Two newly released papers using very different approaches spell bad news for the fracking industry, and for the people who live near wells. Epidemiological research has found living near fracking increases the danger of high-risk pregnancies, while laboratory research has shown chemicals used in fracking are toxic to mice even in small quantities.

The fracturing of rock using high pressure liquids, known as fracking, to release natural gas has transformed fossil fuel production in recent years, displacing coal and slowing the rise of renewable energy as gas prices have plunged. In the United States, fracking's heartland, natural gas has gone from powering 16% to 35% of electricity production in 15 years.

This rise has been extremely controversial, with fracking blamed for earthquakes and health effects such as heart disease. New York State has banned fracking over these concerns, and Pennsylvania recently fined an operator $8.9 million (£5.8 million) for water contamination, but the industry has responded by looking to new regions, including the U.K. 

A paper in Epidemiology suggests concerns about the health effects of fracking, at least during pregnancy, are solidly based. Pennsylvania has gone from 100 unconventional gas wells (a category that includes fracking) in 2006 to more than 8,000 today, senior author Professor Brian Schwartz of Johns Hopkins University noted in a statement, adding, “The growth in the fracking industry has gotten way out ahead of our ability to assess what the environmental and, just as importantly, public health impacts, are.”

Schwartz examined records of the births of 10,946 babies in north and central Pennsylvania between 2009 and 2013 and compared the mothers' addresses to gas well locations, taking factors such as well depth and quantity of gas produced into account. The mothers living in the most actively drilled locations were 40% more likely to have premature babies than those well away from fracking zones. Obstetricians were also 30% more likely to label the pregnancy as “high risk”, based on factors such as high blood pressure and excessive weight gain.

Preterm births are the single largest cause of infant deaths in the United States, and associated with a range of long-term health effects.

An exceptional number of stillbirths around Vernal, Utah, a town with astonishing fracking intensity, attracted worldwide attention, but could have been a result of uniquely local factors.

Schwartz's work suggests the problem is serious and widespread, while a study in Endrocrinology may point to the mechanisms. A team including Susan Nagel of the University of Missouri tested 24 chemicals used in fracking and found 23 of them lowered sperm counts in mice that were exposed before birth, while 30% interfered with thyroid hormones.

It's not hard to prove damage from chemicals in sufficient concentrations, but Nagel only exposed the mice to levels found around fracking wells. Moreover, she observed that some combinations of chemicals caused more damage than either on their own. "It is clear endocrine-disrupting chemicals used in fracking can act alone or in combination with other chemicals to interfere with the body's hormone function," Nagle said in a statement.