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Risk Assessment
Bruce Case
Risk Assessment: Lecture Outline
1. Definitions: Risk Analysis, Risk Assessment
(Evaluation) and their components
2. A detailed look at HAZARD EVALUATION
3. Risk Perception, Risk Communication, Risk
Management
4. An example of risk assessment: Mesothelioma
among Quebec asbestos mining area women.
5. Risk and the precautionary principle
Buzzword Alert!
 There are a number of technical
terms in this lecture
 Yes, you have to know them!
 These terms have precise
meaning, even though you will
often see them MIS-used.
 Since risk assessment is (or aims
to be) a scientific activity we must
agree on terminology
 This is the overall term for all of
Risk Science
 It has four elements:
 - Risk Assessment (Risk
Evaluation)
 - Risk Communication
 - Risk Perception
 - Risk Management (Risk
Characterization (EPA))
Risk Analysis
Definition of Risk
Assessment
 Risk Assessment, or risk evaluation,
is a scientific/ mathematical discipline
which is
 a substantive, changing and
controversial field
Definition of Risk Assessment
 at the margin of our understanding of
the health effects of chemicals and
other substances
 best defined as the determination of
pathology caused by human
production and activity, with the
understanding that "pathology" is a
change in some aspect of human
anatomical structure or function
Risk Assessment: Two Roads
 Qualitative
 - virtually the same thing as
“hazard evaluation” step of
“Quantitative” Risk
Assessment
 - is the material harmful to
humans under any
circumstances
 - Codified by agencies,
especially for cancer
 Quantitative
 A formal process
with four steps
 Ends with a
mathematical
estimation of
actual risk,
usually quantified
as deaths per
1,000,000 per
year or less.
Risk Management:
Putting the
elements together
(in many instances the three further steps are not taken)
Examples: EPA, IARC Cancer Monographs
“Hazard Evaluation” is the equivalent of
Qualitative Risk Assessment.
Types of Study Available for Hazard
Evaluation
 BEST: Human Evidence
(Epidemiology)
 Next best: Whole animal studies
(toxicology; animals exposed to
known dose and allowed to live to
times of sacrifice or natural death)
Types of Study Available for Hazard
Evaluation
 Other:
In-vitro studies (studies on cells in
culture)
Structure-function relationship
study and similar
Identification of active compounds
in metabolism
Study for Hazard Evaluation: Human
 Case reports (example: angiosarcoma of
liver)
 Case series (example: mesothelioma in
S. Africa)
 Descriptive epidemiology (much like
geographic study; ecological fallacy is a
problem)
Study for Hazard Evaluation: Human
 Analytical epidemiology:
 best: cohort studies: following exposed
humans through time
 second best: case-referent studies:
comparing “cases” of given disease to
MATCHED referents and noting
differences in exposure.
Study for Hazard Evaluation: Animal
 Studies of cells (in vitro studies: example
O2-
)
 Acute toxicity studies (how much does it
take to kill half of all the animals?)
 Chronic toxicity studies:
Best method but very expensive and
time-consuming
Proper design (doses, sacrifice times,
animal selection) a must.
Study for Hazard Evaluation: Animal: Problems
 Ethical Concerns (see: papers by Peter Singer and
Henry Spira):
 e.g. Rack L, Spira H. Animal rights and modern
toxicology Toxicol Ind Health 1989 Jan;5(1):133-43.
 Conversely: non-realistic models may be
useless;
 e.g. animal intra-tracheal injection versus
inhalation
 e.g. use of rats (who do not have the same
respiratory tract structure as humans: HOGS
are best!!!)
Study for Hazard Evaluation: Human: Problems
 Ethical Concerns
 Expense
 LATENCY
 Practical considerations: for example the
use of questionnaires or interviews in a
case-referent study and:
- sample size, response rate
- selection bias and other bias
Hazard Evaluation: Synthesis: IARC Group 1
 GROUP 1: AGENT CARCINOGENIC TO HUMANS
 Assignment to this category is based on a finding
of "sufficient" evidence of carcinogenicity in
humans. This implies a causal relationship
between exposure to a chemical and cancer in
epidemiological studies in which "...chance, bias
and confounding could be ruled out with
reasonable confidence"13
.
Hazard Evaluation: Synthesis: IARC 2A
 GROUP 2A: AGENT PROBABLY CARCINOGENIC TO
HUMANS
 “limited” or inadequate evidence in
epidemiological studies for carcinogenicity:
 the agent falls into this category if there is
"sufficient" evidence from experimental animal
work. Causal relationship has been shown in two
or more species of animals OR in two or more
independent studies in one species.
Hazard Evaluation: Synthesis: IARC 2B
 GROUP 2B: AGENT POSSIBLY CARCINOGENIC TO
HUMANS
 sufficient evidence for carcinogenicity neither in
humans nor in experimental animals.
 a "credible" causal HUMAN relationship is
suggested but bias, chance and confounding
cannot be ruled out AND sufficient animal evidence
OR
 "inadequate" evidence in humans but "sufficient"
animal evidence.
Hazard Evaluation: Synthesis: IARC 3:
 GROUP 3: AGENT NOT CLASSIFIABLE FOR HUMAN
CARCINOGENICITY
 category for agents which cannot otherwise be
classified.
 Really a “garbage” category scientifically, but
corresponds to some extent to the Precautionary
Principle
 GMOs could possibly fit this category
Hazard Evaluation: Synthesis: IARC 4
 GROUP 4: AGENT "PROBABLY"
NOT CARCINOGENIC TO HUMANS
 animal studies in at least two
species showing that the
substance is “not carcinogenic”.
 If there is a large body of
negative animal evidence:
 the agent will fall into this
category even if there is some,
but "inadequate", epidemiological
Exposure Assessment 1
 How much of a pollutant do people
inhale/ ingest ?
 In what period of time?
 How many people will be exposed?
 To what? Or which (e.g. PCB)?
 From what source(s)?
 With what interaction(s) (e.g.
smoking)
Exposure Assessment 2
 Example: Total suspended
particulates
 Sample stacks; sample
environment; sample PEOPLE
 Characterize the particles
(carbon? Asbestos?)
Exposure Assessment 3
 Model the exposure (using for
example wind speed)
 Determine the source(s)
 Find out anything “special” about
the population
Exposure Assessment
Dose-response relationships
 "how much is dangerous" ?
 Animal data and (preferably) human
occupational data used: example:
BEIR IV
 The problem of thresholds
 Extrapolation: most common
convention is the use of some
multiple of the upper bound of the
95% confidence interval
SLOPE (b) of the lung cancer/ exposure curve:
SMR = 100 + [b times (cumulative exposure)]
Mining: .05
Textile: 1.0
Manufacture
(mixed): 0.2
Slope
(extent per
unit
exposure)
of risk
Degree of exposure ----
Different principles for
cancer and non-cancer
The threshold issue
Issue: Which
line is correct?
Exposure ---
D
I
S
E
A
S
E
The threshold problem:
points are at high dose
Jones
1956
Smith
1989
Tremblay
1998
 What Is the Extra Risk to Health?
 Maximum Individual Lifetime Cancer Risks:
Risk Characterization/
Management 1
 What Is the Distribution of Individual Risks?
Risk Characterization/
Management 2
Population
Cancer Risks can
be calculated
from the
Distributed
Individual Risks
This is where
we “do the
math”
Risk Perception; Risk
Communication
 The balance between “risk” and
“outrage”
 High risk/ low outrage: radon and lung
cancer?
 Low risk/ high outrage: asbestos in
schools?
 The media as an "amplifier"
 Voluntary vs. Involuntary Risk
(smoking vs. hazardous waste siting)
 Known vs. Unknown Risk (lead pipes;
lead in gas)
Risk assessment based
on the
linear exposure-effect
model
Cumulative exposure
1.0
+
background risk
Exposure
assessment
R.A.
Žx
Žy
b = Žx
Žy

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  • 2. Risk Assessment: Lecture Outline 1. Definitions: Risk Analysis, Risk Assessment (Evaluation) and their components 2. A detailed look at HAZARD EVALUATION 3. Risk Perception, Risk Communication, Risk Management 4. An example of risk assessment: Mesothelioma among Quebec asbestos mining area women. 5. Risk and the precautionary principle
  • 3. Buzzword Alert!  There are a number of technical terms in this lecture  Yes, you have to know them!  These terms have precise meaning, even though you will often see them MIS-used.  Since risk assessment is (or aims to be) a scientific activity we must agree on terminology
  • 4.  This is the overall term for all of Risk Science  It has four elements:  - Risk Assessment (Risk Evaluation)  - Risk Communication  - Risk Perception  - Risk Management (Risk Characterization (EPA)) Risk Analysis
  • 5. Definition of Risk Assessment  Risk Assessment, or risk evaluation, is a scientific/ mathematical discipline which is  a substantive, changing and controversial field
  • 6. Definition of Risk Assessment  at the margin of our understanding of the health effects of chemicals and other substances  best defined as the determination of pathology caused by human production and activity, with the understanding that "pathology" is a change in some aspect of human anatomical structure or function
  • 7. Risk Assessment: Two Roads  Qualitative  - virtually the same thing as “hazard evaluation” step of “Quantitative” Risk Assessment  - is the material harmful to humans under any circumstances  - Codified by agencies, especially for cancer  Quantitative  A formal process with four steps  Ends with a mathematical estimation of actual risk, usually quantified as deaths per 1,000,000 per year or less.
  • 9.
  • 10. (in many instances the three further steps are not taken) Examples: EPA, IARC Cancer Monographs “Hazard Evaluation” is the equivalent of Qualitative Risk Assessment.
  • 11. Types of Study Available for Hazard Evaluation  BEST: Human Evidence (Epidemiology)  Next best: Whole animal studies (toxicology; animals exposed to known dose and allowed to live to times of sacrifice or natural death)
  • 12. Types of Study Available for Hazard Evaluation  Other: In-vitro studies (studies on cells in culture) Structure-function relationship study and similar Identification of active compounds in metabolism
  • 13. Study for Hazard Evaluation: Human  Case reports (example: angiosarcoma of liver)  Case series (example: mesothelioma in S. Africa)  Descriptive epidemiology (much like geographic study; ecological fallacy is a problem)
  • 14. Study for Hazard Evaluation: Human  Analytical epidemiology:  best: cohort studies: following exposed humans through time  second best: case-referent studies: comparing “cases” of given disease to MATCHED referents and noting differences in exposure.
  • 15. Study for Hazard Evaluation: Animal  Studies of cells (in vitro studies: example O2- )  Acute toxicity studies (how much does it take to kill half of all the animals?)  Chronic toxicity studies: Best method but very expensive and time-consuming Proper design (doses, sacrifice times, animal selection) a must.
  • 16. Study for Hazard Evaluation: Animal: Problems  Ethical Concerns (see: papers by Peter Singer and Henry Spira):  e.g. Rack L, Spira H. Animal rights and modern toxicology Toxicol Ind Health 1989 Jan;5(1):133-43.  Conversely: non-realistic models may be useless;  e.g. animal intra-tracheal injection versus inhalation  e.g. use of rats (who do not have the same respiratory tract structure as humans: HOGS are best!!!)
  • 17. Study for Hazard Evaluation: Human: Problems  Ethical Concerns  Expense  LATENCY  Practical considerations: for example the use of questionnaires or interviews in a case-referent study and: - sample size, response rate - selection bias and other bias
  • 18. Hazard Evaluation: Synthesis: IARC Group 1  GROUP 1: AGENT CARCINOGENIC TO HUMANS  Assignment to this category is based on a finding of "sufficient" evidence of carcinogenicity in humans. This implies a causal relationship between exposure to a chemical and cancer in epidemiological studies in which "...chance, bias and confounding could be ruled out with reasonable confidence"13 .
  • 19. Hazard Evaluation: Synthesis: IARC 2A  GROUP 2A: AGENT PROBABLY CARCINOGENIC TO HUMANS  “limited” or inadequate evidence in epidemiological studies for carcinogenicity:  the agent falls into this category if there is "sufficient" evidence from experimental animal work. Causal relationship has been shown in two or more species of animals OR in two or more independent studies in one species.
  • 20. Hazard Evaluation: Synthesis: IARC 2B  GROUP 2B: AGENT POSSIBLY CARCINOGENIC TO HUMANS  sufficient evidence for carcinogenicity neither in humans nor in experimental animals.  a "credible" causal HUMAN relationship is suggested but bias, chance and confounding cannot be ruled out AND sufficient animal evidence OR  "inadequate" evidence in humans but "sufficient" animal evidence.
  • 21. Hazard Evaluation: Synthesis: IARC 3:  GROUP 3: AGENT NOT CLASSIFIABLE FOR HUMAN CARCINOGENICITY  category for agents which cannot otherwise be classified.  Really a “garbage” category scientifically, but corresponds to some extent to the Precautionary Principle  GMOs could possibly fit this category
  • 22. Hazard Evaluation: Synthesis: IARC 4  GROUP 4: AGENT "PROBABLY" NOT CARCINOGENIC TO HUMANS  animal studies in at least two species showing that the substance is “not carcinogenic”.  If there is a large body of negative animal evidence:  the agent will fall into this category even if there is some, but "inadequate", epidemiological
  • 23. Exposure Assessment 1  How much of a pollutant do people inhale/ ingest ?  In what period of time?  How many people will be exposed?  To what? Or which (e.g. PCB)?  From what source(s)?  With what interaction(s) (e.g. smoking)
  • 24. Exposure Assessment 2  Example: Total suspended particulates  Sample stacks; sample environment; sample PEOPLE  Characterize the particles (carbon? Asbestos?)
  • 25. Exposure Assessment 3  Model the exposure (using for example wind speed)  Determine the source(s)  Find out anything “special” about the population
  • 27. Dose-response relationships  "how much is dangerous" ?  Animal data and (preferably) human occupational data used: example: BEIR IV  The problem of thresholds  Extrapolation: most common convention is the use of some multiple of the upper bound of the 95% confidence interval
  • 28. SLOPE (b) of the lung cancer/ exposure curve: SMR = 100 + [b times (cumulative exposure)] Mining: .05 Textile: 1.0 Manufacture (mixed): 0.2 Slope (extent per unit exposure) of risk Degree of exposure ----
  • 30. The threshold issue Issue: Which line is correct? Exposure --- D I S E A S E
  • 31. The threshold problem: points are at high dose Jones 1956 Smith 1989 Tremblay 1998
  • 32.  What Is the Extra Risk to Health?  Maximum Individual Lifetime Cancer Risks: Risk Characterization/ Management 1
  • 33.  What Is the Distribution of Individual Risks? Risk Characterization/ Management 2 Population Cancer Risks can be calculated from the Distributed Individual Risks This is where we “do the math”
  • 34. Risk Perception; Risk Communication  The balance between “risk” and “outrage”  High risk/ low outrage: radon and lung cancer?  Low risk/ high outrage: asbestos in schools?  The media as an "amplifier"  Voluntary vs. Involuntary Risk (smoking vs. hazardous waste siting)  Known vs. Unknown Risk (lead pipes; lead in gas)
  • 35. Risk assessment based on the linear exposure-effect model Cumulative exposure 1.0 + background risk Exposure assessment R.A. Žx Žy b = Žx Žy

Editor's Notes

  1. Before it can be determined in any quantitative way what risk exists, it is necessary to determine whether ANY risk (hazard) exists. This is usually done through a systematic evaluation of the available human and animal studies.
  2. Explanation: For asbestos exposure and lung cancer, for example, there is evidence that INDUSTRIAL PROCESS affects the slope of the risk. Thus, those employed in asbestos mining and milling had measureable, but shallow risk (lower risk at highest exposures), while those who made asbestos textiles had highest risks.
  3. If the black line intersecting zero is “correct”, there is theoretically some “risk” at any level of exposure (although the probability of that risk may be effectively none at zero). This is almost a convention in cancer risk assessment, but may be wrong if the GREEN line is correct, which suggests that there is ZERO theoretical risk below the exposure at which the green line intersects the X (exposure) axis.
  4. The problem is thus that the studies do not actually identify any points which are low on the dose level; whether human or (especially) animal. The resulting PROJECTIONS may be largely either guesswork, convention (as in the linear no-threshold model), or both.
  5. Remember that this is called Risk MANAGEMENT by EPA but Risk CHARACTERIZATION by many others. Since management is a whole other ballgame, I prefer characterization: this is simply a mathematical modelling of risk.
  6. This slide strictly for the mathematically unchallenged!