Mycoremediation

I was reading (well, someone quoted to me) a passage from what I understand is an educational book aimed at young teenagers about how radioactive waste can be “eaten” (the author's word, not mine) by fungi.

Leaving aside the gross oversimplification, this did get me thinking about the implications of fungi for bioremediation. I mean, in the case of “radioactive waste”, you are still going to end up with the same isotopes with the same decay rates, so even if fungi are going to bioaccumulate the radioactive isotopes, you still end up with the same quantity of radioactive isotopes (because physics), but possibly in a state you can gather and possibly reprocess (which might also apply to some heavy metals) or dispose of in a less hazardous fashion – although this would involve a permie in partnership with someone who could handle the reprocessing, which starts getting complicated.

The thing is, there is a broader question about the use of fungi for bioremediation. Presumably this is only going to work if you have a substrate the fungi will grow on. I mean, fungi will take on some tough materials (lignin chains, heavy hydrocarbons; Paul Stamets has some stuff on this), but what are the realistic limits for removal of heavy metals, radioactive isotopes and natural (eg juglone) and artificial (there must be some energy in the triazine (used as the basis for several pesticides, as well as in other industries) ring, for example, but maybe aerobic bacteria would be more suited to that problem) toxins? How much of this would be a matter of locking substances up in a non bioavailable form (or, presumably, if you're not careful, the opposite!!!), how much of it might involve actual decomposition of toxic substances (not relevant with heavy or radioactive elements, obviously) and how much of this is simply a matter or creating more toxic waste that you have to cart away?

EDIT: I want to add that there's another thread on this subject with a lot of unsourced assertions that I would not want to put to the test as regards mushrooms locking up heavy metals in a non bioavailable form. Can anyone provide evidence on this? I know we're not supposed to ask for citations, but I think this is one case where safety dictates we need to be looking at good research.

myco handling of radiation in Japan today

Stamets on Fukushima

mushrooms and Chornobyl

Those three links should give you some solid research that is already available on this subject.

I know it isn't as serious as radiation, but we are looking at using mushrooms as a "filter" for runoff from the road that will be coming through our property and around the utility poles to keep the "treatment" from leeching into the surrounding soil. We are also looking at a mycofilter for our greywater system. Any ideas for the best types? How reliable are the reports that filter mushrooms are still edible?

One of the best mushrooms for filtering things like road run off and grey water systems is the oyster mushroom.

When you use edible mushrooms for remediation filtering you have to remember that the fruits will contain many if not all of the contaminates that you wanted them to filter out.
If you also plan to eat these same fruits, you need to know that you will be eating those contaminates so some of that uncommon resource (common sense) should be utilized prior to consumption of said mushrooms.

In the case of Radiation, it is simple, you do not eat that which will kill you.
In the case of remedial filtering mushrooms, I personally do not eat the fruits that were produced by those filtering spawns I installed for the removal of contaminates.

You could gather some and submit them to a lab for contaminate testing first, that way you can make a truly informed decision on whether or not to eat those particular mushrooms.

Neil Layton wrote:mushrooms locking up heavy metals in a non bioavailable form.

I personally don't see how that could work. I think you would have to remove the mushrooms, because as soon as they die and decompose, the metals would return to the food web.

@Bryant R.: "When you use edible mushrooms for remediation filtering you have to remember that the fruits will contain many if not all of the contaminates that you wanted them to filter out."

Yeah, I would agree with this. The different species will vary in whether, and the extent to which, they will be able to transform the toxics of concern to less harmful chemicals. That will make it a crap shoot as to how much of any toxic compound remains in the edible parts of the 'shroom. But as noted, if you really wanted to consume from these locations, it would be prudent to have it tested. Radionuclides are a different story as they will not be transformed and will still need to decay to their resting state. In both cases, however, if the concern is further movement of the toxic from it's current location, one could imagine a rhizosphere/mycosphere that may do a better job of immobilizing the toxic compounds so that there is reduced availability to other biota and resistance to translocation from the contaminated site.

@Tyler L.:"... as soon as they die and decompose, the metals would return to the food web. "

It's conceivable that, given a dense network of dying and re-emerging hyphae of one massive mycelium with affinity for that particular heavy metal, the minute a heavy metal atom/complex is released from a decomposing hyphae, it is taken up and re-sequestered by a young one from the same mycelium. Can't imagine this has been carefully studied in nature, but I would not be surprised if it has been tested in the laboratory.

My two bits:

Fungi across phyla and niches are known to break down a range of persistant compounds. Most research has focused on white rot fungi as they are the only things in nature that can break down the complex and persistant lignins in trees/woody plants. Lignin is a large 3-D phenolic compound that is water (and enzyme) repellent. Fungi break down lignin through a multi-step oxidation process by releasing free radicals that disasemble lignins. This same oxidation process coincidentally works on industrial phenolic compounds and others with aromatic rings. Though I have not found a study on fungi vs juglone, I would bet a lot of money that a white rotter could break it down as it is a simple two-ring chemical.

During the degradation process, the fungus may accumulate some of the compound in its tissue. The by products of the degradation may be inert or also toxic.. it depends on the parent compound. The fungus may not break it down 100%.

For metals, many soil fungi do create insoluble metal complexes through the release of various acids and other compounds. Some of these complexes are quite stable, others are not. Its hard to measure and it influenced by soil pH.

I hope that helps!
Peter