1. Risk Assessment: A Conceptual Introduction
Tee L. Guidotti
Occupational Health Program
University of Alberta

2. Risk Assessment
Risk assessment is the systematic evaluation of the likelihood of an adverse effect arising from exposure in a defined population.
Risk assessment is “a systematic process for describing and qualifying the risks associated with hazardous substances, action or events.” (Covello)

3. Other Important Terms Hazard Risk Opportunity
the intrinsic potential for harm
toxicity, injury, damage, cost
specific to an exposure level
Risk
probability of (adverse) outcome
Opportunity
likelihood that significant exposure will occur

4. Hazard  Exposure  Opportunity  Population (at Risk)
A Definition of Risk
Risk = (H, E, O, P)
Hazard  Exposure  Opportunity  Population (at Risk)

5. Risk Analysis, Risk Management
Hazard identification 
Risk assessment 
Risk evaluation
Risk Management
Option generation
Option evaluation
Option selection
Implementation and enforcement

6. Types of Risk Assessment
Qualitative
knowledge of hazard
knowledge of exposure opportunity
estimates of exposure magnitude
knowledge of exposure-response
informed judgement
Quantitative
quantification of hazard
estimates of population at risk
exposure assessment
known or extrapolated exposure-response
estimate of risk

7. Steps in Risk Assessment - 1
Release assessment
potential of emission, effluent, contact
pathways of exposure
subject to change
Exposure assessment
intensity
frequency
duration

8. Steps in Risk Assessment - 2
Consequence assessment
human health-related outcomes
ecological impact
psychological impact
cost impact
Risk estimation
probability of adverse effect for individual
probability of adverse effect in population

9. Step by Step through Risk Assessment

10. Step 1. Release Assessment - 1
Identification of the characteristics of “risk source” or “risk agent” that may predict failure or release:
monitoring (recording past experience)
performance (simulation or experiential)
testing (systematic trials)
incident evaluation (detailed investigation)
modeling (e.g. fault trees , failure analysis)

11. Step 1. Release Assessment - 2
Outcomes:
probability of failure or exposure event
understanding of how this may happen
identification of critical faults or failures
Problems:
analysis is counterintuitive, complicated
may miss multifactoral outcomes
assumes a perfect understanding of the system

12. Step 2. Exposure Assessment - 1
Essential elements:
pathway and route of exposure
“fate and disposition”, dilution, degradation
distribution, duration and magnitude of exposures at point of contact
multiple exposures and multiple sources of exposure
susceptible populations

13. Step 2. Exposure Assessment - 2
Methods:
Direct measurement
environmental measurement
personal measurement
biological exposure monitoring
Indirect measurement
biological effect monitoring
biomarkers of exposure (narrowly defined)
surveys, consumption records

14. Step 2. Exposure Assessment - 3
Indirect Exposure Estimation
extrapolation, ecological association
categorization (exposure matrices)
simulation
surrogate measurements
modeling
surface water
groundwater
air dispersion

15. Step 3. Consequence Assessment
General framework:

16. Step 3. Consequence Assessment
Identify plausible outcomes associated with exposure levels implied by exposure assessment
Consider susceptible populations and atypical responses
Consider health effects as: acute, chronic, lethal
Interest in subclinical effects growing

17. Step 3. Consequence Assessment
Key information in Consequence Assessment:
exposure-response relationships
extrapolation from animal studies
toxicological exposure-response relationship
epidemiologic exposure-response relationship
“low-dose” extrapolation problem
stochastic effects
modeling

18. Step 4. Risk Estimation - 1 Expressions of risk estimates:
most likely, nominal, “best guess”
worst case, conservative assumptions
range of probabilities
Analyses of sensitivity:
critical assumptions
behaviour of model (e.g. Monte Carlo)
multiple models, assess convergence of prediction

19. Step 4. Risk Estimation - 2 Assumptions:
Human (epidemiological) data preferable to extrapolated data from animal studies
If animal data must be used, correct for BSA
Conservative assumptions; 95% UL
Humans considered as sensitive as most sensitive known animal species
Linear, non-threshold model is the UL of response

20. Step 4. Risk Estimation - 3 A generic mathematical model:
Correcting for BSA, assume B = slope
B = p/d, p = 95% UL frequency, d = dose
Exposure assessment derives estimate for d, based on 70 y lifetime
Risk = Bd, if set at 10-6, then derive
D (allowable) = 106•B per lifetime

21. Some Problems of Risk Assessment
Quantification (conversion to lives, $, P)
Comparability
Exposure-response relationships at low levels
Chronic low-level v. rare catastrophes
Uncertainty bands

22. What Determines When a Risk is Acceptable?

23. Acceptability of Risk - 1
Catastrophic potential –
Familiarity +
Understanding of risk +
Scientific uncertainty –
Controllability + (may be an illusion!)
Voluntariness +
Obvious benefit to community +

24. Acceptability of Risk - 2
Impact on children, future generations –
Victim identity – (put a face to the number)
Dread –
Institutional trust + (few institutions trusted)
Media attention –
History +
Equity + (inequity, maldistribution of risk –)

25. Acceptability of Risk - 3
Reversibility +
Personal or family stake in outcome –
Attributability – (responsible party)
Also:
Cultural differences in acceptability ±
Outrage (Sandeman), distinct from equity –
Profundity – (threat to social stability)

26. Utility of Risk Assessment
Facilitates communication
Framework for critical review of data, assumptions
Allows problem to be disaggregated into component parts
Gaps analysis
Comparison of policy options
Risk comparison

27. Standardization of Risk Assessment
U.S. federal approach
EPA
NAS/NRC/IOM
Interagency Regulatory Liaison Group: EPA, OSHA, CPSC, FDA, FSQS (now defunct)
Health Canada, Health Protection Branch
European Community
World Health Organization