Estimation of bioaerosol risk of infection to residents adjacent to a land applied biosolids site using an empirically derived transport model

Aim: The purpose of this study was to develop an empirically derived transport model, which could be used to predict downwind concentrations of viruses and bacteria during land application of liquid biosolids and subsequently assess microbial risk associated with this practice. Methods and Results: To develop the model, coliphage MS-2 and Escherichia coli were aerosolized after addition to water within a biosolids spray application truck, and bioaerosols were collected at discrete downwind distances ranging from 2 to 70 m. Although coliphage were routinely detected, E. coli did not frequently survive aerosolization. Data on aerosolized coliphage was then used to generate a virus transport model. Risks of infection were calculated for various ranges of human virus concentrations that could be found in biosolids. Conclusions: A conservative estimate at 30.5 m (assumed to be nearest adjacent residences) downwind, resulted in risks of infection of 1 : 100 000, to the more realistic 1 : 10 000 000 per exposure. Conservative annual risks were calculated to be no more than 7 : 100 000 where as a more realistic risk was no greater than 7 : 10 000 000. Overall, the viral risk to residences adjacent to land application sites appears to be low, both for one time and annual probabilities of infection. Significance and Impact of the Study: This study demonstrated a simple approach towards modelling viral pathogens aerosolized from land applied liquid biosolids, and offers insight into the associated viral risk.