People who live near fracking operations should be monitored for chemical contaminants and health problems, according to researchers who surveyed the risks posed by substances used in the process. Scientists in the US found that many of the 750 or so chemicals that are pumped into the ground at high pressure to fracture shale rock were associated with fertility and developmental problems. But very little is known about the levels of chemicals that people are actually exposed to from fracking operations, making it impossible to assess the real risk. The scientists' study drew on published scientific reports into the health impacts of chemicals such as benzene and toluene, and elements including cadmium and arsenic that are released from rocks in the drilling process. The team, led by Susan Nagel at the University of Missouri, fear that fracking chemicals could contaminate air, water and soil, and expose workers and local communities to the substances. "We desperately need biomonitoring data from these people. What are people actually exposed to? What are the blood levels of people living in these areas? What are the levels in the workers?" said Nagel. "It is absolutely in the realm of possibility that at current human exposure levels, we might expect to see some of these effects, and at the very least, we should be looking for them," she added. The rapid rise of what are called unconventional oil and natural gas (UOG) operations, that combine horizontal drilling and hydraulic fracturing of rock, increases the risk of air and water pollution, the scientists write in Reviews on Environmental Health. In the US, more than 15m people live within 1.5km of UOG operations. Professor Richard Sharpe, who leads a research team on male reproductive health at the MRC Centre for Reproductive Health at Edinburgh University, agreed that good data from people living near fracking sites was needed. "It's impossible to say how much of a potential issue this is. I certainly wouldn't dismiss it lightly, but I think we will have to wait for detailed prospective data from well-organised studies to get that," he said. "The one thing that is certain in all of this is that there should be a voice asking that the necessary surveillance and monitoring should be automatically put in place with such novel developments, in order that we can be reassured that we are not going to recreate another DDT scenario some way down the line," he added.