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Cherry picking and a challenge to “everyone knows”

OK everyone knows xyz abc blagh blagh blagh, you must have heard it before.

If you are a person who does not want to blindly follow like a sheep by now it must be grating on your nerves just like a person dragging their nails over a blackboard. I want to address this problem of the fallacy and also at the same time consider cherry picking of the literature and data.

I am sure that many people hold the view that plutonium is the most dangerous substance known by man; some might even view it as a blasphemous horror element. It is often thought of by many people as a corruptor of goodness and a destroyer of all that is wholesome and good. It is often thought of as a substance which will extinguish all life forms. I guess by now that you understand what I am writing about.

It is widely assumed that it is a super toxic substance, but when you look at the evidence things are not quite what everyone thinks it they will be. While the fact that internal contamination with plutonium is not healthy, a great debate exists over how unhealthy is it to be contaminated with plutonium and the other actinides.

Some years ago I heard a talk by Mary Neu who works in the USA on plutonium chemistry, she is responsible for a rare study in which the chemical toxicity of plutonium is compared with other (more mundane) metals. What her group did was to grow bacteria with or without toxic metals present in the growth medium. For the paper see C.E. Ruggiero, H. Boukhalfa, J.H. Forsythe, J.G. Lack, L.E. Heresman and M.P. Neu, Environmental Microbiology, 2005, 7(1), 88-97.

She found firstly that the effect of plutonium on soil bacteria was independent of the radioactivity level but dependant on the chemical concentration of the plutonium. She did this by using different isotopes of plutonium. She used a short-lived (238Pu), “normal” (239Pu) and a very long lived plutonium isotope (242Pu). So this suggests that to the bacteria that the plutonium is a chemical poison to the soil bacteria and not a radioactive poison to the bacteria. This was quite a surprise to me.

Next she compared a series of metals; in her test she worked out how high a concentration is needed to stop 70 % of the growth of the germs. I find it interesting that for the two types of bacteria which Mary used that copper and zinc appear to be more toxic than plutonium.

Bar chart of toxicity data for bacteria (Pseudoomonas Putida) for some elements a range of toxicity has been estimated, bars are shown for the upper and lower estimates.

Now the work of Mary Neu is interesting in several ways, firstly it challenges the idea that plutonium is the supreme and universal poison which many people think it is. It also offers an insight into the problem of cherry picking. It is noteworthy that one of the two bacteria which Mary did use is one (Deinococcus radiodurans) which is very radiation resistant.

Secondly, if you were to use Mary Neu’s paper as your only information source on plutonium and living things then you would assume that plutonium is close to harmless. This is clearly wrong; this would be an example of cherry picking. It is far better to use a large and diverse range of serious sources on the subject.

I am aware that a range of different people try to cherry pick data and the literature to suit a political end.

By the way Mary’s biological work is good it would be interesting if as the next step someone was to extend it to a human cell line and the Salmonella strain used for the Ames test.


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