Limitations to mould growth on museum collections in hot, humid climatic conditions : the possible role of variable atmospheric relative humidity

  • Graeme Scott

    Student thesis: Master's Thesis


    This study investigates the possible role of climatic variability, natural or induced, in preventing mould growth on museum collections in tropical environments. The report questions preconceptions about tropical conditions and reviews published information about relevant subjects. The terms used are defined. Factors influencing mould growth in tropical regions, including climatic conditions, are then discussed before four hypotheses are proposed. The experiments designed to test these are explained and their results are presented. Statistical analyses and physiological details of mould species found at a site in Queensland are presented in appendices.
    From testing the hypotheses the conclusions were:
    • germination of mould spores takes longer if the water activity of a substrate is lowered before inoculation
    • atmospheric conditions which vary in a daily cycle between 50% and 90% RH produce lower average growth rates than constant conditions of the daily average RH of the cycle
    • lower average growth rates result from cycles with relatively long periods at RH levels below the minimum required for growth - though relatively long periods close to optimum growth conditions within a cycle will negate this effect
    • minimum levels of RH in cycles cannot, in themselves, be used to predict the potential for growth in any particular circumstance - the previous three conclusions must also be considered From the physiological data published for the mould species tested and from the experimental results, the following can be stated:
    • At optimum RH conditions, there is a minimum delay before germination occurs. For the species tested the shortest time before germination occurs is between 12 and 48 hours at around 90%RH. Germination of some species may therefore occur only during daily cycles in which RH remains high continuously for longer than 12 hours. Germination is less likely to occur in daily cycles where RH is lower on average and more variable in extent and rapidity.
    • Should conditions favourable for germination and growth persist, lower rates of growth will result from cycles of relatively low average RH and relatively high variability
    • Before an effective environmental control strategy based on this approach could be recommended to museums, more data is required on the detailed effects of these individual factors.
    The general conclusions from the study are:
    • that mould germination and growth is influenced by changes induced in moisture content of surface layers of materials, and not solely as a result of physical movement of air over surfaces;
    • that the daily variations of atmospheric temperature and relative humidity experienced in Northern Australia can, if transmitted to surface layers of balsa wood, extend mould germination times and limit growth rates to a significant extent;
    • that ventilation and air movement may induce changes in moisture content of surface layers of materials by means other than those investigated here.
    Date of Award1999
    Original languageEnglish

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