Biosolids Microbes Pose Manageable Risk to Workers

Class B biosolids are sewage sludges that have been treated to contain fewer than 2.0 x 106 fecal coliforms/dry gram. The USEPA estimates that 6.3 million tonnes of Class B biosolids are generated in the United States each year, and that by 2010, the amount generated per year will increase to 7.4 million tonnes.

Biosolids produced during municipal sewage treatment are most commonly applied to land as a fertilizer at agricultural sites throughout the United States. Class B biosolids, which are the principal type of biosolids applied to land, contain a variety of enteric pathogens.

Land application of biosolids has received national attention due to the potential for off-site transport of disease-causing microorganisms through soil, water, and air. Workers face greater exposure to bioaerosols 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 microorganisms in air immediately downwind of land application operations and estimated occupational risks from aerosolized microorganisms.

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 bioaerosols 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 windspeed. Coliform bacteria were detected only when biosolids were being applied to land or loaded into land applicators. Risks from aerosolized microorganisms at biosolids land application sites appear to be lower than those at wastewater treatment plants, based on previously reported literature.

The full article is available for no charge for 30 days following the date of this summary. View the abstract at http://jeq.scijournals.org/cgi/content/abstract/37/6/2311.

The Journal of Environmental Quality, http://jeq.scijournals.org is a peer-reviewed, international journal of environmental quality in natural and agricultural ecosystems published six times a year by the American Society of Agronomy (ASA), Crop Science Society of America (CSSA), and the Soil Science Society of America (SSSA). The Journal of Environmental Quality covers various aspects of anthropogenic impacts on the environment, including terrestrial, atmospheric, and aquatic systems.

The Soil Science Society of America (SSSA) is a progressive, international scientific society that fosters the transfer of knowledge and practices to sustain global soils. Based in Madison, WI, and founded in 1936, SSSA is the professional home for 6,000+ members dedicated to advancing the field of soil science. It provides information about soils in relation to crop production, environmental quality, ecosystem sustainability, bioremediation, waste management, recycling, and wise land use.

SSSA supports its members by providing quality research-based publications, educational programs, certifications, and science policy initiatives via a Washington, DC, office. For more information, visit www.soils.org.

SSSA is the founding sponsor of an approximately 5,000-square foot exhibition, Dig It! The Secrets of Soil, which opened on July 19, 2008 at the Smithsonian's Natural History Museum in Washington, DC.