The Identification of Hazardous Biocide Residues on Herbarium Material

Victoria Purewal
Department of Biodiversity and Systematic Biology, National Museum Wales, Cardiff

Belinda Colston PhD CSci CChem FRSC
School of Natural & Applied Sciences, University of Lincoln

The NMW herbarium consists of c. 500,000 botanical specimens that have been donated, collected in house, or purchased primarily from Wales, Great Britain and Europe. These collections have been protected from pest and mould attack, in the past, by the applications of chemicals, including mercuric chloride, arsenic trioxide, lead arsenate and barium fluorosilicate, and organic fumigants, such as naphthalene. These chemicals are extremely toxic and even over hundreds of years their residues still pose a threat to visitors and staff members handling the collections.

Unfortunately, it is not always possible to determine whether a herbarium specimen has been treated or not, as often, no data accompanies the specimen, and this has made handling the collections and prioritising which specimens to re-mount, a difficult decision-making process.

It was noticed that certain areas on the support sheets, beneath and around the specimen, fluoresced under ultra violet light. The fluorescence appeared to coincide with liquid application, often with splash marks and spots. Research was undertaken to determine if the fluorescing areas corresponded to chemical treatments – if so, this would be a very useful, cheap and quick method to determine whether historic treatments have been made, and aid in prioritising the re-mounting process.

The fluorescent areas varied in colour, and it was hoped that this colour was correlated to the metal species present. To determine the metal content of the fluorescent areas, a sensitive and precise trace-elemental method was required.

Through the EU-ARTECH Programme, the fluorescent areas of the backing papers were analysed by Particle Induced X-ray Emission (PIXE) at the Centre de Recherche et de Restauration des Musées de France, the Louvre, Paris. 177 samples were analysed.

The papers on which the specimens are mounted come from all over the world, and consequently, each sheet is different from the next – different fillers or brighteners added; and varying metal ion content. Control samples were therefore taken from the edge of each sheet – the assumption being made that little or no treatment residue was present in these areas. In this way, a comparison of treated and untreated areas could be made.

Botanical material was also analysed, showing that the heavy metal content of the specimen was much less, even undetected, whereas the sample paper below held high concentrations. Due to the waxy coating of the specimen much of the pesticide application would run off onto the paper below. The specimen itself would not be preserved at all, but the paper sheet that staff and visitors would be handling would have very high concentrations!

This work is on-going.

 Purewal, V., Colston, B. and Rörhs, S. (2007). The identification of historic pesticide and fungicide residues present on herbarium material housed within the National Museum Wales. X-Ray Spectrometry (in press).