Dioxin exposure linked to infertility, difficulty conceiving.

Apr 09, 2010

Eskenazi, B, Mwarner, AR Marks, S Samuels, L Needham, P Brambilla and P Mocarelli. 2010. Serum dioxin concentrations and time to pregnancy. Epidemiology 21:224-231.

Synopsis by Emily Barrett

Blood levels of the chemical dioxin are related to difficulty conceiving and higher rates of infertility in a group of Italian women.

Women with higher levels of dioxin in their blood when they tried to get pregnant took longer to conceive than women with lower levels, researchers report in a followup study. The women were exposed to high levels of the chemical when a manufacturing plant in Seveso, Italy, exploded in 1976.

This is the first study to look the relationship between dioxin and probability of conception.

Previous research has identified multiple aspects of reproduction that might be affected by dioxin exposure, including reproductive hormone levels, early embryonic development and earlier menarche and longer menestrual cycles for those exposed prior to puberty. Analogous research in men has found decreased sperm quality among men who lived through Italy's Seveso disaster as children.

Dioxins are a class of chemicals that persist in wildlife, people and the environment. They are produced during burning associated with industrial activities. Very high levels of the chemical were released from the Seveso explosion and contaminated soil, air, water and people living nearby.

Shortly after the accident, levels of one particular dioxin, TCDD, were measured in the blood of the surrounding population. Then, 20 years later as part of the Seveso Women’s Health Study, the researchers interviewed 278 local women who had been 0-40 years of age at the time of the explosion. The women were asked about their pregnancy histories after the event, particularly how long it took them to conceive after stopping contraceptive use. Differences in time to pregnancy among women may indicate underlying differences in their ability to conceive.

The women's average age was 17 at the time of the explosion and 38 at the time of the interview. Blood dioxin levels averaged 50 parts per thousand after the accident and 13.4 parts per thousand at the time of conception – similar to background levels measured in other parts of Europe. The researchers statistically controlled for variables such as smoking, age and use of contraceptives.

They found that women who had higher blood levels of TCDD took longer to conceive. In fact, every 10-fold rise in TCDD levels was associated with a 25 percent longer time until conception (for example, trying to conceive for 10 months, rather than eight). Having high levels of TCDD also doubled a woman's chances of taking more than 12 months to conceive – thereby meeting the clinical definition of infertility.

The study’s authors note that the level of dioxin exposure in Seveso was extremely high. However, in some areas of Europe today, levels of dioxin contamination approach those that were found in Seveso after the disaster. This suggests that dioxin may impact fertility even in areas with less obvious and dramatic exposure to the environmental chemical.

Studies are underway to determine if the women's exposure may affect reproduction in their children. Additional work is necessary to fully understand how dioxin might affect fertility at lower concentrations.