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Cancer Risk From Fracking Chemicals Needs Some Perspective

By Donovan Schafer

The Colorado School of Public Health (CSPH) at the University of 
Colorado recently published an article in Science of the Total 
Environment presenting results from a study on air pollution due to 
oil and gas development (including hydraulic fracturing or “fracking”) 
in Garfield County.

Benzene and other 
”potentially toxic” chemicals were found at concentrations potentially 
hazardous to human health, the article said. But before this study, or any similar 
study, can be taken as a basis for alarm, several questions should be 
answered: What are these “potentially toxic” chemicals? Where do they 
come from? And how dangerous are they really?

To answer these questions, it will be helpful to focus on just one 
chemical, benzene, which is the chemical most often associated oil 
and gas development, and in the case of the CSPH study, “the major 
contributor to lifetime excess cancer risk.”

Benzene is inextricably linked to oil and gas development because it 
is a natural hydrocarbon- like methane, propane, octane, and the 
hundreds of other chemicals in the mixtures we call “crude oil” and 
”natural gas.”

Consequently, benzene also is found in gasoline, diesel 
fuel, and engine exhaust. And, because benzene is a powerful solvent, 
small amounts (in a mixture called “petroleum distillate”) are added 
to fracking fluids to make it easier for the other chemicals to 

Also, benzene is used as a feedstock in manufacturing 
other products, including nylon, plastics, polymers, resins, and 

Given these uses, it should not be surprising that benzene can be 
found everywhere, not just near oil and gas development.

“Benzene is ubiquitous 
in the atmosphere,” according to the U.S. Department of Health and Human Services. Not only does it come from tailpipes, but also 
cigarettes, volcanoes, forest fires, and even campfires.

agencies, however, are not alarmed by the benzene in our daily lives, 
because they recognize that the mere presence of a substance (the fact 
that a laboratory can physically detect it) does not automatically 
pose a threat to public health. It is equally important to determine 
what concentrations can actually do harm.

At what level, then, does benzene become a problem? The truth is, we 
don’t know. The EPA does the best it can to estimate the risks at 
various levels; however, its data is limited. In the case of benzene, 
the EPA uses a 1987 study, in which workers were exposed to 
concentrations of benzene literally thousands of times higher than the 
levels the EPA is trying to estimate.

The EPA then extrapolates (i.e. 
draws a best-fit line) from the data to estimate a concentration that 
will result in 10 additional cancer cases (not necessarily deaths) per 
million people exposed.

This is essentially the same as increasing the 
cancer risk of an individual by one-thousandth of a percent (0.001%).

For benzene, the EPA estimates that a 0.001% increase in cancer risk 
corresponds to exposures of 0.4 parts per billion (ppb) in the air and 
10 ppb in drinking water. For even greater caution, the actual limit 
on drinking water, enforceable under the Safe Drinking Water Act, has 
been set at 5 ppb.

While a 0.001% risk may seem small to begin with, there are two 
critical assumptions built into these estimates that need to be 
remembered: First, the estimated concentrations represent the lowest 
concentrations within wide ranges of uncertainty.

As explained by the 
EPA, there is an “equal scientific plausibility” that the real levels 
of benzene that cause a 0.001% increase in cancer risk are 3-times 
higher than the current estimates.

Second, the estimates assume a 
person will be exposed to the same concentrations during their entire 
lifetime. This is especially unlikely in the case of benzene, which is biodegradable and does not last long in the air. (The CSPH 
study does make adjustments for the second assumption; however, this 
is often not the case in other studies, or at least, in how they are 
presented to the public.)

Understanding the assumptions built into EPA estimates is essential to 
evaluating studies like the CSPH one, because these studies almost 
always express their findings in relation to EPA estimates. Without 
such an understanding, the studies can give an exaggerated perception 
of the risks involved.

It is equally important to consider a study’s findings in context. The 
CSPH study calculated an increased cancer risk of 10 cases per million 
people living near oil and gas development.

However, according to the 
EPA’s National-Scale Air Toxics Assessment (NATA), the average 
increased cancer risk nationwide due to air pollution is 50 cases per 
million. The risk in Denver is even higher (80 per million) simply 
because it is an urban environment.

In Garfield County, where the CSPH 
study was conducted, the NATA risk is 20 per million.

Thus, a person 
living near oil and gas development in Garfield County will experience 
a total increased cancer risk of roughly 30 per million, far below the 
national average, and less than half the risk from living in an urban 

While benzene and other air pollutants should not be ignored when 
discussing oil and gas development, it is important for the public to 
recognize that estimates and limits set by the EPA represent very small
-though perhaps not insignificant-risks, and that these risks are 
comparable to the risks associated with automobile emissions, urban 
living, and industrial activities in general.

This article originally appeared in the Denver Business Journal, June 22, 2012.