Characterization of airborne particulate matter and microbes inside cultural heritage collections

Abstract

Abstract Measurements of airborne particulate matter mass concentration, mass size distribution, chemical speciation and microbial levels were performed in two museums and a library in Greece over a two-year period. The three cultural heritage sites were located in different environments [coastal (Heraklion), urban (Athens) and mountainous (Zagori)], and their collections consist mainly of organic materials. Particulate mass size distribution measurements (PM10) (cut-off diameters at 10, 9, 5.8, 4.7, 3.3, 2.1, 1.1, 0.7 and 0.4 μm) were performed inside the museums in conjunction with measurements of viable, cultivable microorganisms in air (heterotrophic bacteria, autotrophic chemolithotrophic bacteria, bacteria with metabolizing capabilities for exhibited organic materials, gelatin hydrolyzing bacteria, acid producing bacteria and fast growing fungi). The particulate matter measurements showed a variability, which was related to outdoor particle concentrations, indoor environmental conditions, infiltration rates and to indoor activities. The PM2.1 fraction of the PM10 mass had a value close to 0.6 indicating a significant outdoor origin. Chemical analysis (ions, carbonaceous material and metals) of particulate matter revealed that ions and organic carbon comprised the major part of the particle mass. Elevated concentrations of Fe, Al-rich and soluble particles were measured indoors in the three sites. An enrichment of bacteria with metabolizing capabilities for bone, parchment, woolen fabric, gelatin, and cellulose was encountered indoors in the cultural heritage sites studied as well as inside closed showcases. An indication of seasonal variations of the airborne microbial load was observed in the three cultural heritage collections. In addition, there were differences in the measured microbial load, indoors, inside the showcases and outdoors.