Mold

Mold questions probably compromise 10-15% of the 1500 questions NEDCC
answers through field service each year.  I just read a very
thought-provoking paper by Mary-Lou Florian ("Conidial Fungi (Mould)
Activity on Artifact Materials--A New Look at Prevention, Control, and
Eradication," Preprints of the 10th Triennial Meeting, ICOM Committee
for Conservation 1993, pp. 868-874 (avail. from Allen Press, Inc., FAX
913-843-1244, Lawrence, KS 66044).  I also talked to Mary-Lou about
questions that paper and her week-long course at the Campbell Center had
raised for NEDCC staff.  I absolve her of all responsibility for what I
pass on, and refer any readers to the original paper, since I may have
gotten things wrong, and Mary-Lou is impeccable about the information
she provides.  I did think, having done this for our staff, others might
find it interesting.  Comments and corrections are welcomed.

A little-recognized and critical factor in mold outbreaks is the
behavior of the "spore" equivalent (conidium) in the types of fungi that
are most frequently found in conjunction with collections materials.
This can be dormant due to the condition of the spore (endogenous or
"constitutional" dormancy) or the environment (exogenous or
environmentally-imposed dormancy).  Exposure to temperatures between
about 104-167 dg F; freezing; and exposure to chemicals commonly used in
conservation treatment in *very low concentrations* (organic solvents,
detergents, and others) can alter the endogenous conditions of the
conidium in poorly understood ways, potentiating its activation *under
favorable environmental conditions* for that form of mold.

One of the most interesting parts of the paper for me was the discussion
of the importance of moisture content of materials in precipitating or
supporting mold growth.  This appears to be more important even than
RH--if the substrate contains enough water, and if it can pass through
the substrate to the conidium (the nature of some materials produces a
reduced rate of osmosis of water), and if there is a large outbreak of
mold, the mold colony itself may store enough water to continue growth,
even when RH is significantly reduced.  Presumably that's an underlying
reason wet material is so vulnerable to mold.

    1.  Alcohol and other organic solvents as activators:  At about 10-2
        M, which is in the ppm range, these can potentiate conidial
        growth.  At the practical concentrations of lab treatments,
        these solvents are biocides, and will kill mold and conidia.
        Mary-Lou worries about contamination as a source of
        post-treatment mold potentiation.  I assume if a sink or tray is
        inadequately flushed, and contained an alcohol-water mix, it
        would be possible to accidentally expose another object in
        treatment to the small concentration of solvent that would
        potentiate growth.

    2.  UV levels for fungi kill:  Mary-Lou referred me to some "old"
        papers from Israel that document that levels of UV effective for
        mold eradication can cause substrate (paper?) damage. Apparently
        this is sufficiently well documented as to make UV an
        inappropriate approach, and I won't pursue it in the literature.

    3.  Can non-aqueous deacidification precipitate mold growth?  In
        theory, because alkaline salts and solvents can activate
        conidia, and because some alkaline salts may enhance mold
        growth, yes.  There is no clinical experience or literature that
        confirms this in the real world.  It would be good to keep this
        in mind when tracking causes for mold outbreaks in client
        institutions or treated objects.

    4.  Temperature effects on fungi:  Under dry conditions, temperature
        of about 98-99 deg. F appears to kill conidia.  Slightly higher
        temperature (about 104-167 deg. F) can activate conidia and
        potentiate mold growth. This would suggest that in an active
        outbreak, if you could keep temperature between about 98-100 and
        dry out the object or space, you would kill mold rather than
        increase growth.  The trick is that if the substrate on which it
        grows or the colony itself contains enough water, the 98 deg.
        temperature may not kill.  Here again, nobody appears to have
        tried this for practical or experimental in situ mold control. I
        believe our normal recommendations to dry out under cool
        conditions with good air circulation in a room that prevents
        recirculation of mold spores throughout additional spaces remain
        sound.  I always tell people with central/mechanical air
        circulation to block the uptake vents if they're working with
        mold, to reduce distribution of additional spores or conidia
        through the air handlers.

    5.  Protocols for treatment/treatment choices for mold:  Clinical
        experience, whatever is known about the object's home
        environment, and common sense should dictate.  There is
        insufficient research or experience to make recommendations.

    6.  Chitinase as an enzyme treatment for mold:  This is an empirical
        recommendation based on microbiology research.  Chitinase
        attacks the connection between the cell wall of mycelium and the
        cell wall of substrates (I think).  Mary-Lou extrapolates that
        the enzyme would thus release mold, but notes that we don't
        actually know the locus of the pigments produced by mold in
        substrate structures.  She says evaluating this would not be
        taxing--just basic microscopy--but apparently no one's done it.
        Chitinase treatment would be experimental, but based on the
        experience of microbiology might work well and might be
        preferable to chemical bleaching treatments.

    7.  Sterilization:  Mary-Lou stresses the importance of
        sterilization of tools, materials, and work surfaces in
        conservation labs.  Apparently starches are loaded with conidia,
        and adhesives should be sterilized and kept sterile; obviously
        so should implements used in their manufacture and application,
        and other tools and materials that come in contact with them.

    8.  Environmental control:  This is still our fall-back position,
        and very important for a host of reasons, but given the
        difficulty and expense of excellent control, we have good
        reasons to explore alternative preventive and intervention
        strategies.

If anyone has practical or experimental knowledge in any of the areas
above, I'd very much appreciate hearing about it.

Karen Motylewski
Northeast Document Conservation Center
100 Brickstone Square
Andover, MA 01810
508-470-1010

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                  Conservation DistList Instance 7:45
                Distributed: Thursday, December 16, 1993
                        Message Id: cdl-7-45-009
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