What is Risk Risk Exposure X Toxicity The magnitude of risk is proportional to both the potency of the chemical and the extent of exposure eg duration and frequency Exposure must first occur for the chemical to present a ID: 677481
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INTRODUCTION TO RISK ASSESSMENT
What is Risk?
Risk
= Exposure X ToxicityThe magnitude of risk is proportional to both the potency of the chemical and the extent of exposure (e.g., duration and frequency).Exposure must first occur for the chemical to present a risk.“The dose makes the poison” (amount of chemical at the target site determines toxicity).
What is Risk Assessment?An objective and quantitative approach to analyzing and interpreting environmental data for the purpose of predicting the potential for adverse health effects. The risk assessment process includes:Planning and scoping (site conceptual model)Exposure AssessmentToxicity AssessmentRisk Characterization
Conceptual Site Model
What is a
conceptual site model?
A
graphical illustration of where the contamination originates, how it moves through the environment, and how humans come into contact with the contaminated media. The conceptual site model includes: Primary and secondary sources of contaminationTransport pathwaysContaminated mediaExposure mediaExposure routeExposed populations
RESIDENT
REC
FACTORY
RELEASE
RECEPTOR
EXPOSURE
ROUTE
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SEDIMENT
SURFACE
WATER
GROUND
WATER
PLANTS
FISH
GAME
INGESTION
INHALATION
DERMAL
INGESTION
INGESTION
INHALATION
DERMAL
INGESTION
INGESTION
INGESTION
INHALATION
DERMAL
PRIMARY
SOURCE
SECONDARY
SOURCE
PATHWAY
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What is the value of a conceptual site model?
Allows
user to see which pathways are important and which are not
Allows user to see which pathways are complete and which are not
Guides and focuses the site-specific data collection
Allows user to see where remediation efforts will be most effective
Exposure Assessment
Toxicity Assessment
An evaluation of
Environmental exposure pathways
Routes of exposure
Magnitude (“how much?”)
Frequency (“how often?”)
Duration (“how long?”)
Consists of
Identification of Chemicals of Potential
Concern (COPC)
Quantification of
exposure
EXPOSURE PATHWAYS
Sources
Release & Transport
Affected media
Receptors
Route of Exposure
Intake Rates
Exposure Frequency
Exposure Duration
Bioavailability
Body Weight
Relationship between soil and dust concentrations
Reasonable Maximum Exposure (
RME
) vs. Central Tendency Exposure (
CTE
)
EXPOSURE PARAMETERS
Inhalation
Ingestion
Dermal
EXPOSURE ROUTES
Quantification of Exposure
Daily Intake (mg/kg-d) = (C x IR x FI x EF x ED) / (BW x AT)
C = concentration of chemical (mg/kg, mg/L, mg/m
3
)
IR = intake rate (mg soil/day, L H
2
0/day)
FI =
bioavailable
fraction (
unitless
)
EF = exposure frequency (days)
ED = exposure duration (years)
BW = body weight (kg)
AT = period over which exposure is averaged (days)
The toxicity assessment includes a qualitative hazard identification and a quantitative dose-response assessment.
The hazard identification weighs available evidence regarding the potential for particular contaminant to cause adverse health effects in exposed
individuals.
Sources of toxicity data
include:
Epidemiologic studies
Occupational exposures
Environmental exposures
Poisonings
Laboratory animal (
in vivo
) studies
In vitro
studies
Metabolism
Genotoxicity
The dose response assessment estimates
the
relationship between the
dose of an agent and the increased likelihood and/or severity of an adverse health effect in the exposed population.
Reference Dose (RfD)
RfD = an estimate of a daily exposure level (mg/kg-day) for the human population that is likely to be without an appreciable risk of deleterious effects during a lifetime
Oral RfDInhalation RfCNoncarcinogenic effects onlyAccounts for sensitive subpopulations, interspecies variability, variable exposure durations, other uncertainties
Slope Factor (SF)
SF
= a quantitative definition of the relationship between dose and response
Generally based on data
from high dose lab animal studies
Derived using mathematical
dose-extrapolation models
Upper bound estimate of the probability of a response per unit intake of a chemical over a lifetime
Represents risk per unit dose (risk per mg/kg-day)
Risk Characterization
The risk characterization integrates the exposure and toxicity assessments into quantitative and qualitative expressions of risk. (Risk = exposure x toxicity)
Risks
are estimated for non-cancer and/ or cancer effects.
Noncancer Risk Characterization
Comparison of estimated daily intake over a specific time
period
with
RfD
Hazard Quotient (HQ) =
Daily Intake
/
RfD
If
HQ < 1.0, no appreciable riskIf HQ > 1.0, possibility of non-cancer effectsFor multiple chemical exposures: Hazard Index (HI) = Sum of HQ values
Concentration x Intake Rate x Exposure Frequency x Exposure
DurationBody Weight x Averaging Time x RfD
HQ =
Cancer Risk Characterization
Defined as the probability of developing cancer over a lifetime as a result of chronic exposure to a contaminant
Cumulative carcinogenic risk is the summation of cancer risk for all chemicals of concernMay be expressed as A “one in a million” chance of cancerA 0.000001 chance of cancer1 x 10-6 or 1E-06
Risk = Daily Intake x Slope Factor
Risk =
Concentration x Intake Rate x Exposure Frequency x Exposure Duration x SF Body Weight x Averaging Time