(Beyond pesticidesAugust 3, 2022) A systematic review of scientific studies on pesticides and fertility finds that exposure is associated with lower sperm quality, DNA fragmentation and chromosomal abnormalities. Published in the journal Andrology, the review is another warning from a long line of researchers sounding the alarm about the link between global fertility and exposure to toxic chemicals. With data from the United States Centers for Disease Control and Prevention (CDC) indicating that approximately 1 in 5 couples are unable to conceive after a year of trying and trends continue to decline, it is critical that contributing factors are identified so that protective changes can be made.
After reviewing more than 1,300 studies, the researchers narrowed down their review to 64 papers assessing sperm parameters and DNA integrity after pesticide exposure. Each study is analyzed for its design, the pesticide studied, the population studied, the controls and the reproductive effects determined.
Pesticides are evaluated for their impacts on sperm quality and DNA integrity based on their chemical class. Organochlorine insecticides, all of which are banned but still persistent in soil, air, water, and food in the United States, include a range of impacts on sperm quality. Higher levels of DDT or its degradation metabolite, DDE, are associated with lower sperm count and lower motility and morphology than normal cut-off values established by the World Health Organization (WHO). (According to the WHO cut-off values, a condition of subfertility is defined by values below the fifth percentile of the general population.) Several studies show that as organochlorine concentrations increase in men, Sperm parameters also decrease. In addition to sperm quality, organochlorines are associated with chromosomal aberrations in several studies, including effects such as sperm disomy, where sperm have extra or missing chromosomes. This can result in viable offspring, but this offspring is at higher risk for abnormalities.
Organophosphates, the class of insecticides that replaced organochlorines as they were phased out, also exhibit a range of deleterious impacts. These chemicals include pesticides like malathion, still widely used, and chlorpyrifos, which has only recently been phased out of agricultural use. Effects on semen parameters are especially pronounced for people living in agricultural areas or with a history of professional work with pesticides. However, general population studies also show cause for concern, finding total sperm counts and concentrations inversely related to urinary metabolites of organophosphate insecticides. In addition to semen quality, the literature reveals several studies showing exposure to organophosphates resulting in missing or extra chromosomes in semen, with particular attention paid to diethylphosphate, a non-specific organophosphate metabolite.
Synthetic pyrethroids are also singled out in the scientific literature for their links to sperm damage. Insecticides are replacing organophosphates, as they are being phased out due to their many health risks. Unfortunately, the mole game played by the pesticide industry with the EPA’s allocation has not resulted in chemicals that are safer for human fertility in the long run. As with organophosphates, occupationally exposed people are particularly affected, with pyrethroid factory workers showing higher rates of sperm abnormalities and lower motility than unexposed people. Factory workers are also more likely to have DNA fragmentation in their semen. Another concentration-dependent relationship is found, with individuals reporting higher levels of urinary 3-phenoxybenzoic acid (3-PBA), a non-specific pyrethroid metabolite, having lower sperm count, disomy and greater likelihood to present a morphology of the spermatozoa lower than the WHO. thresholds.
Beyond these three classes, scientists have found evidence of negative associations with carbamate-class insecticides, fungicides, and herbicides, but the small number of studies does not allow for in-depth analysis. Mixtures of various pesticides are cited as having similar effects to the three main classes of pesticides studied, although firm results have been difficult to pinpoint due to the lack of comprehensive information. In general, occupationally exposed workers are most at risk, with chronic exposure being associated with greater semen abnormalities.
The results of the study are concerning given the steady decline in sperm count. A 2017 study found that sperm counts since 1973 have dropped nearly 60%. One of the study’s authors, Shanna Swan, PhD, brought sperm decline to public attention through her book Countdown, which delves into the impact of environmental chemicals on human fertility. Watch Dr. Swan’s talk, Modern Life and the Threat to the Future, at the 2021 Beyond Pesticides National Forum, Cultivate healthy communities.
Researchers have been sounding the alarm about the impact of pesticides on fertility for decades. In 2013, a previous literature review assessing the impacts of pesticides on fertility found that pesticides were strongly associated with lower sperm count. As she recounted in a presentation at Beyond Pesticides’ 2021 National Pesticide Forum, Dr. Swan’s own work is the result of efforts to try to refute a 1992 paper by Carlsen et al. evidence of a significant decline in sperm quality since the late 1930s.
As human civilization grapples with a series of cascading crises, from climate change to the insect apocalypse and the global biodiversity crisis, we may be missing the opportunity to address one of the most critical of the continuation of humanity as we know it now. For more on the fertility crisis, see Dr. Swan’s presentation to the National Pesticide Forum on the Beyond Pesticides Youtube page.
All unattributed positions and opinions in this article are those of Beyond Pesticides.