyldichloroethylene) — formed when the pesticide DDT degrades in the environment — decreased pregnancy odds by 17 to 29%.
“Our findings suggest that persistent organochlorine pollutants may play a role in pregnancy delay,” concluded Dr Louis, study author.
Buck Louis et al (2013) Persistent environmental pollutants and couple fecundity: the LIFE study. Environ Health Perspect. 121(2):231-236