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

MAP OF VASQUEZ BLVD AND I-70

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?

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

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

SOIL RESULTS FOR ARSENIC AND LEAD

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

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

TOXICITY ASSESSMENT

•Risk = Site specific exposure/ toxicity of a chemical

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)

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.

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.

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%)

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%)

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

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%)

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.

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 ?.

QUESTIONS?