: Preventive Conservation

What is the best way to store insect collections? Recently an enquiry was posted on NHCOLL-L (electronic forum for the care and use of natural history collections) about the use of wood as a material for insect storage cabinets. The question was:

What kind of preservative should be used to treat some new storage cabinets made of eucalyptus wood, that would not harm the insect specimens stored inside them?

The post sparked a discussion about ideal insect storage. Below is a little summary of the factors to consider when planning storage for your entomology collection.

The ideal solution

The ideal solution for insect storage in most situations are metal cabinets, which are robust, relatively cheap, made with a high degree of consistency and can be made air tight (well, almost). This will protect the collection against insect infestations, airborne pollutants and humidity fluctuations (although not temperature fluctuations – cf. Szcepanowska et al. 2013.

Why use wood preservatives?

However, if you do need to use wood for the cabinets, you should consider the following concerns.

Usually, the reasons for treating wood with preservatives are either:

• to make it more hard-wearing (in the case of wooden floors), or
• to stop it being attacked by fungi or insects, or
• to prevent it from greying when exposed to UV light.

Most of these issues are problems mainly in outdoor applications of wood, and there are a number of ways of dealing with these: wood can be varnished to make it protect it from physical impacts, stained to protect it from UV light, and pressure-treated or painted with insecticides and fungicides (ranging from highly toxic substances, such as pentachlorophenol, to less hazardous ones, such as borax).

Assuming the entomology store is dry, has a low relative humidity, clean and there is no problem with insect pests – which should all be the case to safeguard the collection, never mind the storage cabinets – there is really no reason why the cabinets need a finish at all. This applies to all woods – whether in a museum or in a domestic situation, wood used indoors should not require any treatment to protect it from fungal or insect infestations, or greying. Coming back to eucalyptus wood in particular: this has a naturally high content of polyphenols, which makes it naturally resistant to mould growth and insect attack, further negating the need to treat it.

There is one exception: if old cabinets are bought from another institution there is a danger that pest insects may be present already, which could introduce them into the new location. It is advisable therefore to check any old cabinets thoroughly before they are installed – better still, before they are transported to the new location. This then gives time to investigate appropriate treatment options, which are not restricted to chemical means; instead, the units may be frozen, heat-treated or treated in a nitrogen chamber. But that is an entirely different subject which shall be discussed in detail elsewhere.

Organic acid emissions

A further question was the issue of emissions of volatile organic compounds (VOCs). Wood naturally emits many different VOCs, including acetic and formic acids, which is a problem in many museum collections (e.g. causing Byne’s disease in Mollusca and egg collections, and enhancing pyrite decay in geological collections). There does not appear to be a problem with VOCs affecting insect specimens themselves, although organic acids frequently lead to pin corrosion in insect collections. Many wood preservatives may exacerbate the problem of VOC emissions from storage cabinets. As we always look for ways of lowering such airborne pollutants in museum stores and galleries there is another reason against the use of wood preservatives in entomology stores – actually, ANY museum stores.

What material to choose for the drawers? Experience has shown that plastic drawers have problems with static electricity charging, which attracts dust. Metal drawers can be heavy and unwieldy. Wooden drawers still appear to be very much the most practical way of storing insects. However, the type of wood used should not emit large amounts of VOCs, and the drawers should have well-fitting lids to keep out pests. If you wanted to use a locally sourced (sustainable and ethical) wood you might have to undertake a little research. Generally, hard woods are better than softwoods (drawers made from softwood can warp with time and often contain large amounts of resin), although many imported tropical woods used in days gone by are now controversial for environmental and social reasons. When researching the potential suitability of different wood types, try tracking down a comparative study of the VOC emissions of different local hardwoods, which would give you an indication of those high emission species to avoid in the construction of drawers.

Further guidance

The UK’s Natural Sciences Collections Association [http://www.natsca.org/] has published some guidance on the construction of insect storage units:

• Walker et al. (1999) (p. 49)
• Carter and Walker (1999) (p. 146)

NHCOLL-L is a general purpose electronic forum for those with an interest in the care, management, computerization, conservation and use of natural history collections. Hosted by Yale University, NHCOLL-L is co-sponsored by the Society of the Preservation of Natural History Collections (SPNHC) and the Association for Systematic Collections (ASC, Natural History Collections Alliance).

Disclaimer: The links in this article are purely examples of potential pest management but by no means an endorsement of particular companies or organisations.

Re-visiting no smoking policies to include non-tobacco replacement products.

AC-NMW has recently banned the use of e-cigarettes from its galleries. E-cigarettes are considered a less harmful version of conventional cigarettes – do they really need to be banned from museums?

What's the problem?

An electronic cigarette, also known as an e-cigarette, is an electronic inhaler that vaporizes a liquid solution into an aerosol mist, simulating the act of tobacco smoking. E-cigarettes use a rechargeable battery to power the vaporizer.

Many people use e-cigarettes as a way of quitting smoking and while this is deemed a positive development, the act of using an e-cigarette does look like smoking which is disconcerting to other people. Users of e-cigarettes should be sensitive to the impression that using the substitute may give to others. For example, there are questions surrounding the appropriateness of smoking e-cigarettes in public, especially around children.

Smoking ordinary cigarettes violates established museum policies and therefore, for the sake of consistency, the use of e-cigarettes has been prohibited at AC-NMW on health and safety grounds (and in line with existing legislation covering smoking in public places) since May 2014.

In addition, there are good conservation reasons against ‘vaping’ in museums. Electronic cigarettes work in a similar way (with a chemical carrier, such as propylene glycol, nicotine and a cocktail of flavouring chemicals) to scent and smoke machines that historic houses and museums have rejected in the past to protect collections from damage.

What is the effect on museum collections?

What does the science say about the effects of e-cigarettes? A summary report recently reviewed 29 studies on the chemistry of e-cigarettes and found that refill solutions and aerosols contain nicotine, tobacco-specific nitrosamines (TSNAs), aldehydes, metals, volatile organic compounds (VOCs), flavours, solvent carriers and tobacco alkaloids (Cheng 2014). However, not all of those chemicals are necessarily emitted by a user exhaling vapour from an e-cigarette. In fact, the average nicotine concentration in e-cigarette vapour is considerably lower than the amount found in tobacco smoke (Czogala et al. 2013).

In addition, e-cigarette vapour does not appear to contain some of the other toxic products found in cigarette smoke. VOCs, including acetone and formaldehyde, are seemingly not emitted at all (Czogala et al. 2013), or at levels considerably lower than from conventional cigarettes (Schripp et al. 2013) – the slightly different results depend on the analytical methods used. Crucially, acetic acid is emitted by e-cigarettes (Schripp et al. 2013).

Acetic acid is very problematic in museum galleries and collections stores. Airborne acetic acid leads to destructive corrosion of metals and minerals, including calcitic bivalve shells and fossils. And while the levels emitted by each individual e-cigarette may be small, many museum conservators and curators have first-hand experience at dealing with damage caused by airborne indoor pollutants.

Pre-cautionary principle applies in museums

We have a duty to maintain our fantastic heritage, and to care for the collections of Wales to ensure their continued and future preservation. It is best to put the objects first and limit the chemical and aerosol exposure of museum collections by prohibiting the use of both conventional and e-cigarettes in museums.  

References

Cheng, T. 2014. Chemical evaluation of electronic cigarettes. Tobacco Control 23: ii11-ii17.

Czogala, J., Goniewicz, M.L., Fidelus, B., Zielinska-Danch, W., Travers, M.J., Sobczak, A. 2013. Secondhand exposure to vapors from electronic cigarettes. Nicotine & Tobacco Research, doi:10.1093/ntr/ntt203.

Schripp, T., Markewitz, D., Uhde, E., Salthammer, T. 2013. Does e-cigarette consumption cause passive vaping? Indoor Air 23: 25-31.