As public health researchers we noted your article on fracking (Friends of the Earth ticked off over claims in anti-fracking leaflet, 4 January) and wish to highlight the following: fracking operations involve pumping millions of litres of water containing fracking fluids underground and a small percentage of wastewater contains returned fracking fluids. Estimates vary depending on geological conditions but recent research suggests typically 4-8%. It is well established in peer-reviewed studies and government reports that fracturing fluids and wastewater have contaminated ground and surface waters.

An early peer-reviewed study on chemicals in fracking fluids found 25% could cause cancer and mutations, 37% could affect the endocrine system, 40-50% could affect the brain/nervous system, kidneys, immune system and cardiovascular systems. More recent studies support these findings, including a systematic evaluation that examined 240 fracking substances and found evidence suggesting 43% were linked to reproductive toxicity and 40% to developmental toxicity.

In 2011, the New York Times reported: “In Texas, which now has about 93,000 natural-gas wells, up from around 58,000 a dozen years ago, a hospital system in six counties with some of the heaviest drilling said in 2010 that it found a 25% asthma rate for young children, more than three times the state rate of about 7%.” A study published in JAMA Internal Medicine this year found asthma sufferers who lived near certain levels of shale gas activity were 1.5 to 4.4 times more likely to have an increased risk of asthma attacks.

Professor Andrew Watterson University of Stirling, Dr Will Dinan University of Stirling, Prof Emeritus Vyvyan Howard University of Ulster, Dr David Brown Southwest Pennsylvania Environmental Health project, Professor Richard Clapp Boston University School of Public Health, Adam Law Weill Cornell Medicine

• You quote Cuadrilla’s Francis Egan (Cuadrilla begins work at Lancashire site, 6 January) as claiming, “we will respect the right for people to make their feelings known”. The people, through their democratically elected representatives in county hall, have made their feelings known loudly and clearly on more than one occasion, rejecting Cuadrilla’s application to continue fracking in Lancashire, only to have that legitimate decision summarily overturned by secretary of state Sajid Javid. It’s one thing having a right to make your feelings known, it’s another to have them fall on determinedly cloth ears.

Austen Lynch

Garstang, Lancashire

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