New Tool for Site-Specific Risk Assessment
The Biosolids Risk Team
Patrick L. Gurian (Principal Investigator), Elizabeth Casman, Sara
Eggers, Heather Galada, Chuck Gerba, Alrica Joe, Arun Kumar,
Mira S. Olson, Ian Pepper, Evan Richter, Nate Rostad, Jingjie Teng, Michael Wardell
Overview
Quantitative Microbial Risk Assessment
The SMART Model
Parameterization of the Model
Case Examples
What is Safe?
How do we make judgments on the
environmental impact of hazards?
The National Academy of
Sciences “Red Book” Approach
The “Red Book” which was
released in 1996 set the formal
approach for assessing the
risks from environmental
chemical hazards in the
environment
Risk Assessment
Risk Analysis
Risk
Management
(policy making)
Risk Communication
Risk AssessmentEstimation of
potential
adverse effects
associated with
exposure of
individuals or
populations to
hazards
It’s all about probability
(the odds of it
happening)
Four Basic Steps in Risk
Assessment
Hazard Identification –identifying the contaminate (i.e. Salmonella)
Dose-Response Assessment -relationship between the concentration of harmful substance and the probability of an adverse outcome (i.e. how many does it take to make you sick or kill you)
Four Basic Steps in Risk
Assessment
Exposure Assessment -Determining the concentration that you are exposed to.
Risk Characterization -Estimating the potential impact (illness, death)
EXPOSURE
How much?
Tapwater do you drink a
day?
Dirt do you
swallow a day?
Fish do you eat in a year?
Quantitative Microbial Risk
Assessment (QMRA)
Use mathematical models to characterize risks of exposure to pathogens
Validated on high dose exposures but can be extrapolated to low dose exposures
Increasingly important in regulatory policy settingStandard setting
New EPA Document under review
“Microbial Risk Assessment Guideline”
SMART Biosolids
Purpose
Provide an easy to use tool to
estimate risks of infection from
microbes in land applied
biosolids under a wide variety
of scenarios and types of
pathogens
SMART BiosolidsSpreadsheet Microbial Assessment of Risk
Tool for Biosolids
A spreadsheet with
environmental dispersion models
dose response models
exposure factors
Model site-specific microbial risk due to
land-applied biosolids
Many of these parameters and models are
not specific to biosolids land application
Why a spreadsheet?
• Visual Basic macros automatically calculate for input and output
• Easier to risks for different pathogens with Monte Carlo uncertainty analysis
SMART Biosolids
Think of it as an archive of
parameters and models
Intended as a framework others can
build on and adapt to other uses
Freely available from Water
Environment Research Foundation
Exposure Pathways
How might SMART Biosolids be used?
Pathway Application
Surface water Wet weather
event/Interpreting
indicators
Air Establishing a setback
distance
Direct Ingestion Failure of site restriction
Flowchart of Parameterization
Example 1: Wet Weather Event
It rains after an application
Did biosolids contaminate a pond used
for swimming?
Realistically monitoring for pathogens is
difficult and expensive
Run model and then evaluate
predictions for indicators
Wet Weather Events
• Runoff-Infiltration modeling
• Overland transport and fate modeling (Surface water)
• Subsurface transport and fate modeling (Ground water)
Modeling Runoff
Rainfall
RunoffMicrobes
Surface water recreation risk
results
Risk < 1:104
=>
AcceptableFarm impoundment
water
Microorganisms concentration (No./mL)
(w/o vegetative filter strip)
ReturnPeriod
(yr)Fecalcoliforms E.coli. Enterococci Coliphage
5 2.73E+02 1.50E+00 4.99E-01 1.81E+04
50 1.35E+02 7.38E-01 2.46E-01 8.90E+03
100 1.01E+02 5.53E-01 1.84E-01 6.68E+03
ReturnPeriod(yr)
Enteroviruses
Salmonella
E.coli.O157:H7
5 2.25E-06 1.74E-05 2.15E-05
50 1.11E-06 8.59E-06 1.06E-05
100 8.33E-07 6.44E-06 7.95E-06
Example 2: Inhalation Risk vs. Setback
Distance
0.00E+00
5.00E-10
1.00E-09
1.50E-09
2.00E-09
2.50E-09
0 2000 4000 6000
Ris
k/ap
plic
atio
n p
erio
d
distance of residence from near edge of field (ft)
adult mild
adult severe
child mild
child severe
Example 3: Scenario of Possible
Concern
Site restrictions not
observed-biosolids
amended soil
handled by
member of the
public or a pet
What is the risk?
Photo courtesy
of Jim Johnson
Ingestion risk of infection per application
period for residential adults
Direct
Ingestion
Surface soil-
biosolidscomposite
Acceptable
Concern
What if 503 Regulations are violated?
Violations are always a legal concern but they may or may not have substantive risk implications
Use risk assessment to evaluate whether a particular violation represents a serious risk
Potatoes are grown in a field amended with Class B Biosolids
Sold at a roadside stand
According to U.S. Title 40 CFR Part 503 this violates the minimum time to harvest
Response must address:
1. Legal issues
2. Public perception issues (perceived risk, reliability and confidence in process)
3. Substantive health risks
For now let’s focus on #3
Pathogen Ascaris
Sub_pop residential_adult
Route ingestion_soil
Distres 250
tsoilconc. 120
pathway population
Life
Threatening
Gastro-
intestinal
illness
Temporarily
Debilitating
Gastro-
intestinal
illness
ingestion
_soil
residential
_adult3.2001E-11 1.0916E-05
According to SMART Biosolids, ascaris would dominate the risk
Risk is below 1 in 10,000 benchmark often used for microbial risk
This may help inform both response and public communication efforts◦ Public confidence will be key issue
Summary: Role of SMART Biosolids Aid in the selection appropriate sites
Formulate setback requirements
Interpret indicator organism
concentrations
Respond to unanticipated events
→ high rainfall events
→ treatment failure (suboptimal)
→ unintentional exposure (pets)
Risk values for various scenarios
Inhalation (residential risk)
Incidental Soil Ingestion
(After 31 days)
Swimming
(100 year
storm event)
Drinking
(100 year
storm event)
Pathogen Slinger
Disk
Incorporation Adult Risk Child Risk
Surface
Water
Groundwater
3 ft deep,
distance to
well 100 ft
Cryptosporidium N/A N/A 1.7 x 10-5 1.7 x 10-4 3.2 × 10-5 3.50 × 10-5
Giardia N/A N/A 7.3 x 10-6 7.0 x 10-5 8.6 × 10-5 8.50 × 10-9
Salmonella 6.9 x 10-14 2.1 x 10-11 1.1 x 10-14 8.1 x 10-12 1.6 × 10-8 0
Shigella 1.73 x 10-11 5.2 x 10-9 4.0 x 10-7 3.9 x10-6 1.7× 10-5 1.39 × 10-9
Adenovirus 5.8 x 10-9 1.7 x 10-6 9.6 x 10-4 9.2 x 10-3 3.5×10-3 3.78 × 10-3
Enteroviruses 2.1 x 10-12 6.2 x 10-10 2.4 x 10-9 2.4 x 10-8 5.3×10-7 2.18 × 10-12
Flowchart of Parameterization
Summary of ParametersPathogen-related parameters Unit
Decay in water (and soil) log per hour
Decay in air log per hour
Microbial release parameter unitless
Occurrence in biosolids MPN (or PFU, or
CFU) /g biosolids
Radius of microorganisms cm
Dose-response through inhalation (and
ingestion)
unitless
Soil-related parameters Unit
Saturated hydraulic conductivity cm/h
Residual volume content unitless
Saturated water content unitless
What are the parameters in
SMART Biosolids and were
did they come from?
Decay of Pathogens and
Indicators in Water
0.00E+00
5.00E-03
1.00E-02
1.50E-02
2.00E-02
2.50E-02
3.00E-02
3.50E-02
De
ca
y r
ate
(lo
g/h
r)
Decay of Pathogens and
Indicators in Air
0.00E+00
2.00E-02
4.00E-02
6.00E-02
8.00E-02
1.00E-01
1.20E-01
1.40E-01
De
ca
y r
ate
(lo
g/h
r)
Decay of Pathogens and Indicators in
MAD Class B Biosolids
0.00E+00
5.00E-02
1.00E-01
1.50E-01
2.00E-01
2.50E-01
3.00E-01
Cry
pto
spo
ridiu
m
En
tam
oe
ba
histo
lytic
a
Gia
rdia
Mic
rosp
orid
ia
Ca
mp
ylo
ba
cte
r
Clo
stridiu
m
E. c
oli O
15
7:H
He
lico
ba
cte
r
Listeria
Sa
lmo
ne
lla
Sh
ige
lla
Vib
rio c
ho
lera
e
Ye
rsinia
Ad
en
ov
irus
Asc
aris
Co
liph
ag
e
En
teric
viru
ses
He
pa
titis A v
irus
He
pa
titis E v
irus
Astro
viru
s
No
rov
irus
Ro
tav
irus
Toxo
pla
sma
Fe
ca
l co
liform
s
E. c
oli
En
tero
co
cc
i
Microbial release fraction from soil or
biosolids
0%1%2%3%4%5%6%7%8%
Adenovirus
from soil with
8% organic
matter
Adenovirus
from soil with
2% organic
matter
Coliphage
from 7%
biosolids
Coliphage
from 2%
biosolids
Poliovirus
and
echovirus
from soil
Radius of Pathogens and
Indicators
0.00E+001.00E-042.00E-043.00E-044.00E-045.00E-046.00E-047.00E-04
Ra
diu
s (c
m)
Mean Occurrence of Pathogens and
Indicators in MAD Class B Biosolids
1.00E-01
1.00E+00
1.00E+01
1.00E+02
1.00E+03
1.00E+04
1.00E+05
1.00E+06
1.00E+07
1.00E+08
1.00E+09
Dose-Response of Pathogens and Indicators
in MAD Class B Biosolids
0.00E+00
1.00E-01
2.00E-01
3.00E-01
4.00E-01
5.00E-01
6.00E-01
7.00E-01
Saturated Hydraulic
Conductivity of Soil Textures
0
5
10
15
20
25
30
35
Sa
tura
ted
hy
dra
ulic
co
nd
uc
tivity
(c
m/h
)
Risk values for various scenarios
Inhalation (residential risk)
Incidental Soil Ingestion
(After 31 days)
Swimming
(100 year
storm event)
Drinking
(100 year
storm event)
Pathogen Slinger
Disk
Incorporation Adult Risk Child Risk
Surface
Water
Groundwater
3 ft deep,
distance to
well 100 ft
Cryptosporidium N/A N/A 1.7 x 10-5 1.7 x 10-4 3.2 × 10-5 3.50 × 10-5
Giardia N/A N/A 7.3 x 10-6 7.0 x 10-5 8.6 × 10-5 8.50 × 10-9
Salmonella 6.9 x 10-14 2.1 x 10-11 1.1 x 10-14 8.1 x 10-12 1.6 × 10-8 0
Shigella 1.73 x 10-11 5.2 x 10-9 4.0 x 10-7 3.9 x10-6 1.7× 10-5 1.39 × 10-9
Adenovirus 5.8 x 10-9 1.7 x 10-6 9.6 x 10-4 9.2 x 10-3 3.5×10-3 3.78 × 10-3
Enteroviruses 2.1 x 10-12 6.2 x 10-10 2.4 x 10-9 2.4 x 10-8 5.3×10-7 2.18 × 10-12
Summary
QMRA has important applications in the
drinking water supply field
SMART Biosolids model focuses on
microbial risk from land applied biosolids
but contains parameters and models
relevant to other domains, including
drinking water
Freely available and intended as a base
for others to build on