Every Conservators' Nemesis...

Pesticides are now no longer routinely used on our collections.  My colleague Kate Jackson, conservator at the Pitt Rivers Museum, has written a post about our current pest management systems:

1923.85.293 Textile from Nagaland, N. India, with active moth infestation

In the past, museum collections were routinely treated with pesticides in an attempt to stop the damage caused by moth, beetle and wood boring insects.  The Museum's Annual report dated 1906 boasts – ‘the addition of a fuming-room, in which specimens infected with moth and beetle may be cured, will be of great convenience, and will greatly lessen the trouble caused by insect depredations’.

Unfortunately there was no 'miracle cure’ and as it transpired the commonly-used pesticides have over time proved to be highly hazardous not only to insect pests but also to us humans and in some cases to the objects themselves. Due to the health and safety issues surrounding the use of pesticides in museums they are no longer widely used, and we must instead find alternative methods of warding off unwanted insect pests.

Up to eighty percent of the Pitt Rivers ethnography collection is made up of objects composed of organic materials such as textile, feather, fur, hair, wool, felt and skin. It is these organic materials that attract every conservator’s nemesis - the common clothes moth (Tineola bisselliella). Due to warmer winters and the decline in pesticide use over past decades the cloths moth has enjoyed a population boom within UK museums. In order to tackle the issues of moth in museums it is vital that we understand what we are dealing with.

Adult common clothes moth

The adult moth, which prefers dry, warm, dark areas, lives for between 70-80 days. The female lays her eggs within undisturbed, organic materials.  As the larvae hatch they feed for between 2-30 months (depending on environment) on any organic material close by. It is this larval stage that can cause devastation to museum objects if left undiscovered. The larvae will eventually cocoon before the adult moth emerges after 8-10 days.

There are 35 pheromone moth traps within the museum, the majority within high-risk cases, with others placed in open areas. The pheromone used on the traps attracts the male moth and the sticky surface holds the moth in the trap. Every week a conservator checks the traps and counts the number of moths caught. The number will indicate if there is a gradual or sudden rise in moth in the area, this will lead us to do a thorough search of the surrounding cases. If an outbreak is found the objects infested are sealed in bags and placed in one of our chest freezers at -30 for three days. This temperature will kill every stage of the moth whether adult, egg, larvae or cocoon. The conservator will then assess the objects, any pest debris will be removed and any damage recorded.

We also have a number of ‘blunder’ traps. These are also sticky, and would hold a blundering beetle if it wandered across the trap. Thankfully we have not had major problems with beetles or wood boring insects for a number of years. If we were to find an outbreak we would use the same freezing method, which would kill the beetle at all stages of its life-cycle.

An unaccessioned Biddenden Biscuit, with biscuit beetle damage.

More about Pesticides

In a previous blog post, I wrote about pesticide residues on museum objects, and the work being done as part of this project to attempt to identify pesticide residues on objects from the Cook-voyage collections at the Pitt Rivers Museum.  

Detail of barkcloth 1886.1.1240, showing staining and associated damage

This week, I've been taking more samples to send off for analysis.  It has been noticeable that many of the barkcloths I've conserved so far have had areas of staining on them, often associated with damage to the structure and weakening in the stained area.  We're starting to suspect that this damage might be the result of the application of pesticides in the past.  

One of the problems when thinking about pesticides and their effects is that the chemicals were available in many different formulations, with lots of ways of applying them.  These methods include dissolving pesticides in water or other solvents and spraying or misting objects, or the objects could just have been dusted with a powder. The same pesticide could have been applied in different ways at different times.

Whilst we understand that the past use of pesticides on museum collections has saved them from the devastating effects of insect damage, and, we suspect, in many cases, continues to do so, the effects of these pesticides both on objects and on those who work with the collections are not yet properly understood.

A 30x30cm area of barkcloth framed within a temporary border

Here, I am taking samples of surface residues from a large barkcloth collected in Tahiti on Cook's second voyage.  The barkcloth is about seven meters long, and there are areas of staining in several places.  I've made a frame so that I can take surface swabs from an 30cm by 30cm section - this may help us to make a rough estimate of how much pesticide remains on the surface of the entire barkcloth.

Using swabs barely dampened with distilled water to remove residues from the surface of the barkcloth

Pesticides on Museum Objects

Part of the Cook-Voyage project at the Pitt Rivers is to look at the question of pesticide residues on objects from the collections.  Chemicals have always been applied to objects in museum collections to protect them from pests, mainly insects, which can cause a lot of damage. 

As the Forster Collection has been in Oxford since 1776, and the Banks collection was at Christchurch even before that, the Cook-voyage collections potentially span virtually the whole history of pesticide use in museums.  Even though we know that chemicals such as arsenic, mercury and DDT, were routinely applied to museum collections, finding evidence of what was actually done is difficult.  

Label from a poncho from the Tahitian Mourner's costume, giving information on the condition of the feather cape.

A label on the Tahitian Mourner's costume, written just before the Ashmolean's ethnographic holdings were transferred to the Pitt Rivers in 1886, records that the cloak was 'now in a very bad condition' and an entry in the Accession Registers goes on to say that this was 'through the moth, and (it) has been removed to the Museum in the Parks (Oxford University Natural History Museum) and placed under the charge of Professor Moseley to be fumigated.'  We don't know, however, what fumigation involved. 

Sometimes, the Pitt Rivers annual reports give us more of a clue.  In 1946-47, the Curator, T.K. Penniman, wrote that 'we have tried the Clymax spray on all of our material, and have found it thoroughly effective in destroying every sort of pest that attacks every sort of material that human beings use.'  Powerful stuff indeed!  There is also a mention of a fumigation chamber being built so that methyl bromide gas could be used to kill pest infestations on museum objects, but it is not clear whether this was ever actually used.  

Jeremy Uden and Kloe Rumsey, conservation intern, taking samples of surface deposits from a Tongan mat.

  

The analysis of pesticide residues is being done for us by Andrew Charlton, an analytical chemist at the Wildlife Incident Unit, part of the Food and Environment Research Agency.  He usually works on investigating pesticide uptake by wildlife, especially honey bees.  The samples he works on are usually destroyed during the analysis - not something that is practical for museum objects.  We are using cotton wool swabs dampened with distilled water to take samples of the surface dirt and residues from objects - we know that the object is not damaged in the process, which is of paramount importance, but we have to accept that we may not be able to get large amounts of any residues remaining on the surface onto the swabs. 

Once Andrew receives the swabs, any residues on them are extracted with an organic solvent for analysis using gas chromatography - mass spectrometry (GC-MS), a highly sensitive technique which can detect parts per billion (ppb) levels of target pesticides.  Each target pesticide is detected in the mass spectrometer by the presence of characteristic molecular fragments providing a unique ‘fingerprint’.  To detect the presence of arsenic or mercury compounds, swabs are extracted with dilute acid for elemental analysis by inductively coupled plasma - mass spectrometry (ICP-MS).  Argon plasma at a very high temperature (approximately 6000 to 10000°C) is used to turn the sample solution into ionised atoms (ions). Each element produces ions with a characteristic mass and charge, which are detected by the mass spectrometer. ICP-MS can detect residues of arsenic or mercury pesticides in the swabs at ppb levels.

Cotton wool swabs used to remove surface deposits from a fragment of feather from the Tahitian Mourner's costume cloak.

The results of the analysis will help us to understand how pesticides were used in the museum, and may help answer questions we are starting to ask about whether the pesticides have contributed to damage, such as staining and deterioration in certain areas of some of the objects.  The results will also help us to make sure that the precautions we routinely take when we handle objects, such as wearing gloves and lab coats, are effective.

Investigating objects

Last week, two of our project partners visited us in Oxford.  Professor Richard Evershed from the University of Bristol came with his postdoctoral student, Lucy Cramp, to take samples of resins from various objects in the Cook-voyage collections.  They will use powerful techniques such as gas chromatography, followed by mass spectroscopy to try and give more information about which plant resins were used.  These analytical techniques require very small samples, and, under the microscope, there are usually tiny loose pieces of resin which can be carefully removed using the end of a scalpel blade.

Removing a sample of resin from a chest ornament, Marquesas (1886.1.1269)

Andrew Charlton from the Food and Environment Research Agency (FERA) also came to the museum last week.  Andrew specialises in the effect of pesticides on wildlife, and the purpose of the visit was to work out a method of taking surface swabs from objects so that he can test them for pesticides residues.  We know that objects in the Pitt Rivers, as in all other museums, were routinely sprayed with pesticides, including arsenic, mercury and more recently developed chemicals such as DDT, to prevent insect attack.  We are interested in finding out if there are residues of these chemicals on the surface of museum objects.  The Cook-voyage collections have been in Oxford since the 1780s so we'd expect a wide range of pesticides to have been used on them.

Jeremy with Kloe Rumney, conservation intern from Cardiff University, taking samples from the surface of a Tongan mat (1886.1.1175)