Examples of radioactivity in nature
November 23, 2005 6:54 AM   Subscribe

Are there any animals that have evolved a use for radioactivity? If so, what ways is it used? If not, why has this not happened?

Creatures have evolved that can use electric energy to search for food or stun their prey. Animals have evolved the ability to use chemical energy to light up their tails or attract food. Animals are well practiced in symbiotic relationships with chemicals, bacteria and each other, but what about radioactive elements?
posted by 0bvious to Science & Nature (32 answers total)
I would guess that because of the rarity of most of the radioactive isotopes and their damaging effects on an organsim's DNA would be the reasons this hasn't occurred. I could be wrong though. Maybe it has occurred and we just haven't found it yet.
posted by LunaticFringe at 7:00 AM on November 23, 2005

I'm assuming here that you're not counting human beings as animals?
posted by mr_crash_davis at 7:00 AM on November 23, 2005 [1 favorite]

I'm no biologist, but I think it has to do with the tenancy of radioactivity to break down cells at a very low level (DNA) combined with the difficulty of controlling radioactivity. Lead, which makes a great shielding material, is extremely poisonous, as are may radioactive materials. Plus it's almost impossible to find naturally occurring radioactive materials and purifying/concentrating such materials is very difficult and usually involves more toxic materials.

For example, the depleted uranium ammunition used by some troops in Iraq is considered dangerous not because it's radioactive (it's "depeleted") but because uranium 235 is really, really toxic. So the toxicity barrier would be the first thing an organism would need to overcome.
posted by GuyZero at 7:06 AM on November 23, 2005

Response by poster: Oxygen is dangerous if used in excess... Surely there are some forms of radioactivity that life could harness?

(OK, so humans are animals too, but...)
posted by 0bvious at 7:09 AM on November 23, 2005

in some sense they have, if the rate of mutation of dna due to radiation is significant. presumably evolution fine-tunes its own process to evolve at the best rate (too fast and your population has too many useless freaks, too slow and someone else beats you to the ecological niche - either way that particular balance is selected against).

but to extract useful energy from radioactivity is difficult. you seem to need both high purity and large quantities of radioactive material - it might be that few or no animals are large enough for that to be possible.

also, i think (i'm not 100% sure of the physics, which is bad, because i probably knew this once) that there should be a correlation between decay rate and energy of the products. in other words, things that decay fast enough to be useful probably tend to emit high energy radiation/particles. high energies are difficult to deal with - they tend to damage things.

for a science fiction novel, one might imagine huge sea-dwelling (or space-dwelling!) animals that filter water for heavy hydrogen and then have some form of cold fusion...
posted by andrew cooke at 7:11 AM on November 23, 2005

Surely there are some forms of radioactivity that life could harness?

What you have to consider is that anything radioactive enough to be poisonous or detrimental to prey is most likely also going to be detrimental to the host on a cellular level. Things like poison or electricity can either be non-toxic to the host due to concentration vs. body mass or by shielding, but with radioactivity your body mass will not matter and any shielding my also be poisonous.
posted by spicynuts at 7:12 AM on November 23, 2005

also, you could imagine "radiation-hardened" sealife existing at deep depths, where the water is very cold except near areas heated by radioactive decay. i don't know if such conditions exist on the earth, though,
posted by andrew cooke at 7:17 AM on November 23, 2005

This isn't quite what you're talking about, but don't I remember there being some plant that lived in radioactive waters that used the heat produced? I seem to remember it actually filtered for the particles and then benefited from the heat of the self-made deposits of radioactivity. Very difficult to search for because plant=green life and plant=energy factory. I did find mentions of algae and bacteria that can live in radioactive water, but nothing about how they might use the radioactivity. This one says that spirulina binds to radioactive substances.
posted by Mo Nickels at 7:21 AM on November 23, 2005

I assume the giant ball of fusion which we circle around once a year is not considered radiation for the purpose of this question either?
posted by Pollomacho at 7:29 AM on November 23, 2005

Actually, I have read about an organism (a bacterial?) which was found in a location over a natural uranium deposit which was using radioactivity as an energy source. Actually, I can't remember if the organism was using the radioactivity directly, or indirectly by using the heat created by the uranium deposits. If I can find the book(s) where I saw the account, I'll post the info.
posted by tdismukes at 7:35 AM on November 23, 2005

Species have evolved to use radioactivity to maintain specific mutation rates — an evolutionary clock.

Species that don't mutate can't evolve and go extinct. Species not hardened with repair enzymes to handle too much mutation die of cell failure.

In this sense, as a population, species have evolved to use background radiation to maintain a mutation rate sufficient for further evolution.

Some species are hardened to higher levels of background radiation than others.

I think you're asking if radioactive materials can be used in metabolic pathways. The answer is yes, but I don't know of any examples where the radiation itself is the source of energy.

We often eat food with various fractions of natural radioactive isotopes in them. Likewise we use "tracers" in medicine. In either case the body will take in these radioactive isotopes and metabolize the compounds they are in, exactly like their non-radioactive brethren.
posted by Rothko at 7:38 AM on November 23, 2005

Deinococcus radiodurans can survive very high levels of radioactivity. It doesn't use it directly, but I guess you could say that it 'uses' the radioactivity to keep competitor organisms out.
posted by atrazine at 7:39 AM on November 23, 2005

D. radiodurans, from the linked articles, seems to be resistant to radioactivity as a side-effect of being able to survive long periods without water (dessication resistance). Apparently, dessication and radiation have similar effects on bacteria when it comes to damaging DNA. So that seems to be more of a coincidence than actually using radioactivity.
posted by GuyZero at 7:54 AM on November 23, 2005

radioactivity and dna don't play nice together. from my understanding certain levels of radiation can split strands, destroy the sugars in the dna and alter the structure of the nucleotide bases. this is partially what happens in radiation therapy in cancer treatment.

it's not an animal but there is an extremophile bacteria called Deinococcus radiodurans that has high resistance to radiation by having rapid dna repair mechanisms and multiple genomes. i guess it can be argued that it is using this radiation in able to survive and therefore reproduce in an environment where there is lack of (or, at least, very little) competition.
posted by tnai at 7:55 AM on November 23, 2005

Species that don't mutate can't evolve and go extinct.
Maybe nit-picking, but it's not necessarily the lack of mutation. All species have mutations over time. It's a matter of the right mutation at the right time to allow for that species to live on (aka, the random chance part of evolution which some ID's have a problem with).

I didn't mean to derail, so here's some thoughts:
In my biochemistry studies of anabolic & metabolic pathways, I never saw anything resembling direct use of radioactive particles. Not only is the radioactivity in of itself a bad thing as already well-described above, but you also have to remember that the breakdown of particles releases massive amounts of energy and heat. Though just speculation on my part, one of the reason cells don't (or possibly very rarely) use fission or fusion is because they can't maintain equilibrium with such a massive release of energy. And then even for fission, there are radioactive isotopes to worry about.
Also, you have to differentiate between steady-state and changes in environment. The given examples of animals which live in a radioactive environment survive because they live in a steady-state of high heat/energy and have adapted as such. Maintaining equilibrium without massive fluxed of energy/heat isn't the biggest problem around; maintaining it with massive fluxes which would happen from internal radioactive processes thus throwing off equilibrium is a larger problem.
posted by jmd82 at 7:57 AM on November 23, 2005

All species have mutations over time. It's a matter of the right mutation at the right time to allow for that species to live on (aka, the random chance part of evolution which some ID's have a problem with).

All I'm saying is that radioactivity is one driver (among many) of mutation, and an important one, insofar as different levels of radiation have driven evolution of different repair mechanisms, in order to maintain a specific mutation rate.

In this sense, all living organisms use radioactivity.
posted by Rothko at 8:13 AM on November 23, 2005

Bacteria evolved since 1953 to live in highly radioactive environments. That is evolution, and that is a survival trait; being able to live where others can't means no competition.

The reasons why there aren't more examples are several-fold: Radioactivity is rarely concentrated in the wild - if your species depends on radioactivity to survive, your range of habitats is very small. Radioactivity has little effect on chemical reactions, which is what most of life uses most of the time. (That is, since radioactive U-235 and stable U-238 are both, chemically, Uranium, how is an organism to selectively retain one of them via a chemical process? Can't.) And radioactivity is difficult to identify using the senses that have evolved in the animal kingdom - "unnatural heat" is the only one that humans can use to identify radioactive materials, and few radioactive materials are "hot" enough to be physically hot. Plus of course radioactivity is destructive to DNA molecules.
posted by jellicle at 8:21 AM on November 23, 2005

I can't back it up, but heard that the amount of K-40 in bananas helped increase the amount of mutation in apes and their descendants.
posted by CrazyJoel at 9:00 AM on November 23, 2005

K-40 is certainly the main source of radiation in most living things. In fact you get a bigger dose of radiation from eating a walnut (high in potassium) than you'd get if you sat outside a nuclear power station for a year (or so I recall hearing once).
posted by edd at 9:32 AM on November 23, 2005

"In this sense, as a population, species have evolved to use background radiation to maintain a mutation rate sufficient for further evolution."

I have to take great issue with this assertion. First, it's asserting group selection, which is very shaky (or non-existent). Second, your statement is extremely teleological.
posted by Ethereal Bligh at 10:18 AM on November 23, 2005

Perhaps a type of creature that generates radioactivity itself, thus being in the presence of a similar kind would be relatively unharmed?
posted by vanoakenfold at 10:21 AM on November 23, 2005

I don't think anything can create radioactivity itself. Actually, I'm sure of it. All known biochemistry happens on the molecular, not the atomic level.

That said, some organisms (walnut trees, apparrently) sequester elements that happen to be particularly radioactive. But they wouldn't change this behavior if they happened to hvae a bunch of pure K-39. They can't choose based on that single neurtron.

I've heard the story about the uranium "reactor", and I think I remember that it is an exploitation. The bacteria tend to concentrate the uranium, which keeps the reactor going at a reasonable rate. And thus keeps them nice and warm.

But I don't know about that. It's probably the clay surrounding the reactor, not the bacteria. But if the bacteria make the clay (which they may well), then you've got your manipulation-of-radioactive-compounds story. (But not your "they-make-radioactivity" story.)
posted by metaculpa at 10:53 AM on November 23, 2005

I have to take great issue with this assertion. First, it's asserting group selection, which is very shaky (or non-existent). Second, your statement is extremely teleological.

Species carry genes for DNA repair enzymes, which is hardly a shaky assertion. I don't know what your group selection has to do with it, but species without repair enzymes don't exist, empirically.

Mutations that don't propagate are deleterious; mutations that propagate are either neutral or beneficial.

Given the known deleterious effects of radiation, species that carry genes for DNA repair propagate, while species that do not have said genes don't survive to reproduce.

Empirically, selection is on whatever level necessary to keep those genes around. Call it whatever you want.
posted by Rothko at 10:57 AM on November 23, 2005

One of the most radioactively contaminated areas in the US is the swamp surrounding the Savannah River Site in South Carolina. The Cs-137 content is so high that the Department of Energy monitors it by flying a detector-loaded airplane over it. Also, even in the summer, the water can be 10 to 15 degrees warmer than normal.

Although the sample harvests occasionally snare a two-headed frog or a deformed fish, the numbers are not statistically different from fresh water. The reason most often given is that mutations don't often survive.

However, the wildlife sampled is very much larger than normal for the area. The algae content of the water is higher and much richer in nutrients than usual. The fish and frogs have a veritable smorgasbord to eat each day, every day.
posted by mischief at 11:00 AM on November 23, 2005

i just realised that in my previous answer i muddled radioactivity and nuclear processes. the high purity/concentration leading to large size assumes you want an animal to construct a self-sustaining nuclear (fission) reactor (one way to detect development of nuclear weapons is to look for the large plants used to process uranium).

if you just want to exploit the energy released during radioactive decay then this is irrelevant.

incidentally, on a similar line to the "what about the sun?" argument, anything that requires a molten earth core (eg earhquakes, geysers, hot ocean vents) indirectly relies on heat from radioactive decay (otherwise the earth would have cooled to a solid by now - there's a related famous argument by Lord Kelvin that, not knowing of radiation, argued for an early age to the earth and so caused problems for evolution and geology; see here (pdf))
posted by andrew cooke at 11:12 AM on November 23, 2005

although if you don't have a nuclear chain reaction, i suspect that the amount of energy released per gram of raadioactive substance would give you an animal with insufficient energy to move itself. the energy density (more correctly, power density, i guess?) looks like it will be pretty low.
posted by andrew cooke at 11:14 AM on November 23, 2005


"For example, the depleted uranium ammunition used by some troops in Iraq is considered dangerous not because it's radioactive (it's "depeleted") but because uranium 235 is really, really toxic."

Derail, but this is a persistant misconception. DU munitions are considered not radioactively dangerous presumably because it is convenient, not because it's true. (The toxicity is in addition to this)
Depleted uranium is not "depleted" of radioactivity, it is depleted of the U235 isotope (from about 0.7% in natural uranium, to 0.3-0.5%, ie about 50%). However, all the uranium isotopes are radioactive. (U235 is special because of its structure - when split in a reactor, it releases enough neutrons to sustain fission, not because of some threshold of radioactivity). Depleted uranium, in terms of a descriptive name, instead of a technical name refering to a refining process people are unfamiliar with, would be called purified uranium. U235 has the stronger gamma signature, so depleted uranium is harder to detect from a distance (so you could say it's diminished in that sense), however the main radiation danger from uranium (be it enriched or depleted) is alpha radiation, not gamma. While alpha is normally easily shielded against (eg paper, or a few inches of air), it is far far more damaging to cells than gamma (it has higher energy by orders of magnatude). While gamma can and does damage DNA, alpha particles make utter puree out of it in comparison. Since the alpha is relatively harmless when it's emitted from a lump of metal outside the body, DU munitions are pretty safe to handle and fire (perhaps just avoid scratching off the paint and eyeball it :-)). But if you inhale uranium (such as being in the vicinity of where the munitions hit and vapourize), you have an active alpha emitter inside your body, and suddenly the harmless alpha particles are more destructive to cells and DNA than strong gamma radiation. That's in addition to the heavy metal toxicity.

Basically, pure uranium (depleted or otherwise) is just not particularly radioactive. There wouldn't be all that much safety difference between using natural non-depleted or depleted uranium for munitions.
Munitions use depleted uranium because it's so cheap for such a heavy metal (it's nuclear waste, the energy industry normally has to pay to get rid of it), not because "depleted" makes it safer. If things were reversed, and natural (non-depleted) uranium were vastly cheaper than depleted and other super-heavy metals, then non-depleted uranium would almost certainly be used instead of DU.

Whether uranium munitions are depleted or not is not especially relevant to the radiological danger. (And that danger, while not terrible, is also not nothing).

"Depleted" just isn't a word to point to when saying DU is/isn't radiologically harmless. It doesn't mean "depleted of radiation", it's jargon for purified uranium with ~0.3% less U235 than the natural mix of a U235-rich uranium metal.
posted by -harlequin- at 11:49 AM on November 23, 2005

The most obvious place where life may have used nuclear energy would be ultra-simple lifeforms using the heat of a nearby natural reactor. In theory, they ran long enough for some evolution to take place too, however, natural reactors haven't been around for a billion years or so, so it's pretty hard to tell :-)
posted by -harlequin- at 12:13 PM on November 23, 2005

harlequin, Thanks, derail or not. I'm don't want to spread misinformation and I definitely appreciate the clarification - hopefully other readers do as well.
posted by GuyZero at 1:22 PM on November 23, 2005

in a less direct way, everything on the planet uses radioactive material. the reason why the earth is still geologically active (unlike the moon or Mars) is because we have radioactive elements in the crust that decay and produce heat, which keeps all the tectonic and volcanic processes going.

without radioactive elements, the earth would have cooled millions of years ago and life, if it existed, would be completely different.

in terms of availability of radioactive elements, there are parts of the crust in central Australia that are naturally quite radioactive. You could make a low level radioactive waste dump in parts of the country and it would actually lower the average radioactivity of the soil.

As for direct uses of radioactivity, i'm not so sure.
posted by twirlypen at 2:30 PM on November 23, 2005

Plants have evolved to harness ultraviolet radiation
posted by fatbobsmith at 5:06 PM on November 23, 2005

Response by poster: All great posts.... Looks like radioactivity is only indirectly used by animal/plant life.

Thanks a lot!
posted by 0bvious at 9:07 PM on November 23, 2005

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