The discussion of the potential hazards of shale gas extraction has been enriched by two recent reports from the UK and the U.S. While the first report seeks to assure skeptics that risks associated with fracking can be controlled, the second expresses concern about the effects of the process on fresh water supplies.

In the UK, the latest of a series of government-touted pro-fracking scenarios designed to underscore its commitment to shale gas for chemical feedstocks and heating fuels plays down the risk of hazards to public health. A 46-page study prepared by the Public Health England (PHE), an executive agency of the Department of Health, contends that the risks of exposure to emissions are low if the operations are properly run and regulated.

As PHE readily acknowledges, the study's conclusions are drawn from experience gained by other countries, such as the U.S. Experience in the UK thus far is inconclusive, as fracking has been carried out only in a small area of Lancashire. Although the moratorium imposed for 18 months from mid-2011 after two minor earthquakes has been lifted, drilling has not yet resumed.

The UK research mainly examined the risk of air pollution, from stationary on-site sources such as radon but it also looked at water pollution from fracking fluids, flowback water and heavy metals - in addition to disposal and treatment of waste water. It did not address questions of occupational health, greenhouse gas emissions, water usage or water sustainability or whether fracking can cause seismic activity.

While noting that due to differing geographies, conditions for shale gas exploration in the U.K. may not match those of North America, the PHE team concluded that most of the potential for pollution appears to stem from poor regulation. It held that contamination of ground water is more likely to be caused by leakage through the vertical borehole than from drilling per se. At the same time, it said surface spills of fracking fluid or waste water may affect groundwater, and emissions to air also could impact health.

Toward better regulation of the fracking industry, PHE recommended "consideration of emission inventories" as part of the approval process, along with public disclosure and risk assessment of chemicals used. It said evidence from the US suggests that maintenance of well integrity, including post operations, as well as appropriate storage and management of fracking fluids and wastes were essential.

The U.S. report, conducted by Downstream Strategies, focused on the impact of fracking in the Marcellus basin on freshwater resources in the states of Pennsylvania and West Virginia. It found that the "sheer volumes of water and waste" are cause for concern.

The fracking boom has "put a major strain on water resources all over the U.S.," the research group said, adding that more than 90% of the water injected into underground frack wells never returns to the surface and is thus permanently removed from the water cycle.

What's more, it said, the fracking industry in West Virginia draws 80% of its water from rivers and streams, with reuse and recycling of flowback fluid making up only 8% of recent water use in West Virginia and 14% in Pennsylvania's Susquehanna River basin.

Another of the researchers' conclusions is that the volume of waste "is increasingly rapidly as the industry expands." A 70% rise, to 610 million gallons, was seen in Pennsylvania between 2010 and 2011.