Is there any biological or environmental factor stopping animals or plants to be farmed for their metal absorbing qualities? Consider we are also counting creatures created through selective breeding, forced hybridization and grafting.

10'000 kilograms of pig liver contains 1.79 kilograms of pure iron, the same amount of mussels contains 0.67 kilograms of iron and around 0.37 to 0.8 kilograms when counting leafy greens like spinach.

In order to make metal farming feasible, organisms must absorb and store more iron than that, is there anything stopping life forms from absorbing up to 100 times more iron than the above examples?

I'm using iron as an example but any other similar metal is fine.

  • $\begingroup$ I'm wondering about the use of metal livestock farming : If you retrieve somehow the iron, shouldn't it be remodified again beyond reshaping to make it useable for buildings or tools? I am not a biologist so I can be wrong, but I think there's mostly iron ions in living beings. Or do you have a plan for something else, like cleansing a place from its iron? $\endgroup$
    – Tortliena
    Jul 5, 2021 at 12:44
  • $\begingroup$ @Tortliena bootkick it into a blast furnace, then divide the metal beads and drops from the ashes and carbons. $\endgroup$
    – Green
    Jul 5, 2021 at 12:49
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    $\begingroup$ See this answer: worldbuilding.stackexchange.com/a/15233/19221 (See also the search box at the top of this website, and the search box at the top of your web browser) $\endgroup$
    – Tom
    Jul 5, 2021 at 12:55
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    $\begingroup$ The Tiberium crystals are calling! Without a good reason to store or use the metals, they're more likely to not try to aborb it, or remove it after getting it in the system (excretion). So what L.Dutch is saying. $\endgroup$
    – Trioxidane
    Jul 5, 2021 at 12:57
  • $\begingroup$ @Tom never figured how the search box works, unless I input specific entire phrases or I know the exact title of the question by memory then it won't find anything useful. $\endgroup$
    – Green
    Jul 5, 2021 at 13:02

4 Answers 4


Living organisms are bound to natural selection, which is a harsh mistress and an even harsher accountant: when checking the bills of the expenditure of each organism, any surplus expenditure will be punished if not justified.

This come to answering your question: what is the tangible benefit for a living organism in concentrating that much metal to make it worth spending a lot of energy in doing it?

Don't forget that the homeostasis keeping an organism alive is a very delicate balance of many chemical reaction, in which the slightly excess, both in the too much or too few direction, can be lethal.

Iron is one of the most abundant metal on Earth, and

For every 1 ton of iron ore concentrate produced approximately 2.5–3.0 tons of iron ore tailings will be discharged.

As you can see those figures are waaay bigger from what you quote as iron content in living beings, at least 4 orders of magnitude.

  • $\begingroup$ I used the nutritional values of foods to calculate it $\endgroup$
    – Green
    Jul 5, 2021 at 16:59

Yes, with some hand waving

There are efforts to breed plants that can absorb different types of materials. This approach is called bioremediation. This article covers one approach. You could use a little handwavium to have scientists lab-engineer plants or trees that could slurp up valuable minerals. Then they could be harvested. Each plant would contain a small level of minerals, so you would want to pick a low maintenance plant that wouldn't require much effort to grow.

  • $\begingroup$ could it be a plant which can grow both on land and water, like rice maybe? but that bulbs or seeds or other parts dedicated to storing minerals? $\endgroup$
    – Green
    Jul 5, 2021 at 15:10

Iron, shmiron. If we are going to use biology to make metal we want valuable metal! This is one of my favorite late afternoon musings: how to get bacteria to get that gold out of seawater.


bacteria w nugs

The soil-living, rod-shaped bacterium Cupriavidus metallidurans is famous, biologically speaking, for being able to survive massive doses of toxic metals. Now, new research reveals that special enzymes within the bacteria are responsible for changing toxic versions of gold into inert solid gold, which creates miniature gold nuggets.

The idea would be to farm sheets of bacteria in waters containing trace amounts of valuable elements, then harvest the bacteria and purify out the elements. A big farm of bacteria like the one depicted at river mouths would be ideal. The problem is finding places with adequate concentrations of the metals you want. This is where GMO comes in - augment the bacteria with hugely more metal avidity than their ancestors. That is pretty easy GMO.

Gold will bring in the crazed cash-fat investors but there are other less sexy but more lucrative ions one could collect with this method.

There are many different ways in which biology can sequester metal. I had a scheme once upon a time (oh my gosh so long ago) using antibodies in algae to accomplish this end. https://www.halfbakery.com/idea/GMO_20Ocean_20Mineral_20Harvest#1042218000l


A believable path could be created, but there is no way to justify it in reality

But, then again, why are we here if we're bound only to reality?

I agree completely with L.Dutch's answer. It's hard to see past the efficiency of iron ore.

Here's the problem: the amount of metal bound within a living organism can never exceed the capacity or need of that organism to live its life. As an example, no more iron could be bound within the human body than would allow that body to move to forage, propagate, and live its life. It cannot unreasonably weigh down muscles, it cannot threaten immune systems, it cannot compromise the oxygen cycle or digestion. life, after all, is a delicate balance.

However, people swallow coins and live their lives with bullets in their bodies. Fragments of metal continue in war survivors. I'm not suggesting that any of these general examples suggest it's easy, only that it's plausible for a life form to be believably presented as having a higher metal content.

But, said another way, iron ore will always be a simpler, more efficient way of obtaining iron than farming a biological factor no matter how well crafted to maximize its metal-carrying abilities. The density of iron ore will always exceed the density of metal in living organisms by many orders of magnitude.

But that's boring

I could suspend my disbelief to enjoy a story that required farming living organisms for metal so long as the substantial inefficiency involved was justified. IMO, it's not enough to rationalize higher metal content in living organisms...

...you also have to rationalize why it doesn't exist in mineable quantities — and yet exists in sufficient dispersed quantities — such that it makes sense to farm animals at all. Then, you need to explain why evolution allowed all that metal to bond to living creatures in the first place.

Let's chase that and see where it leads us

Disclaimer: Biology is NOT my strong suit. If someone practiced in the art reads this and find themselves capable of typing a comment to point out my error amidst their convulsions of laughter, I'd be grateful.

Lactoferrin is a nutrient classically found in mammalian milk. It binds iron and is transferred via a variety of receptors into and between cells, serum, bile, and cerebrospinal fluid. It has important immunological properties, and is both antibacterial and antiviral. In particular, there is evidence that it can bind to at least some of the receptors used by coronaviruses and thereby block their entry. (Source)

We have a world that has a lot of iron, but for some reason, that iron is never found in a chunk bigger than the tip of one's finger. It's thoroughly dispersed through the soil, where it can easily be picked up by plants. Plants will draw almost anything from the soil, but I want to jump a step further and justify that extra iron in an animal.

The quote above explains that there is a mammalian protein that binds iron: Lactoferrin. The animal will consume iron via the plants thanks to the high concentration of what we'll call molecular iron in the soil. The lactoferrin gets it into the body and has the potential of keeping it there.

But why?

As L.Dutch said, evolution is a harsh mistress and an even harsher accountant. For example, in humans too much iron can compromise zinc absorption, and that compromises the immune system. But that same link explains that we humans need iron to produce hemoglobin, a protein in red blood cells.

Cool, so why would life on your planet need higher concentrations of hemoglobin? Among its uses, it carries oxygen to cells and carries away carbon-dioxide.

Which means, using suspension-of-disbelief as the criteria, you could suggest that your planet has a higher percentage of carbon-dioxide in its atmosphere, requiring a greater quantity of hemoglobin to better carry in the limited oxygen and carry out the too-abundant CO2, which means more iron is needed... and we have Lectoferrin as one possible rationalization for how to do that.

And as mentioned earlier, it's all because on your planet there are no iron deposits anywhere. Perhaps (and I'm skipping to a simple explanation because I'm out of time to write this answer), volcanism is long-past on your world, and erosion has scattered the iron and bound it with oxygen (helping to rationalize the limited oxygen supply). In other words, your world has rust dust everywhere.

But no iron mines anywhere....


I believe you can rationalize higher metal content in living organisms such that they could be mined for metal. But even with the increases you're suggesting, it's an horrifically inefficient process. This suggests that you need to further rationalize why no iron mines can exist on your world — and binding the two together as cause-and-effect can solve your problem.


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