Pesticides & male infertility: Harm from
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, and male fertility appears to be particularly at risk. Worldwide, sperm counts are down and infertility rates are up. The Association of Reproductive Health Professionals highlights concerning trends[i] in male reproductive health, including:
Rising rates of testicular cancer
Falling sperm counts
Decline in testosterone levels
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. Endocrine disrupting chemicals 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.
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 a triggering chemical just when the reproductive organs are forming — or the brain developing, or immune system coalescing — can experience harm that can play out over the course of a lifetime. The Endocrine Disruption Exchange has a compelling online tool[ii] illustrating the vulnerabilities of a fetus at various stages of development.
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.[iii]
In other words, exposure to certain chemicals when an infant's reproductive system is developing can completely derail the process. But the effects won’t become evident until years later, when problems arise during puberty or when trying to conceive.
Adult exposures to pesticides can influence male fertility as well. Authors of a 2013 review published in Toxicology[iv] examined 17 studies published between 2007 and 2012, all exploring how environmental and occupational exposures to pesticides affect semen quality. Some studies looked at individual chemicals (such as DDT and hexachlorocyclohexane), others looked at classes of pesticides such as organophosphates and pyrethroids. The majority of these studies (15 of the 17) found significant links between pesticide exposure and lower semen quality, with decreased sperm concentration the most commonly reported finding.
Links between pesticide exposure and damage to men's reproductive ability are hardly new. The classic example is Dow's fumigant Nemogen (DBCP), which sterilized workers both in the California factory where it was produced and in the Nicaraguan banana plantations[v] where it was heavily applied. And exposure to current-use pesticides like atrazine and diazinon[vi] has also been shown to undermine sperm viability and function.
Pesticides can damage the male reproductive system in a number of ways. Some chemicals can kill or damage cells; if these are sperm cells, infertility can result. Others alter DNA structure, causing gene mutations that may result in birth defects or an inability to conceive. And still others cause what are known as "epigenetic" effects, meaning they change the way genes are expressed.[vii]
It’s been known for some time that pollutants can strip or add chemical tags to DNA, locking the expression of these genes on or off and changing how they function. These changes are called “epigenetic tags,” and have been linked to various health effects including death of sperm-forming cells.
Perhaps most sobering of all, emerging science shows that these genetic changes can be passed from one generation to the next. Recent studies from Spain[viii] and Washington state[ix] found that exposure to some chemicals can override the genetic “reset button” designed to protect a developing fetus from such changes. These trans-generational effects give new urgency to efforts to reduce our use of and exposure to harmful pesticides.
[i] Association of Reproductive Health Professionals “The links between environmental exposures and reproductive health” Environmental Impacts on Reproductive Health, Jan 2010. http://www.arhp.org/publications-and-resources/clinical-proceedings/RHE/Environmental-Exposures
[ii] See the TEDX “Critical Windows of Development” tool at http://endocrinedisruption.org/prenatal-origins-of-endocrine-disruption/critical-windows-of-development/overview
[iii] Diamanti-Kandarakis, E. et al “Endocrine-Disrutping Chemicals: An Endocrine Society Scientific Statement,” Endocrine Reviews, Vol 30, Issue 4; June 1 2009. http://press.endocrine.org/doi/full/10.1210/er.2009-0002
[iv] Martenies, S.E., Perry, M.J., Environmental and Occupational Pesticide Exposure and Human Sperm Parameters: A Systematic Review, Toxicology (2013), http://dx.doi.org/10.1016/j.tox.2013.02.005
[v] PANUPS “Banana workers win against Dow, Shell and Standard Fruit" Jan 6, 2003. http://www.panna.org/legacy/panups/panup_20030106.dv.html
[vi] Swan, SH. Semen quality in fertile US men in relation to geographical area and pesticide exposure. Int. J. Androl. 2006 Feb 29 (1) 62-8. http://www.panna.org/legacy/panups/panup_20030106.dv.html
[vii] See Generations at Risk by Ted Schettler, for a more detailed explanation of these mechanisms — and compelling evidence of the scope of the problem. http://www.sehn.org/ecomedpublications.html
[viii] Collatta, M. et al “Epigenetics and pesticides,” Toxicology 307 (2013) 35-41.
[ix] Raloff, Janet; “Pollutants long gone, but disease carries on: Certain chemicals cause epigenetic changes that foster illness in rats’ offspring” ScienceNews, Feb 28, 2012. https://www.sciencenews.org/article/pollutants-long-gone-disease-carries