According to the China Population Association, more than 40 million Chinese people are diagnosed with infertility
According to the China Population Association, more than 40 million Chinese people are infertileReuters

China's pollution is believed to be a factor in a growing national infertility crisis, leading rich Chinese to hire out the wombs of working-class American women.

It's estimated that 500,000 people in China die prematurely every year due to air pollution, according to Chen Zhu, the former Chinese health minister.

Chinese inquiries to agencies that match couples from around the world with American surrogates have risen tenfold since 2012 and are expected to double again in the next two years, according to a Times report.

The increase coincides with infertility rates rising to 12.5% of all adults in China of child-bearing age.

Around 20 years ago, the level was at 3%, and worryingly, sperm counts have dropped by 80% in Chinese men in 80 years.

A national study of air pollution and how it affects fertility is under way in China. In other investigations, the Chinese Academy of Sciences is looking into the effects of pollutants such as arsenic, plastic solvents and melamine on male infertility.

Across China, over 40 million people have been diagnosed as infertile.

"Customers often say that they have consulted doctors and been told that pollution is the cause of the infertility," said one Chinese surrogacy agent.

Surrogacy is against the law in China, so many infertile couples are using American agencies. John Weltman, president of Circle Surrogacy, a Boston agency, said that North America was "unequivocally the safest country to do surrogacy in".

American surrogacy offered Chinese couples the choice of deciding on the gender of the child, which is illegal in China. In China, there are 34 million more men than women.

The American surrogate mother, the so-called "gestation carriers", are mostly working class and come from the rural South or the Midwest. The fee for renting out their wombs ranges from £48,000 to £72,000.

While some experts believe that 70% of female infertility and 50% of male infertility are the result of unhealthy lifestyles, others believe that environmental factors may also play a role.

"New chemicals appear in our lives every day, and the problem is that we don't know if these new chemicals will pose risks to our health," Zhang Jun, lead researcher of the infertility study told the South China Morning Post.

"So our study will be significant in providing evidence to prove if these chemicals are harmful. And based on that we can make our policies prevent any hazards from such environmental pollution."

Watch a video on how Chinese Herbal Medicines may help with infertility