(NOTE: I will not be allowing any comments except for Avery's to avoid potential distraction from our discussion.)
Avery,
Sorry to suddenly jump out of the comment section, but this post grew too large. Hope you are already enjoying your weekend. Looking forward to continuing this discussion.
Regarding your opening arguments (P1, P2), I completely understand. When you first start an online
discussion with someone, you do not know how much time and care they will spend
on trying to understand your message, so you try to present the strongest
conclusions possible based on a set of unexplained assumptions. This is very
common practice when addressing an unknown audience in a persuasive style.
Consequently, when both sides to an argument do this, the difference between
the sides seems greater because each differing assumption leads to an even more
differing conclusion. However, now that we have established some precedence of
the amount of care we will be using in order to try to understand each point,
we can focus more energy on our differing underlying assumptions (which should
be less different than our differing conclusions based on those assumptions).
Again, I want to thank you for participating in this open debate, because I do
not think this quality of a debate is possible in an anonymous forum.
Anyway, I think I would like to focus on point P4 next, as
I think it represents a significant difference in our views. Accordingly, I
think this post will get lengthy . . . but it is critical to our debate to
delve into this point deeply.
P4) External exposure models can explain internal exposure
risks
P4_S1_P1) Summary of the experiment. Establish that it is
measuring external exposure and that its results are being applied to situations
of internal exposure:
The paper describing this experiment states the following
methods:
- Flood phantoms were filled with Iodine 125 in order to consistently expose mice with gamma radiation.
- The mice were exposed for 5 weeks.
- Techniques were used to test for DNA damage.
The description of the methodology indicates that the mice
were only exposed externally to gamma radiation and were not exposed to
radioactive contamination in a way that they could be exposed internally.
The results are then used to support statements by the
researchers that many residents may have been needlessly evacuated from around
the Fukushima power plant (Supported by P4_S1).
P4_S1_P2) Why was an experiment that better matched the
situation around Fukushima not performed instead?
A more realistic scenario would expose the mice to
radioactive contamination of a mix of gamma, beta, and alpha emitting particles
that would result in internal exposure. Why was the experiment performed so
differently? Let us explore the possibilities:
- Lack of funding? The timely importance of research in this area would imply otherwise.
- Poor experimentation planning? As you pointed out, MIT is a very prestigious institution, and I think this would be a difficult argument to support.
- Biased methodology? Bias is extremely hard to prove and disprove. And, again, we are dealing with a first class institution, let's give them the benefit of doubt.
- Technological limitation? This is 2012. We are practically in the time of flying cars . . . But how WOULD they have tested the mice more realistically? They used flood phantoms to expose the mice because this method is supposed to be very uniform and consistent (I believe the method is used for gamma photography). To have a meaningful experiment, they have to minimize the factors they are testing because each factor adds significant complexity and risk to the quality of the experiment. So they have a uniform exposure source, they have the distance to the source, and they have the length of time. Gamma radiation happily goes through the mice uniformly, as well. No worries about half cooked mice (just kidding, they turned out not so cooked after all, but all died anyway. Sad story.) All this works out great to come to some very clear conclusions using some really simple math.
How many factors would an experiment analogous to the
Fukushima accident require? Let's think of some:
- Radioactive particle mix: Do we know the ratios of all the different radioactive materials released by the Fukushima plant? Well, kind of. The estimates keep on changing, but maybe we can create an accurate model. After all, we do understand how all of these materials decay. Alright, how about how they were dispersed? Well, maybe we do know this, because we have had helicopters map out the gamma emitting contamination (goes down the East coast and curves inland like a tentacle right where my house in Japan is). But what about the alpha and beta emitters? Do we assume they were dispersed the same as the gamma emitters? Maybe not, because we are actually talking about elements with very different atomic weights, so the physics in how the wind might carry them would probably be quite different. Furthermore, just because these particles are radioactive does not mean they are not chemically active. So now our model needs to take into account the dispersion of the various different forms of molecules that might form out of this mess. Some will even be water soluble. . . And you know what, there probably is a range of mixes all over the area. Like radioactive snowflakes, no two areas will have the same mix of radioactive materials. Alright, so we can try to model the most common mixes (or mixes in the highest population densities) and then we will test a range of these mixes. So the radioactive particle mix is really complicated to experiment with, which is unfortunate because this was just our first factor.
- Internal exposure vectors: OK, so we have used some really complicated modeling, but we have come up with a magic set of mixes to test. How should we test? Unfortunately, mice are no longer a very good proxy since we are getting into human behavioral science (can we coax the mice to slide down very small slides while screaming "Weee!"?), but that is not going to stop us. For each mix, we can create a separate weighting of vectors that corresponds to a different demographic segment. So you have different respiration rates for segments with different levels of physical activity. You have different food exposure rates for segments with different eating habits (taking into account food easier to screen vs foods harder to screen). Then you have the 3 year old and under segment that basically puts every foreign object into their mouths (perhaps the mice do not have to be specially trained to represent this segment).
- Bio-concentration: So now we have our experiments running and we have internal exposure occurring. How do we image what area is getting what dosage? Well that is easy. Gamma radiation will just fly through the body and we can detect that with our internal radiation detectors. What about alpha and beta? Not so easy . . . which kind of is a problem because those are the most damaging forms of radiation internally. And this is a really critical factor because it determines which types of tissue will be exposed to what kind of dosage (different tissues have different risks). Without this, we do still know some bio-concentration tendencies (cesium to muscles, strontium to bones, iodine to thyroid glands), but certainly there remains a lot of unknowns or, at least as pointed out above, we cannot just contaminate a mouse and take a picture to easily show where everything ends up in every case (i.e. alpha and beta). Perhaps we can methodically expose different mice to different alpha and beta emitters, remove each organ, and search for trace elements (let's hope the spectroscopy guys have not been goofing off and this is currently within our reach). Tedious, but possible. However, how accurate will this mouse model be for humans? And we are not just dealing with pure elements/isotopes but molecular variants. Those are a lot of variations to test where in the body they will end up.
- Time: 5 weeks is a long time, but you cannot just "turn off" internal exposure like you can external exposure. Even if the radioactive material gets expelled by the body, it isn't necessarily contained and could likely enter another body at some point, or even the same body (an appetizing thought . . .). So what is the time limit? Probably more than 5 weeks, but no more than 10 half lives of the radioactive particle with the longest half life. That can be quite a range . . .
- Tissue propensity for carcinogenesis: Tissues that regenerate more quickly will be higher at risk of DNA damage since mitosis is when the worse damage can occur. However, the extent of DNA damage to a single cell does not necessarily have a positive correlation to carcinogenesis. It has to be the right type of damage, so we have to be sure to include that in our model, as well. Additionally, certain tissues may have a higher propensity to different types of radiation.
- Biological half-life: Of course, another critical factor to specific tissue dosage amount is time. This is determined by how the body interacts with the various forms of radioactive elements/isotopes (including various molecular forms), which depends a lot on bio-concentration (is bone tissue pulling it in or muscle tissue?).
And though I have probably left a lot of factors out (again,
finance guy here. . . no one is going to give me a lab coat anytime soon . .
.), just going through the above really gave me a sense of why the MIT
experiment was done the way it was, and, in fact, why exposure risk models
focus on external exposure measurements. We, as a species, are just not capable
of doing any better at this point of time. The MIT experiment represents our
state of the art. They did what was feasible with our current techniques.
Agreement Proposal: "The reason that internal exposure
experiments are not performed is that the technology currently does not exist
to do so accurately and in a way that will provide meaningful results."
So back to: P4) External exposure models can explain
internal exposure risks
So fine . . . it is REALLY hard to create an internal
exposure risk model because of the crazy number of different variables and the
inability to detect the most damaging forms of radiation within the body. We are
just human, so let's just do the best we can do with current technology. Well,
the problem is that the same level of contamination that results in low doses
when external also results in extremely high doses to extremely small parts of
tissue when internal. Why is this? Because the distance to the exposure source
is a critical factor to dosage. When you go from meters to micrometers, the
dosage to the effected tissue skyrockets, especially when talking about alpha
and beta emitters which release much higher energy over short distances than
gamma emitters. OK, but we are talking very small tissue sizes, right? Maybe
hundreds of cells at a time? What is the big deal? Well, it only takes one
cell's DNA damaged just the right way to cause cancer. Alpha and Beta radiation
does the most internal damage, but our current models and experiments cannot
even take those forms of radiation into account. Sure, external exposure models
deal with radiation, so it is kind of on the right track. But when trying to
explain internal exposure, I get the feeling it is closer to phrenology than
MRI imaging.
Agreement Proposal: "External exposure models cannot
explain internal exposure risks, but they are the closest thing we've got so
that is why we use them."
Again, looking forward to your comments. Please let me know
which points you can agree with and which need more discussion.
