Air Quality in the Barnett Shale - Part 7: Benzene Exposure and the No Significant Risk Level.

Carcinogens are a bit trickier to deal with in terms of determining a safe level.  This is because there is no concentration other than zero that one can say will present no chance of getting cancer from exposure to it.  Instead of a threshold dose, we look at a exposure level determined to present "no significant risk."

This level is defined as the level which is calculated to result in not more than one excess case of cancer in 100,000 individuals exposed over a 70-year lifetime. In other words, if you are exposed to the chemical in question at this level every day for 70 years, theoretically it will increase your chances of getting cancer by no more than 1 case in 100,000 individuals so exposed. (5)

What it does not mean is that one person per 100,000 individuals will get cancer.  This is the same concept behind rolling a six sided die.  You expect to see a "one" show up every six rolls, but you could roll it 50 times without ever rolling a one.

Basically, the ESL and AMCV are calculated the same way:

• (chronic)ESL = 0.00001 / URF
• (chronic)AMCV = 0.00001 / URF

The URF or "Unit Risk Factor" for carcinogens do not have a threshold dose at which below that concentration no cancer would take place. What this means is that any exposure has the chance to cause cancer and that the more exposures the more chances for cancer to manifest itself result.  This makes exposure to "Benzene, a know human cancer causing agent" a scary thing to read over and over again in a report (7).  This is where context and explanation are critical components to any report involving a complex formula, a number, and the words "know human cancer causing agent."  This is also where Alisa Rich, who - need I remind you again - has a Master in Public Health, failed to convey the risk properly.

Why did Alisa Rich and Wilma Subra fail to put this information in context?  Maybe it's because they lack a basic understanding of how the "no significant risk" is calculated and how to compare the 24 hour values with this risk.  It is quite possible that we receive a much better education in our MPH program at Texas A&M's School of Rural Public Health than one receives at the University of  North Texas, but I know that is not the case here.  So instead I will assume that both of  these experts just don't fully understand the topic they sell themselves as knowledgeable in.

Here is how TCEQ explains it in their 2006 document called "Guidelines to Develop Effects Screening Levels, Reference Values, and Unit Risk Factors" in 1.5.2:

For adverse effects associated with a linear dose-response [such as carcinogens], it is assumed that an effects threshold does not exist. Therefore, a linear extrapolation from the POD [point of departure] to the origin of the inhalation dose-response curve is performed to estimate excess lifetime risk at lower doses. The slope of the line from this linear extrapolation is the inhalation URF, which is defined as the upper-bound excess risk estimated to result from continuous lifetime exposure to an agent at a concentration of 1 μg/m3 in air (i.e., risk estimate per μg/m3). 

Confusing?  Lets look at this in terms of Benzene: (8)

• EPA uses mathematical models, based on human and animal studies, to estimate the probability of a person developing cancer from breathing air containing a specified concentration of a chemical. EPA calculated a range of 2.2 x 10-6 to 7.8 x 10-6 as the increase in the lifetime risk of an individual who is continuously exposed to 1 µg/m3 of benzene in the air over their lifetime.  
• EPA estimates that, if an individual were to continuously breathe air containing benzene at an average of 0.13 to 0.45 µg/m3 over his or her entire lifetime, that person would theoretically have no more than a one-in-a-million increased chance of developing cancer as a direct result of continuously breathing air containing this chemical.
• Similarly, EPA estimates that continuously breathing air containing 1.3 to 4.5 µg/m3 would result in not greater than a one-in-a-hundred thousand increased chance of developing cancer, and air containing 13 to 45 µg/m3 would result in not greater than a one-in-ten thousand increased chance of developing cancer.

So the Benzene values obtained from a single 24 hour sampling event performed by Wolf Eagle Environmental were

Now on first glance, one might think "I'm going to get cancer because of Samples 2, 3,and 4."  But that is not the case.  There are two things necessary for one to develop cancer from breathing this particular air.  The first is you would need to breath that air - at the concentration - for 70 years.  Secondly, your body would have to have develop a cancer from the uptake of that particular contaminant.  

It's a lot like flipping a coin.  If you have a 50% chance of the coin landing on tails - when you flip the coin - either heads or tails can come up.  So if I told you you had a 1 in 2 increased chance in developing cancer, you might not want to be exposed.  Now lets change that coin for a single die with six sides.  If you exceed that level over a lifetime, you roll the die and if the number "one" shows up you get cancer.  That would be a one in six increased lifetime chance.  Now lets change out that 6-sided die for one of those funky die they use when playing Dungeons and  Dragons, only in this case, it will have 100,000 sides to it with the numbers 1 to 100,000.  Now if you continuously breath air containing 1.3 to 4.5 µg/m3 of Benzene for a lifetime, you would roll this 100,000 sided die and if the number "1" came up you would get cancer.

For samples 2, 3, and 4, the benzene level is higher than the amount deemed no significant risk.  In this case, the risk - if one were to be exposed at that level in sample 4 constantly over a 70 year lifetime-  would be between:

• 247.9 x  0.0000022 = 0.0005   and    247.9 x 0.0000078 =  0.002

Or an added - or excess - lifetime risk between 1 in 500 and 1 in 2000.  At these elevated levels, the cancer risk has increased, but that is only if the exposure remains at 247.9 ug/m3 and the body fails to repair itself and develops a cancer.  Obviously the levels of benzene detected are too high and additional investigation should be done to determine the cause and fix the problem.  But even at these levels, cancer from benzene is not inevitable.

So looking at this in context, exposure to benzene has the potential to cause cancer but unless the levels are high and sustained over a lifetime, the risk of cancer is not significant.  You may be the unlucky person that rolls the "1".  This is where evaluating risk comes into play and the concept of accepted risk and risk that is forced upon you.  One may reasonably conclude that any risk is a risk too many.  But is eliminating the potential for a one in 100,000 possibility at something negative happening worth the benefits obtained from having it?  I can't make this decision for someone who is potentially impacted by the risk coming from those benefits.  What I can do is try and put it in perspective.   Because even if you eliminated every gas well and drilling rig from the area, exposure to Benzene will still take place and cancer - from lots of other sources - will still manifest itself.

There are a lot of factors in place for citizens in and around gas production activities.  The fact that we find chemicals in the air on one particular day does not mean that exposure at that level will take place the other 364.  And even if there is exposure at that level, we still do not know if the second to final step in the K. C. Donnelly Risk Paradigm - uptake - takes place.  And even if uptake does happen, the body is very good at dealing with contaminants through a process called pharmacokinetics.  And even if we end up with a negative health effect we have very good medical procedures to treat this.

And even if the die rolls a one, we are still unable to pinpoint the culprit, for we have no background data on what levels of these contaminants were present before the gas operation began.  All of this must be taken into consideration befor you say "yes" or "no" to assuming the risk.

Now lest you think I am giving the oil and gas industry a free ride here, I am not.  I will deal with their issues at the conclusion.  What I am writing about in these posts is how Wolf Eagle Environmental and Wilma Subra have painted a picture that does not represent fully and accurately the reality the citizens of the Town of DISH Texas are facing.  That is unfair to them, unfair to the Oil & Gas industry, and unfair and damaging to my profession which is dedicated to protecting the environmental and public health.

Next post: Air Quality in the Barnett Shale - Part 8: Benzene is like a bull...

Note: 2/16/11 A bio found on the internet lead me to incorrectly assume that Alisa Rich received her MPH and was working on her Ph.D from UT.  An email I received from Barnett Shale News included a Deposition from her stating she got her MPH from UNT's Health Science Center and is working on her Ph.D at UT Arlington.
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Air Quality in the Barnett Shale - Part 6: Cumulative Risk & ESL Development

In my last post, I wrote that the TCEQ, makes a rather unambiguous statement regarding the health concerns in the Barnett Shale stating explicitly:

"[T]here are no immediate health concerns from air quality in the area."

Now you can read into that what you will.  You can ignore it, you can disagree with it, you can doubt it, or you can follow up with, 'but what about long-term health concerns?' For which the TCEQ addresses by stating:

"[T]hat when they are properly managed and maintained, oil and gas operations do not cause harmful excess air emissions.”

There are two issues I am trying to address with these posts.  The first is Wolf Eagle Environmental assertion that the chemicals present pose an acute and/or physical hazard:

While atmospheric Methane concentrations recorded over the past year in the Town of Dish do not exceed TCEQ ESLs, the intrinsic quality of Methane to be an asphyxiant should not be overlooked.  In addition, Methanes is highly flammable and can form explosive mixtures in high concntrations in air." (1)

"In addition, several locations confirmed exceedences in a chemical identified by TCEQ with the capability for 'disaster potential'," (2)

The second asks the question does exposure to these chemicals at the levels detected in the one hour and annual averaging - as well as the levels reported by Wolf Eagle Environmental pose a chronic health concern?  That's the $64k question, since some adverse health effects take decades to manifest themselves.  So what toxicologists and health officials do is try to determine a "safe" level.  Unfortunately we are exposed to many chemicals at different concentrations throughout the day and over our lifetime.  Because two or more chemicals can interact synergistically, additively, antagonistically, or be potentiating, a cumulative risk approach is adopted.

In the process of determining risk and/or a 'safe' level, the culprit releasing the chemical of concern is not important.  So when ambient air monitoring is performed it takes a snapshot of all the different chemicals that were present in the air at the one location in time.  What has been shown is that single chemical contaminants can be detected intermittently over time and a single chemical detected at that one location may come from multiple sources. (3)

TCEQs ESLs are "intended to be comparison levels used in the TCEQ’s air permitting process to help ensure that authorized emissions of air contaminants do not cause or contribute to a condition of air pollution."  ESLs are used for air permitting whereas the “air monitoring comparison values” or AMCVs are used for comparing air monitoring results.  ESLs are chemical specific concentrations modeled on a worst-case ground-level air concentration of a single chemical exposure and the potential for an adverse effect due to operation of the facility.  ESLs are very conservative in how they are calculated so when a measured concentration is above the ESL, a review of the actual toxicity data on that chemical may conclude that health effects would not be likely to occur at that level. ((AMCV Document))

Say what?!?  Yeah...which is why the TCEQ goes on to say:

"This broad conservative application of the ESLs has resulted in misunderstandings among the public because the ESLs did not represent the predictive toxicity of the chemical. ESLs continue to be useful screening values for air permitting, but more realistic, predictive values are needed for use in the review of ambient air monitoring data."

Why would they do this?  Why would the purposely develop a method that - for the most part - says - It is a health problem if it exceeds the level unless it isn't a health problem.  That's what Dr. Robin Autenrieth meant when she said "the people demand a number."

Because chemicals do not follow the same drummer, coming up with a uniform way to categorize their toxicological health risk - the "number" we can compare to - creates situations where on one hand it exceeds the level that indicates a health risk but on the other hand there is no data showing a health risk at that level.

And we wonder why the public can be confused, and - in the case of data presented by two experts - misled to believe there are problems because of the number of times a contaminant exceeded this level.  And if I have not beat this dead horse enough, it is inexcusable for Alisa Rich - who holds a Master in Public Health from the University of Texas - to not have understood this and addressed it accordingly in her reports to the good people in the Town of DISH, Texas.

But I digress.  So if the people demand a number, how is this number derived?  Well it basically boils down to this - "the no significant risk level for an individual chemical" defined as:

• the concentration associated with a hazard quotient (HQ) of 1, and...
• the concentration associated with a theoretical excess lifetime cancer risk of one in 100,000 (1 x 10-5).

This where the math that is needed to derive the number comes into play.  Mathematics follow very hard and fast rules.  Two plus two always equals four.  But in toxicology, there are very few hard and fast rules.  Almost everyone has heard stories of someone who drinks like a fish and/or smokes like a chimney and lives to be 90!

So to level the playing field as to what is 'safe' the HQ is used for concentrations of non-cancer chemicals and the theoretical excess lifetime cancer risk of one in 100,000 is used for cancer causing chemicals.  Because there is both cumulative and aggregate exposure to chemicals, the TCEQ uses an HQ of 0.3 to calculate Short-term and Long-term ESLs for the bulk of chemicals.  This is why an ESL is described as "70% lower than the reference value" itself. (6)  In most risk assessments, the HQ is set at "1" which is how the AMCV is calculated.

Why the difference for air permitting and air monitoring?  I am not quite sure, what I suspect is that air monitoring assumes a baseline amount - that is - there is nothing that can be done about that concentration we are exposed to.  When a business wants to start up an operation that will produce and potentially add those chemicals into the mix, the cumulative and aggregate exposure may result in an increase in health concerns that would not bee seen if we were only addressing that particular contaminate by itself.  So, to be extra protective, the level (number) applicable to air permitting is derived using an HQ of 0.3.  This is why the TCEQ states:

ESLs are used in the air permitting process to assess the protectiveness of substance-specific emission rate limits for facilities undergoing air permit reviews. Evaluations of modeled worst-case ground-level air concentrations are conducted to determine the potential for adverse effects to occur due to the operation of a proposed facility. They are comparison levels, not ambient air standards. If predicted airborne levels of a chemical exceed its ESL, adverse health or welfare effects would not necessarily be expected to result, but a more in-depth review would be triggered. (7)

AMCVs and ESLs  that are derived from a HQ are for non-cancer causing chemicals.  Air contaminants that are known or suspected carcinogens receive a comparison value derived from a mathematical formula that assumes that at that value there will be no significant risk for cancer.

For a chemical that is listed as a carcinogen, the "no significant risk" level is defined as the level which is calculated to result in not more than one excess case of cancer in 100,000 individuals exposed over a 70-year lifetime. In other words, if you are exposed to the chemical in question at this level every day for 70 years, theoretically it will increase your chances of getting cancer by no more than 1 case in 100,000 individuals so exposed. (5)

For non-cancer causing chemicals and chemicals that show a nonlinear effect, the formula:

• (acute)ESL = 0.3 x (acute)ReV
• (chronic)ESL = 0.3 x (chronic)ReV
• (acute)AMCV = (acute)ReV
• (chronic)AMCV = (chronic)ReV

Both the ESL and the Reference Value (ReV) must be expressed in the same units (micro-grams/cubic meter)  and represent the same exposure period.  This means that if you are going to compare your sample data to an ESL or AMCV, the units and exposure period must be the same.  When Wolf-Environmental and Wilma Subra report 16 volatile organic chemicals exceeded the TCEQ ESLs they used data from a sampling exposure period that was 24 times to long for the short-term and was not averaged over a one year period for the long-term.

This would be like trying to run a restaurant knowing that one coffee pot can effectively serve enough coffee for 100 people per hour. So you hire Wolf Eagle Environmental and Wilma Subra to find out how many coffee pots you need.  They monitor the store for 24 hours and report 800 people.  They then tell you that this exceeded the manufacture's stated value of 100 people by over 8 times!

OK...OK...they were they screwed up when they compared a 24 hour sample to a one hour level.  But were not talking about coffee here.  Even if they had taken the sample for an hour, it appears that they detected Benzene.  And Benzene, according to their reports is a known cancer causing contaminant!  I read on the internets that there is no safe level for a cancer causing compound.  That any exposure increases the risk of cancer.  If there is Benzene in their samples and I am exposed to that, will I get cancer?

Probably not.


Probably?? Is that the best answer you can give?


Well...that's the only answer anyone really can give.  Although - for most chemicals -I can say  with with a very high degree of certainty 'if you stay below this value, you will have no adverse health effects', carcinogens require me to say there is 'no significant risk' if you stay below this level.

Next post:  Air Quality in the Barnett Shale - Part 7: Benzene Exposure and the No Significant Risk Level.

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