Decreasing Semen Quality

Sperm counts in men have declined by about 50% during the time period 1940-90, from an average of 113 million per milliliter of semen in 1940 to an average of 66 million in 1990. During the same time frame there has been a decrease in seminal volume from 3.40 to 2.75 ml. 51 The reasons for the observed decline in semen quality are exposures to pesticide mixtures 52 and other xenobiotic endocrine disruptors, 53 maternal consumption of beef-containing anabolic steroids 54 and other xenobiotics, and tobacco smoking. 55  

---

Ramlau Hansen CH, Thulstrup AM, Aggerholm AS, et al. Is smoking a risk factor for decreased semen quality A cross-sectional analysis. Hum Reprod 2007 22(1) 188 96. 

Europe, the USA and Japan are under way. In these studies, semen analysis methodology and subject selection criteria have been standardised to address whether there are region-specific differences in semen quality. These data can then be used as a reference point for any studies on future decline in sperm counts. More importantly, it still remains to be demonstrated whether the reported decrease in semen quality is sufficient to compromise fertility. 

Factors that alter the level of testosterone, by decreasing synthesis, increasing metabolic clearance or blocking the androgen receptor, can adversely affect the amount or quality of semen. It has been reported that exposure to environmental chemicals may lead to reduced semen quality (see chapter 4). 

No studies were found in the literature that examined potential female reproductive effects or developmental effects of JP-8 or other jet fuels in humans. One study assessed male reproductive effects of inhalation of jet fuel (type not specified) and hydrocarbon solvents after 15 and 30 wk of exposure. In that study, exposure to jet fuel increased sperm concentration in workers who fueled jets and decreased sperm linearity in flight-line workers exposure to jet fuels did not appear to affect semen quality in aircraft-maintenance workers. 

Reproductive system Environmental arsenic exposure can impair male fertility. A case-control study in China concluded that elevated inorganic arsenate (Asi(V)) exposure is associated with arsenic-induced male infertility. The mechanism of toxicity by arsenic species may involve oxidative stress and sexual hormone disruption measured by biomarkers including acylcamitines, aspartic acid and hydroxyestrone, which were negatively associated with infertility, and uridine and methylxanthine, which were positively associated [44 ]. Arsenic exposme is also correlated to a decrease in human semen quality as reported in a reproductive-age Chinese cohort. The study demonstrated significant association of dimethyl arsenic species (DMA) concentration with low sperm concentrations [45 -]. 

Fumes from welding mild steel can reasonably be expected to include vapors and particulates of the earlier list as well as carbon monoxide, carbon dioxide, fluorides, oxides of nitrogen, and ozone [78], Welders of mild steel, but not stainless steel, have been found to have reduced semen quality and decreased fecundity compared with non-welders [79], Welders are exposed to complex chemical mixtures that act via an unknown mechanism. It is interesting to note that one might have expected stainless steel welders to have a more adverse reaction due to the presence of chromium, which is an endocrine-disrupting chemical, but this is not the case. 

Carlsen, E., Giwercman, A., and Keiding, N. et al. (1992). Evidence for decreasing quality of semen during past 50 Years. British Medical Journal 305, 609-613. 

Carlson E, Giwercman A, Keiding N, Skakkebaek NE (1992) Evidence for decreasing quality of semen during the past 50 years. Br Med J, 305 609-613. 

---