Biosolids: Our Approach
Society has used biosolids as a soil amendment for as long as we have
treated municipal wastewater. Land application has increased over the
past 20 years, to the point where more than 50 percent of the sewage
sludge produced in the United States is land-applied as biosolids. A
longstanding issue remains, however: what is the best way to manage
possible exposure to pathogens associated with land application of
This WERF research will explore advancements in pathogen risk
assessment. It will also bring forth the complementary and equally
important science of risk communication practices. The research will lay
out some risk assessment and communication options – all in a
single, integrated process – for utilities, land appliers,
regulators and local public administrators at the local, state and
Researchers will use state-of-the-science data and assumptions for
biosolids pathogens, and will access ongoing research on other important
issues related to pathogens in general, and specifically to land
application of biosolids. Other research is looking for more precise
information on infectious doses; more reliable indicator organisms and
analytical methods; and better information on the emergence of
antibiotic resistant microorganisms. WERF will factor the latest
information into future refinements of both the risk assessment and
communication practices components of this project.
Quantitative Microbial Risk Assessment
Using risk-based methodologies as part of the Standards for the
Use and Disposal of Sewage Sludge (Part 503), EPA developed maximum
allowable levels for chemical contaminants in biosolids. They based
maximum allowable levels of microbial contaminants on treatment-based
performance – rather than risk levels – because
pathogen risk assessment methodologies were not yet accepted for
biosolids. The treatments cited in the Part 503 rule include general
requirements, management practices, and operational standards for land
This research may help put pathogen risk assessment for biosolids
into common practice.
Microbial health risk studies to date have predominantly focused on
the fate of pathogens during treatment and in the environment. Through
work on several related projects, WERF developed a quantitative pathogen
health risks methodology for land application of biosolids, which offers
one logical starting point for this research. Researchers will
supplement that approach with other pathogen risk assessment
Microbial risk assessment (QMRA) has four fundamental components:
• Hazard identification (also referred to as problem
formulation) identifies pathogens and potential exposure pathways,
including the types of illnesses that could occur.
• Exposure assessments estimate the quantity of pathogens
(dose) to which individuals or populations are exposed.
• In a dose-response assessment, the dose is entered into a
health effects model that quantitatively estimates the risk associated
with a specific pathogen-exposure scenario, in this case the occurrence
of illness/disease for an individual or target population.
• The risk characterization step then examines risk estimates
for different pathogen exposure scenarios to provide an overall risk
summary. The risk summary allows for the estimation of incremental
increased risk above background risk.
Strategic Risk Communications
An integral and equally important aspect of this research is
application of the best risk communications science and practices.
Effective strategic risk communications involve stakeholders from the
outset and throughout the entire process. It provides purposeful
interaction and appropriate information, and helps decision-makers and
stakeholders make well-informed decisions leading to effective risk
management.(Stakeholders are individuals, groups, or organizations that
may affect, be affected by, or perceive itself to be affected by a
Strategic risk communications includes all communication content and
interactions that can influence risk decisions and behavior.
• Such content may be included in announcements, warnings,
and guidance documents.
• Content may appear in verbal statements, pictures,
advertisements, publications, legal briefs, labels, warning signs, or
• Content may describe risks or characterize their
importance. It may also advocate actions regarding risks, hazards, and
technologies, including ways to mitigate them.
• Interactions include everything from engaging individuals
and/or groups in one-on-one or small group settings to broader and often
more formal citizen engagement and consultation processes.
Effective risk communications must reflect the best available
knowledge. Such knowledge should be selected for its relevance to
decisions facing stakeholders and framed in terms that address their
beliefs and feelings.