engleski

Gamma-irradiation for cultural heritage – treatment of selected fungi on linen textile

Background of the study. A common carrier for paintings is glue-coated linen that is vulnerable to fungal biodeterioration. The study aimed to assess antifungal effect of gamma-irradiation doses and dose rates against naturally occurring mycobiota and artificially inoculated primary, secondary and tertiary fungal colonizers common for cellulose materials like linen. The composition of natural mycobiota on glue-coated linen (initial level) and eventual post-irradiation recovery of mycobiota were analyzed. Methodology. The initial level of common fungal colony-forming mycobiota on model glue-coated linen textile was determined by plate count method upon 7 days of incubation (at 25°C and 70-80% r.h.) and the data expressed as the number of colony-forming units per gram (CFU/g). Next, linen samples were separately inoculated with selected primary (Aspergillus jensenii), secondary (Cladosporium spaherospermum) and tertiary colonizers (Trichoderma harzianum) at concentration of 104 CFU/g. Inoculated linen and controls were incubated as described. One group of samples was analysed immediately upon the incubation while the rest of the samples were irradiated at 60-Co gamma source at RCDL to doses of 2, 7, 20 and 50 kGy, at dose rates of 0.1 and 9.8 Gy/s and analysed after incubation for 0, 7, 14 and 28 days. Results. Alternaria spp., Aspergillus spp., Cladosporium spp. Fusarium spp., Penicillium spp. and yeasts comprised naturally occurring mycobiota, in initial concentrations of 103 CFU/g (molds) and 104 CFU/g (yeasts). These fungi were non-homogeneously dispersed on glue-coated linen. On incubation in humid atmosphere the concentration of mycobiota increased for four orders of magnitude. Similar increase was obtained for non-irradiated artificially inoculated samples. All applied doses and dose rates were effective against primary and tertiary colonizers but not for secondary colonizers and linen mycobiota. Doses of 2 and 7 kGy was ineffective in reduction of linen mycobiota to the initial level ; after 28 days of incubation fungi were recovered in concentrations up to 106 and 105 CFU/g, respectivelly. Dose of 20 kGy (0.1 Gy/s) reduced Cladosporium spp., and Alternaria spp. to 104 CFU/g ; Penicillium spp. was reduced to the initial level while yeasts, Aspergillus spp., and Fusarium spp. recovered in concentrations below initial. For both 7 and 20 kGy dose rate of 9.8 Gy/s was more effective in fungal elimination than 0.1. Gy/s while for 2 kGy the dose rate effect was inconsistent. Upon exposure to 50 kGy sterile white mycelia was recovered on few plates after incubation periods. Secondary colonizer, C. sphaerospermum survived radiation with 2, 7 and 20 kGy, and showed the similar recovery pattern as obtained for Cladosporium spp. After treatment with 7 and 20 kGy (0.1 Gy/s) cladosporia recovered between 7th (or 14th) and 28th day in concentrations between 103 and 106 CFU/g. The same doses with dose rate 9.8 Gy/s inhibited recovery of C. sphaerospermum. Conclusion. For successful gamma-radiation reduction of fungal contamination on cultural heritage it is essential to determine mycobiota composition and to irradiate at an appropriate dose rate.

gamma radiation ; cultural heritage ; fungi ; radiation dose ; mycobiota

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