Beijing air pollution
The Chinese capital has for many years suffered from serious air pollution. Primary sources of pollutants include exhaust emission from Beijing's more than five million motor vehicles, coal burning in neighbouring regions, dust storms from the north and local construction dust. A particularly severe smog engulfed the city for weeks in early 2013, elevating public awareness to unprecedented levels and prompting the government to roll out emergency measures.
Smog crisis in China leads to increased research into effect of pollution on fertility
Beijing's funding for research into how chronic pollution is affecting childbearing triples in last five years, with the situation 'particularly grim'
As China's environmental woes grow, typified by recent toxic smog, Beijing has been increasing funding for research into how pollution affects fertility.
The number of studies funded by the National Natural Science Foundation of China, the leading research institute, has tripled in the last five years.
It has supported 68 such research projects this year, compared to just 23 in 2008.
Dr Liu Liangpo, a researcher with the Institute of Urban Environment at the Chinese Academy of Sciences, said this showed the government's "deep concern" about the growing crisis.
He said infertility was a global issue, but the situation in China was "particularly grim" due to the severe pollution. And he warned: "Polluted water, unsafe food, bad air ... so many things are threatening the reproductive capacity of Chinese people.
"If the situation gets worse, China's birth-control policy would become redundant."
The infertility rate among all Chinese of childbearing age rose to 12.5 per cent in 2010 from just 3 per cent two decades earlier, Xinhua reported recently.
More than 40 million people on the mainland have been diagnosed as infertile.
While some experts believe unhealthy lifestyles are to blame for 70 per cent of infertility in women and 50 per cent of infertility in men, others say that environmental conditions may also play a role.
The majority of government research grants are for studies about the impact of worsening pollution on the quality of sperm.
Of studies the science foundation funded this year, 59 concerned sperm and just nine focused on women's eggs.
Last year, it gave 60 grants for sperm studies and just six for research on eggs and most of those studies were focused on infertility.
Of the 23 such studies it funded five years ago, all but two dealt with sperm.
Liu and his team are studying how various pollutants such as arsenic, plasticisers and melamine affect the health of sperm.
Arsenic, which can be found at high levels in many underground water sources across the North China plain, can damage sperm DNA, leaving men infertile. But its effect on eggs remains unknown. According to a report by the China Population Association last year, the average sperm count in Chinese men had dropped from 100 million per litre about 40 years ago to as low as 20 million last year.
The "liveliness" of the sperm had dropped significantly as well, reducing their ability to find and enter an egg.
Most of the patients with infertility were relatively young, aged between 25 and 30.
The government hopes Liu's research can help determine the safe levels of waste from factories and other sources of pollution.
"Sperm and eggs respond differently to environmental pollution. Sperm is generally much more vulnerable due to its molecular structure," Liu said.
"The infertility problem in China is getting serious and most of the problems are coming from males. That's why the government has funded more research on sperm than on eggs."
Dr Wang Qiang, a researcher with Nanjing Medical University, received funding to study women's eggs this year.
He said clinical surveys had found eggs were also vulnerable to the effects of a worsening environment, and some of the issues could present problems for newborns later on.
The rapid increase in the incidence of diabetes on the mainland, for instance, had increased the chance of a genetic defect in eggs that would lead to obesity.
"An increasing amount of clinical evidence suggests that eggs contribute equally, if not more, to the infertility problems in China," Wang said.
"Environmental pollutants such as BPA [Bisphenol A, a carbon-based synthetic compound commonly used to make plastic products clear and tough] can do serious damage to eggs.
"It is scientifically erroneous to allege that eggs are less vulnerable to pollution than sperm."
Wang added: "If the sperm has a defect, there are many methods to cure it.
"But if the eggs have a problem, in most cases there is no cure. Our knowledge about treatment for eggs is very limited."
Video: Eastern areas of China cloaked in smog