A bit more detail about spalting....
So Rob-are there spores in the wood, and not toxin??? and therefore safe?? Can the spores make toxin in the woodturner lungs?? Can these spores get into the users lungs when a "finish" may disappear from the bowl years down the road?? Or is there just too few spores that would make toxin??
Does kiln drying do anything to the spores?? Thanks for your expertise, Gretch
Good Questions Gretch!
Growth and Metabolism
In general, wood rotting fungi exist in the wood as thin filaments - known as hyphae (the collective mass of these is known as a mycelium). These are living cells that secrete enzymes and other chemicals into the wood to digest it, and then absorb the nutrients into the filamentous cells for the organism's nutrition.
None of this cellular activity produces spores within the wood (see below). In some fungi, additional products of metabolism are organic chemicals that are toxic to some other microbes, such as bacteria. Thus, fungal sources are where we get many of our antibiotic drugs (e.g. penicillin, streptomycin, etc.). In some cases these additional compounds can be considered toxic, depending on what organisms are being considered. Most wood rotting fungi that I am aware of do not produce aflatoxins or other serious toxins that we need to be worried about.
BTW - the reason why there are spalt lines (i.e. black 'zone' lines) in the wood is that there are different fungal clones or different species growing in the wood at the same time. They are competing for the same resource (the wood and its many carbohydrates and nutrients), and when they come in contact with one another in the wood, they wall-off their own zone from competing fungi with dark-colored compounds, and we are the beneficiaries of this process through the creation of the black lines and other discoloration produced by the fungi as a defensive strategy.
Reproduction
When the fungus organism has matured sufficiently, and the environmental conditions are correct, it wants to reproduce (...or at least try.....like most of us!). To do so it wants to produce cells that will help spread the fungus around the environment. It would make no sense to develop these spore-producing structures
in the wood, so it produces them
on the surface of the wood in a variety of different structures (somewhat inaccurately called "fruiting bodies") which can be seen as mushrooms, bracket fungi, puff-ball like structures, etc. - all of which are on the wood surface and in contact with the air. When the spores mature and are released from these structures, they are carried around in air currents ("wind") to be deposited where they may germinate and grow into a new fungal organism (...they are
not plants!). Because the fungal (or "mold") spores are living organisms, they contain proteins and a few other compounds that elicit an allergic reaction that develops in humans, with severity depending on individual sensitivity. Thus, people DO have allergic reactions to fungi, whether they get their antigens from airborne fungal spores, or from airborne fungal hyphae liberated from the wood through cutting or sanding. This is where turners need to be careful about fungal allergies. If you remove any spore producing structures from the surfaces of the spalted wood, the chances of inhaling spores is greatly reduced. There should be no spores found
within the wood itself (...of course there's always the possibility of surface contamination from external sources of spores, I suppose). Finished and dried bowls and other turned forms should not elicit allergic reactions unless the wood is damaged and inhaled (or otherwise given contact to the immune system). I suppose in hypersensitive individuals there could be some reaction, but this would certainly be an extreme case [disclaimer].
Pathogenicity
Spores from fungi that spalt wood have adapted to decompose
wood and generally do not act pathogenically within lungs. The
Cryptococcus fungi mentioned above are not generally associated with wood or wood spalting, especially in temperate regions. These spores need to be inhaled for them to become pathogenic. While one may have allergic reactions to inhaled fungal spores, it would be an extreme case for spores from wood spalting fungi to germinate within the lungs or bronchial tubes to develop a
bona fide fungal infection (pulmonary mycosis).
Kiln drying of wood would serve to kill living fungal hyphae through dehydration and thermal denaturing of proteins, but likely will
not eliminate the allergenic effects of inhaling dust-borne pieces of fungal hyphae. One would still have to take precautions against inhaling ANY fungal products (hyphae or spores) to reduce or eliminate the chances of developing or inciting an allergic reaction. Kiln dried wood dust could cause allergic response if inhaled, etc. so take precautions with this too.
Perhaps this is more than you asked or wanted to know (?), however I hope this makes understanding spalted wood a bit more easy for the woodturner, and what precautions need to be taken.
(Let me know if there are still questions....)
Rob Wallace
