On April 16, 2011, House Democrats representing the Energy and Commerce Committee (Henry A. Waxman), Natural Resources Committee (Edward J. Markey), and Oversight and Investigations Subcommittee (Dina DeGette) released a report that summarizes the types, volumes, and chemical contents of the hydraulic fracturing products used by the 14 leading oil and gas service companies in the U.S. The report purports to contain "the first comprehensive national inventory of chemicals used by hydraulic fracturing companies during the drilling process."1

During the last Congress, the Committee commenced an investigation into the practice of hydraulic fracturing and its potential impact on water quality across the United States, asking the leading oil and gas service companies to disclose information on the type and volume of chemicals used in this process between 2005 and 2009.

The Democratic Committee staff analyzed the data provided by the companies about their practices, finding that the 14 leading oil and gas service companies used more than 2,500 hydraulic fracturing products containing 750 chemicals and other components. The components used in the hydraulic fracturing products ranged from generally harmless and common substances, such as salt and citric acid, to toxic substances, such as benzene and lead. Committee staff found that between 2005 and 2009, the oil and gas service companies used hydraulic fracturing products containing 29 chemicals that are either (1) "known or possible human carcinogens," (2) "regulated under the Safe Drinking Water Act (SDWA) for their risks to human health," or (3) "listed as hazardous air pollutants under the Clean Air Act."2

The Committee report states that some of the chemicals used in hydraulic fracturing "could pose a severe risk to human health or the environment."3 Yet the Committee staff present no scientific data to support this assertion and ignore fundamental principles of toxicology, epidemiology, and risk assessment that would be needed to determine, scientifically, whether hydraulic fracturing chemicals could be harmful to people or the environment. The report's conclusion that "questions about the safety of hydraulic fracturing persist" cannot fairly be drawn from the data presented.

Hydraulic Fracturing

Hydraulic fracturing is the practice of injecting water, mixed with chemicals and propping agents like sand, under high pressure into wells to release oil and natural gas trapped in underground rock formations. As the Committee report notes:

Hydraulic fracturing has helped to expand natural gas production in the United States, unlocking large natural gas supplies in shale and other unconventional formations across the country. As a result of hydraulic fracturing and advances in horizontal drilling technology, natural gas production in 2010 reached the highest level in decades. According to new estimates by the Energy Information Administration (EIA), the United States possesses natural gas resources sufficient to supply the United States for approximately 110 years.4

Basic Principles of Toxicology, Epidemiology and Risk Assessment

Three scientific disciplines—toxicology, epidemiology and risk assessment—come into play in the determination of whether a chemical or other substance is capable of causing harm to individuals or populations and/or to the environment.

Toxicology is the study of the adverse effects of chemical, physical or biological agents on living organisms and the ecosystem. Epidemiology is the study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the control of health problems. Risk assessment is an estimate of the likelihood of adverse effects posed by a specific level of exposure to certain health hazards, such as pollutants in the environment.

Scientists understand that "all substances are poisons; there is none that is not a poison. The right dose differentiates a poison and a remedy."5 Thus, rather than ban all "toxic chemicals" from the workplace, for example, regulators establish permissible exposure limits in workplaces. "TLV" is the threshold limit value and is used by the American Conference of Governmental Industrial Hygienists (ACGIH) to express the maximum airborne concentration of a material to which most workers can be exposed during a normal daily and weekly work schedule without adverse effects. "PEL" is the permissible exposure limit and is used by the Occupational Health and Safety Administration (OSHA). Values for TLV and PEL are usually equivalent; each is the average concentration of a chemical in the air to which most people can be exposed and show no ill effect.

Scientists also understand that a chemical's dose is dependent upon the environmental concentration, the properties of the toxic substance, the frequency of exposure, the length of exposure, and the exposure "pathway." Thus, a chemical that might be cancer-causing ("carcinogenic") when inhaled may not necessarily be carcinogenic when ingested, and vice versa. Similarly, a chemical may present a high risk of harm to the environment when released into the air, yet may present minimal risk to the environment when buried in the ground. This is because the exposure pathways are different.

To the scientist tasked with determining whether a chemical presents a risk of harm to human health or the environment, the inquiry does not end with the understanding that a chemical is a "known or possible human carcinogen." This is only the beginning of the scientist's assessment of whether the chemical is likely to cause human or environmental harm. The scientist must determine the route of exposure, the level of exposure likely to cause adverse health or environmental effects, and whether there are potential adverse effects based on reliable published science. In the case of certain chemicals that have been identified as a "known or possible human carcinogen," there may be no laboratory or clinical evidence that the chemical has one more specific types of cancers. In such instances, scientists refer to published epidemiologic studies indicating whether exposure to the chemical is associated with a "statistically significant" increased risk of one or more cancers in the studied populations who have been exposed to the chemical.

Misleading Findings in the Committee Report

The Committee report is not a toxicological review of chemicals used in hydraulic fracturing, nor does it attempt to provide a scientific assessment of potential exposures to the chemicals or the risks, if any, such estimated chemical exposures pose to human health or the environment. Instead, the report omits information that is important for context and contains a number of misleading findings and statements.

At the outset, the report fails to note that hydraulic fracturing fluid is 98% water and sand, along with a small amount of special-purpose additives used to allow hydraulic fracturing to be conducted safely and effectively. Thus the report does not disclose the volume of allegedly hazardous chemicals contained within the "780 million gallons of hydraulic fracturing fluid" used by the 14 oil and gas service companies between 2005 and 2009. Nor does the report disclose how many hydraulic fracturing operations were conducted within the 2005-2009 timeframe—a fact providing context for the use of such chemicals in the environment.

Table 3 of the report identifies "chemical components of concern" and includes "carcinogens." The "carcinogens" listed include diesel, naphthalene, formaldehyde, sulfuric acid and ethylene oxide, among others. The "carcinogen" classification is highly misleading for some of these chemicals. Sulfuric acid, for example, has only been implicated as a carcinogen when released into the atmosphere as a mist.6 Diesel exhaust—not diesel fuel itself—is a suspect for lung cancer.7 Naphthalene has been designated as a suspect or probable carcinogen based on animal—not human—studies.8 Formaldehyde has only recently been classified as a carcinogen and only as to nasal cancer.9 In sum, many of these classifications are meaningless when referring to a constituent of a fluid such as hydraulic fracturing fluid, and given the most likely potential pathway of exposure—drinking water.

Even chemicals such as 2-butoxyethanol (2-BE), which as the report correctly notes is relatively easily absorbed by inhalation, dermal exposure or ingestion, have fairly high TLV/PEL levels, meaning regulators have determined that humans can be exposed to relatively high concentrations of 2-BE in the workplace and suffer no ill effect.


The Committee report's conclusion that "questions about the safety of hydraulic fracturing persist" cannot fairly be drawn from the data presented in the report. In order to determine whether chemicals used in hydraulic fracturing fluids would present a risk of harm to human health or the environment, each chemical's toxicological profile would need to be reviewed and a scientific risk assessment performed. A reliable risk assessment would need to take into account the dose of the chemical to which humans or the environment likely would be exposed. Dose would depend upon the environmental concentration, the properties of the chemical, the frequency and length of exposure, and the exposure pathway.

While the Committee's report is interesting in that it identifies the specific chemical components that appear most often in hydraulic fracturing products, the total volume of hydraulic fracturing fluids used in various states, and that some of the chemicals are known or suspected carcinogens, these facts tell us nothing about whether these chemicals, as used in hydraulic fracturing, are or are not potentially harmful to humans and the environment. Further analysis of the factors outlined above is needed to support the Committee staff's premature conclusion that the public should be concerned about the data in its report. The motivation for and reliability of the Committee's determination are especially questionable in light of ongoing study by the United States Environmental Protection Agency (US EPA), initiated at the direction of Congress, of the potential risks to drinking water posed by hydraulic fracturing of formations including coalbeds and shale for the extraction of natural gas. 10