In my previous entry, we explored how female exposure to air pollution might create undue stress during pregnancy and lead to birth complications. But the growing number of fertility woes worldwide suggest that pregnancy itself cannot be taken for granted. How might fertility be impacted by men’s exposure to air pollution?
According to Kumar and Singh (2022), nearly half of global infertility cases are primarily caused by “male-factors”. Air pollution is one of various environmental factors that reduces semen quality, which is a “major predictor” of male fertility. Moreover, air pollutants may directly cause male infertility through hormonal disruption, oxidative stress, and sperm DNA alteration.
Figure 1. Impacts of environmental factors (including air pollution) on semen quality and male fertility (Kumar and Singh, 2022)
Figure 1 depicts several example parameters that quantify semen quality. Zhao et al. (2022) investigated the effects of air pollution on semen quality. Although they did not discover a relationship between exposure to particulate matter and sperm count or concentration, it was concluded that higher exposure to particulate matter leads to decreases in sperm motility.
So how does this relationship tie in with fertility? Sperm motility, otherwise known as the movement or swimming of sperm, is a key mechanism in achieving fertilisation (Weingus, 2022). Aside from lower total motility (proportion of sperm that is able to “swim”), lower progressive motility (proportion of sperm that is able to “swim” effectively in straight lines or large circles) further reduces the odds of fertilisation. Therefore, the results presented in Figure 2 suggest that male fertility is impeded by higher exposure to PM2.5 and PM10 through lowered total and progressive sperm motility.
Figure 2. Estimated changes in total and progressive sperm motility based on quartile of particulate matter exposure (Zhao et al., 2022)
Meanwhile, Nobles et al. (2018) discovered a negative association between exposure to particulate matter finer than 2.5 microns and sperm head length, area, as well as width. Again, what sort of fertility-related implications might this have?
According to the Center for Fertility & IVF at Loma Linda University (n.d.), sperm head size is an aspect of sperm morphology. At least 4% of sperm in a semen sample must adhere to “normal” morphology standards for “fertility potential”, falling below which will cause fertility to be “extremely impaired”. The results obtained by Nobles et al. (2018) in Figure 3 indicate that sperm head sizes are smaller than average given higher exposure to air pollution. Small-headed sperm are associated with microcephaly, a condition in which the sperm may have defective acrosome hindering entry into the egg to be fertilised (Center for Fertility & IVF, n.d.). Hence, increased air pollution will lower the proportion of sperm that aligns with “normal” morphology criteria and reduce fertility.
Figure 3. Associations between air pollution and sperm head parameters (Nobles et al., 2018)
Figure 4. Normal-shaped sperm (Center for Fertility & IVF, n.d.) 
Figure 5. Microcephaly (or small-headed sperm) (Center for Fertility & IVF, n.d.)
Lastly, Bosco et al. (2018) discovered that exposure to air pollution results in higher sperm DNA Fragmentation Index (DFI) values. In their study of steel plant workers exposed to air pollution both at work and home, it was found that the oxidative stress associated with air pollution caused the study subjects to have DFI values exceeding the 30% threshold that reflects “clear sperm damage” and lowers the pregnancy rate “up to zero”.
Everything discussed in this entry only serves to implore us to persevere in our efforts to curb air pollution. Considering that studies have shown how the removal of pollution can restore “normal” sperm motility levels (Comhaire et al., 2007), it is safe to say that not all hope is lost. That being said, it is absolutely imperative for both men and women to recognise that fertility, pregnancy, and birth are not responsibilities of a sole gender. Since it takes two hands to clap, then both hands should be put to work.
Until the next entry, breathe safe and be safe!
References
Bosco, L., Notari, T., Ruvolo, G., Roccheri, M. C., Martino, C., Chiappetta, R., Carone, D., Lo Bosco, G., Carrillo, L., Raimondo, S., Guglielmino, A., & Montano, L. (2018). Sperm DNA fragmentation: An early and reliable marker of Air Pollution. Environmental Toxicology and Pharmacology, 58, 243–249. https://doi.org/10.1016/j.etap.2018.02.001
Center for Fertility & IVF. (2018). Sperm Morphology (Size and Shape). Loma Linda University. Retrieved March 18, 2023, from https://lomalindafertility.com/infertility/men/sperm-morphology/
Comhaire, F. H., Mahmoud, A. M. A., & Schoonjans, F. (2007). Sperm quality, birth rates and the environment in Flanders (Belgium). Reproductive Toxicology, 23(2), 133–137. https://doi.org/10.1016/j.reprotox.2006.11.001
Kumar, N., & Singh, A. K. (2022). Impact of environmental factors on human semen quality and male fertility: A narrative review. Environmental Sciences Europe, 34(1). https://doi.org/10.1186/s12302-021-00585-w
Nobles, C. J., Schisterman, E. F., Ha, S., Kim, K., Mumford, S. L., Buck Louis, G. M., Chen, Z., Liu, D., Sherman, S., & Mendola, P. (2018). Ambient air pollution and semen quality. Environmental Research, 163, 228–236. https://doi.org/10.1016/j.envres.2018.02.004
Weingus, L. (2023). What is ‘normal’ sperm motility? Forbes. Retrieved March 18, 2023, from https://www.forbes.com/health/family/sperm-motility/
Zhao, Y., Zhu, Q., Lin, J., & Cai, J. (2022). Association of exposure to particulate matter air pollution with semen quality among men in China. JAMA Network Open, 5(2). https://doi.org/10.1001/jamanetworkopen.2021.48684