COST IE0601 : Evaluation of two methods for the decontamination of pesticide contaminated wooden museum objects : An analytical approach

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 insects and fungi. Today, some of these toxic pesticides such as DDT have effloresced on the surfaces of the objects forming a white layer of crystals or 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. In this COST project, two decontamination methods are evaluated: A vacuum washing method and a vacuum temperature method. The COST project was divided into three main parts. In the first part, oak dummies were immersed in a mixture of the pesticides dichlorobenzene, pentachlorophenol, lindane und DDT and the distribution of the pesticides in the wooden tissus were determined by GC-MS, neutron radiography and μ-XRF. As a result qualitative and quantitative concentration profiles could be created which show that most of the pesticides are concentrated on the surface of the wooden objects. PCP penetrates the wooden structure completely while the permeation of lindane and DDT was lower during impregnation. In radial direction (into the tangential surface) lindane and DDT penetrated only to a depth of about 2 mm. In a second step of this project the two decontamination methods were adopted to the wooden dummies. The first method, a vacuum washing system, was developed by the German company bhd Bautenschutz u. Hygienediensteleistungen GmbH in Dresden. With this method wooden surfaces can be cleaned from pesticides and dust by a special suction head which sprays water (or a cleaning solution) on the surface while removing it instantly by an adjustable vacuum. With regard to the application on valuable museum objects, the dummies were decontaminated only by clean water with a relatively low pressure of 2 bar. In this way, the method only affects the pesticide crystals on the surface of the object. The penetration depth of this method was determined by neutron radiography and μ-XRF. The results show a penetration depth of only 0.5 to 0.8 mm. With the second method, the vacuum temperature method, the wooden dummies were heated in a closed chamber to a temperature of 80 degrees and a low pressure of 10 mbar was applied for 8 houres. The rate of decontamination with the vacuum temperature method was determined by GC-MS. The results show a reduction of 25 percent of the pesticide concentration in the whole corpus of the wooden dummies. In the third part of the project the decontamination by the vacuum washing system was applied to historical objects and the efficiency was evaluated by μ-XRF mappings. The pesticides on the surface of the objects were reduced to 30 percent after one washing step. A second washing step reduced the surface concentration to 20 percent and a third washing step to 10 percent. Calcultated to the whole corpus the effect is not very high, but the method is a good alternative to the second method with regard to the lack of sample chambers of bigger sizes for the latter one.