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  • 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 SlingerDisk

    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 SlingerDisk

    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