Air Quality in the Barnett Shale - Part 18: Dr. Sattler's Deposition - 70% means what?

For the last four posts I've been looking at how Alisa Rich with Wolf Eagle Environmental and Dr. Sattler with UTA could have concluded that the results of air dispersion modeling performed on six ambient air samples collected over a 24-hour period indicated a problem with the air the good people of the Town of Dish, Texas, were having to breath now that a bunch of gas compressors were located in their town.

I've been critical of their work on many fronts, but it all seems to revolve around the use of ESLs to compare ambient air samples.  This is not what ESLs are to be used for, but Alisa Rich, with the assistance of Dr. Sattler, decided that it would be appropriate to use them in their reports.

The two of them have been unable to get their heads wrapped around why the ESL shouldn't be used, going so far as to accuse the TCEQ of not being technically competent when they tried to rectify this misuse with the issuance of the AMCV for ambient air samples, like the ones collected by Alisa Rich.

In their thinking, a value that is 70% lower than another must be, somehow, more safe.

So is the ESL that is 70% lower than this new AMCV value the TCEQ wants to use a better value to use?

No.


ESLs and AMCVs are based on an inhalation Reference Value (ReV) which is defined:

[a]s an estimate of an inhalation exposure concentration for a given duration to the human population (including susceptible subgroups) that is likely to be without an appreciable risk of adverse effects. ReVs are based on the most sensitive adverse health effect relevant for humans reported in the literature.

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

For chemicals suspected to cause cancer the ESL and AMCV are the same.

The ESL is one third the ReV.  And the ReV is the value which is based on the most sensitive adverse health effects relevant for humans.

So if the AMCV = the ReV, and the ReV is the value which is based on the most sensitive adverse health effects relevant for humans, will lowering the value by 70% bring about any more protection?

No.

Another way to look at it is like this:  If the maximum temperature that a hot tub will go is 104F, is 104F the maximum temperature deemed safe for humans?

Yes.

If we lower the temperature to 90F, will we have made it any more safer?  How about to 65F?

No.

Now the thing about temperature is this.  If you add 90F water to 90F water, the water will be 90F.  But if you add 60 ppb of Benzene from one source with 60 ppb of Benzene from another source, you could get 120 ppb of Benzene in the ambient air.

If the ESL for Benzene is 54 ppb, the two sources would be putting more Benzene into the air than they should, but it would still be at a safe level.  Even when the two concentrations are added together (120 ppb) it is still safe because 120 is less than the ReV which is 180 ppb.

And you know what the AMCV for short term Benzene is?  180 ppb.

Since Benzene is also a suspected carcinogen, the long-term (chronic) level is set to 1.4 ppb for an average over a lifetime for both the ESL and the AMCV.

So there you have it.  You could be exposed to 180 ppb for up to one hour with no adverse health effects and as long as your average (for a lifetime) does not exceed 1.4 ppb, you should have no adverse health effects from Benzene.

That's how it works.

Now go check the TCEQ's ambient air monitoring web site to see what the one-hour levels for Benzene are. (make sure to check; measured in ppb-v, clear all checkboxes, check benzene, generate report)

I'll wait.

See?  Feel better now?

So just so we are clear on this.  The AMCV is the ReV.  The ReV is based on the most sensitive adverse health effect relevant for humans reported in the literature.  The ESL is 70% lower than the AMCV.

Next Post: Air Quality in the Barnett Shale - Part 19: Dr. Sattler's Deposition - Down with bad science!

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