Microbial risk assessment framework for exposure to amended sludge projects.
BACKGROUND
Although the U.S. Environmental Protection Agency has a long history of using risk-based approaches for regulatory purposes, pollutant limits for pathogens in biosolids are not currently based on quantitative risk assessments.


OBJECTIVE
We developed and demonstrated a risk-based methodology for assessing the risk to human health from exposure to pathogens via biosolids.


METHODS
Four models were developed, incorporating direct ingestion, groundwater, and aerosol exposure pathways. Three sources of environmental data were used to estimate risk: pathogen monitoring of sludge, efficacy of sludge treatment, and pathogen monitoring of biosolids.


RESULTS
Risk estimates were obtainable even for Class A biosolids, where posttreatment monitoring data are below detectable levels, demonstrating that risk assessments for biosolids exposure are practical. Model analyses suggest that: a) a two-digester design decreases the probability of risks >10(-4) compared with one-digester designs, b) risks associated with exposures to groundwater and aerosol pathways were, in general, lower than exposures to the direct ingestion pathway, and c) secondary transmission can be an important factor in risk estimation.


CONCLUSIONS
The risk-based approach presented here provides a tool to a) help biosolids producers interpret the results of biosolids monitoring data in terms of its health implications, b) help treatment plant engineers evaluate the risk-based benefits of operational changes to existing or projected treatment processes, and c) help environmental managers evaluate potential capital improvements and/or land application site placement issues. Regulation of pathogens can now be based on human health risk in a manner parallel to other water-related risks.
Eisenberg
Joseph N S
JN
Department of Epidemiology, University of Michigan, Ann Arbor, Michigan 48109, USA. jnse@umich.edu
Moore
Kelly
K
Soller
Jeffery A
JA
Eisenberg
Don
D
Colford
John M
JM
D004781:Environmental Exposure / Q000032:analysis / Q000592:standards*; D004784:Environmental Monitoring; D006801:Humans; D008962:Models, Theoretical; D018570:Risk Assessment; D012722:Sewage / Q000382:microbiology*; D014481:United States; D014484:United States Environmental Protection Agency / Q000592:standards
D012722:Sewage