Any problems publicised so far - such as in the US - are the result of operational failure or poor regulation. 

 

The study, by Public Health England, an agency of the Department of Health, reviewed the latest research.

 

It focused on the risks of emissions² of the chemicals used in fracking and radioactive material released with the gas.

 

The central conclusion is that "potential risks to public health from exposure to the emissions associated with shale gas extraction are low if the operations are properly run and regulated". 

 

The report recommends environmental monitoring through the lifetime of any project and public disclosure of chemicals used in the fracking fluid. 

 

The findings have been welcomed by the government which is pressing for the development of shale gas in the UK.

 

Environmental campaigners opposed to fracking say the study highlights the risks and the lack of oversight³. 

 

So far exploratory fracking has been limited to one site in Lancashire but the British Geological Survey (BGS) estimates UK shale could yield 150 billion cubic metres of gas, so commercial interest is growing.

 

 

The report draws on American research to conclude that though pollutants⁴ can enter the air from gas flaring⁵ or leaks, "these emissions are relatively⁶ small, intermittent⁷（间歇的） and certainly not unique to shale gas extraction…"

 

One quoted study - from the Barnett Shale in Texas in 2010 - found 70 individual volatile⁸ organic compounds including ethane（乙烷）, propane（丙烷）, butane（丁烷） and pentanes（戊烷） close to shale gas activity but observed these to be "localised" and significantly diminished downwind. 

 

But the authors recognise that there is relatively little evidence to go on - the only detailed⁹ peer reviewed study of the impact of air emissions was published last year by the Colorado School of Public Health.

 

That work found that people living within half-a-mile of gas wells had an elevated risk of health conditions including neurological and respiratory effects.

 

However the Colorado study was criticised for having a small sample size and the Public Health England report says local weather and topography（地势） may mean that similar results may not be likely in Britain.

 

The PHE report acknowledges that extracting shale gas could produce residues¹⁰ containing naturally-occurring radioactive materials - but it argues that these risks would be similar to those in the existing oil and gas industry.

 

On the dangers of groundwater being contaminated, the study quotes a 2011 paper by MIT researchers who found that nearly half of 43 pollution incidents were related to drilling operations - mainly because of faulty sealing of wells.

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