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