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The Health Consequences of Unconventional Gas Extraction ("Fracking")
Jerome A. Paulson, M.D.

Dr. Paulson is Professor of Pediatrics and Associate Research Professor of Public Health, George Washington University; Medical Director for National & Global Affairs, Child Health Advocacy Institute & Director, Mid-Atlantic Center for Children’s Health & the Environment Children’s National Medical Center, Washington, DC.

Within the past 12 months, Dr. Paulson has provided factual information to lawyers regarding the potential health impact of natural gas extraction with hydraulic fracturing.

Release Date: 05/13/2013
Termination Date: 05/13/2016

Albert Einstein College of Medicine designates this enduring material for a maximum of 1.0 AMA PRA Category 1 Credit(s)™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

Albert Einstein College of Medicine is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.
Learning Objectives
Upon completion of this Cyberounds®, you should be able to:
  • Describe the process of natural gas extraction using high volume, slickwater hydraulic fracturing from long laterals from clustered multi-well pads (AKA unconventional gas extraction)
  • Describe some of the toxicants associated with unconventional gas extraction
  • List the potential health hazards associated with natural gas extraction with hydraulic fracturing.


This presentation may include discussion of commercial products and services.

This material was developed by the Mid-Atlantic Center for Children’s Health & the Environment and funded under the cooperative agreement award number 1U61TS000118-03 from the Agency for Toxic Substances and Disease Registry (ATSDR).

Acknowledgement: The U.S. Environmental Protection Agency (EPA) supports the PEHSU by providing funds to ATSDR under Inter-Agency Agreement number DW-75-92301301-0. Neither EPA nor ATSDR endorse the purchase of any commercial products or services mentioned in PEHSU publications.

Natural gas extraction using high-volume, slick water hydraulic fracturing from long laterals, known by its popular name fracking, is an unconventional natural gas extraction process that is currently the focus of controversy. Throughout this Cyberounds® presentation, the process will be referred to as unconventional gas extraction. I avoid the use of the term "fracking" because my concerns about potential health impacts extend beyond just the hydraulic fracturing and include other aspects of the complete process.

Unconventional gas extraction is not isolated to Western New York State or other states that are underlain by the Marcellus Shale. The pink areas on the map below indicate other parts of the US where shale formations (known as Shale Gas Plays) exist. Development is now ongoing in some areas; subsequent future development will be influenced by the economics of the energy sector. As one can also see, unconventional gas extraction has the potential to occur in many parts of the globe.

Public Policy Issues Related to Unconventional Gas Extraction

The National Environmental Policy Act (NEPA) was enacted in 1970; and is the original environmental health law in the United States. It sets basic policy for all the laws that followed. The Energy Policy Act of 2005 amended NEPA to remove the regulation of several oil and gas related activities.

The Clean Air Act was originally passed in 1970. As it was originally written it exempted oil and gas wells, and in some instances pipelines, compressors, and pump stations from regulation. It was amended in 1991 to remove hydrogen sulfide from the list of hazardous air pollutants.

The Clean Water Act was originally passed in 1972. It was amended in 1978 to exempt oil and gas production from the permit program for stormwater runoff. The Clean Water Act was further amended by the Energy Policy Pct of 2005 which redefine settlement as a non-pollutant.

The Safe Drinking Water Act was originally passed in 1974. It was amended by the Energy Policy Act of 2005 which exempted hydraulic fracturing from Safe Drinking Water Act oversight.

The Resource Conservation and Recovery Act was originally passed in 1976. It regulates disposal of solid and hazardous waste. In 1980 Congress exempted oil field waste; and the EPA delegated the regulation of those wastes to the states. This means that the regulation may be different in each state.

The Comprehensive Environmental Response, Compensation and Liability Act, which is also known as the Superfund law, was passed in 1980. As originally enacted, it exempted benzene, toluene, ethylbenzene, and xylene if they came from oil or gas production. It also excludes natural gas, natural gas liquids, liquefied natural gas, and synthetic gas usable for fuel from the definition of hazardous substance. The Emergency Planning and Community Right-to-Know Act was originally passed in 1986. As originally passed, oil and gas facilities were not required to report toxic releases.

Unconventional Gas Extraction

It is important to understand the differences in the process for unconventional gas extraction, illustrated on the left, and conventional gas extraction illustrated on the right. In conventional gas extraction, a well is drilled into a cavity underground that holds the natural gas. Essentially a straw is placed into the gas reservoir, and the gas then comes to the surface under pressure. In unconventional gas extraction, the natural gas is locked up inside tiny cavities in the shale rock. Think of the shale rock as a petrified sponge. The holes in the sponge contain the gas; and unless the sponge is “squeezed,” the gas cannot come out. In reality, the shale rock is pulverized underground, then the gas comes out and rises to the surface.

Potential health impacts extend beyond just the hydraulic fracturing and include other aspects of the complete process.

In many of the advertisements about unconventional natural gas extraction, you will see/hear the claim that this is an "old technology" that has been used for a long time. What has been used for a long time is vertical drilling with fracturing. On the right-hand side of this image you can see where a vertical well has been drilled and then the fracturing takes place in the vertical drill hole.

One of the reasons that unconventional natural gas extraction is labeled as unconventional is that it requires the new technique of vertical drilling followed by horizontal drilling and then fracturing. On the left-hand side of the image you can see a vertical wellbore; and then, when the drill bit gets down to the relatively thin layer of shale, it is turned horizontally and the drill hole is continued out for thousands of feet. It is in this horizontal drill hole that the fracturing for unconventional gas extraction takes place. This new process requires much greater volumes of water and chemicals in the frack fluid compared to vertical hydraulic fracturing.

The process of unconventional gas extraction involves multiple steps: pad construction, drill set-up, drilling hydraulic fracturing or fracking, natural gas extraction, well decommissioning and land restoration. While each of the steps in the process of unconventional gas extraction may have health consequences, public health concerns arise from drilling, the hydraulic fracturing and the natural gas extraction stages. Pad construction and drills set-up have potential adverse health impacts related to the workers but generally not to the public.

The initial step in unconventional gas extraction is the construction of a drill pad. The photograph on this slide below shows a partly completed drill pad. When the land is cleared to construct the pad, all of the trees or any other ground cover is removed. The site is then leveled, and roads connecting one drill pad site to another are built. The large rectangle or depression that you can see on the left-hand side of the drill pad is an impoundment pond where waste fracking fluids are collected.

In order for unconventional gas extraction to be financially successful, multiple drill pads must be located close to one another. These two side-by-side images show an area in Washington County, Pennsylvania, before the installation of drill pads (on the left) and after the installation of the drill pads (on the right). Notice the series of interconnecting roadways that are necessary to link one drill pad to another.

In conventional drilling for natural gas, a single well bore into the large underground reservoir is sufficient to extract all of the gas in that reservoir. However, in unconventional gas extraction, the gas can only be recovered from that part of the shale rock that is immediately contiguous to the horizontal drill hole and which has been fractured. In the image below, the drill hole has been turned to the right. Any gas that is in the shale layer to the left of the vertical drill hole or in the plane of shale rock either coming toward you from the plane of the image or going back away from you in the plane of the image will not be extracted. Additional horizontal boreholes are required, radiating out in every direction from the vertical borehole in order to crush all of the underground rock and capture its natural gas.

Multiple vertical wells are required and each of those vertical wells is associated with multiple horizontal drill bores. On the left-hand side of the below image, multiple horizontal drill bores go out from a single central vertical drill bore. On the right side of the image is a photograph of a plot of ground with a map showing horizontal drill bores overlaid in color on the map.

Once the drill pad is completed and the drill rig set up, wastewater starts to flow into the impoundment pond. In the image below, there are several prefabricated office trailers on the drill pad. In addition, the drill pad has multiple diesel generators, water-recycling containers, and sand or chemical storage containers.

Drill pads are often situated close to homes. In this image from National Geographic, a drill pad that has been established at a site close to several homes. Notice the scale of the drill pad itself relative to the land around the homes, the scale of the equipment to the scale of the homes and the proximity of the pad to the homes. Any toxicant that is on the pad does not have to travel far to reach the homes. In effect, an industrial site has been established in a non-industrial area.

Drilling the borehole requires drilling fluid for lubrication, as the drill head goes through rock and other material underground. The drilling fluid can be water-based, petroleum-based, or gaseous-based. The risks of exposures to the chemicals in the drilling fluid and the chemicals which are returned from underground that have been added to the drilling fluid are primarily risks to the workers.

The proximity of the pad to the homes....an industrial site has been established in a non-industrial area.
If, however, there is an explosion on the drill pad, drilling fluid can be dispersed widely, potentially exposing the general population. In addition, the standard practice for long-term disposal of the drilling mud seems to be burial on the drill pad site. This assumes that the site will forever remain undisturbed by flooding or other activities. If there is flooding or if there is any digging in the future on the old pad site, the workers and others may be exposed to the drilling mud with its contaminants and chemicals brought up from below ground.

The Overall Process

Examine the image above closely. Moving from the left of the image at ground level, you notice trucks that bring the large volumes of water and sand as well as other chemicals to the pad site. You see pumping trucks that inject the fracture fluid into the ground. Then you will see the wellhead.

When the drilling is in progress and the fracturing is occurring, there is a drill rig in place. After the drilling and fracturing are completed, the drilling rig is disassembled and a wellhead is placed. Next to the wellhead, hydraulic fracturing fluids returning from underground collect in a pit. Nearby, a truck waits to transport the hydraulic fracturing fluid off-site. The adjacent tanks and other equipment process the natural gas, which is then inserted into the natural gas transmission pipelines for national distribution.

Underground, at about 100 to several hundred feet below the surface, we find the groundwater layer. The drill bore must go through this layer and then through several thousand feet of earth and rock to reach the shale layer. At that point, the borehole is turned laterally to create the long laterals. It is in these lateral boreholes that explosives are placed, which, when detonated, create the fractures in the shale rock that allows for the escape of the natural gas into the borehole. Water, sand and various chemicals are pumped into the hole to facilitate the recovery of gas. For example, the sand, which is termed “propent,” functions as a stent to keep the minute fractures open while the gas escapes.

Air Pollution

Natural gas extraction creates many sources of air pollution. It takes thousands of truck trips to the drilling pad to transport the water, sand and chemicals required to make the fracture fluid.(See next slide.) All of these trucks use diesel fuel and produce air pollution both as they idle on the pad and as they make their trips to and from the pad. On the pad itself, multiple diesel generators produce electricity to light the pad and power the pumps that send the fluid down underground. These diesel generators also produce exhausts that contain both ozone and particulates, creating local air pollution.

The US EPA estimates that it takes approximately 1667 truckloads of water for the hydraulic fracturing on a single well. This assumes that approximately 5M gallons of water are needed to frack a single well and that each tank truck brings in about 3000 gallons of water. In addition, each dump truck full of sand, which is used as the propent, contains about 2000 pounds of sand. Therefore, it takes approximately 750 truckloads of sand to bring the 1.5 million pounds of sand to the wellhead each time the well is fracked. Moreover, each well is fractured between 1 and 10 times.

There are additional sources of air pollution associated with unconventional gas extraction. Misters are in essence gigantic nebulizers. They are placed in containment ponds to spray water into the air and reduce the volume of material in the pond by evaporation. However, as medical professionals know, nebulizers place chemicals dissolved or suspended in the fluid into the air as well. For people, animals, crops and other vegetation located down-wind from the containment pond with misters, these materials, including volatile organic compounds used to create the hydraulic fracturing fluid, volatile organic compounds from underground, other underground chemicals that become dissolved in the fracturing fluid, all end up in the air to be inhaled or to settle out on land and vegetation.

Natural gas, as supplied to a consumer, is methane (CH4). When it comes from the ground, natural gas may be contaminated with benzene, toluene, ethylbenzene, xylene (the BETEX chemicals), hydrogen sulfide (H2S) and other chemicals. All the methane is not captured and some is unintentionally released from condensers, storage tanks and transmission lines. If the gas from the wellhead is not released directly to the atmosphere, it can be burned (called flaring).

Additionally, the release of gases from the well, condensers, pumps, storage tanks and transmission lines contributes to the formation of ground level ozone. Flaring increases the concentration of particulate matter in the atmosphere. Depending on the local geology, the extracted gases may be accompanied by radon. Long-term exposure to radon is, of course, associated with the development of lung cancer.

Ozone is produced in the atmosphere as a result of the presence of volatile organic compounds (VOCs), oxygen and sunlight. Therefore, the release of VOCs from the wellhead or from flaring contributes to the production of ozone, a pulmonary and mucous membrane irritant. Particulate matter produced by flaring is associated with myocardial infarctions and strokes.

Methane, when released to the atmosphere, is a much more potent greenhouse gas than carbon dioxide (CO2). One of the primary purposes for the extraction of methane is to reduce greenhouse gas production caused by the burning of fossil fuels to generate electricity, i.e., substituting methane for the coal or oil burned in electricity generating plants. However, this benefit may be offset by the release of methane to the atmosphere.

Ozone in the stratosphere is good for humans. Ozone at ground level is not.

Ozone in the stratosphere is good for humans. Ozone at ground level is not. Unconventional gas extraction, which releases methane, other volatile organic compounds and oxides of nitrogen (NOx) into the atmosphere (as do flaring and diesel exhaust), unfortunately creates ground-level ozone.

Ozone and particulate matter are among the best-studied air pollutants. Both are associated with hazards to individuals of any age, as noted in the chart below.

Several ecological studies show an association between exposure to benzene and adverse outcomes in children. These studies were not done in the context of unconventional gas extraction and were not designed to show cause-and-effect; however, the results are very relevant to the exposures that occur with unconventional gas extraction. All were published in Environmental Health Perspectives, the leading environmental health journal globally.

Lupo et al. demonstrated an association between pregnant women living close to a Texas oil refinery and the outcome of neural tube defect in the offspring. The study by Whitworth et al., also done in Texas, showed an association between pregnant women living close to a refinery and the development of acute lymphocytic leukemia in their offspring. The Slama et al. study, done in France, found an association between living close to a major highway during pregnancy and children being born small for gestational age. There is also an un-peer reviewed study from Pennsylvania, which is posted on the internet, showing an association between living close to a natural gas drilling site during pregnancy and children being born small for gestational age.

Water Pollution

There are a number of potential sources of water pollution associated with unconventional gas extraction. Some of the water and other chemicals pumped into the well return to the surface. That water, now referred to as produced water, contains the chemicals added initially to produce the hydraulic fracturing fluid plus naturally occurring chemicals that have been contained underground, but have now been dissolved in and return to the surface with the produced water.

Since the shale formation itself is the result of sedimentation in an ancient sea, some of the materials that have been underground include various salts. Depending on the specific local geology, radon may come to the surface in the produced water.

Unclear whether the water injected into the well can migrate...through 5-7,000 feet of rock and earth to the ground water layer.

While it is unclear whether the water injected into the well can migrate from the distal portions of the well-bore through 5-7,000 feet of rock and earth to the ground water layer, which is from several hundred to a thousand feet below ground, it is well known that some wells leak near the surface where the well-bore initially goes through the ground water layer. In addition, produced water stored in the pit can overflow from rains or can leak through defects in the pit liner or walls. When the water is pumped into tank trucks, it may leak from the truck during an accident.

Drilling and energy companies point out that hydraulic fracturing fluid is 98-99.5% water and sand. Their pro forma standard statement suggests that the amount of other chemicals is de minimis and that the public need not worry about them. However, when 1-10 million gallons of fluid are used in each fracturing episode and wells can be fractured up to 10 times, then the volume of the other chemicals added to the fluid becomes large.

The public knows very little about the chemical identities added to the water and sand. Trade names are used for some of the products and their chemical composition is not revealed. The minority staff of the Committee on Energy & Commerce of the US House of Representatives did collate the information that was available about chemicals used between 2005 and 2009. They found that the seven most commonly occurring chemicals were methanol (methyl alcohol), isopropanol (isopropyl alcohol, propan-2-ol), crystalline silica - quartz (SiO2), ethylene glycol monobutyl ether (2-butoxyethanol), ethylene glycol (1,2-ethanediol), hydrotreated light petroleum distillates and sodium hydroxide (caustic soda).

Another way to look at this information is to categorize the chemicals as if they were controlled by the laws that regulate hazardous materials in many other industries but not the oil and gas sector. On this this chart, the most commonly used chemicals that otherwise would be regulated as hazardous air pollutants (HAP) under the Clean Air Act are identified, as are chemicals that would be regulated under the Safe Drinking Water Act (SDWA), or would be listed as carcinogens.

The drilling and extraction companies do provide information on chemicals used in individual wells after then have been drilled and fracturing is completed. This information is available at frackfocus.org but is provided post-hoc and may not identify the actual chemicals or their concentrations in branded products.

Not all of the hydraulic fracturing fluid that is pumped underground is returned. However, what is returned can contain chemicals that were in the rock underground and not in the original fluid. Because the shale layer containing the gas was the flood of an ancient sea, materials that were in that sea such as chlorides, bromides, heavy metals and others return with the fluid that comes back up in what we call produced water. The produced water can also contain dissolved volatile organic compounds and, depending on the local geology, normally occurring radioactive materials (NORMs) such as radon and uranium.

One of the main questions that is asked about unconventional gas extraction is whether the ground water in the surrounding area becomes contaminated with either materials from the hydraulic fracturing fluid or the volatile organic compounds that are the target of the well. There are hundreds, if not thousands, of anecdotes about water contaminated with methane. Videos of tap water that can be ignited with a flame are available on YouTube. Beyond the anecdotes, there are some well-documented episodes of well water contaminated with methane from unconventional gas extraction in Dimock, PA, and Parker County, TX. It is true that oral ingestion of methane in drinking water has very low toxicity. However, it is important to recognize that methane serves as an easily measured marker of water contamination in this situation. Other chemicals will migrate to the water including hydrogen sulfide, benzene, ethyl benzene and other volatile organic compounds.

The other question about methane in the drinking water is whether it is from deep underground, formed eons ago, or if it is derived from other sources of contamination that are closer to the surface. For example, when leaves fall from trees and decay, or when an animal dies in the forest and decays, methane is produced and conceivably could enter the ground water.

Osborne et al. from Duke University elegantly documented that, in some instances, the methane in the wells is ancient and, therefore, must originate from deep under the earth. They looked at the proximity of water wells to gas wells (on the X-axis) and plotted proximity against methane concentration (on the Y-axis). They demonstrated that water wells closer to gas wells had higher concentrations of methane. The important part of their study was the subsequent step -- methane produced eons ago had different ratios of isotopes of carbon than did methane produced more recently. They demonstrated that the methane recovered from the water wells close to the gas wells had the isotopic signature of ancient methane.

The containment ponds are a potential source of contamination of ground or surface water. The ponds are lined with plastic which may leak as may the earthen walls of the pond. When there are heavy rains or large snow falls, the ponds may overflow due to the additional volume of water.

The disposal of flowback water is also problematic. In Pennsylvania the practice, which has since been stopped, was to ship this material to publically owned treatment works (POTW). Researchers from the University of Pittsburgh School of Public Health documented that the effluent released from these plants that was being used to purify flowback water contained much higher levels of various ions and some organic compounds than did water in the river above-stream from the treatment plants. In other words, the treatment plants could not remove the contaminants for the water used for hydraulic fracturing. Much of this flowback water is now disposed on in deep underground injection wells.

Another issue that needs to be considered is water depletion. It requires 1- 10 million gallons of water each time a well is fracked and individual wells can be fracked up to 10 times. In areas of the country where water is already in limited supply or in other areas at times of drought, the diversion of these huge volumes can have a significant impact on water available for human consumption, animal husbandry, crop irrigation and recreational use.

Climate Change

One of the reasons given for extracting natural gas from shale is that when burned in a generating plant, burning methane produces much less CO2, a major greenhouse gas, per unit of electricity than does burning coal. However methane is a more potent, though short-lived, greenhouse gas than carbon dioxide.

When the well first starts producing, several million cubic feet of methane may be released per day for several days. After the well is connected to the purification systems and the pipelines, there is additional leakage of methane. If, in those first few days, the methane is not vented directly to the atmosphere, it is burned, a process known as flaring. Burning the methane of course produces all of the byproducts of combustion such as CO2, particulate matter, oxides of sulfur and nitrogen, without any benefit whatsoever. Anthony Ingraffea from Cornell University School of Engineering has calculated that when all of these factors are considered, the net-climate-change-benefit of burning methane from shale is much lower than if you just calculated the benefit by only looking at what happens when different fuels are burned in a power plant.


During the drilling and hydraulic fracturing phases of the unconventional gas extraction process, the sites often run 24 hours per day, seven days a week, with extremely bright lights illuminating the pad. During all phases of the unconventional gas extraction process, noisy diesel trucks come and go and diesel equipment runs (often continuously or intermittently throughout the 24-hour day). When flaring is employed, this noisy process also goes on continuously or intermittently throughout the day and night. All the intense light and noise can lead to sleep deprivation and to physical/psychological stress.

It is well known that sleep deprivation affects concentration. In children this can lead to poor school performance and in adults to safety issues on the job and on the road. There is also a growing body of evidence that that stress adversely affects the cardiovascular, immune and other systems.


It is important to recognize some basic principles of toxicology. First and foremost, for a toxic substance to actually harm a human or an animal, the substance must reach the organism and the target organ in the organism. In other words, there must be a “completed pathway of exposure” before toxicity occurs. Second, the exposure must be sufficient to actually cause harm. Formerly, we thought that “the dose makes the poison;” i.e., the greater the exposure, the worse the harm. It is now recognized that this is not true of every toxicant. Some toxicants have U- or J-shaped dose response curves. Moreover, some toxicants are thought to have thresholds of toxicity, a dose below which no harm occurs; and others, such as lead, have no recognizable threshold.

It is also the responsibility of industry to reveal to the public the full description of and quantities of all chemicals used in fracking.

In unconventional gas extraction there are toxicants which can potentially or have been documented to reach humans. Many of these toxicants are well documented to be human health hazards.

“Children are not little adults” is often the first truism that a health professional learns during professional training. Assumptions underlying decisions to protect adults from hazardous materials or situations will not necessarily be valid for children. Children live longer than adults (have a longer shelf-life). The implication of this fact is that the outcome of a toxic exposure may appear many years after the exposure itself. Often the adult may die from another cause before the adverse outcome is manifest but a child is likely to live long enough to experience the outcome.

Some exposures to toxicant occur in men and women who will become parents and will adversely affect their sperm or egg and adversely affect the child that is ultimately conceived either in utero or after birth. From the moment of conception, there are changes in the embryo, fetus and child that continue until completion of the myelination of the frontal lobes around 25 years of age. Perturbations of these processes by toxicants can influence outcomes throughout the life span.


Presently there are no data that document widespread, adverse human health consequences occurring as a result of natural gas extraction using high volume, slickwater hydraulic fracturing from long laterals from clustered multi-well pads. However, hazardous chemicals are used in and produced by unconventional gas extraction. Researchers have documented, however, several very plausible routes of human exposure.

The author believes that drilling and energy companies must demonstrate that the drilling and gas recovery can be done in a way that minimizes the threat to human and ecosystem health. These corporations should establish an independent foundation to fund such research. There are examples in other industries where this has been done, producing very credible research uninfluenced by the funders. The public should not be asked to fund research to determine whether hydraulic fracturing and natural gas recovery from shale is dangerous after the fact. It is also the responsibility of industry to reveal to the public the full description of and quantities of all chemicals used in fracking.

Anyone be they health care provider, public health official, parent, teacher or other person with a question about a child or children, health and the environment can contact the pediatric environmental health specialty unit (PEHSU) within their region.

PEHSUs deal with a wide range of issues. Some are listed below but anything that anyone believes links a child, the environment and health is fair game for a query.

The Pediatric Environmental Health Specialty Unit (PEHSU) Program is funded by:

There is a cooperative agreement between the Agency for Toxic Substances and Disease Registry and the Association of Occupational and Environmental Clinics which funds the PEHSU program. EPA also provides some funds to the cooperative agreement. AOEC provides grants on a competitive basis to the PEHSU in each of the 10 federal regions. PEHSUs receive no funding or other resources from any industry. This map below shows where each of the PEHSUs is located.

The PEHSUs have developed a fact sheet on unconventional gas extraction for health professionals. It, and all of the contact information for each PEHSU, can be found here.

Information and fact sheets for parents and community members are also available from the PEHSU website. For any questions related to hydraulic fracturing or any other pediatric environmental health issue, please contact the PEHSU that serves your region: