Risks of unsatisfactory airborne bacteria level in air-conditioned offices of subtropical climates

Adjustment of the indoor air temperature and relative humidity set points for energy conservation is adopted in many air-conditioned offices in the subtropics. This study examines the environmental risks in an air-conditioned office with a ‘readjusted’ thermal environment from the perspective of the probable airborne bacteria level exceeding certain limits. In particular, a cross-sectional study of bacteria concentrations in 422 air-conditioned offices in Hong Kong was conducted, and a mathematical expression was proposed to correlate the indoor bacteria level with the indoor air temperature and relative humidity in an air-conditioned office. With the proposed correlation, the probability of an air-conditioned office having an unsatisfactory airborne bacteria level could be determined. The model results were verified with the measurement results from some other studies. This model would be a useful tool for preliminary assessment of the environmental risks, regarding the airborne bacteria level while balancing some energy conservation measures, in an air-conditioned office in the subtropics. The study also provides a template for developing an environmental risk assessment model in air-conditioned spaces elsewhere.     

Exposure to culturable airborne bioaerosols during noodle manufacturing in central Taiwan

Biological hazards associated with the manufacturing of noodles have not been well characterized in Taiwan. This is an issue that flour workers can be exposed to bioaerosols (airborne fungi and bacteria) resulting flour-induced occupational asthma or allergic diseases. This study is to survey the species and concentrations of bioaerosols at different sites within a noodle factory for one year, and to investigate the effects of environmental factors on concentrations of bioaerosols. Air samples were taken twice a day, one day each month using a MAS-100 bioaerosol sampler.Nine species of culturable fungi were identified, with the main airborne fungi being Cladosporium, Penicillium, Aspergillus spp., non-sporing isolates and yeasts. Cladosporium, Penicillium and Aspergillus were the dominant fungal isolates in the indoor and outdoor air samples. Micrococcus spp. and Staphylococcus xylosus were the dominant bacterial isolates. Peak fungal and bacterial concentrations occurred at the crushing site, with mean values of 3082 and 12,616 CFU/m³. Meanwhile, the most prevalent fungi and bacteria at the crushing site were in ranges of 2.1-1.1 μm and 1.1-0.65 μm, respectively. Significant seasonal differences in total bacterial concentration were observed at all sampling sites (?P < 0.05). Moreover, significant seasonal differences were observed for most of the fungal genera except Fusarium. Levels of Aspergillus and Rhizopus differed significantly during the two sampling times, as did levels of Micrococcus spp. and Staphylococcus arlettae.Regarding the same operation procedures, relative humidity affected fungi levels more than temperature did. However, crushing generated the highest concentration of bioaerosols among all operation procedures. Furthermore, levels of bacteria at sites fitted with ventilation systems were lower than at sites without ventilation systems, especially at the crushing site. Therefore, we recommend these workers at the crushing site wear breathing protection and improve the local ventilation systems to minimize the biological hazards.     

Investigation of bacterial and fungal communities in indoor and outdoor air of elementary school classrooms by 16S rRNA gene and ITS region sequencing

The advent of high-throughput sequencing methods allowed researchers to fully characterize microbial community in environmental samples, which is crucial to better understand their health effects upon exposures. In our study, we investigated bacterial and fungal community in indoor and outdoor air of nine classrooms in three elementary schools in Seoul, Korea. The extracted bacterial 16S rRNA gene and fungal ITS regions were sequenced, and their taxa were identified. Quantitative polymerase chain reaction for total bacteria DNA was also performed. The bacterial community was richer in outdoor air than classroom air, whereas fungal diversity was similar indoors and outdoors. Bacteria such as Enhydrobacter, Micrococcus, and Staphylococcus that are generally found in human skin, mucous membrane, and intestine were found in great abundance. For fungi, Cladosporium, Clitocybe, and Daedaleopsis were the most abundant genera in classroom air and mostly related to outdoor plants. Bacterial community composition in classroom air was similar among all classrooms but differed from that in outdoor air. However, indoor and outdoor fungal community compositions were similar for the same school but different among schools. Our study indicated the main source of airborne bacteria in classrooms was likely human occupants; however, classroom airborne fungi most likely originated from outdoors.     

Indoor air quality investigation at air-conditioned and non-air-conditioned markets in Hong Kong

To characterize indoor air quality at the markets in Hong Kong, three non-air-conditioned and two air-conditioned markets were selected for this study. The indoor air pollutants measured included PM(10) (particulate matters with aerodynamic diameter less than 10 microm), total bacteria count (TBC), carbon monoxide (CO), nitric oxide (NO), nitrogen dioxide (NO(2)) and sulfur dioxide (SO(2)). The indoor and outdoor concentrations of these target air pollutants at these markets were measured and compared. The effects of air conditioning, temperature/relative humidity variation and different stalls on the indoor air quality were also investigated. The results indicated that all of the average indoor concentrations of PM(10), TBC, CO and NO(2) at the markets were below the Hong Kong Indoor Air Quality Objectives (HKIAQO) standards with a few exceptions for PM(10) and TBC. The elevated PM(10) concentrations at Hung Hom, Ngau Tau Kok and Wan Chai markets were probably due to the air filtration of outdoor airborne particulates emitted from vehicular exhaust, whereas high concentrations of airborne bacteria at Sai Ying Pun and Tin Shing markets were linked to the use of air conditioning. Correlation analysis demonstrated that indoor bacteria concentrations were correlated with temperature and relative humidity. The operation of air conditioning did not significantly reduce the levels of air pollutants at the markets. However, the higher indoor/outdoor ratios demonstrated that the operation of air conditioning had influence on the levels of bacteria at the markets. It was found that average PM(10) concentration at poultry stalls was higher than the HKIAQO standard of 180 microg/m(3), and was over two times that measured at vegetable, fish and meat stalls. Furthermore, the concentration of airborne bacteria at the poultry stalls was as high as 1031 CFU/m(3), which was above the HKIAQO standard of 1000 CFU/m(3). The bacteria levels at other three stalls were all below the HKIAQO standard. Statistical analysis indicated that there were no significant differences among the four stalls for CO, NO(x) and SO(2).     

建筑室内外空气真菌浓度相关性案例测试分析

选取某高校学生办公室进行室内外空气真菌浓度相关性和粒径的研究。结果表明:室内空气真菌浓度变化范围为1698~4429 cfu/m³,最大值出现在12:00;室外浓度范围为3569~29452 cfu/m³,最大值也出现在12:00。室内外空气真菌浓度比值均小于1,Spearman相关性分析显示室内外空气真菌呈显著正相关,且线性回归分析表明室外空气真菌是室内空气真菌的显著影响因子,可推断本研究的室外空气真菌是室内的主要来源。室内空气真菌浓度与室内人数呈显著正相关。室内外空气真菌均从Ⅰ级到Ⅳ级逐渐增加,而后Ⅴ级到Ⅵ级逐渐减小,最大值出现在第Ⅳ级,可进入人体下呼吸道的室内外空气真菌粒径占比达85.0%以上。     

Changing microbial concentrations are associated with ventilation performance in Taiwan's air-conditioned office buildings

Our study conducted serial environmental measurements in 12 large office buildings with two different ventilation designs to obtain airborne microbial concentrations in typical office buildings, and to examine the effects of occupant density, ventilation type and air exchange efficiency on indoor microbial concentrations. Duplicate samples of airborne fungi and bacteria, a total of 2477 measurements, were collected based on a scheme of conducting sampling three times a day for at least seven consecutive days at every study building. Air change rates (ACHs) were also estimated by tracer gas concentration decay method, and measured by continuous Multi-Gas monitor for each building. Most sampling sites were with total fungal and bacteria concentrations higher than 1000 CFU/m(3), an often-quoted guideline in earlier research. Significantly higher concentrations of fungi and bacteria, as well as higher indoor/outdoor (I/O) ratios across most groups of airborne microbes, were identified in buildings with fan coil unit (FCU) system than those with air-handling unit (AHU) system (Student's t test, P < 0.0001). Older buildings and higher air exchange rates were statistically associated with greater indoor bacteria levels in FCU ventilated buildings (R(2) = 0.452); a pattern not found in AHU buildings. Increasing ACH seemed to be the determinant factor for rising indoor fungal and Cladosporium concentrations in those FCU buildings (R(2) = 0.346; 0.518). Our data indicated that FCU ventilated buildings might have provided more outdoor matters into indoor environments through direct penetration of outdoor air. Results also demonstrated a quantitative association between rising numbers of occupants and increasing indoor levels of yeast in both FCU and AHU ventilated buildings. The regression model identified in this study may be considered a reference value for proposing an optimal ACH, while with adequate filtration of fresh air, as an effective strategy in lowering indoor microbial concentrations in air-conditioned buildings. PRACTICAL IMPLICATIONS: As control of indoor microbial contamination has become an increasing concern around the world, feasibility and effectiveness of adopting ventilation approach has attracted a significant interest. This field investigation demonstrated, quantitatively, critical variables to be taken into consideration while applying such a measure, including the kinds of microbes to be removed and the types of ventilation system already in place.     

Airborne microbiological characteristics in public buildings of Korea

Characteristics of airborne bacteria and fungi were surveyed in the public buildings regulated in Korea, with the six-stage cascade impactor. The total concentrations of airborne bacteria and fungi were averaged to 404 and 382 cfu m⁻³ in hospital, 931 and 536 cfu m⁻³ in kindergarten, 294 and 334 cfu m⁻³ in elderly welfare facility, and 586 and 371 cfu m⁻³ in postpartum nurse center. Mean respirable concentrations of airborne bacteria and fungi were 194 and 292 cfu m⁻³ in hospital, 358 and 347 cfu m⁻³ in kindergarten, 134 and 266 cfu m⁻³ in elderly welfare facility, and 254 and 289 cfu m⁻³ in postpartum nurse center, respectively. Based on this results, total and respirable concentrations of airborne bacteria and fungi were significantly highest in kindergarten and lowest in elderly welfare facility (p<0.05$p<0.05$). The ratios of indoor and outdoor concentration for airborne bacteria and fungi were below 1.0 in all the investigated public buildings regardless of size distribution. The dominant genera identified in the public buildings were Staphylococcus spp., Micrococcus spp., Corynebacterium spp., and Bacillus spp., for airborne bacteria and Penicillium spp., Cladosporium spp., and Aspergillus spp., for airborne fungi, respectively. Size distributions of airborne bacteria and fungi in terms of the dominant genera were not observed consistently except for Staphylococcus spp., which was detected mainly on the first stage (>7.0 μm) and second stage(4.7–7.0 μm), and Penicillium spp., and Cladosporium spp., showing the highest collection rate at stage 3 (3.3–4.7 μm) regardless of the kind of the public buildings.     

Characterizing airborne fungal and bacterial concentrations and emission rates in six occupied children's classrooms

Baseline information on size‐resolved bacterial, fungal, and particulate matter (PM) indoor air concentrations and emission rates is presented for six school classrooms sampled in four countries. Human occupancy resulted in significantly elevated airborne bacterial (81 times on average), fungal (15 times), and PM mass (nine times) concentrations as compared to vacant conditions. Occupied indoor/outdoor (I/O) ratios consistently exceeded vacant I/O ratios. Regarding size distributions, average room‐occupied bacterial, fungal, and PM geometric mean particle sizes were similar to one another while geometric means estimated for bacteria, fungi, and PM mass during vacant sampling were consistently lower than when occupied. Occupancy also resulted in elevated indoor bacterial‐to‐PM mass‐based and number‐based ratios above corresponding outdoor levels. Mean emission rates due to human occupancy were 14 million cells/person/h for bacteria, 14 million spore equivalents/person/h for fungi, and 22 mg/person/h for PM mass. Across all locations, indoor emissions contributed 83 ± 27% (bacteria), 66 ± 19% (fungi), and 83 ± 24% (PM mass) of the average indoor air concentrations during occupied times.     

Use of temporal/seasonal- and size-dependent bioaerosol data to characterize the contribution of outdoor fungi to residential exposures

With the use of published temporal/seasonal and particle size distribution of outdoor bioaerosol data and meteorological information in the subtropical climate, we characterized the airborne fungal concentration indoor/outdoor/personal exposure relationships in a wind-induced naturally ventilated residence. We applied a size-dependent indoor/outdoor ratio model coupled with a compartmental lung model based on a hygroscopic growth factor as a function of relative humidity on aerodynamic diameter and concentration of fungal spores. The higher indoor airborne fungal concentrations occurred in early morning and late afternoon in which median values were 699.29 and 626.20 CFU m(-3) in summer as well as 138.71 and 99.01 CFU m(-3) in winter, respectively, at 2 am and 8 pm. In the absence of indoor sources, summer has higher mean indoor/outdoor ratios of airborne fungal concentration (0.29-0.58) than that in winter (0.12-0.16). Lung region of extrathoracic (ET) has higher fungal concentration lung/indoor ratios (0.7-0.8) than that in bronchial (BB; 0.41-0.60), bronchiolar (bb; 0.12-0.40), and alveolar-interstitial (AI); 0.01-0.24) regions. The highest airborne fungal deposition dose (95th-percentile is 4600 CFU) occurred in 11 pm-5 am in region AI in that the 95th-percentile fungal deposition rate was 0.22 CFU s(-1).     

Can we use indoor fungi as bioindicators of indoor air quality? Historical perspectives and open questions

Microbiological analysis of atmospheres witnessed substantial technical improvements in the 1940s to 1960s. May's cascade impactor and Hirst's spore trap allowed the counting of total cells but had limited capacity for identification of the spores. Bourdillon's sampler enabled the counting of cultivable fungi and their identification. A great step forward was given with the Andersen's six-stage impactor, which allowed discrimination of particles by size, counting of cultivable cells, and species identification. This period also witnessed the development of impingers, namely, the AGI-30 described by Malligo and Idoine, and the three-stage model designed by K. R. May. The 1990s to 2000s witnessed innovative discoveries on the biology of indoor fungi. Work carried out in several laboratories showed that indoor fungi can release groups of spores, individual spores and fungal fragments, and produce volatile organic compounds and mycotoxins. Integrating all findings a holistic interpretation emerged for the sick building syndrome. Healthy houses and buildings, with low indoor humidity, display no appreciable indoor fungal growth, and outdoor Cladosporium dominates. On the contrary, in sick houses and buildings, high indoor humidity allows fungal growth (mainly of Penicillium and Aspergillus), with concomitant release of conidia and fragments into the atmosphere. The intoxication probably results from a chronic exposure to volatile organic compounds and mycotoxins produced by Penicillium, Aspergillus, and Stachybotrys.Very clean atmospheres are difficult to study by conventional methods. However, some of these atmospheres, namely, those of hospital rooms, should be monitored. Sedimentary sampling, chemical methods applied to impinger's collection liquid, and selected molecular methods can be useful in this context.It was concluded that fungi can be useful indicators of indoor air quality and that it is important to deepen the studies of indoor atmospheres in order to promote air quality, the health and well-being of all, and a better understanding of the biology of indoor fungi.     

Indoor Air Quality Investigations at Five Classrooms

Abstract Five classrooms, air-conditioned or naturally ventilated, at five different schools were chosen for comparison of indoor and outdoor air quality. Temperature, relative humidity (RH), carbon dioxide (CO₂), sulphur dioxide (SO₂), nitric oxide (NO), nitrogen dioxide (NO₂), particulate matter with diameter less than 10 mm (PM₁₀), formaldehyde (HCHO), and total bacteria counts were monitored at indoor and outdoor locations simultaneously. Respirable particulate matter was found to be the worst among parameters measured in this study. The indoor and outdoor average PM₁₀ concentrations exceeded the Hong Kong standards, and the maximum indoor PM₁₀ level was even at 472 μ;g/m³. Air cleaners could be used in classrooms to reduce the high PM₁₀ concentration. Indoor CO₂ concentrations often exceeded 1,000 μl/l indicating inadequate ventilation. Lowering the occupancy and increasing breaks between classes could alleviate the high CO₂ concentrations. Though the maximum indoor CO₂ level reached 5,900 μl/l during class at one of the sites, CO₂ concentrations were still at levels that pose no health threats.     

An energy impact assessment of ventilation for indoor airborne bacteria exposure risk in air-conditioned offices

Treatment of fresh air in ventilation systems for air-conditioned offices consumes a significant amount of energy and affects the indoor air quality (IAQ). In this study, energy impact on the ventilation systems was examined against certain IAQ objectives for indoor airborne bacteria exposure risk in air-conditioned offices of Hong Kong. The relationship between thermal energy consumptions and indoor airborne bacteria exposure levels based on regional surveys was investigated. The thermal energy consumptions of ventilation systems operating for carbon dioxide (CO₂) exposure concentrations between 800 and 1200 ppmv for typical office buildings and the corresponding failure probability against some target bacteria exposure levels were evaluated. The results showed that, for a reference indoor environment at a CO₂ exposure concentration of 1000 ppmv, the predicted average thermal energy saving of ventilation system for a unit increment of the expected risk of unsatisfactory IAQ of 1% was 55 MJ m⁻² yr⁻¹ and for a unit decrement of 1%, the predicted additional thermal energy consumption was 58 MJ m⁻² yr⁻¹ respectively. This study would be a useful source of reference in evaluation of the energy performance of ventilation strategies in air-conditioned offices at a quantified exposure risk of airborne bacteria.     

Association between indoor mold and asthma among children in Buffalo, New York

Asthma is a leading chronic disease among children and places a significant burden on public health. Exposure to indoor mold has been associated with asthma symptoms. However, many mold assessments have relied on visual or other identification of damp conditions and mold presence, thus have not examined associations with specific fungal genera. The objective of this case-control study was to examine the relationship between airborne mold concentrations and asthma status among children and to identify the contribution from specific mold genera in air. Participants completed a questionnaire of home environmental conditions and underwent indoor air sampling in the home, from which viable and total-count fungal spores were quantified. The most prevalent fungi in the homes were the allergenic molds Cladosporium (98% and 87% of homes from viable and total count samples, respectively) and Penicillium (91% and 73%). There were no significant differences in mean fungal concentrations between the homes of cases and controls, although the observed rate of exposure to several molds was higher among the cases. Among children who lacked a family history of asthma, cases had significantly higher exposures to viable Aspergillus. Measured humidity levels in the home corresponded with some self-reported indicators of mold and dampness. PRACTICAL IMPLICATIONS: The results of this study support existing literature that indoor fungal exposures play a role in current asthma status and that some qualitative assessments of mold exposure correspond to fungi present in indoor air.     

Diurnal distribution of airborne bacteria and fungi in the atmosphere of Helwan area, Egypt

Airborne bacterial and fungal composition in an industrial town of Helwan, Egypt, was studied using a slit impactor sampler during the period from March 2006 to February 2007. Airborne bacterial concentrations were usually higher than fungi. Bacteria and fungi had similar diurnal variation patterns. Airborne microorganisms reached their concentration peaks in the evening and gradually decreased during the night time. The hourly concentration peaks of the bacteria and fungi appeared at 20:00 h. A significant difference (P ≤ 0.05) was found between the hourly mean concentrations of airborne fungi in winter compared to other seasons. Fungi concentrations were significantly higher (P ≤ 0.05) on working weekdays than weekends. Aspergillus, Penicillium, Alternaria and Cladosporium were the most predominant airborne fungal genera. Aspergillus showed double peak patterns whereas Penicillium, Alternaria and Cladosporium showed one peak pattern. The diurnal variations of the bacteria and fungi could be divided into four periods: 1) the morning maximum concentration (6:00 h-10:00 h), 2) midday to afternoon pattern (10:00 h-16:00 h), 3) the evening concentration peak (18:00 h-20:00 h) and 4) the gradual decrease of night time concentration (22:00 h-24:00 h). Geographical location, human activity, growth cycle of organisms and meteorological factors were the main criteria controlling the temporal variations of the air microorganisms in the Wadi Hof area.     

Changes in profiles of airborne fungi in flooded homes in southern Taiwan after Typhoon Morakot

In August 2009, the historic Typhoon Morakot brought extreme rainfall and resulted in flooding which spread throughout southern Taiwan. This study compared the difference between fungal concentrations before and after the disaster in selected homes of the Tainan metropolitan area, which were hit hardest by the catastrophe. A group of 83 households available from a prior cohort established with random sampling out of a regional population in southern Taiwan was contacted successfully by telephone. Twenty-five of these reported to have suffered from floods of various degrees at this time. Around 2 weeks after the event, at which time most of the remedial process had been completed by self-efforts and public health endeavours, 14 of these 25 (56%) agreed to participate in measurements of the airborne microbial concentrations. The averages (standard deviation) of the total culturable fungal concentrations in children's bedrooms and flooded rooms were 18,181 (25,854) colony-forming units per cubic metre (CFU/m³) and 13,440 (11,033) CFU/m³, respectively. The airborne fungal spore levels in the 2 above-mentioned indoor sites were 221,536 (169,640) spores/m³ and 201,582 (137,091) spores/m³, respectively. The average indoor/outdoor ratios in the children's bedrooms were 4.2 for culturable fungi and 1.4 for fungal spores. These values were higher than the respective values measured in the same homes during the previous year: 1.1 and 0.6. In terms of the specific fungal profile, the percentages of Aspergillus spp. increased significantly in both the indoor and outdoor environments after the event. To this date, this study is among the limited research that has been conducted to quantitatively demonstrate that fungal manifestation is likely to persist in flooded homes even after seemingly robust remedial measures have been put into place. Studies to examine the potential health implications and effectiveness of better remedial technology remain much needed.     

不同气候区城市公共建筑内微生物浓度对比分析

为研究不同气候区公共建筑室内微生物污染状况,选取昆明和南京分别代表温和地区和夏热冬冷地区,对医院和办公楼2类公共建筑内的微生物浓度进行了测量和分析。结果表明:温和气候区内医院细菌和真菌平均浓度分别为520、316 cfu/m³,办公楼细菌和真菌平均浓度分别为369、520 cfu/m³,均高于夏热冬冷气候区对应类型公共建筑;2个气候区室内细菌、真菌粒径分布相似,峰值均出现在粒径范围Ⅳ级(2.1~3.3μm)和Ⅴ级(1.1~2.1μm);2个气候区公共建筑室内相对湿度和空气真菌浓度存在确定关系,除此之外,仅在昆明医院内发现温度和微生物浓度之间存在显著相关性。     

Construction of a nomogram for predicting the risk of allergic rhinitis among employees of long-distance bus stations in China

This study examined indoor air pollutants and their health effects on allergic rhinitis in 3194 employees of 226 bus station halls and then constructed a nomogram model to predict allergic rhinitis risk in those employees. Indoor air temperature, relative humidity, PM₁₀, PM_2.5, total bacteria, and total fungi were measured, and questionnaires were used to collect basic station information and employee health information. The results revealed that the over-standard rates of PM₁₀, PM_2.5, total bacteria, and total fungi were 18.16%, 31.13%, 2.22%, and 55.89%, respectively. Seasonal variations were found in temperature, relative humidity, and PM_2.5. Passenger flow could affect temperature, and total bacteria. Central air conditioning could affect total bacteria. A total of 15.90% of the employees were diagnosed as allergic rhinitis by physicians. Relative humidity, fungi, self-reported allergic rhinitis symptoms, and exposure to smoking were the influencing factors for allergic rhinitis. These four variables were incorporated to construct a nomogram. The concordance index of the nomogram was 0.775 (95% CI: 0.745-0.806) and 0.749 (95% CI: 0.715-0.783) for the training cohort and test cohort, respectively. The calibration plot revealed that the nomogram model exhibited good discrimination and consistency. This nomogram model may help predict the occurrence of allergic rhinitis.     

Indoor exposure levels of bacteria and fungi in residences,schools, and offices in China: A systematic review

Microbes in buildings have attracted extensive attention from both the research community and the general public due to their close relationship with human health. However, there still lacks comprehensive information on the indoor exposure level of microbes in China. This study systematically reviews exposure levels, the community structures, and the impact factors of airborne bacteria and fungi in residences, schools, and offices in China. We reviewed the major literature databases between 1980 and 2019 and selected 55 original studies based on a set of criteria. Results show that the concentration of indoor bacteria varies from 72.5 to 7500 CFU/m³, with a median value of 1000 CFU/m³, and the concentration of fungi varies from 12 to 9730 CFU/m³, with a median value of 526 CFU/m³. The concentration level of microbes varies in different climate zones, with higher bacterial concentrations in the severe cold zone, and higher fungal concentrations in the hot summer and warm winter zone. Among different buildings, classrooms have the highest average bacteria and fungi levels. This review reveals that a unified assessment system based on health effects is needed for evaluating the exposure levels of bacteria and fungi.     

Biodeterioration of sandstone under the influence of different humidity levels in laboratory conditions

Excessive moisture in building materials supports microbial growth. It has been referred that relative humidity more than 55% promotes the microbial growth. To test the effect of different relative humidity tropical chamber test was set up at 52%, 76%, 85% and 96% RH and maximum diversity of fungi was found at 85% and 96% RH. Two fungi Aspergillus sydowi and Aspergillus flavipes were present throughout the course of study from moderate to highly abundant form. It was observed that Fusarium moniliforme, Cephalosporium acremonium, Papulospora sp. proliferated at higher relative humidity (i.e. at 85% and 96.6% RH) and Fusarium roseum, Fusarium oxysporum only at 96% RH level. The relative humidity level lower than 62%, i.e. at 52% level exhibited no fungal growth on sandstone surface during two-year observations. During the study pattern it was noticed that diversity decreased gradually and dominance of particular species increased with the time factor. Analysis of sandstone after fungal colonization by X-ray diffraction and SEM showed the formation of newly formed biomineral.