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The effect of mercuric chloride treatment as biocide for herbaria on the indoor air quality

Author: Havermans, J.B.G.A. · Dekker, R. · Sportel, R.
Source:Heritage Science, 3, 1-8
Identifier: 530180
Keywords: Materials · Herbarium · Mercury emission · Indoor air quality · Occupational health · Environment & Sustainability · Urbanisation · Urban Mobility & Environment · AEC - Applied Environmental Chemistry · ELSS - Earth, Life and Social Sciences


One of the most previous conservation treatments for plant specimen in herbarium collections was mercuric chloride (HgCl2). However, due time HgCl2 may decompose and it may cause (metallic) mercury (Hg) emission. Hg vapour in indoor air should be avoided as mercury poisoning can already occur at levels of 6 μg/m3. Both field and laboratory studies were carried out while the Hg concentration was analysed in the air. Field studied included analysis of the indoor air in the repository and analysis of the concentration inside a herbarium box. Subsequently lab experiments were carried out on measuring the Hg emission using a small scale emission chamber. The lab studies proved that the emission of Hg from collections is according to the theories of Hoetjer–Berger–Fuji and therefore it can be seen as a continuous emission. Field studies concluded that workers and visitors may be subjected to a high mercury concentration in the repositories. Opening a herbarium box may even cause a peak concentration of over 80 μg/m3. The highest concentration observed in the repositories was 13 μg/m3. Although this value is lower than the official Dutch threshold levels of 20 μg/m3 (time weight average over 8 h for work places), this concentration has to be considered as high. Based on the lab studies, it can be concluded that by adjusting the ventilation rate in work rooms and repositories,