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Risk Assessment
Risk Assessment Topics
What is Risk? Risk, Hazard and Exposure How is Risk Expressed? Risk Categories What is Risk Assessment? Risk Assessment Applications
What is Risk?
Risk is the probability or likelihood of an adverse effect due to some hazardous situation
Safety is the complement of risk, or the probability that an adverse effect will not occur
Risk = f ( Hazard, Exposure)
Magnitude or severity of risk are a function of the type of harm i.e. Hazard and the extent or likelihood of Exposure
Leaking Pipe
Risk and Hazard Determination
Leaking Pipe
Leaking Pipe
Hazard : Potential for creating undesired adverse consequences.In this case it remains same as chemical flowing through pipe is same.
Leaking Pipe
Exposure : Vulnerability to hazardPipe 2 poses greatest risk of exposure due to leakage.
How is risk expressed?
Probability of adverse effects associated with a particular activity
Unitless From 0-1E.g. 1x10-1 - One in 101x10-2 - One in 100
Factors in Risk Acceptability Voluntary
– Smoking– Bungee Jumping– Diet
Nonvoluntary– Risk resulting from uncontrollable actions of others (Occupational
exposure, pesticide residues)– Natural disasters
Degree of control Magnitude of the outcome Awareness Catastrophic Potential Group involvement Cost of alternatives
Activity Annual RiskSmoking 10 cigarettes/day 1 x 10-3
Motor vehicle accidents 2 x 10-4
Manufacturing work accident 8 x 10-5
Pedestrian hit by automobiles 4 x 10-5
Drinking two beers/day 4 x 10-5
Person in a room with a smoker 1 x 10-5
Peanut butter (4 teaspoons/d) 8 x 10-6
Drinking water with EPA limit of Trichloroethene 2 x 10-9
Risk Values
What is Risk Assessment?
Analytical tool for studying situations that could result in adverse consequences
Qualitative and quantitative assessment of environmental status
Process to identify and quantify the risk and select necessary action
Risk Assessment Applications
Identification of any ecological risk
Identification of the need for additional data collection
Site remediation alternative selection
Establishment of cleanup standards
Remediation Options?
No Action
Excavation, Incineration/re-
landfilling
In place containment, groundwater pumping
and retreatment alternative
No Action
No capital cost Groundwater contamination is definite
In place containment, groundwater pumping
and retreatment alternative
Creating a barrier to prevent or extend the
groundwater contamination around the site
Construction of containment
facility
Air Stripping
Volatilization and Particulate migration
Volatilization
Excavation Incineration/
Re-Landfilling
Vehicular transport to incinerator
Stockpiling at
incinerator Incinerator
Re- Landfilling
Particulate migration /
Volatilization
Flue Gas Emissions
Process
H a z a r d
D a t a
I d e n t i f i c a t io n
D o s e - R e s p o n s e
R is k M a n a g e m e n t
W h a t a g e n t s a r e p o t e n t i a l l y h a r m f u l ?
W h o w i l l b e e x p o s e d t ow h a t a n d f o r h o w lo n g ?
H o w i s in t a k e o r d o s er e la t e d t o a d v e r s e e f f e c t s ?
W h a t e f f e c t s a r e l ik e l y o n h u m a n h e a l th a n d e n v i r o n m e n t?
Exposure
Assessment
Risk
Assessment
Characteristics
Risk Assessment ProcessHazard
Identification
Dose Response
Exposure Assessment
Risk characterizatio
n
Hazard Identification
Toxicity assessment determines whether exposure to a chemical, physical, or biological agent can cause an increase in the incidence of an adverse effect.
Necessary condition for a health or safety risk Physical, metabolic, and chemical properties
of the agent; Potential routes of exposure; toxicological
effects; results of animal studies (dose-response); and site characteristics
Hazard Identification – Toxicity ScoreRanking of chemicals from contaminated
sites depending upon their toxicity scoresHelp in identifying contaminants with a
significant impact at the site Need data from the contaminated site
Hazard Identification – Toxicity Score – Non=carcinogensToxicity score (TS) = Cmax / RfD
Cmax = Maximum Concentration
RfD = Chronic Reference Dose i.e. acceptable daily intake
TS = Toxicity score
Hazard Identification – Toxicity Score - Carcinogens
Toxicity score (TS) = Cmax * CSF
Cmax = Maximum Concentration
CSF = Cancer Slope factor
TS = Toxicity score
Hazard Identification – Toxicity Score – Example Landfill ABC
Chemicals Air (mg/m3) Groundwater (mg/L)
Soil (mg/kg)
Mean Max Mean Max Mean Max
Chlorobenzene (NC)
4.09E-08
8.09E-08 2.5E-04
1.10E-02
1.39E+00
6.40E+00
Chloroform (C, NC)
1.12E-12
3.12E-12 3.3E-04
7.60E-03
1.12E+00
4.10E+00
1,2-Dichloroethan
e (NC)
1.12E-08
2.40E-08 2.1E-04
2.00E-03
ND ND
BEHP (C, NC) 3.29E-07
8.29E-07 ND ND 1.03E+02
2.30E+02
ND – Not Detected; C= Carcinogenic, NC = Non-carcinogenic
Hazard Identification – Toxicity Score
Chemicals RfD ( mg/kg-day)
Soil (mg/kg)
Mean Cmax
Chlorobenzene 2.00E-02 1.39E+00 6.40E+00
Chloroform 1.00E-02 1.12E+00 4.10E+00
1,2-Dichloroethane
NA ND ND
BEHP 2.00E-02 1.03E+02 2.30E+02
ND – Not Detected; NA-Not Applicable
Rank the non-carcinogenic chemicals for soil
Hazard Identification – Toxicity Score
Chemicals RfD ( mg/kg-
day)
Soil (mg/kg) TS = Cmax/RfD
Rank
Mean Cmax
Chlorobenzene 2.00E-02 1.39E+00
6.40E+00 320 3
Chloroform 1.00E-02 1.12E+00
4.10E+00 410 2
1,2-Dichloroethane
NA ND ND NA
BEHP 2.00E-02 1.03E+02
2.30E+02 11,500 1
ND – Not Detected; NA-Not Applicable
BEHP poses the greatest risk for the given site followed by chloroform and Chlorobenzene.
Hazard Identification – Toxicity Score
Selection of chemicals by TS method is followed by further evaluation which deals with other properties of that contaminant like mobility, persistence in environment, treatability etc. depending on the purpose of assessment.
Hazard Identification – Toxicity Score
Now try the same problems for carcinogens.
Also find RfD for the same contaminants in groundwater and air, on web and perform TS calculations
Risk Assessment ProcessHazard
Identification
Dose Response
Exposure Assessment
Risk Characterizati
on
Risk Assessment Process
Dose Response
How large a dose causes what magnitude of
effect?
Dose-Response AssessmentDose-response assessment is the process
of characterizing the relation between the dose of target contaminant administered or received, and the incidence of an adverse health effect in exposed populations, and estimating the incidence of the effect as a function of human exposure to the agent.
Represents variations in response of receptor at different contaminant levels
Generally, increasing the dose of contaminant will result in a proportional increase in both the incidence of an adverse effect as well as the severity of the effect.
Quantitative relationship between exposure and toxic effects
Enables risk assessor to estimate a safe dose Actual dose is compared with safe dose in risk
assessment process
Dose-Response Curve
Dose-Response CurveD
ose
Response
XX
XX
XRfD
NOAEL Threshold
Dose: mg chemical/kg of body weight
Response: % population affected by dose.
Curvature of dose response curve illustrates varying sensitivity of exposed population.
No-Observed-Adverse-Effect-Level (NOAL)
– the greatest test dose level at which no adverse effect is noted
Lowest-Observed-Adverse-Effect-Level (LOAEL)
– Lowest level at which an adverse effect is detected
Cancer Response-Dose Curve
Dose: mg chemical/kg of body weight
Response: % population cancer
Extrapolate to low dose/risk
Response
Dose
X
X
X X
No Threshold, Linearat Low Doses
Slope = Cancer Slope Factor
Reference Dose
RfD: An estimate of daily exposure to the human population that is likely to be without appreciable risk of deleterious effects during a lifetime
Expressed as mg pollutant / kg body weight/day
Also expressed as Reference Concentration (RfC), mg/m3
Reference Dose
RfD = NOAEL /(FAFHFSFLFD)Where:
NOAEL: No-Observed-Adverse-Effect-Level
FA: An adjustment factor to extrapolate from animal to human population
FH: Adjustment factor for differences in human susceptibility
FL: An adjustment factor applied when LOAEL is used instead of NOAEL
FS: An adjustment factor applied when data set is dubious or incomplete
Reference Dose - Problem
In a three month subchronic study in mice, the NOAEL for tris-(1,3-dichloro-2-propyl) phosphate was 15.3 mg/kg body weight per day; the LOAEL was 62 mg/kg at which dose abnormal liver effects were noted. If each of the adjustment factor is equal to 10, calculate the reference dose for chemical.
Reference Dose - Problem
Given: NOAEL = 15.3 mg/kg body weight per dayLOAEL = 62 mg/kg (no need here as NOAEL is
given)Calculate RfD using NOAEL and LOAEL
RfD = NOAEL / (FA FH FS FLFD)
Adjustment factors applicable for this problem are: FA, FH, Fs
RfD = 15.3/(10*10*10) = 0.015 mg/kg-day
Reference Dose - Problem
Using LOAEL :
RfD = LOAEL/(FA FH FS FLFD)Adjustment factors applicable are : FA, FH, Fs
and FL
RfD = 62/(10*10*10*10) = 0.0062 mg/kg-day
Reference Dose - Problem
RfD = 0.015 mg/kg-day (Using NOAEL)
RfD = 0.0062 mg/kg-day (using LOAEL)
The lowest of two values will be the reference dose for tris-phosphate i.e. 0.0062 mg/kg-day
Reference Dose - Problem
Repeat the RfD calculations for tris-phosphate for which NOAEL was determined to be 22mg/kg-day and the LOAEL was found to be 44 mg/kg-day for increased weight of liver and kidneys in rat.
Risk Assessment ProcessHazard
Identification
Dose Response
Exposure Assessment
Risk characterizatio
n
Exposure Assessment
Exposure Assessment
Deals with various exposure pathways for released contaminant
Exposure Assessment - PathwaysSource (e.g. landfill, lagoon)Chemical release mechanism (e.g.
leaching)Transport mechanism (e.g. groundwater)Transfer mechanism (e.g. sorption)Transformation mechanism (e.g.
biodegradation)Exposure point (e.g. residential well)Receptor Exposure route ( e.g ingestion, inhale)
Means of Exposure
Occupational Exposure, i.e. exposure at workplace
Community Exposure, i.e. exposure at workplace
Exposure Assessment
Exposure Assessment
Lungs Exposure(Inhalatio
n)
Routes of Exposure
Dermal Exposure
(Skin) Ingestion
Exposure Assessment
Process
Air
Inhalation Ingestion
Work Surface
Skin
Dermal Absorptio
n
Exposure
Duration (Time)
Severity (mass/time)
Breathing/Ingestion
Rate (volume/tim
e)
Env. concentratio
n (mass/volum
e) Period (time/exposure)
Frequency (no. exposures)
Inhalation/Ingestion Exposure Framework
Exposure (mass)
Severity (mass/time)
Absorption (mass/area/inciden
t)
Surface (area skin exposed)
Frequency (no. incidents)
Dermal Exposure Framework
NSP: Nanoscale particles
( C x CR x EF x ED)
I = --------------------------
(BW x AT)I = Intake (mg/kg of body weight per day)
C = Concentration at exposure point (e.g. mg/L in water or mg/m3 in air)
CR = Contact Rate ( e.g L/day or m3/day)
EF = Frequency (day/year)
ED = Exposure Duration (yr)
BW = Body weight (kg)
AT = Averaging Time (days)
Calculation
Standard Parameters for Calculating Exposure and Intake
Parameter Adults Child Age (6-12) Child Age ( 2-6)
Average Body Weight (kg)
70 29 16
Skin surface are (cm2) 18,150 10470 6980
Water Ingested (L/day) 2 2 1
Air breathed (m3/hour) 0.83 0.46 0.25
Retention rate (inhaled air)
100% 100% 100%
Absorption rate (inhaled air)
100% 100% 100%
Soil ingested (mg/day) 100 100 200
Bathing duration (minutes)
30 30 30
Exposure frequency (days)
365 365 365
Exposure duration (years)
30 6 4
Intake Rate Calculation
Determine the chronic daily inhalation intake, by adults, of a non-carcinogenic chemical as a function of concentration in fugitive dust at a landfill ABC.
Intake Rate Calculation
( C x CR x EF x Ed x RR x ABS)I = -----------------------------------------
(BW x AT)Air breathing rate for adults = 0.83 m3/hrCR = 0.83 x 24 = 19.92 m3/dayEF = 365 days ED = 30 years ( For chronic exposure, non-carcinogen)RR = 1, ABS = 1 ( Assumption in the absence of any
data)AT = 365 days x 30 years
Intake Rate Calculation
I = (C x 19.92 x (365 x 30) x 1x1)/ (70 x (365x60))
I = 0.285 m3/kg-day x C
C = Exposure point concentration (mg/m3)
Risk Assessment ProcessHazard
Identification
Dose Response
Exposure Assessment
Risk characterizatio
n
Risk Characterization
Final step of risk assessment process
Integration of hazard identification, dose response assessment and exposure assessment.
Risk Characterization
Carcinogenic RiskNon-carcinogenic
Risk
Risk Characterization
Risk Characterization - Carcinogens
Risk = CDI x SF
Where:
CDI = Chronic daily intake (mg/kg-day) hazard assessment
SF = carcinogenic slope factor (kg-day/mg)
Risk Characterization - CarcinogenicCalculate the average carcinogenic risk from chloroform due
to dermal contact of soil by workers at the landfill ABC.
From TS calculation table: C = 1.12 mg/kg
From carcinogenic dose intake calculations I = 2.9 x 10-9 x C = 3.26 x 10-9 mg/kg-daySF for Chloroform = 6.1 x 10-3
Risk = 6.1 x 10-3 x 3.26 x 10-9 mg/kg-day
Risk= 1.99 x 10-11
Risk Characterization: Non-carcinogenicNormally characterized in terms of
hazard index (HI) HI = (CDI/RfD) where
• CDI = Chronic daily intake (mg/kg-day)• RfD = Reference dose (mg/kg-day)• HI = Hazard Index (Unitless)
HI < 1.0 is acceptable
Risk Characterization: Non -carcinogenic
Calculate the hazard index for chlorobenzene, based on intake calculated for landfill ABC.
Solution:
HI = CDI/RfD
RfD = 2 x 10-2 ; CDI = 2.82 x 10-7
HI = 1.41 x 10-5 < 1 OK
Risk Management
Regulatory actionDecision to mitigate riskAction level
Uncertainty
The risk assessment process is extremely conservative in nature and utilizes measurements which are uncertain.
Insufficient data or information gaps often exist in characterizing the potential risk of an agent, necessitating the need for assumptions or educated guesses.
Uncertainty
Use computational tools from the field of decision analysis to account for the uncertainties in the process
These tools allow risk to be expressed as a probability distribution rather than a single number which can then be used to make a more informed decision during risk management
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Last updated October 2008 by Dr. Reinhart