Let's deal with Benzene first, since it is recognized as a human carcinogen.
Lets say I lived in a house that boarders a very large pasture. Surrounding this pasture are three other neighbors. My neighbors and I walk along a well traveled path through the field to the town hall, where we all like to meet nightly to socialize and whittle sticks into pointy spears.
"I heard about him" neighbor 3 says, "He sets up on our town and lets loose bulls and rams in our pasture! I think we need to do a little bit more research before we say yes to this offer."
"Well I just looked it up on the Google," neighbor 2 yells excitedly. "Says on the Internet that living near bulls and rams can bring all sorts of harm. In fact, bulls are known to gouge which can become infected causing death! I have two small children that walk in that pasture! I'm going to have to say 'no' now"
"Hold on a minute!" neighbor 1 says a bit perturbed. "I've been around bulls and rams all my life, and nothing has ever happened to me! I don't know what y'all are afraid of, look at the money we would all be getting? So what if they add some bulls and rams to our pasture. It's worth it in my opinion."
"I have a suggestion" I say. "Why don't we contact one of those Bullologists from the local University and see what an expert has to say."
The next day, a man looking just like a college professor, shows up at our town hall and tells us his name is Professor Paracelsus. "Call me Dr. P" he says with a smile.
"So the concern is over the bulls and rams that this out-of-town fellow will be adding to your pasture," Dr. P says. "I can see you have been researching this on the Internet and have little doubt why some of you are now very afraid. Let's look at the rams first shall we."
"We look at exposure to rams and bulls..." Dr. P continued, "...based on their acute (short-term) and chronic (long-term) adverse effects. We then determine the number of bulls and rams a person can be exposed to - called a dose - and the health effect that will result - called the response."
"Because rams have horns that bend inward they are unable to gouge you if you come in contact with one. No gouging means no infection. Now rams can still cause harm, but you need a bunch of them. One can knock you over, but the only way you can be seriously hurt is if a bunch trample over you.
"Now the number we determine will cause harm is dependent on the population that will be exposed. Young children, older folks, and those that are sick are most vulnerable to being trampled so we set the "safe" amount of rams you can be around daily based on this. This dose-response level is called a threshold or Reference Value (ReV) - a dose below which no effect is observed. In scientific terms, we call this a non-linear nonlinear dose-response relationships."
"Acute ReVs are the number of non-gouging animals a person can be exposed to and are typically derived for a 1-hour exposure time with that animal. Chronic ReVs are are derived for a lifetime exposure duration to non-gouging animals and assume that constant exposure that causes bruising, sprains and broken bone may cause arthritis or amputations in a person's later years."
"So being exposed periodically to rams will allow for a much higher number than if you were to constantly be exposed to them throughout a lifetime. ReVs are designed to protect the most sensitive individuals in a population by inclusion of uncertainty/variability factors (UFs). UFs account for differences between the test populations we study, variability within the human species (football players take less damage than ballerinas), and uncertainties related to the applicability and completeness of the available data. Since UFs are incorporated to address these data gaps, variability, and other uncertainties, exceeding the ReV does not automatically indicate that an adverse health effect would occur."
"So how many rams could my children and I be exposed to?" neighbor 2 asks.
"Well, based on what data is available, your short-term level is 14 rams and the long-term level is 9 rams. So your kids should be safe as long as the number of rams they are exposed to periodically is below 14. And as long as it does not go above 9 rams each and every day, there should not be any short or long term health effects at all."
"Well that's all well and good for rams," neighbor 3 says. "But what about them bulls! All it takes is one to gouge you and you could get an infection and die!"
"Well...in a round about way," Dr. P. responds. "Gouging is a bit harder to give a "safe" number for the animal since all it takes is one. That's why with animals that can gouge we use the term relative risk as the safe level."
"Oh, you mean that one in a hundred-thousand infection nonsense? neighbor 2 pipes in. "Yeah...safe huh? How would you like your child to be that "one" that does get the infection and dies?"
"Er...yeah, that's what it sounds like, but that's not how it works," Dr. P. says. "What we do is use mathematical models which are based on human and animal studies to estimate the probability of a person developing infection from being gouged while exposed to a specified number of that particular gouging animal. A range is then calculated for the increase in the lifetime risk of an individual who is continuously exposed to that particular number each and every day over their lifetime."
"So the Center for Horn Gouging has estimated that continuously walking in a pasture with 7 to 9 bulls would result in not greater than a one-in-a-hundred thousand increased chance of getting an infection. Now remember, that's an increase chance, it is not a given. And even if you were to get an infection, it can often times be cured or is very slow in developing."
"Still, I don't like it!" neighbor 3 says adamantly. "This out-of-town fellow is going to be bringing rams and bulls into our pasture. If we say "no" we will not be exposed to any bulls or rams."
"Not so fast," neighbor 1 says. "You have been walking in this pasture for a long time now. We have bulls and rams living there and - up till now - you have never paid them any attention or concern! Every pasture you walk through is going to have some type of animal that can cause you harm."
"That's correct," Dr. P. interjected. "You cannot escape exposure to gouging and non-gouging animals. They are everywhere you go and are part of your everyday existence. As long as this out-of-town fellow uses proper bull and ram reproductive prevention devices, living with this increased exposure will present no immediate health concerns from their presence in your pasture."
"Well I still don't like it," neighbor 3 says.
"That's understandable" Dr. P. reassured her. "But until we find a better way to do without them, these types of risk will always be with us. My job is to present you with factual information. Your job is to weigh the pros and cons and to make sure that out-of-town fellow does everything he possibly can to minimize your risk. You can say "yes" and be safe, but that fellow has got to do his part in making sure his bulls and rams stay well confined and in small enough numbers so that you are not harmed."
"Oh, and stop reading stuff on the Internet unless you know it's from a reliable and reputable source. There are a lot of people out there with an agenda that will mislead you to believe what they want you to believe."
Next post: Air Quality in the Barnett Shale - Part 9: Dose and Dogs
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