Men who dream of becoming a father may want to make sure they're living in a place with good air quality. A new study has found a link between air pollution and abnormal sperm, potentially leading to infertility.

The research, led by scientists from the Chinese University of Hong Kong, studied the sperm of 6,475 male participants in Taiwan. All of the volunteers were between the ages of 15 and 49, and participated in a standard medical examination program between 2001 and 2014.

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The goal of the research was to investigate the effect that PM2.5 - the smallest and most harmful particle in the air - has on sperm quality. PM2.5 is caused by vehicles, construction dust, and wood burning.

To determine this, the scientists studied multiple sperm samples from each man, creating three-month and two-year averages. "Because a spermatogenic cycle is around three months, we calculated three-month average concentration...to assess the short-term effects. We also calculated two-year average concentration...as an indicator of long-term exposure to ambient PM2.5 air pollution," the researchers wrote. They noted that semen quality was "assessed according to the WHO (World Health Organization) 1999 guidelines."

The scientists matched each sperm sample date with records of air quality surrounding each participant's home during the relevant time period. "The south-western and middle-eastern areas [of Taiwan] were generally the most and least heavily polluted, respectively. Most of the participants lived in the western area with apparent gradients of exposure," the researchers wrote.

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The scientists ultimately found a strong link between PM2.5 exposure and abnormal sperm size and shape. They noted that every increment of 5 µg/m3 in a two-year average of PM2.5 is associated with a decrease of 1.29 percent in normal sperm morphology and a 26-percent increased risk of being in the bottom 10 percent of normal morphology.

The findings could, according to the researchers, "result in a significant number of couples with infertility." They noted, however, that they did not assess any potential fertility problems of the men which could have affected their sperm morphology. "We therefore could not exclude the possible influence of infertility disorders for some of the participants, but it should not affect our conclusions because PM2.5 exposure was unlikely to be differentially distributed among fertile and infertile participants," they wrote.

In their conclusion, the researchers advocated global strategies on the mitigation of air pollution in order to improve reproductive health. They also called for further studies on the topic.

The research was published in the journal BMJ Open. It is believed to be the largest study investigating the health effects of PM2.5 air pollution on semen quality.