Calming Troubled Waters

Researchers Provide Concerned Communities with Expert Assessment of Human Health Risks from Using Sewage Sludge Products as Agricultural Fertilizer

University of Arizona  researchers at the NSF-supported Industry/ University Cooperative Research Center on Water Quality (also known as the Arizona Water Quality Center, or WQC) have documented that the use of treated sewage sludge as an agricultural fertilizer is unlikely to expose humans and the environment to disease-causing microorganisms. The scientists undertook their work in the wake of a published report that raised concerns about bacterial infections detected in some individuals living near sites where so-called biosolids-organic residues produced by treating municipal sewage to remove bacteria and other human pathogens-had been applied to farmland. Conducted at geographically diverse sites around the United States, the WQC's research has shown that the risks of exposure to pathogenic organisms, including bacteria and viruses that inhabit the human digestive system, are very low as little as 200 feet away from the sites where biosolid fertilizers are applied.

 

Although the land application of biosolids is highly controversial in many communities, to date there has been little scientific evidence to quantify the risks of offsite human exposure to disease-causing organisms. Communities are often concerned about whether the use of biosolid fertilizers could lead to migration of bacteria and viruses away from the site of application, for instance in aerosols carried by air currents or by movement of pathogens through soil and into groundwater. WQC scientists have devoted particular attention to the issue of human exposure to bioaerosols, analyzing more than 1,000 air samples collected at various biosolid application sites around the country, including northern Arizona, southern Arizona (near Tucson), Seattle, eastern Washington state, Houston, Chicago, and Loudoun County, Virginia (west of Washington, DC).

 

The study is the first to examine the potential for exposure to actual human enteric (that is, gut-dwelling) viruses, including the viruses that cause polio and encephalitis. Exposure was also assessed for several different bacterial species, including Salmonella, E. coli, and Staphylococcus aureus.

 

WQC's analysis shows that human exposure takes place only during actual application of biosolids. The potential for exposure exists for less than one minute and only in the vicinity of equipment that spreads biosolids on agricultural fields. Just a few hundred feet from the application site, the risk of exposure to pathogens in bioaerosols drops dramatically.

 

Advocates on both sides of this politically controversial issue (for and against the use of biosolids as an agricultural fertilizer) support the need for the kind of research being done by WQC. The researchers have conducted scientific briefings for county and state health officials in several different communities wrestling with this issue and are currently preparing reports on bioaerosol exposure for four scientific and technical publications. Initial findings have also been reported in the Arizona Daily Star newspaper as well as the scientific journal Environmental Science and Technology.

 

WQC is one of 51 NSF-supported Industry/University Cooperative Research Centers (I/UCRCs), which develop long-term partnerships between researchers in academia and private industry. Involving both the University of Arizona and Arizona State University, the research program at the Arizona Water Quality Center focuses on investigation of the physical, chemical, and microbial processes that affect water quality, in both surface waterways and groundwater, including drinking water supplies.

 

For more information, contact Ian Pepper, Director of the Water Quality Center at ipepper@ag.arizona.edu, (520) 626-3328. Information can also be found in Environmental Science & Technology (2003), vol. 37, pp. 4027-4030.