Pest control in museums and heritage objects: the use of inert gases

The universe of National Material Heritage is made up of both public and private property of the National State, Provincial and Municipal States and property of individuals, whether natural or legal persons. The appearance of an animal species in the heritage may or may not be enough to consider it a pest; this will be determined by its population level and dispersion in the affected heritage. Consequently, we could focus in the first instance on pests according to Dispersion in Urban, rural and wild areas. This dispersal will be favored according to the ethological behavior of the species and the natural and artificial conditions of the space, since this behavior will be naturally marked in the species by the natural search for shelter, food and nesting. This is why the problematic pest in cultural heritage has general characteristics but is specific to each case – and will be determined according to the pest species: It will not only be related by the type of heritage to be preserved but also its context and the radius to be considered according to the material composition of the collection (biotic and biological conditions to which it is subjected), the characteristics of its immediate context (physical and mechanical characteristics) and its periphery (geographical location and its environment). The plagues are not of the heritage, but of the geographical determination in which the heritage is immersed and this will frame the

criteria and theoretical and practical frameworks for its study and treatment. To address the problem of pests in heritage, it is necessary to establish specific protocols within the conservation plan for the collections that in turn contemplate the aspects currently covered by the home health system since it does not contemplate in its chemical, physical and mechanical treatment the specificity of the pests and the materiality of the collection or the historical-artistic buildings. In Argentina there is currently work carried out on pests with specific elimination treatments on objects or the appearance of pests in some collections, but not in an integral way within the conservation plan with protocols and statistical measurements of the problem.

pests from a comprehensive and formal point of view. Comprehensive pest management is a proactive system that prevents the incidence of pest impact in which a variety of strategic elements are used depending on where it is applied: physical, mechanical, chemical, biological, genetic, legal and cultural (related to the field of application with its specific protocols) for pest control. It is a method that aims to reduce the use of pesticides and minimize their impact on the environment where it is applied. Beyond the need to establish appropriate pest management protocols in spaces and objects of heritage importance, the need to have control strategies in general that minimize the use of pesticides is becoming increasingly prevalent.

The treatment of xylophages is complicated, because the insects spend a large part of their cycle inside the wood, far from the reach of any pesticide, while they attack by building galleries. Many times the damage is evident when structurally little remains of the piece. To avoid this difficult access, toxic gases were traditionally used which, despite their high toxicity in humans and their environmental impact, seemed to be the definitive solution due to their penetrating power. Methyl bromide, and especially phosphine (released into the environment through the hydrolysis of solid metal phosphides) was widely used not only in furniture and wooden structures (beams, braces, etc.) but also in the collection and transportation of stored grains. Of course, the use of this product has very harmful consequences and has been responsible for serious toxicological accidents, which disables its use. Furthermore, as it is a very reactive chemical agent, it attacks the treated metal parts, which is why its use on metallic materials, or with metals in its composition (pianos, for example), is not feasible. In Argentina, the toxic fumigants generally approved for residential use were methyl bromide, ethylene oxide and phosphine. However, in museum facilities, the use of toxic gases is strongly discouraged, mainly for safety reasons. But if it were necessary to find an additional reason to advise against them, the visual effect of the two gases on painting materials could be considered. Koestler and colleagues (1993) evaluated the impact of some toxic gases in thirty combinations of linen, rabbit fur glue size, white lead oil base, and oil-based paints using eleven different inorganic pigments. The comparison was based on a visual evaluation by two paint conservators of color change, gloss change, scalding, topography change and precipitation. These studies demonstrate that although there are many ways to eliminate insect populations from museums, none are safer or more protective of the integrity of objects than the use of a controlled atmosphere. We will briefly describe here a physical treatment option, the use of non-toxic gases (argon, nitrogen and carbon dioxide) to eliminate pest insects on museum or heritage objects. Conservators are selecting this approach because they feel more comfortable and confident that using inert gases is much less likely to damage objects than other procedures. Healers have been known to insist anoxia (defined as a deficiency of oxygen reaching body tissues of such severity that it causes permanent damage) in clear plastic bags in low oxygen transmission materials so that they can monitor their loads during treatment. Freezing and thermal methods are also effective when carried out correctly. They are popular because they allow large quantities of material to be transported and treated. But freezing and heating, by their nature, must bring objects to unusual temperatures where they often

unwanted changes occur. In contrast, treating cultural property in an inert atmosphere rather than air provides a more stable environment where deterioration is less likely. For example, using a low oxygen environment will impede biological growth, prevent surface oxidation, and slow color fading. Studies by Burke (1992), Arney, Jacobs and Newman (1979) and others show that the longevity of most organic dyes increases substantially in a nitrogen atmosphere with less than 1000 ppm oxygen. One such study examined several inorganic pigments under these conditions and found that three of them, litharge (PbO), cinnabar (HgS), and sienna (mainly Fe2O3), showed slight color changes after a month's exposure. Furthermore, Valentín (1990) found that low oxygen levels

They can be used to inhibit the growth of both bacteria and fungi. The above discussion helps explain the rapid growth of anoxia and carbon dioxide fumigation as conservation procedures. In 1990, these methods were virtually unknown in the museum community, although studies were being conducted at several facilities. In most places, these studies quickly gave way to practice. Appreciation of this new preservation technology has spread rapidly through periodical publications, papers presented at meetings, and anoxia training courses. Nieves Valentín, of the Institute of Spanish Historical Heritage (formerly the Institute of Conservation and Restoration of Cultural Assets) in Madrid, conducted workshops in Spain and Latin America and brought this approach to pest control to Spanish institutions such as the Prado Museum, the Fundació Joan Miró, the Museum of Decorative Arts and the National Palace of Fine Arts, as well as the National General Archives of Colombia and the National Palace of Fine Arts of Cuba. John Burke, with the Oakland Museum Conservation Center, provided training to conservators in California through a variety of formats, including a workshop at the San Diego Museum of Natural History in 1996 titled “Pests in Collections: Insect and Fungal Control in Cultural Collections,” which included carbon dioxide treatment. The Getty Conservation Institute offered programs on museum pest management and control in Los Angeles in 1994 and London in 1996. The biochemistry of nitrogen and argon mortality differs somewhat from that of carbon dioxide, but all of these gases owe their effectiveness to desiccation. It is important for conservators to understand this because factors that impact desiccation, such as temperature and humidity, are important in the design and operation of treatment systems. In view of this background, our company recommends the application of Argon as an inert gas in the treatment of heritage assets. Despite the much higher cost, it has certain advantages over nitrogen and carbon dioxide. It is a heavier gas than air, which means more efficient displacement of oxygen in the system. The times of mortality

in exposed insects is considerably lower than for the use of other gases. In addition, certain xylophagous fungi fix nitrogen, favoring their development. The carbonation or acidification of some substrates is the weak point of carbon dioxide treatment. The treatment consists of coating (in oxygen and water vapor barrier material) the piece to be treated, maintaining constant temperature and humidity patterns throughout the application time. Both these parameters and the oxygen concentration (never greater than 1000 ppm) are monitored during the treatment, for a total duration of approximately ten days, a sufficient period to control all the insects in all stages present (eggs, larvae, pupae and adults), no matter how deep they are. The system will have an atmosphere of inert gas (argon in this case) with positive pressure throughout the treatment, regulated by a differential pressure control system. This strategy is extremely effective and environmentally friendly, and controls not only xylophages due to its great penetrating power, but is also applicable to other pests that affect pictorial works, such as moths, lice and thysanurae in bibliographic material, and its use can be extended to other environments or important situations, such as stored grains, processed and packaged foods, etc. Its application requires special materials to achieve the situation of very low oxygen concentrations, temperature and humidity control systems to avoid sudden changes in sensitive parts, equipment to heat seal the film with low oxygen permeability, and highly sensitive oxygen detectors. Therefore, this strategy should be practiced by those companies with experience in the subject, not only in the technical aspect and the implementation of the system, but also in the management of the parts targeted for treatment,

often of enormous heritage, cultural and economic value.

“Freezing and thermal methods are also effective when carried out correctly”