Almost 34 years ago, an industrial accident in a small chemical plant near Milan, Italy, resulted in the highest known dioxin exposure in residential populations. The Seveso disaster — named after Seveso, Italy, the small town with a population of 17,000 that was most affected by the incident — gave rise to numerous scientific studies on the effects of dioxin exposure on humans and the environment.

But let me back up a bit and explain what dioxin is, for those that don't already know. Dioxins are a class of chemicals that persist in wildlife, people and the environment. They are produced during burning associated with industrial activities — most notably, the production of chlorine. So they are released into the environment during the production of bleached paper and other chlorinated products like PVC plastics.

The Seveso study, published in the journal Epidemiology, was the first study to look the relationship between dioxin and probability of conception.

Shortly after the 1976 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. 

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. 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 other variables that could affect contraception such as smoking, age and the 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. 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.

Of course, it's important to remember that the level of dioxin exposure that the researchers were examining in Seveso was extremely high. However, the study's authors noted that 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.

Dioxin linked to infertility
Study finds blood levels of the chemical dioxin are related to difficulty conceiving and higher rates of infertility.