MUSEUM staff now have a way to detoxify pesticide-laden artefacts in their care. Using supercritical carbon dioxide, they can remove the dangerous amounts of DDT, PCBs and lindane that were once sprayed onto wooden statues and pieces of cloth to protect them from insects.
One way to get rid of the hazardous and unsightly white crust of pesticides that leaches out of these artworks is simply to wash them with water. But that is only a temporary solution, as the crust will re-form. And soaking artefacts for longer only damages them further, says Andreas Weber from the Fraunhofer Institute for Environment, Safety and Energy Technology in Oberhausen, Germany.
So Weber鈥檚 team turned instead to supercritical CO2, a solvent used by the food industry to extract caffeine from coffee. It has the properties both of a liquid and a gas, and has an extremely low surface tension, which allows it to penetrate porous materials such as wood without swelling and cracking the cells.
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The team used a pressure of 350 atmospheres to drive the solvent into small DDT-contaminated wooden artefacts held at 40 掳C. They then carefully depressurised and cooled the system, sucking the solvent back out and bringing 75 per cent of the DDT with it (Pesticide Outlook, 2003, p 7). The technique is gentle enough not to wrinkle gilded surfaces or dissolve important resins. 鈥淚t works very well for textiles too 鈥� that鈥檚 actually easier,鈥� says Weber.
The technique could help rescue thousands of Native American artefacts that have been treated with dangerous pesticides in museums (快猫短视频, 1 March, p 8). Chemist Pete Palmer at San Francisco State University thinks the solvent will probably not wash out inorganic poisons such as mercury, and it might wash away valuable organic dyes. But returning a slightly damaged artefact that can once again be used in cultural ceremonies may be better than not being able to clean it all.