steps of a human health risk assessment...toxicity assessment •risk = site specific exposure/...
TRANSCRIPT
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STEPS OF A HUMAN HEALTH RISK ASSESSMENT
• Purpose of a risk assessment
• Development of the site conceptual model
• Sampling for risk assessment
• Exposure Assessment
• Toxicity Assessment
• Risk Characterization
• Development of Preliminary Remediation Goals
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MAP OF VASQUEZ BLVD AND I-70
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WHY DO WE NEED A RISK ASSESSMENT?
• CERCLA program/ NCP Regulation
• NCP requires all remedial actions to be protective of human health and the
environment
• A risk assessment looks at the contaminates present at a site and determines if
they pose an unacceptable risk to human or ecologic receptors
• Acceptable risk doesn’t mean no risk
• What defines acceptable risk?
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SITE CONCEPTUAL MODEL(WHO COULD BE EXPOSED AND HOW ARE THEY EXPOSED?)
• Current and Future Residents
• Ingestion and dermal exposure to soil
• Inhalation of soil particulates
• Ingestion and dermal exposure to indoor dust
• Ingestion of home-grown garden produce
• Minor Exposure Pathways Not Quantified
• Groundwater
• Surface water and sediment
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WHAT WAS SAMPLED AND ANALYZED FOR?
• Media Sampled
• Soil in yards
• 2986 properties
• 30 surface soil samples from each property
• Soil from 10 schools and 1 park
• Indoor Dust
• Garden Produce
• 72 samples of different produce with co-located
soil samples
• Paint and tap water collected during Phase II
• Contaminant Analyzed
• 23 metals on EPA’s Target Analyte List
• Metals typically associated with smelting
operations include lead, arsenic, cadmium, zinc
and mercury.
• Lead and arsenic were identified as the
contaminants of concern
• The bioavailability of lead and arsenic in soil
was also analyzed
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SOIL RESULTS FOR ARSENIC AND LEAD
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EXPOSURE ASSESSMENT
• Risk = Site specific exposure/ toxicity of a chemical
• Use equations to estimate how often and how much people contact a given
media to derive a site-specific estimate of exposure
• Site-specific exposures are calculated by using the environmental sampling
data and exposure patterns specific to the community
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EXPOSURE ASSESSMENT
• What values are input to the parameters?
• For each land use and each pathway we estimate the highest exposure that a person
could reasonably receive
• This is called the Reasonable Maximum Exposed (RME) individual in the baseline risk
assessment
• If adequate site-specific data was available it was used in the exposure assessment
• If not, EPA recommends the use of standard RME default values based on a
comprehensive national database
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TOXICITY ASSESSMENT
•Risk = Site specific exposure/ toxicity of a chemical
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Father of Modern Toxicology
Paracelsus—1564
“All things are poisonous, only the dose makes it non-poisonous.”
Dose alone determines toxicity
All chemicals—synthetic or natural—have the capacity
to be toxic
Dose THE KEY CONCEPT in Toxicology
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The Dose Makes the Poison
An apparently nontoxic chemical
can be toxic at high doses. (Too
much of a good thing can be
bad).
Highly toxic chemicals can be life
saving when given in appropriate
doses. (Poisons are not harmful
at a sufficiently low dose).
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Dose
Determines Whether a Chemical Will Be Beneficial or Poisonous
Beneficial Dose Toxic Dose
Aspirin 300 – 1,000 mg 1,000 – 30,000 mg
Vitamin A 5000 units/day 50,000 units/day
Oxygen 20% (Air) 50 – 80% (Air)
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Fundamental Rules of Toxicology
Exposure must first occur for the chemical to present a risk.
The magnitude of risk is proportional to both the potency of the chemical and the extent of exposure.
“The dose makes the poison” (amount of chemical at the target site determines toxicity).
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TOXICITY ASSESSMENT
• Risk = Site specific exposure/ toxicity of a chemical
• Exposures are compared to toxicity benchmarks which are protective of the most
susceptible members of the population, for example, the elderly, the very young, etc.
• These toxicity benchmarks are for cancer effects (known as cancer slope factors), or
systemic effects (e.g., liver, kidney, reproductive toxicity) known as Reference Doses
or Reference Concentrations. They are based on an external dose.
• The toxicity of lead is based on a reference blood lead level or internal dose.
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CHARACTERIZING RISK
• Risk = Site specific exposure/ toxicity of a chemical
• Systemic risk (liver, kidney, reproductive, developmental, etc.)
• A threshold exists for adverse effects
• This risk is expressed as a single number called a hazard index
• If the hazard index >1, there is a chance of an adverse health effect occurring
• Cancer risk
• EPA policy (though not scientific consensus) is that no threshold exists for carcinogenic effects
• Expressed as the chance that an individual who receives the highest amount of exposure reasonable may come down
with cancer.
• If the cancer risk for an individual exceeds a 1 in 10,000 chance, EPA generally recommends action.
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NON-CANCER RISK FROM ARSENIC IN SOIL AND DUST AT VB I70
Neighborhood Number of
Properties
Hazard Quotient <=1 Hazard Quotient >1
Clayton 902 895 (99%) 7 (0.8%)
Cole 796 786 (99%) 10 (1%)
Elyria 59 59 (100%) 0 (0%)
Globeville 63 63 (100%) 0 0%)
Swansea 1166 1163 (99.7%) 3 (0.3%)
All Neighborhoods 2986 2966 (99%) 20 (0.7%)
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CANCER RISK FROM ARSENIC IN SOIL AND DUST AT VB I70
Neighborhood Number of
Properties
<= 1 in 10,000 > 1 in 10,000
Clayton 902 864 (96%) 38 (4%)
Cole 796 773 (97%) 23 (3%)
Elyria 59 58 (98%) 1 (2%)
Globeville 63 61 (97%) 2 (3%)
Swansea 1166 1138 (98%) 28 (2%)
All Neighborhoods 2986 2894 (97%) 92 (3%)
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DAILY INTAKES OF ARSENIC IN THE U.S. COMPARED TO PRODUCE FROM VB I70 PROPERTIES
Parameter Value (ug/kg-day)
Total Arsenic Inorganic Arsenic
Typical dietary intake of arsenic
Gunderson 1995
Yost et al 1998
0.36 – 0.81
0.75
0.20
Estimated Intake at VB I70
properties
Property 6 (including onion)
Property 6 (excluding onion)
Property 11
All other properties
0.07
0.04
0.02
0.01
0.04
0.02
0.01
0.004
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RISKS TO CHILDREN FROM LEAD IN SOIL AND DUST AT VB I70
Neighborhood Number of
Properties
<= 5% chance of
exceeding blood lead
level of 10 ug/dl
> 5% chance of exceeding blood
lead level of 10 ug/dl
Clayton 902 712 (79%) 190 (21%)
Cole 796 169 (21%) 627 (79%)
Elyria 59 6 (10%) 53 (90%)
Globeville 63 7 (11%) 56 (89%)
Swansea 1166 761 (65%) 405 (35%)
All Neighborhoods 2986 1655 (55%) 1331 (45%)
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RISK CHARACTERIZATION
• Both cancer and non-cancer risks exceeded EPA’s risk decision criteria for arsenic in
soil and housedust at a few residential properties
• Risks to children from lead in soil and dust exceeded EPA’s risk decision criteria at a
substantial number of residential properties
• Risks from arsenic in homegrown produce were acceptable at all except two
properties. All properties were well below average daily intakes of arsenic in the
U.S. diet.
• No uptake of lead in from soil into produce was observed. Exposure to lead from
homegrown produce is not a health concern.
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RISK CHARACTERIZATION/ DECISION MAKING
• If risks are judged to be unacceptable, preliminary remediation goals are developed
• These are remediation goals based solely on risk alone
• Risk = Site specific exposure/ toxicity of a chemical
• EPA uses the same exposure assumptions and toxicity benchmarks used in the baseline risk
assessment except for the soil concentration. Risk decision criteria are set for acceptable risk
levels (e.g., non-cancer hazard quotient = 1). Solve for the acceptable soil level.
• Preliminary remediation goals for VB I70 were ? For lead and ? For arsenic in soil and dust ?.
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QUESTIONS?