Due to the absence of established dose response relationships it is not possible to estimate the health risk associated with elevated bioaerosol concentrations in residential micro-environments. At present there are no established threshold limit values for bioaerosols in residential indoor settings. Some organizations have provided guidelines on the levels of indoor bioaerosols. The American Conference of Governmental Industrial Hygienists (ACGIH 1999) does not provide any numerical guideline to interpret the environmental measurements.
5 Conclusion
The present study was carried out to investigate the levels of airborne bacteria and fungi in rural and urban residential micro-environments in Pakistan. The results showed that concentrations at these sites were highly variable, especially for fungi. This is the first detailed study on levels of indoor bioaerosols in Pakistan and draws attention to the possible increased respiratory exposure of inhabitants to bioaerosols in both rural and urban areas. Farming activities and livestock rearing can be associated with the higher bioaerosol concentration in the rural areas. Nonetheless the levels at the urban sites, especially for bacteria, were not significantly lower than those for rural areas. The poor sanitation conditions might make a considerable contribution to elevated levels in both rural and urban areas. However, the size distribution profile of bacteria, indoors and outdoors, suggested the presence of indoor sources, especially at Rural site II and the urban site.
The present study highlights the limited usefulness of a standard approach to compare indoor/outdoor bioaerosol concentrations to determine if indoor microbial air quality is typical or atypical in rural communities. In addition, knowledge of the size distribution profile of bioaerosols at different locations is not only important with regard to their airborne behaviour and deposition in the human respiratory system but can also improve our understanding of bioaerosol sources. It is of note that the present study employed culture based method. Due to the specific incubation temperature and medium used to culture the bioaerosols, it is very likely that it would not recover a large number of the viable but not culturable bioaerosols. Hence the exposure risk could be far greater than expected. Furthermore, this investigation was carried out in one province of Pakistan and the concentration in other geographical regions may well vary. There is a need for detailed studies from different regions of the country keeping in view the household conditions and socio-economic differences.