The seasonal distribution of bioaerosols in municipal landfill sites: a 3-yr study

Landfill is the most common way to dispose waste in many countries, and most landfill sites after closure are often considered for public recreation purposes. It is important that the pollutant levels of closed landfill areas are free of adverse health concerns. However, only limited studies have investigated the airborne biological contamination in closed landfill sites. The objective of this study was to document the bioaerosol levels in a closed landfill site while the temporal, seasonal, and meteorological effects were also taken into accounts. Study site was at one sanitary landfill, taking mostly municipal wastes, in southern Taiwan. Airborne bacteria and fungi were collected on tryptic soy agar (Difco) and malt extract agar (Difco) by a Burkard impactor (Burkard Manufacturing Co. Ltd.) operating at about 10 l m−3 for 30 s. Air samples were collected sequentially in winter, spring, summer and fall in 1998, winter, spring, summer in 1999, as well as summer and fall in 2000. In addition, sampling was conducted in the morning, at noon, in the evening and the following morning during each field assessment. Levels of airborne bacteria and fungi were all far above 103 CFU m−3. The concentrations of culturable bacteria and fungi were higher in winter than in other seasons. The difference of bioaerosol level and fungal percentages between the undergoing-closure and closed areas was obvious, and the concentrations were higher in closed area. We therefore recommend that before any complete investigation can be conducted to assure the safety, the closed area of landfill site is probably not ready for immediate public use.