Human reproduction is a delicate bio-chemical process, guided at every step by powerful hormones. Reproductive health involves everything from the physical ability to reproduce to the many behavioral and developmental effects of sex hormones.
This finely tuned system is under threat. Worldwide, sperm counts are down and infertility rates are up. Girls are menstruating at an earlier age, leaving them at higher risk for breast cancer later in life. The Association of Reproductive Health Professionals highlights the following concerning trends in reproductive health:
- More testicular cancer
- Falling sperm counts
- Decline in testosterone levels
- Earlier puberty in girls
- Fewer males being born
- Increases in certain types of birth defects
Science tells us that pesticides and other chemicals are at least partly to blame. One group of chemicals — endocrine disruptors — are particularly adept at interfering with reproductive health, even when exposure levels are extremely low. Some of these chemicals are structurally similar to human hormones, and can block (or put into overdrive) the body's natural system of biological signals.
Exposure at Critical Times Can Be Devastating
An infant in the womb is particularly vulnerable to such disruption, as hormones are busy regulating the differentiation of cells and development of organs. Infants exposed to the wrong chemical just when the reproductive organs are forming — or the brain developing, or immune system coalescing — can experience harm that plays out over the course of a lifetime.
Scientists from the national Endocrine Society explain why the timing of exposure is so important:
. . . there are critical developmental periods during which there may be increased susceptibility to environmental endocrine disruptors. In those cases in which disruption is directed toward programming of a function, e.g., reproductive health, this may interfere with early life organization, followed by a latent period, after which the function becomes activated and the dysfunction can become obvious.
In other words, exposure to chemicals when an infant's reproductive system is developing can completely derail the process. But we don't know it's happened until years later, when problems arise during puberty or when trying to conceive.
Endocrine disruptors can block (or put into overdrive) the body's complex system of biological signals.
Some chemicals pass through the body quickly, others are carried in our blood and tissue for years — even decades. Throughout a lifetime, chemicals can damage the reproductive system in a number of ways. Some kill or damage cells; if these cells are sperm cells or oocytes, infertility can result. Others alter DNA structure, causing gene mutations that may result in birth defects or an inability to conceive. And some cause what is called an "epigenic" effect, meaning they change the way genes are expressed.
A more detailed explanation of these mechanisms — and compelling evidence of the scope of the problem — are outlined in Generations at Risk, a book co-authored by PAN Board Member Dr. Ted Schettler.
Pesticides & Reproductive Health
Many pesticides are endocrine disruptors, or are harmful to the reproductive system in other ways. Scientists now understand that exposure to pesticides can cause a wide range of reproductive harms affecting men, women and children alike. A few recent studies:
- Boys exposed to the toxic insecticide endosulfan experienced delayed puberty compared with children who were not exposed.
- Exposure to the herbicide atrazine has been linked to menstrual disorders, abnormal sperm and low-birth weight babies.
- Men from Missouri with elevated levels of the pesticides alachlor, diazinon or atrazine in their urine were more likely to have poor sperm quality.
Pesticides have also been implicated in miscarriage, premature birth, reduced fertility in both men and women, altered sex ratio (fewer boys being born) and a number of developmental defects.
Beyond Pesticides, a PAN Partner, has compiled recent studies of the impacts of pesticides on reproductive health, and the Collaborative on Health and the Environment's database shows the strength of the evidence linking chemicals to reproductive harms among both men and women. The Our Stolen Future website, an outgrowth of the groundbreaking book on endocrine disruptors and human health, also tracks the latest science on pesticides and other chemicals that threaten the complex process of human reproduction.