Airborne Fungi

Brief:

In Hong Kong, assessment of indoor airborne fungi is not incorporated in many IAQ audits of air-conditioned offices, although the exposure to airborne fungi could cause a variety of adverse health effects. An IAQ assessment for a local office will audit 12 parameters, including air temperature, relative humidity, air velocity, carbon dioxide, carbon monoxide, respirable suspended particulates, nitrogen dioxide, ozone, formaldehyde, total volatile organic compounds, radon, and airborne bacteria. We reviewed recent studies of the indoor airborne fungi levels and IAQ assessments in some air-conditioned offices of Hong Kong and evaluates the contribution of the airborne fungi to an unsatisfactory IAQ in the environment. The unsatisfactory rates regarding the assessment parameters were evaluated using the Monte Carlo simulations with measured data in Hong Kong Offices. In particular, the impact of selecting representative IAQ assessment parameters was examined against an express assessment protocol (EAP), which assessed some dominant contributors of satisfactory IAQ. The results reported that the three top ranked contributors for unsatisfactory IAQ were total volatile organic compounds (TVOC), indoor airborne fungi count (AFC) and airborne bacteria count (ABC) for air-conditioned offices of Hong Kong. The assessments of airborne fungi levels in office environment is an important issue and further investigations for the airborne fungi in the IAQ audits were thus recommended.

Thermal environment and fungi levels

Indoor airborne bacteria and fungi levels can be selected as indicators of a healthy indoor environment. Weinvestigated the relationships between the airborne bacteria levels, fungi levels and thermal environmental parameters, i.e. air temperature and relative humidity, in some offices with a Mechanical Ventilation and Air-Conditioning (MVAC) system operated. There was evidence that the operation of the MVAC system would have significant influence on both of the indoor airborne bacteria and fungi levels. The results showed that no significant difference in airborne bacteria and fungi levels was observed between offices having similar thermal environments. However, significantly higher airborne bacteria and fungi levels were found in the sameoffice during non-office hours when the air-conditioning system was shut down. It was also reported that the airborne bacteria and fungi levels would be correlated with the thermal environmental parameters in some offices.

Composition and exposure risk

We examined the feasibility of using a proposed relative index of fungi exposure (RIFE) as a quantitative measure to specify the enclosure effect of an indoor environment in Hong Kong air-conditioned offices. The airborne fungi count ranged from 2 to 92 CFU m⁻³. Yeast, Aspergillus, Cladosporium and Penicillium were reported as dominant in the offices. The RIFE of Yeast, Aspergillus and Penicillium were 1.26, 1.21 and 1.02 respectively, and it would confirm a higher indoor exposure risk relative to the outdoor. The RIFE of the common outdoor fungi Cladosporium was 0.48.

An assessment of exposure levels to common indoor airborne fungi, such as Aspergillus, Cladosporium, Penicillium and yeast in Hong Kong air-conditioned offices reveals that an excellent office environment with good thermal and indoor air quality control would associate with a significantly lower airborne fungi count. A significant different pattern of indoor airborne fungi were observed that a significantly higher relative abundance of Aspergillus and lower relative abundance of Cladosporium were reported.

Further information:

Mui KW, Chan WY, Wong LT, Hui PS, 2007. Fungi−an indoor air quality assessment parameter for air-conditioned offices, Building Services Engineering Research and Technology 28(3) 265-274.

Wong LT, Mui KW, Hui PS, Chan WY, Law AKY, 2008. Thermal Environmental Interference with airborne bacteria and fungi levels in air-conditioned offices, Indoor and Built Environment 17(2) 122-127.

Wong LT, Chan WY, Mui KW, Hui PS, 2009. An assessment of airborne fungi exposure risk level in air-conditioned offices, Indoor and Built Environment 18(6) 553-561.

Mui KW, Chan WY, Wong LT, Hui PS, 2010. Scoping indoor airborne fungi in an excellent indoor air quality office building in Hong Kong, Building Services Engineering Research and Technology 31(2) 191-199.