The four components of biodeterioration are: the organisms, the materials of the collective memory heritage objects, the environment of the heritage object, and the people who come in contact with the heritage object, that is the staff who cares for or the person who uses, or accesses the heritage object. All four components are interconnected and we cannot talk about one without talking about them all.
Preservation is really prevention. To preserve our collective memory objects we must prevent bio deterioration by preventing activity of deliterious organisms; prevent material aesthetic and physical damage; prevent conducive environments that support biodeteriorating organisms and environments which are damaging to the objects; as well as make sure the heritage objects and their environment are not a health hazard to people.
In discussing these components we will be discussing mainly biology, the living and dead organisms and the organic materials of biological origin but we can not talk about them without involving their environment and chemistry. Often in research only one aspect is researched without reference to the whole picture. We must learn to be more interdisciplinary.
In talking about our collective memory and considering my antiquity, it would seem topical to review the history of biodeterioration of archival materials, but today we are having to look at the information available to us from many disciplines and select what is relevant to the problem of biodeterioration. It is often difficult to cast aside trends of the past and look at problems in a new light, but we must. Thus history is not reviewed in this paper but the present status is presented and future directions suggested. Presenting new approaches to solving problem is not a negative critique of past trends.
2 The organisms
The main organisms that are the major concerns with archival, photographs, slides, paper, parchment, leather and textile book bindings etc are insects and fungi. Bacteria may be a problem only if the material becomes wet from a disaster such as fire or extreme weather, or simple condensation.
2.1 The insects
The insects are commonly the booklice and silverfish which are indicator insects. They indicate a environment, micro or macro, with a high humidity. Booklice eat fungi on materials and silverfish graze mainly on starch and sugar sizes or grounds on paper. Both leave a mess behind them. The so called book worms, the larval stages of beetles, are also a problem. They usually utilize oily materials such as leather bindings and gelatin glues, but bore through anything between them and their food. Mites have also been found on old books but their role in deterioration is not clear. They are likely eating either the fungi or the insects present not the archival materials.
Buildings always have their own population of insects. One must have an integrated insect pest management program which includes continuos insect monitoring to determine who and how many insects are present. It also requires that the collections are cleaned of insect evidence so as to establish a zero point. The monitoring data will alert one to a change in the building population which then requires a response - finding the source. This is prevention. In the Royal British Columbia Museum we have a population of varied carpet beetles, the Megatoma beetle, lady-bird beetles and house flies- not many though. The varied carpet beetle lives on the dead fly bodies, the lady bird beetles on any thing alive and we are not sure where the Megatoma beetle fits in. Monitoring is done every week using the windows as light traps as well as some electric light, yellow sticky traps. The data is put in a computer program and compared with the past to alert us to a change. One change occurred in February a number of years ago. The varied carpet beetle population rose as it did in the spring but a month earlier. It was discovered that the floors in the offices had been wet stripped for waxing , increasing the RH over a period of two days, just sufficient enough to trigger their pupation. We knew that there was not a problem, we have just disrupted its normal cycle.
Having such a program for a large building seems ominous, but it is made easy when everyone in the building is helping with the monitoring and establishing a zero point.
2.2 The fungi
In assessing the fungal infestation the questions that are asked: - Where did they come from?, Why are they growing?, What damage are they doing?, What health hazard do they present?, How can they be removed from materials?, How can this be prevented in the future? , - all have to be answered.
2.2.1 Who are they and where do they come from?
The fungi are cosmopolitan ubiquitous fungal species which are present, by chance, on all surfaces. They may be carried in the air. The airborne fungal structures simply settle on the surfaces of the materials, contaminating them. The air borne fungal structures include conidia, hyphal fragments and some ascospores, which make up in the air a specific composition called the airspora or bioaerosol. The airspora inside a building may originate from outside air and from mouldy materials in the building- called amplifiers-, such as fungi growing on window frames, damp walls, on humidifiers, in garbage, on food, mouldy archival materials, etc.
In an air filtered air conditioned building the indoor airspora is mainly from amplifiers and is quite different in species and amounts than the outdoor airspora. In a building using window opening for ventilation, the indoor air will contain internally generated airspora as well as a reduced amount of outdoor airspora. Thus the airspora of indoor air is different than outdoor air.
Besides contamination from indoor airspora , materials may be brought into a building already contaminated. This could be as an active fungal infestations, or from contamination from mouldy materials such as card board boxes or during the manufacturing process. These fungal structures can cross contaminate the collections and if they are viable can cause a problem in the future if a conducive environment for fungal growth occurs. Thus a surface growth on a paper may be caused by these fungi or surface deposited or air borne fungal structures.
As a prevention it is logical to monitor the total fungal structures present in the airspora in rooms of concern. Four seasonal airspora samples should be taken to determine the normal concentration of airborne fungal structures, in a building or room, over a year. This can then be used as a standard reference to determine changes. A change will indicate the presence of an amplifier which then has to be found and the fungal structures removed . We rarely have indoor references, because in the past monitoring has been done only after a problem is perceived. Outdoor air has been used in the past for references, but this is almost meaningless. We need references for the rooms of concern.
Other preventative measure to eliminate fungal structures surface contamination are; maintenance, mainly dust removal and inspection procedures to prevent the entrance of mouldy materials into collections. Even with stringent maintenance and inspection the heritage objects will be inevitably, always contaminated. Germination of conidia and subsequent growth must be prevented. Remember there are specific stages to the conidia, dormancy, activation, germination and subsequent colonial growth. The goal is to prevent the conidia germination as well as growth.
2.2.2 Physiology of fungi as it relates to prevention
The knowledge of the physiology of fungal species causing surface growth is paramount in interpretation of the cause of germination and growth. There are, as in all populations, fungi that survive in extremes of temperature, moisture and chemicals. Most of the species involved in infestations of heritage archival materials are mesophilic, moderate, in their requirements, but there are always exceptions.
We have in the past considered that controlling water vapour in the air, measured as RH, will control fungal activity. It may, but not the way we think it does, and not always. An understanding of the materials, the environment and the fungal species and their interactions is needed to help us understand water requirements of fungi.
It's the water in materials that fungi utilize, they can not utilize water vapour alone. Materials vary greatly in their chemical and physical characteristics. We all are aware of the differences in carded paper, rag paper, rice paper, starch or gelatine sized paper, gelatine coated films or slides, etc. Because of these differences, each material has a different susceptibility to fungal growth. Each material must contain enough water and the right water activity to support growth. Thus there are two characteristics of water, quantity and the activity of water.
The total amount of water in materials is influenced by the available water vapour in air and its temperature. This water vapour in air is measured as relative humidity(RH). We normally consider, the higher the RH the higher the moisture content in materials at equilibrium(EMC) with the ambient RH, but there are other reasons that determine this amount. The adsorption of water vapour of the material is due also to its porosity, amount of adsorptive surface areas, and the water bonding sites of chemicals present. For example the presence of glycerol increases the water content because of the extensive water bonding ability of this molecule. But glycerol lowers the water activity making the water unavailable for fungal activity. Thus even if there is a high moisture content, if there are dissolved chemicals which lower the water activity, fungi may not grow.
Water activity may be a new concept for heritage literature but is the common way of describing water utilized by fungi in mycology and the food industry. In conservation literature the term water activity was first discuss in relationship to xerophylic species on old hemp paper. Water activity is the vapour pressure of water in solutions. For example, water with dissolved chemicals in it has a lower water vapour pressure than pure water, thus a lower water activity. The dissolved chemicals in materials are salts, sugars, alcohols etc. which are between the fibers of the material and originate from the manufacturing processes, treatments or use. To utilize the water in materials, fungi have to overcome the strength of the water bonds to these chemicals. Water activity is measured as the ratio of its vapor pressure to that of pure water, thus is recorded from 1.0aw for pure water downwards. Bacteria require 0.99 aw. Fungi can only utilize water between the range of aw 0.98-0.80. This means that fungi can not use pure water or water with solutes that change the water activity below aw 0.80. The fungi that can germinate on materials with water activity around 0.80 to close to 0.97 are the xerophylic fungi, mesophilic fungi(common fungi), can not germinate below aw 0.98. Water activity is influenced by water vapour adsorption, the more water adsorbed the more dilute the solution thus the higher the water activity- everything is inter- connected.
Some xerophylic species, which germinate under low RH, have high moisture content in their conidia which allows them to germinate on dry materials, whereas most fungal conidia have extremely low conidial moisture content and require a higher moisture content and water activity in the substrate materials for germination. Some xerophylic species can grow in substrates with low water activity which may be caused by dehydration of materials or a high solute concentration. Xerophylic species have been identified as the cause of specific fox spots on paper in a 145 year old book. The fungi that produce vegetative growth at low water activity, have the ability to alter the material water activity so it can be adsorption for subsequent growth by producing chemicals such as glycerol. Thus there are different water requirements for different species.
Temperature also influences the amount of water in materials. At the same RH but a high and low temperature, the material under high temperature will contain less EMC than that at the low temperature. The reason for this is the influence of temperature on water vapour pressure, its volatility. It is more volatile and more easily moves out of materials at high temperatures than at low temperatures.
Many mass treatments, introducing chemical buffers to prevent acid damage in papers, which may lower the water activity. I wonder if they have determined the vulnerability of these treated materials to fungal infestation.
This all shows that the variability of materials water activity and species requirements makes it difficult to determine a suitable environmental parameters for prevention of conidia germination and subsequent growth. The underlying suggestion is a high temperature and low relative humidity. This may seem at odds when we know that high temperatures usually increase rate of growth. But our first step is preventing germination. Low moisture content and low water activity in materials is the goal.
The growth of fungi occurs from slightly below freezing temperatures, as long as there is still some unfrozen water, to around 37oC. The growth rates vary with temperature and species. If materials are stored at low( 4oC-refrigeration) temperatures as a protection against fungal growth, growth will occur, but at a slow rate. Often these slow growing fungi are under stress and as a response produce black insoluble melanin in their hyphae which are attached to substrate fibers and are virtually impossible to remove.
Responses to water and temperature are only two physiological aspects, but just these two show that there is great degree of variation with different species. Thus to give general parameters of growth is almost meaningless. The growth depends on the species and the state of water in the materials and its adsorptive nature as well as the environmental parameters.
There are other aspects of their physiology such as conidiation, sporulation, sclerotia development, antigen and toxin production etc., which we must be aware of to understand completely the fungal problem.
2.2.3 Fungal antigens, microbial volatile organic chemicals (MVOC) and toxins
Beta-glucans is the main antigen produced by fungi. This is the main health concern with fungal infestations. The cell walls of fungal structures are composed in part of beta-glucans and it is the major component of mycofibrils and slime on the surfaces of hyphae. Some fungi hyphae may be smooth or have encrustments of mycofibrils and slime. Those with encrusted hyphae may be the hyperallergenic species. The fungal structures are carried in the air and can be breathed in, causing an antibody- antigen reaction resulting in upper respiratory discomfort similar to hay fever. Today only hyphal fragments are monitored. The mycofibrils are small ( less than a micron to nanometers in size). They must easily become airborne and are almost impossible to physically observe. Thus besides monitoring the presence of fungal structures, the antigen beta-glucans should also be monitored, this would include the mycofibrils.
MVOC are the odors of fungi. We do not know their health hazards but their presence has been attributed to some human discomfort. The production of these chemicals is under active research in monitoring and mycological research. The odors as well as the toxins are produced only under special growth conditions, thus their absence in monitoring does not mean that fungal growth is not present.
There are a few fungal species which produce a toxin in their cell walls which give a toxic response if inhaled. One such species is Stachybotrys chartarum, but this species is not readily airborne because it grows and is adhered to damp wall board in buildings internal structures. Aspergillus fumigatus is a pathogen which if inhaled may grow in the lungs causing the disease Aspergillosis. It only occurs in workers who are continuously exposed to the fungus species such as in flour or grain mills and composting centers.
2.2.4 Species identification
Often knowing the species on the surface of infested materials is not necessary. One can not wait around for species identification. The staff response to a fungal infestation must be immediate and the procedures are common to all infestations. Some species are more allergenic that others thus the general precaution of using all personal safety measures and prevention of cross contamination by using aseptic techniques must be taken.
If species identification is necessary for documentation or to determine its source or its allergenic properties, the method of identification must be such that the identification of the causative species is accomplished. Culturing tells you who is viable not necessarily the causative species.
We have very little information on species longevity. We do know that it varies with species and the environmental history of the infested material. The fungi in the infestation may be dead, culturing is useless, thus microscope( light or scanning electron microscopy) analysis is necessary This allows a study of the population of all species and their numbers. This can then be used to determine which species identified is the cause of the infestation. There is a body of literature on the identification by species using conidia ornamentation for Penicillium and Aspergillus species in stored grain. Many of these species are common contaminants on all surfaces thus these works are useful for the common species on heritage objects. These species are not substrate specific they will grow anywhere the environmental parameters are conducive and the substrate water is available.
Molecular analysis using DNA and polymerase chain reaction (PCR) technology, also has the weakness of culturing. It shows only the presence of species with usable DNA, not relative amounts or the causative species. A mixture of DNAs of a population is analysed, thus it is impossible to determine the problem species or causative species. The population may also include a few airborne organisms along with those from the infestation. Only if it is obvious that there is a single species is it meaningful. Also the development of the enzymes used in PCR is a research project in its self.
3 The material
The influence of the material on surface fungal contaminants is mainly as a source of water. We have a good understanding of fungi and their enzymes which allow them to utilize structural organic materials such as cellulose. But the common fungal species on surfaces of materials are usually utilizing only free amino acids, some small peptides, monosaccharides and some disaccharide, present in the dust or on a deteriorated surface. Fungi may after depletion of this readily adsorbable nutrient source and due to a feed back mechanism from the presence of cellulose in the material, will only then, produce enzymes to digest the cellulose. This may occur if cellulose materials are left for a long period of time under excessively damp environments.
Only a few fungi can hydrolyse the structural protein molecules, commonly on wet materials it's the bacteria that digest the proteins. The fungi that can utilize keratin, a structural protein, are dermatitis species or those that damage hair in natural environment.
Deterioration of the materials may influence their vulnerability to fungal infestations. For example leather bindings usually contain some free amino acids which are from deteriorated collagen bundles of the hide. The amino acid, proline is one of these amino acids and is a stimulator of conidia germination and subsequent growth. Its presence on deteriorated surfaces may be one reason that leathers are prone to surface fungal growth in damp environments.
The effects of a fungal infestation on the materials are variable. Fortunately the majority of small infestation do not cause structural damage, but are aesthetically unpleasing and may present a health or cross contamination problem and thus have to be removed. Textiles left in a conducive environment for fungal activity over a period of time, may develop black spots containing fungal sclerotia or pigmented hyphae which are difficult to remove because they are intertwined with the textile fibers.
On cleaning infested materials -mechanical removal of the fungal structure is the main method of removal. Despite its common use there is no definitive research that proves its success. We can see the reduction of color when colored conidia are present but we do not know how many, if any, are left behind. The majority have been removed and this seems logical because as soon as a cleaned object is placed in the air it becomes contaminated again. Mechanical removal of the fungal structures is important in reducing the health hazard. Killing the fungi in situ, alone, is illogical it does not eliminate the health hazard- fungal structures whether dead or alive are allergenic must be removed- but it does prevent cross contamination.
Besides the fungal structures there is the slime. My major research of late, has been on fungal fox spots on old paper. The beta-glucans slime is a major component of the fox colored spot. I wonder if when we just remove only the fungal structures from contemporary fungal spots, in 50 or so years, will fox spots occur. Should we be removing the beta- glucans slime in the substrate. Just vacuuming will not remove this from the substrate it will have to be solubulized by aqueous alkaline solutions. We also must determine if in archival storage and libraries that are experiencing sick building syndromes, if beta-glucans has become air borne from the vestiges of old fungal infestations. Beta-glucans has been connected to a feeling of lethargy in buildings.
4 The environment
4.1 Influence on materials
The importance of the role of water activity and the equilibrium moisture content(EMC) of materials on fungal activity is paramount. It has already been discussed under fungi. The water activity and amount of water in materials, EMC, are influenced by the RH and temperature of the air. Increase in RH increases the amount of water in materials and this alters the water activity.
Fluctuations of RH theoretically can make materials more vulnerable to biodeterioration because of the hysteresis phenomena. An organic material adsorbs water at a specific rate but on dehydration the rate is slower. This means that there is more moisture content in materials, at the same temperature and RH, during dehydration that adsorption. Continuous fluctuations may increase the moisture content of material, and if the water activity is conducive, to the stage that it will support fungal activity at a much lower RH than expected.
4.2 Influence on fungi
As already mentioned the temperature range which supports fungal growth is wide, but the rate of growth varies.
In air conditioned buildings we set environmental parameters in storage and work areas which contain archival materials for human comfort. Luckily these parameters, usually 50%RH and 20oC, often give the materials protection from fungal activity. But fungal activity may occur in microenvironments, which are due to lack of air circulation, cold surfaces and materials with unusual thermal characteristics(black surfaces) or a high adsorptive nature.
In buildings without environmental control with extremes of RH, prevention of fungal activity is difficult. The latest research is on air circulation. It seems to be important in preventing moisture extremes on surfaces and may be even prevent fungal structures settling.
4.3 Influence on insects
The insects are sensitive to RH changes. Even wet mopping floors may cause microenvironments with increased RH near base boards were the booklice and silverfish can breed and will allow beetle and moth pupae to adsorb enough water vapour to pupate into an adult.
Anoxic treatment or fumigation will not solve booklice and silverfish, because it is the environment that needs to be changed. The booklice and silverfish are very sensitive to dehydration thus reducing the RH is a more logical control measure. Often the breeding places of these insects are away from the collection they are grazing on, thus it is important to look for poor environments in damp areas around hot water pipes, drains, sinks etc. Fixing a leaky pipe is much easier than fumigating a room.
To kill insects on heritage objects made of dry organic adsorptive material, i.e., infested books and paper, they can be placed in closed containers in freezers at -20oC, to freeze the living insects. Conservation professionals must advise on the special freezing procedures and determine that the materials can be subjected to this reduced temperature. There is research which shows that repeated freezing does not affect new papers.
5 Health issues
We are presently learning more about the health hazards of fungi and insects in our environments. But we still have a lot of unanswered questions.
The antigen, the fungal beta-glucans from the cell walls of hyphae, the volatile chemicals such as the musty odors of fungi and the characteristic odors of a varied carpet beetle infestation, dermestid frass and dust mites all may be health hazards. It, of course, depends on the size of the dose. We rarely think about insects as presenting a health hazard but there are reports of allergic responses to these insects. We are familiar with the dust mite allergic problem.
There is a lot of literature on fungal health problem. We are just beginning to understand what the problems are. We now know that beta-glucans is the major fungal antigen. It is active in the hyphae and conidia, no matter whether dead or alive. In the analysis by CFU , whether the source of the colony is a conidium or hyphal fragment is not determined. Fungal fragments are often counted by microscopy and their amounts may suggest a major source of the allergen. Bioaerosol monitoring today should include beta-glucans analysis, this will account for all sources of the antigen. The analysis of the concentration of the beta-glucans , which is done with a commercially available antigen- antibody reaction is possible. Seasonal air monitoring of buildings should not only include the microscopic count of conidia and fungal fragments but the antibody/antigen immune reaction analysis of the amounts of beta-glucans, to give data which is meaningful. As I mentioned, everything is toxic, but it depends on the dose. Today we do not have TLC( threshold limit concentration) to guide us. But monitoring seasonally will give one the possibility of seeing a change, and thus evoke a response to determine the cause of the change.