Land application of biosolids has received national attention due to the potential for off-site transport of disease-causing micro organisms through soil, water, and air. Workers face greater exposure to bio aerosols from biosolids than those not associated with the operation. A new study published in the November-December issue of Journal of Environmental Quality investigated levels of micro organisms in air immediately downwind of land application operations and estimated occupational risks from aerosolized micro organisms.
The authors report that risks of aerosol-borne infection for biosolids workers are generally low, at less than 1 or 2% per year. Overall, occupational exposure to bio aerosols from biosolids appears to be less risky than similar exposures among wastewater treatment workers.
In all, more than 300 air samples were collected downwind of biosolids application sites at various locations within the United States. Coliform bacteria, coliphages, and heterotrophic plate count (HPC) bacteria were enumerated from air and biosolids at each site. Concentrations of coliforms relative to Salmonella and concentrations of coliphage relative to enteroviruses in biosolids were used, in conjunction with levels of coliforms and coliphages measured in air during this study, to estimate exposure to Salmonella and enteroviruses in air. The HPC bacteria were ubiquitous in air near land application sites whether or not biosolids were being applied, and concentrations were positively correlated to wind speed. Coliform bacteria were detected only when biosolids were being applied to land or loaded into land applicators. Risks from aerosolized micro organisms at biosolids land application sites appear to be lower than those at wastewater treatment plants, based on previously reported literature.
