KEYNOTE: HUMAN EXPOSURE AND HEALTH IMPACTS ASSOCIATED WITH THE LAND APPLICATION OF SEWAGE SLUDGE

The majority of the 8 million tons of processed sewage sludge (commonly termed biosolids) produced each year in the U.S. is applied to agricultural land. This use of biosolids, however, is a present environmental, public health, and public acceptance concern, largely due to the potential for aerosol-based pathogen exposure to residents who live near land application sites. We have integrated field-based aerosol emission and transport studies with in vitro lung cell toxicity investigations, genetics-based pathogen assessment techniques, and quantitative risk assessment to understand human exposure to and infective risk associated with sewage aerosolized during land application.

Key impacts thus far include providing a clear demonstration that respirable biosolids material is released into the atmosphere during land application and subsequent wind aerosolization, and that these aerosols can be transported to off-site locations. We have demonstrated that the setback distances promulgated by federal and most state governments allow for human inhalation of aerosolized biosolids and that the respirable mass of biosolids has a significantly greater inflammatory potential and cytotoxicity than background soil-derived aerosols and animal manure. Viral metagenomic studies showed that viral pathogens in biosolids exist in higher concentration and greater diversity than previously believed when U.S. federal land application regulations were originally developed. This suite of field aerosol and pathogen assessment work has culminated in an informed infectious risk analysis that clearly demonstrated how limitations in current U.S. regulations can allow for higher than expected infectious risk, and also provided concrete land application management options to reduce risk.