Evaluation of decontamination methods of pesticide contaminated wooden objects in museum collections: Efficiency of the treatments and influence on the wooden structure

Abstract

Abstract In the second half of the 20th century, many valuable wooden museum objects were massively treated with toxic chloride pesticides (such as DDT, pentachlorophenol [PCP] or lindane) to protect them against insect and mold infestation. In the following years, synthetic pyrethroids replaced the classic pesticides or the objects were even treated with mixtures of chemicals. Today, some of these toxic pesticides such as DDT have effloresced on the objects surfaces forming a white layer of crystals or they are emitted into the indoor air of storage rooms or exhibitions. In order to prevent the conservators as well as the visitors from health risks, it is inevitable to decontaminate these objects. Two COST projects were started in order to evaluate suitable decontamination methods and to investigate their influence on the wooden microstructure, the second project basing on the results of the first one. In the first project (SER COST project C07.0110 “Evaluation on the effectiveness of decontamination methods for wooden art objects treated with wood preservatives”), dummies of oak wood were soaked with a mixture of the pesticides pentachlorophenol, lindane und DDT and the distribution of the pesticides in the wood structure was determined by GC/MS, neutron radiography and μ-XRF. Then two decontamination methods were adopted to the wooden dummies: a vacuum washing system (bhd-decon ® , developed by the German company bhd Bautenschutz u. Hygienediensteleistungen GmbH, Dresden) and a vacuum temperature method (developed by the Berne University of Applied Sciences (Architecture, Wood and Civil Engineering) in collaboration with the Berne University of Applied Sciences (Berne University of the Arts). The efficiency of both methods was evaluated by GC/MS and μ-XRF, creating depth profiles of the distribution of the remaining pesticides. The vacuum temperature method turned out to be too rough in means of temperature and pressure and was limited to a relatively small sample chamber. Therefore, the vacuum washing method was applied to historical objects and the efficiency was evaluated by μ-XRF mappings. During the investigations by passive sample measurements on the surface of museum objects, it became apparent that the pesticide concentration in the historical objects is much higher than assumed and, furthermore, that they contain a mixture of classic pesticides with synthetic pyrethroids as a result of repeated treatment. For this reason and for the investigation of a possible change of the wooden microstructure during decontamination, a second project (SER No. C09.0031 “Studies on the distribution of wood preservatives and on structural changes of the wooden structure during decontamination treatment of museum objects polluted by chlorinated and pyrethroid preservatives”) was started. In this project, the wooden dummies were soaked in a mixture of pesticides of a higher concentration and the penetration depth was investigated depending on the use of different solvents by GC/MS and μ-XRF. The microstructure of the wood was investigated by micro X-ray tomography and 3D microscopy before and after decontamination treatment.