Transcript vapor intrusion risk assessment considerations

BASELINE RISK
ASSESSMENT
OVERVIEW
Dawn A. Ioven
Senior Toxicologist
U.S. EPA – Region III
4 April 2012
WHAT IS RISK?
 Definition:
probability of harm or loss
 Risk = Hazard x Exposure
 Risk can be voluntary or involuntary
 Interpretation of risk differs for each of us
 Predictive risk assessment (U.S. EPA) vs.
health study (ATSDR, Health Department)
PURPOSE OF BASELINE RISK
ASSESSMENT
 Characterize
current and potential future
risks to human health and the environment
 Determine the need for remedial action
 Aid stakeholders in understanding
potential site-related risks
 Satisfy Federal regulations requiring the
assessment of risk at Superfund sites
BASELINE RISK
ASSESSMENT PROCESS
 Hazard
Identification
 Exposure Assessment
 Toxicity Assessment
 Risk Characterization
 Uncertainty Analysis
HAZARD IDENTIFICATION
 Gather
and analyze relevant site data
 Identify Chemicals of Potential
Concern (CoPCs)
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CoPCs are chemicals that may contribute significantly
to site-related risks
Determined by comparison to generic risk-based
screening levels or regulatory criteria
Identification process also considers essentiality,
frequency of detection, and background conditions
EXPOSURE ASSESSMENT
 Analyze
contaminant releases
 Identify potentially-exposed populations
(current and future)
 Identify potential exposure pathways
 Estimate exposure point concentrations for
CoPCs
 Estimate contaminant intake (dose) for
each CoPC
EXPOSURE ASSESSMENT (cont.)
Common Land-Use Scenarios
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Residential
Occupational
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Commercial / Industrial
Construction
Recreational
Other
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Agricultural
Trespassing
Maintenance (Landscaping)
EXPOSURE ASSESSMENT (cont.)
Common Exposure Pathways
 Surface
soil
 Subsurface soil
 Ground water
 Air
 Surface water
 Sediment
EXPOSURE ASSESSMENT (cont.)
Common Exposure Routes
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Ingestion
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Soil
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Ground water
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Surface water
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Sediment
Dermal contact
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Soil
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Ground water (bathing)
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Surface water
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Sediment
Inhalation
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Soil (outdoor vapors, airborne particulate, vapor intrusion)
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Ground water (showering, vapor intrusion)
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Air
EXPOSURE ASSESSMENT (cont.)
Generic Dose Equation - Ingestion
Dose = (C x CR x EF x ED) / (BW x AT)
where:
C = contaminant concentration, media-dependent
CR = contact rate, media-dependent
EF (days/yr) = exposure frequency
ED (yrs) = exposure duration
BW (kg) = body weight
AT (days) = averaging time
Generic Dose Equation - Inhalation
Exposure Concentration = (CA x ET x EF x ED x CF) / AT
where:
CA (ug/m3) = contaminant concentration in air
ET (hrs/day) = exposure time
EF (days/yr) = exposure frequency
ED (yrs) = exposure duration
CF (1 day/24 hrs) = conversion factor
AT (days) = averaging time
TOXICITY ASSESSMENT
 Collect
qualitative and quantitative toxicity
information for CoPCs
 Determine appropriate toxicity values for
CoPCs to estimate risks
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Reference Dose (RfD)
Inhalation Reference Concentration (RfC)
Carcinogenic Slope Factor (CSF)
Inhalation Unit Risk (IUR)
RISK CHARACTERIZATION
 Combine
Exposure Assessment with
Toxicity Assessment to describe potential
for adverse health effects
RISK CHARACTERIZATION
(cont.)
Cancer Risks
Risk = CSF x Dose
where:
CSF (mg/kg/day)-1 = Carcinogenic Slope Factor
Risk = IUR x EC
where:
IUR (ug/m3)-1 = Inhalation Unit Risk, chemical-specific
EC (ug/m3) = exposure concentration
Non-Cancer Risks
HQ = Dose / RfD
where:
HQ (unitless) = Hazard Quotient
RfD (mg/kg/day) = Reference Dose
HQ = EC / (RfC x 1000 ug/mg)
where:
HQ (unitless) = Hazard Quotient
EC (ug/m3) = exposure concentration
RfC (mg/m3) = Reference Concentration, chemical-specific
RISK CHARACTERIZATION
(cont.)
 Unacceptable

Risk
Excess cancer risk greater than 1E-04
• probability of developing cancer from defined
exposure is greater than 1 in 10,000
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For non-cancer impacts, sum of HQs for
similar target organs is greater than 1
• “safe” dose is exceeded
UNCERTAINTY ANALYSIS
 Describe
assumptions and significant
unknowns associated with risk
assessment process
 Quantitative measure of variability and
sensitivity of each input parameter can be
performed via Monte Carlo Analysis
NATIONAL RESEARCH COUNCIL
RISK ASSESSMENT PARADIGM
Risk Assessment
Dose-Response
Assessment
Hazard
Identification
Statutory and Legal
Considerations
Public Health
Considerations
Risk
Characterization
Exposure
Assessment
Regulatory
Decisions
Control
Social
Options
Factors
Economic
Factors
Risk Management
National Research Council, 1983
Asbestos
 Two
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mineral groups
Serpentine
• Single asbestosform variety (chrysotile)
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Amphibole
• Several asbestosform varieties (crocidolite,
amosite, anthophyllite, tremolite, actinolite)
Asbestos Investigations
 No
method has been found that reliably
predicts asbestos concentrations in air
given concentrations at the source.
 Levels of asbestos in air from source
disturbance are measured, not predicted.
 Activity-Based Sampling (ABS)
Asbestos ABS Sampling
 Potential
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limitations
Representativeness of samples over an area
of concern
Generalizing snapshot findings to future
exposures
Engaging in dissimilar activities
Differing environmental conditions
Asbestos ABS Sampling (cont.)
 Remedy
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to limitations
Bias sampling towards most contaminated
asbestos sources
Perform aggressive soil disturbance (raking),
to generate maximum air concentrations
Sample when environmental conditions are
favorable to maximum airborne release
Apply conservative exposure assumptions
and tox criteria in Baseline Risk Assessment
Asbestos Risks
 Inhalation
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Carcinogenic
•
•
•
•
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Lung cancer
Mesothelioma
Laryngopharyngeal cancer
GI tumors (possibly)
Non-Cancer
• Asbestosis
• Pleural disease
Asbestos Risk Equation
Generic Risk Equation - Inhalation
ELCR = EPC x TWF x IUR
where:
ELCR = Excess Lifetime Cancer Risk, the risk of
developing cancer due to site-related exposure
EPC = Exposure Point Concentration, the
concentration of asbestos fibers in air (f/cc)
IUR = Inhalation Unit Risk (f/cc)-1
TWF = Time Weighting Factor, to account for
less-than-continuous exposure during a one-year
exposure, where:
TWF = [Exposure time (hours exposed/day ) / 24] x [Exposure
frequency (days/year ) / 365]
Example TWFs
TWFs for Example Exposure Scenarios
Exposure Scenario
Hrs/Day
Days/Year
TWF
Continuous
Baseline residential
Gardening
Recreational
Child playing in soil
24
24
10
1
2
365
350
50
156
350
1
0.96
0.057
0.018
0.080
TWF = [Exposure time (hours exposed/day ) / 24] x [Exposure frequency (days/year ) / 365]
Asbestos IURs
 Cancer
risk estimates depend not only on
EF and ED, but also on age at first
exposure
 Refer to handout (Table 2 and Table 3
from EPA Asbestos Framework) for IURs
Estimation of Potential
Cumulative Risk from Asbestos
ELCRc = Σ EPCi • TWFi • IURLTLi
where:
ELCRc = the cumulative excess cancer risk
to an individual from exposure to multiple
environments or multiple scenarios
Example Risk Calculation for
Asbestos
 Refer
to handout (Example 3 from EPA
Asbestos Framework)