Assessing airborne biological hazard from urban wastewater treatment

The production of microbial aerosols by urban sewage treatment plants may h ave wide hygienic implications which call for careful evaluation: exposure to such aerosols may in fact represent a health hazard for plant workers an d nearby residents alike. This paper describes the results of a study analy sing the degree of microbial contamination at different levels of treatment at several plants in the City of Leghorn (Livorno, Italy). Monthly aerosol samples were collected with an agar impact sampler from January to Novembe r 1996, from different sites at an activated sludge plant, an anaerobic slu dge plant and a wastewater washing station. The total bacterial and colifor m counts were determined, and pathogenic enteric bacteria and viruses were determined. These same parameters were also measured in wastewater and slud ge samples obtained at the same sites. The results revealed that high-grade airborne contamination existed at several of the studied sites. In particu lar, pathogenic enteric bacteria (Salmonella enteritidis and S. boydii) wer e isolated in 2% of the samples (540 l per sample), reovirus in 46% and ent erovirus in 9% (1800 litres per sample in indoor environment and 3000 l out door), always in association with the former virus. The biological paramete rs measured had no evident correlation with meteorological factors such as temperature, relative humidity or wind characteristics. Viral contamination proved to be quite wide-spread and detectable even in the presence of low levels of bacterial contamination. Although virological analysis have been only qualitative, and the different volumes examined for viruses and bacter ia cannot allow us to appraise with accuracy the association between these two parameters, the viral presence along with low bacteria contamination su ggests more dedicated studies to address with greater accuracy the quantita tive aspects of this association. However the monitoring performed allowed for a determination of the areas of greatest potential risk for plant worke rs, and the preventive measures most suitable to guaranteeing their safety. (C) 2000 Elsevier Science Ltd. All rights reserved.