Size-segregated aerosol samplings were carried out during 2013-14 at Okhla landfills, Delhi, which is a municipal solid waste dumping station. Aerosol samples were collected on quartz filters using an Andersen impactor sampler having 9-stages with cut-off diameter >9.0, 9.0-5.8, 5.8-4.7, 4.7-3.3, 3.3-2.1, 2.1-1.1, 1.1-0.65, 0.65-0.43, <0.43 mu m at flow rate 28.3 lpm. Additionally, a low-volume handy sampler was also used to measure total culturable microbial concentrations operates at flow rate of 2 lpm. The culturable total bacterial and fungal concentrations across the seasons ranged from 8.3x10(5)-1.8x10(7) cfu/m(3) and 1.2x10(3)-2.5x10(5) cfu/m(3), respectively and also varied across the impactor stages. Major concentration peaks found during winter could be associated with high particulate matter concentration and favourable meteorological conditions in Delhi. On the other hand, comparatively lower concentrations were observed in summer. This is possibly because of microbial lethal effects of adverse meteorological conditions (high temperature and solar radiation) which are more prominent than that of release of microbial flux due to solar ground heating effect in summer. Size distribution analysis shows that bacteria were mostly abundant in fine particle sizes, i.e. <0.43-2.1 mu m, but few peaks were also observed in size ranges between 5.8->9.0 mu m. Fungal spores mostly peaked in coarse sizes (2.1-5.8 mu m) and showed unimodal size distribution. Predominant identified bacterial strains were mostly belonged to Bacillus, Staphylococcus, Streptococcus, Klebseilla and Escherichia genera. Most of the identified fungal spores are known for adverse health effects causing numerous allergic and pathogenic inflammations. These results suggest that the open-solid waste dumping sites are a major source of bioaerosols, and residents living in the nearby areas of landfills are at high health risks. (C) 2016 Published by Elsevier B.V.
