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Risk Assessment: A Conceptual Introduction

Risk Assessment: A Conceptual Introduction. Tee L. Guidotti Occupational Health Program University of Alberta. Risk Assessment. Risk assessment is the systematic evaluation of the likelihood of an adverse effect arising from exposure in a defined population.

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Risk Assessment: A Conceptual Introduction

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

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

  6. 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 Types of Risk Assessment

  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

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