人类健康与环境代写-EESA10
时间:2022-04-13
Risk Assessment
Lecture 10
EESA10 Dr. Silvija Stefanovic 1
What is the Risk?
• Risk - possibility or
probability of suffering
harm from a hazard ????
EESA10 Dr. Silvija Stefanovic 2
Risk Paradigm
Contaminants Receptors
Exposure
pathways
No Risk
Contaminants
Receptors
Exposure
pathways
Risk
EESA10 Dr. Silvija Stefanovic 3
Introduction to Risk Assessment,
a Regulatory Science
• Why risk assessment?
– Must sometimes take action without full scientific
understanding of hazard
– Risk assessment sets default procedures for
bridging gaps in scientific understanding
– Basic framework: evaluate exposure and toxicity;
bring this information together to characterize a
health risk →
EESA10 Dr. Silvija Stefanovic 4
Environmental Sites Assessment
What is Risk Assessment?
PHASE
I
PHASE
II
PHASE
III
PHASE
IV
Assessment Characterization Remediation/
Management
Verification
Document Review
Interviews
Site Inspection
Contact
Authorities
Intrusive Sampling
Investigation
Physical Testing
Contaminant
Destruction or
Removal
Risk Assessment
Verification Sampling
to Confirm Estimates
Management Plan
“… technical, scientific assessment of
the nature and magnitude of risks”
(from MOE Guidance document)
Risk assessment – scientific process
in estimating how much harm a
particular hazard can cause
EESA10 Dr. Silvija Stefanovic 5
Benefits of Risk Assessment
(extracted from Natural Research Council)
• When agent suspected of causing diseases
• Testing new chemical
• Help rank contribution to overall risk
• Help identify risks that are easily reduced or
eliminated
• Help clarified what is known and not known about
situation
• Can provide quantitative information for decision
making
EESA10 Dr. Silvija Stefanovic 6
Applications
• Health Canada – regulations for foods and drugs
• Canada Council of Ministers of the Environment
◦ National Contaminated Sites Program
◦ Canada-Wide Environmental Standards (CWES)
• Ontario Ministry of Environment
◦ Site-specific clean-up guidelines for contaminated soils
• CEPA (Canadian Environmental Protection Agency)
◦ 23 000 substances currently in use
◦ Persistent, bioaccumulation, toxic ????
EESA10 Dr. Silvija Stefanovic 7
Stages of Risk Assessment
1. Problem Definition
2. Identify Contaminant
3. Receptor Analysis
4. Pathways Analyses
5. Exposure Assessment
6. Toxicity Assessment
7. Risk Characterisation
8. Uncertainties
9. Critique
EESA10 Dr. Silvija Stefanovic 8
In the past
Risk Assessment Framework
Problem Definition
Contaminant
Screening
Receptor
Screening
Pathway
Analysis
Conceptual Exposure Model
Exposure
Assessment
Toxicity
Assessment
Risk
Characterization
Qualitative
Stage
Quantitative
Stage
EESA10 Dr. Silvija Stefanovic 9
1. Problem Definition
• Purpose
• Management goals
• Policy context
• Audience?
• Hazard definition
• Receptors ?
• Level of funding
EESA10 Dr. Silvija Stefanovic 10
2. Identify Contaminant
• Single compounds or
• Complex mixture with a few compounds
driving toxicity
• Contaminated soil, and/or air pollution
and/or …?
EESA10 Dr. Silvija Stefanovic 11
3. Receptor Analysis
• Organism, species or groups of species exposed to stressor
• Define scenario:
– Length of exposure (life time, 20 years – latency for cancer)
– Incremental or total exposure
– Define routes of exposure (ingestion, inhalation, dermal)
– Determine rate of exposure from each route
– Characterized activity pattern that results in exposure
– Human: who? average person, age, gender
– Average & worst case
– Sensitive subpopulation (recent interest in children)
EESA10 Dr. Silvija Stefanovic 12
4. Pathways Analyses
• Determine environmental fate that results in
exposure to receptor
• Evaluate routes of exposure
• Quantify amount of exposure (DOSE)
• Methods
– Measurements (how representative ??)
– Modeling
EESA10 Dr. Silvija Stefanovic 13
5. Exposure Assessment (1)
• Multiple routes of exposure
• Quantify exposure from:
– Air (indoor/outdoor)
– Water (drinking, showering, …)
– Soil
– Sediments
– Diet (many varieties)
– Other
EESA10 Dr. Silvija Stefanovic 14
5. Exposure Assessment (2)
• Exposure (g of chemical / day) is :
CONCENTRATION x INTAKE RATE
OR
Cf X IRf = exposure from ingestion (food)
Ca X IRa = exposure from inhalation (air)
Cd X IRd = exposure from dermal contact
Where
Cf,a,d is concentration (e.g. g of chemical / kg of food)
IR is intake rate (e.g. kg of food / day)
Total exposure = exposure 1 (food) + exposure 2
(air) + exposure 3 (dermal ) + ……
EESA10 Dr. Silvija Stefanovic
15
5. Exposure Assessment (3)
• EDI - Estimated Daily Intake (estimate dose, for each
exposure medium)
EDI = IR x C x B X EF x ED
BW AT
EDI is estimated daily intake , mg/kg body weight /day
IR is intake rate, m3 air /day or kg food/day
C is chemical concentration, mg/m3 air or mg/kg food
B is bioavailability factor, dimensionless, fraction of chemical
available for uptake in organism
EF is exposure frequency, d/y
ED is exposure duration, d
BW is body weight, kg
AT is averaging time, d
Exposure factor
Exposure
EESA10 Dr. Silvija Stefanovic 16
Considers biologically
effective dose
Example
• A child is exposed to contaminated soil at her
nursery school. She attends the school 3 days
a week over 4 years
• Exposure factor : 3 d/week x 52 weeks/y x 4 y
4y x 365 d /y
EF x ED
AT
Exposure factor
EESA10 Dr. Silvija Stefanovic 17
Total EDI
EDI - Estimated Daily Intake (estimate dose, for each
exposure medium)
Total EDI = EDI (food) + EDI (air) + EDI (dermal)
+ ……
EESA10 Dr. Silvija Stefanovic 18
6,7. Toxicity and Risk Assessment
• A fundamental assumption in chemical risk
assessment:
– Noncancer effects have thresholds
– Carcinogenicity has no threshold
• Therefore, key steps in risk assessment play
out differently for cancer (no threshold) and
non cancer (threshold) effects
EESA10 Dr. Silvija Stefanovic 19
Assessment of non-carcinogenic
Hazard
1. Exposure assessment—measure or
estimate dose in mg/(kg*day)
2. Hazard identification—establish range of
noncancer effects; select one as basis
EESA10 Dr. Silvija Stefanovic 20
Assessment of non-carcinogenic
Hazard
3. Dose-response assessment
– Determine dose-response relationship (Chronic rodent
bioassay)
– Determine NOAEL and LOAEL from the graph
– Derive reference dose (RfD) in mg/(kg*day)—dose expected to
have no adverse effects in sensitive people with lifelong
exposure
– How??? Derive RfD from rodent NOAEL or LOAEL, by dividing it
by uncertainty factors (to make RfD lower and thus more
protective)
4. Risk characterization:
– Hazard quotient (unitless) = actual or EDI (estimated dose) /
reference dose
– Hazard quotient >1.0 indicates potential for harm at actual or
estimated dose
EESA10 Dr. Silvija Stefanovic 21
Assessment of Carcinogenic Hazard
• No safe dose
• Theoretically 1 molecule could induce 1 tumour
1. Exposure assessment—measure or estimate
dose in mg/(kg*day)
2. Hazard identification—assess toxicant’s
potential to cause cancer in humans. How???
EESA10 Dr. Silvija Stefanovic 22
Assessment of Carcinogenic Hazard
Weight-of-the-evidence categories for
carcinogenicity, as defined by IARC:
– Group 1: Carcinogenic to humans
– Group 2A: Probably carcinogenic to humans
– Group 2B: Possibly carcinogenic to humans
– Group 3: Not classifiable as to carcinogenicity to
humans
– Group 4: Probably not carcinogenic to humans
EESA10 Dr. Silvija Stefanovic 23
IARC- International
Agency for Research on
Cancer
Assessment of Carcinogenic Hazard
3. Dose-response assessment
• Determine dose-response relationship (Chronic rodent
bioassay)
• Derive cancer slope factor —estimate of potency
(cancer risk per mg/(kg*day)
4. Risk characterization
• Incremental lifetime risk (probability) = actual or EDI
(estimated dose) * slope factor
• Hazard quotient >1.0 indicates potential for cancer at
actual or estimated dose
EESA10 Dr. Silvija Stefanovic 24
Assessment of Carcinogenic
Hazard
RMOS -Calculate exposure that will result in acceptable risk
RMOS (Relative margin of safety)= EDI
RsD
RsD (Risk specific Dose) = Acceptable risk
Slope factor
Decision Point:
OK if RMOS < 1
Not OK if RMOS >1
EESA10 Dr. Silvija Stefanovic 25
8. Uncertainties
• Pathways analyses
– Insufficient data
– Measurement errors
– Capturing natural variability
– Future predictions (assume conditions same as today)
• Exposure analysis EDI
– Difficult to estimate for children
– Bioavailability
• Toxicity Assessment
– RsD, RMOS, establish relevant dose-response relationship
EESA10 Dr. Silvija Stefanovic 26
9. Critique
• Best developed for human carcinogens
• What about others????
• Based on numerous assumptions and large
uncertainties
EESA10 Dr. Silvija Stefanovic 27
Risk Analyses
• Comparative risk analyses - Ranking risk
• Risk management – options and decisions about
reducing or eliminating risk
• Risk communication –informing decision makers and
public
EESA10 Dr. Silvija Stefanovic 28
Risk Management
• Actions taken, often by government agencies,
to control or reduce environmental risks to
human health
• Considers magnitude of the health risk,
regulatory framework, technical options for
controlling the hazard, costs, and social
context including environmental justice
EESA10 Dr. Silvija Stefanovic 29
Risk Management
• Individual chemicals (e.g., in drinking water or
workplace air)
– Decisions about goals for standards
– Decisions about feasible standards
• Contaminated sites
– Complex: multiple chemicals, multiple media
– Consider: toxicity, future uses of site,
effectiveness of cleanup options, costs
EESA10 Dr. Silvija Stefanovic 30
Other Examples of
Risk Management
• Limits on emissions, requirements to treat wastes
• Changes to industrial processes, isolation of a
hazardous process in the workplace
• Incentives for compliance, penalties for noncompliance
• Publicly available information as incentive
• Work of local health departments
EESA10 Dr. Silvija Stefanovic 31
Risk Communication
• Risk communication = exchange of
information about a hazard between experts
and those affected
• Public perception of environmental health
risks as “hazard plus outrage”
• Specific features of environmental hazards
often generate outrage
EESA10 Dr. Silvija Stefanovic 32
The Precautionary Principle
• The 1998 Wingspread Statement on the Precautionary Principle
summarizes the principle this way:
"When an activity raises threats of harm to human health or the
environment, precautionary measures should be taken even if some cause
and effect relationships are not fully established scientifically."
• The February 2, 2000 European Commission Communication on the
Precautionary Principle notes:
"The precautionary principle applies where scientific evidence is insufficient,
inconclusive or uncertain and preliminary scientific evaluation indicates
that there are reasonable grounds for concern that the potentially
dangerous effects on the environment, human, animal or plant health
may be inconsistent with the high level of protection chosen by the EU".
EESA10 Dr. Silvija Stefanovic 33
The Precautionary Principle
• Examples of precautionary approach
– International agreements
• Kyoto Protocol on global climate change
• Montreal Protocol on ozone-depleting chemicals
– US Toxic Substances Control Act
– European Union’s REACH program for new
chemicals
– CCA wood preservative
EESA10 Dr. Silvija Stefanovic 34
The Precautionary Principle
• Some lost opportunities for precaution
– Widespread, long-term use of asbestos
– Large-scale development and use of synthetic
organic chemicals
• eg.DDT
– Depletion of global fisheries
– Food industry practices that amplified “mad cow
disease” and caused human illness
EESA10 Dr. Silvija Stefanovic 35


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