Diesel exhaust reduces sperm production in mice exposed before birth.

Hemmingsen JG, KS Hougaard, C Talsness, A Wellejus, S Loft, H Wallin and P Moller. 2009. Prenatal exposure to diesel exhaust particles and effect on the male reproductive system in mice. Toxicology doi:10.1016/j.tox.2009.07.012.

A new study with mice provides evidence that prenatal exposure to the small particles released when diesel fuel is burned could compromise male fertility.

The results add to a small but growing series of studies that suggest exposure to diesel exhaust can disrupt the proper development of the testis in rats and mice and perhaps affect reproduction.

The adult male mice, exposed to air pollution particles in utero, had significantly lower sperm counts than male mice born to mothers that were not exposed to the particles, according to the findings published online in the journal Toxicology. Sperm problems – such as low counts or misshapen sperm –  are a main cause of infertility in US men.

Exposure to particles found in diesel exhaust and other emissions that contribute to air pollution is associated with a number of diseases, including respiratory disease, cardiovascular disease and lung cancer. Although this study just looked at the impact of particles found in diesel exhaust, this critical source of air pollution also contains vapors and nitrogen oxides. These compounds are also known to contribute to disease in humans, particularly respiratory disease.

According to the US Occupational Safety and Health Administration (OSHA) more than a million workers in the US are exposed to diesel exhaust at levels known to cause disease, including cancer and respiratory disease. In addition, exposure occurs in areas with high air pollution, especially in homes and businesses located near major roadways.

The researchers in Denmark had pregnant mice inhale either clean air or polluted air made up of 20 milligrams per cubic meter of a standardized mixture of particles. This mixture simulated the particle composition of diesel exhaust.

The females were exposed 13 times for one hour a day during mid to late pregnancy. This method and dose of exposure in mice corresponds to about 10 years worth of exposure to air pollution in humans.

The sperm counts of the male offspring were examined at six months of age, which corresponds to “middle age” for mice.

Parameters not affected by particle exposure in the womb included body weight, testis weight, testosterone levels, the expression of estrogen receptors in the testis and other factors.

Some of these factors would indicate if the particles were acting like endocrine disrupting compounds. Since these factors were not affected, endocrine disruption is not a likely way for how the particles affected sperm production.

The results did not determine how the particulate matter altered the developing mice, so future studies will be needed to determine why in utero exposure to diesel exhaust particles affect sperm production in adulthood.