Sounds pretty scary doesn't it? It's all true too. And if you were to read this in a scientific report written by experts who tout their purpose as helping "ordinary citizens understand, cope with and combat environmental issues" you might have reason for concern, especially if your kid was, in deed, being exposed.
No one wants to have themselves or their family - especially children - forced into a situation where there is "exposure" to a chemical that has scientific data indicating that it is "lethal" or a "neorotoxin" or a "known human cancer causing agent."
So when the citizens of the Town of DISH Texas read a report located on their city's webpage titled "Evaluation of Town of DISH, Texas Ambient Air Monitoring Analysis written by someone who was "Vice-Chair of the EnvironmentalProtection Agency National Advisory Council for Environmental Policy and Technology (NACEPT)" they could not be faulted for coming to the conclusion that the development of the Barnett Shale gas industry in a residential area could lead to immediate or long-term health concerns due to the production of harmful excess air emissions.
Now it is not my intention to say the that there is, or is not, a health concern posed by this operation. The TCEQ indicates that their monitoring "after several months of operation....reinforces [their] conclusion that there are no immediate health concerns from air quality in the area." The sampling performed by Wolf Eagle Environmental indicates concentrations above the TCEQs established short-term and long-term ESLs
Assuming that the Wolf Eagle Environmental data used for the conclusion in the report is correct; does exposure exceeding by "2 times" the ESL for meta- or para-xylene put the citizens of the Town of DISH at risk for "neurological effects" or "kidney injury and renal carcinomas?"
In other words, if a chemical is known to cause a health effect, will exposure to it result in that negative health effect happening? What if the exposure is twice the amount deemed to be a safe level? This concern - valid in my opinion - becomes particularly disconcerting when you talk about exposure to a chemical that is described as a "known human carcinogen" since cancers do not show up until many years later.
It is at this point that a little bit of background information on toxicity and exposure is necessary. For the general public at large - misinformed by those with an agenda or fed information that is misleading, incomplete, or out of context - potential exposure - not of one's own choosing - to a chemical is almost always perceived as one that will or has caused a health effect.
But it is much more complex than that, and both Ms. Subra and Dr. Rich (with an MPH no less!) should have understood this paradigm. At SRPH, we are drilled over and over on what we were told was called the "EPA Risk Paradigm." Unfortunately, the promoter of this paradigm - Dr. K.C. Donnelly - passed away two years ago from pancreatic cancer and was never able to tell us why he called it that. The EPA Risk Paradigm used by the EPA has a much different format and context. The EPA's does not have the elegance of the one Dr. Donnelly taught us. The original author is not know, so in hopes that he/she will not mind, I will henceforth refer to this as the K.C. Donnelly Risk Paradigm:
In a nutshell, just because a chemical is there, or could be generated, does not mean it will result in an adverse health effect. Not only does it need to be released into the environment, it has to travel to the receptor, the receptor has to be exposed to it, and the chemical then has to enter into the body. Even then there is no automatic negative health effect guaranteed since the body does a really good job of ridding these nasty chemicals as well as fixing the problems - including damage to DNA that could result in cancer - even if uptake does occur.
For air contaminants, the first five are easily met. So looking at toluene for example; it is present as a constituent of fuel and petroleum products, so the chemical is present. It is released into the air through exhaust or leaks, it is transported in the air, and if a person is in that path, exposure can take place. Once exposed, the receptor - through breathing - can uptake the chemical through the lungs and into the blood stream. All that is left is to see if the chemical now in the system will produce a negative health effect.
So lets look at our dihydrogen oxide example discussed at the start of this blog. It is a chemical - having a Chemical Abstract Services number (CAS) of 7732-18-5. It is intentionally released by the parent when the faucet is turned on to fill up the bathtub. It is transported through the water system pipes into the bath tub where the child is exposed to it when they are placed into the bathtub. The dihydrogen oxide enters into the child through breathing of vapors - especially if the bath is hot. It is also sometimes consumed orally by the child as well as absorbed through the skin and through cuts and abrasions on the surface of the skin. So uptake does, in deed, take place. So will this exposure and uptake result in an adverse health effect?
This depends on one important criteria for all chemical health effects: the dose.
Now dihydrogen oxide has a median lethal dose (LD50) of >90 ml per Kg of body weight. What this means is that a five year old weighing 20 kilograms (Kg) would need to have an uptake (dose) of 20 x 90 = 1800 ml or 1.8 liters to have a 50/50 chance of the negative health effect of death. 1.8 liters is a little less than drinking a two liter bottle of coke all at one time. Now if the child sits in a bathtub full of this chemical, the amount exposed to (80 liters) is over 44 times the amount needed to cause death! How could you let this happen to little Billy?
Now if you have not figured it out by now, dihydrogen oxide is a fancy chemistry way of saying water. And yes, water has a toxic effect, just like any other chemical out there. Drinking too much water can cause death if the amount consumed is over the LD50 of 90 ml/Kg. This toxic effect is called water intoxication.
So you can see in this example that it is possible to kill a five year old in a bath tub from something other than drowning. In this case, like in the Town of DISH, exposure to a chemical has taken place. But the dose needed to illicit a negative health effect - death - from the uptake of water is quite high, making death by water from other than drowning possible, but not probable.
In the case of a child exposed to water we know two things. One, the safe amount of water that can be consumed (threshold) and two, the amount that will cause a negative health effect - death. Water, is also one of those special chemicals that can cause a toxic effect if two little is consumed as well as too much.
In the Town of DISH, all we know - according to the findings by Wolf Eagle Environmental - is that there are chemicals present in the ambient air and that their concentrations are above TCEQs ESL which are "chemical-specific air concentrations set to protect human health and welfare."
What we need to figure out - and this is where the two reports failed (in my opinion) - is what type of health effects would be possible at the concentrations reported?
If you read the conclusion in both reports, emphasis on the fact that "high concentrations of carcinogenic and neurotoxin compounds in ambient air near and/or on residential property" was found, and "many of the compounds in the air exceeded the Short-term and Long-term Effects Screening Levels (ESLs) according to [TCEQ] regulations." is stressed over and over again This appears to imply that the health effects possible (cancer, neurological) are plausible because of the concentrations exceeding the safe level (threshold) established by the TCEQ in the form of an ESL.
What's in play here is really no different than that of water. the effects may be different as well as the threshold needed to be exceeded, but the basics of exposure - dose - is exactly the same.
Next post: Air Quality in the Barnett Shale - Part 3: TCEQs Effects Screening Levels.
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