University of Arizona Responds to Biosolids Questions.

Dr. Ian Pepper, Director, University of Arizona, NSF Water Quality Center responded on 4-9-03 to several questions raised relating to research into the potential presence of Staphylococcus aureus and bioaerosol transmission in
biosolids. Dr. Pepper was one of the panelists that participated in the National Academy of Sciences (NAS) July 2002 biosolids report, “Biosolids Applied to Land: Advancing Standards and Practices.” The following are his responses to questions raised by Greg Kester, also a panelist that participated in the NAS biosolids review:

1. Can you summarize the work you have done to investigate the occurrence of Staphylococcus aureus in Class A and Class B biosolids and what, if any, conclusions you have drawn from that work?

The W-Q-C study in 2002 looked at all major types of Class A & B biosolids for the presence of Staphylococcus aureus. Results are as follows:
. S. aureus found in 60% of all raw sewage samples.
. S. aureus never found in biosolids (Class A or B)
. S. aureus never found in bioaerosol samples taken close (2m to 20m) to fields with land-applied biosolids.

Based on these data we conclude that:
. This study provides evidence for the absence of S. aureus in biosolids
. Class B biosolids are not a source of human exposure to S. aureus
The latest “theory” that irritant chemicals from biosolids promote S. aureus infections (from ubiquitous sources) is pure speculation. There is no precedent for this type of interaction with this microbe or chemical.

2. Can you summarize the work you have done in evaluating the potential for bioaerosol transport from land application of biosolids? Additionally, can you summarize any conclusions that may be drawn regarding the potential for adverse health effects from bioaerosol transport?

To date we have taken approximately 500 aerosol samples in the Western USA in a) Tucson, Arizona; b) Mojave, Arizona; c) Solano County, California; d) Seattle, Washington; e) Yakima, Washington. The number of samples and the diversity of microbes monitored are greater than in any previous study.
The results can be summarized as follows:
. No human pathogens (bacteria or virus) detected as bioaerosols
. Indicator organisms occasionally found
. Recent studies with seeded water to which viruses had been added indicate
that majority of viruses are sorbed to solid phase biosolids and not available to be aerosolized
. Overall risk of infection from aerosols emanating from land-applied biosolids is exceedingly low
3. Can you provide an interpretation of the Dowd et al. paper published in the Journal of Environmental Quality in 2000 (29:343–348), and why its findings may differ from your own?

The Dowd paper was published in 2000 (J. Environ. Qual 29:343–348). This paper was a preliminary evaluation of the potential for bioaerosol transport from landapplied biosolids. We consider it preliminary for the following reasons:
. This was a virtual study—no analyses were made. All data and contents used in this study were derived from a variety of sources and with a variety of assumptions, some dating back several decades.
. Using the Sierra Blanca study from 1996, indicator organisms’ aerosol
concentrations were used to model human pathogens with respect to transport.
. No attempt was ever made to analyze for human viruses.
. The only human bacteria analyzed for was Salmonella. This organism can
only infect chickens as an aerosol—not humans.
. Die-off factors for the modeling were based on laboratory studies not field
studies.
. The highest risks calculated in this study were based on wind speeds of over 25 mph. Under these conditions land application of biosolids is not allowed in
Solano County.
. Overall, the models used in this study deliberately overestimated risks i.e.,
ultra conservative.

Based on these shortcomings, our present study has evaluated the presence of actual pathogens under field conditions. Risks based on the current study are dramatically lower than those predicted by the Dowd paper. Although the Dowd paper illustrates the application of theoretical transport modeling it has no relevance to the potential for bioaerosols from land application.

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