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At the end of lecture of week 13 studentwill
Be able to define the definition of risk Be able to identify the purpose of risk
assessment
Be able to calculate and interpret thestage of risk assessment
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Introduction
Purpose of risk assessment
Stages of risk assessment› Hazard Identification
› Exposure Assessment
›
Toxicity Assessment› Risk Characterization
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Definition of RISK:› The probability of suffering harm or loss.› Is a tool for understanding the health
and environment hazards associatedwith hazardous waste and can greatlyimprove the basis on which to makehazardous waste management
decisions.› Risk = (probability) x (severity of consequence)› The term quantitative – to describe the process
of using scientific principles to calculatequantitative estimates of risk.
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Provide information to decisionmakers as to the consequences ofpossible actions.
Play major role in the decisionmaking for the remediation ofcontaminated sites.
To quantify potential human health
and ecological risks stemming fromtoxic contaminants that maytransported to potential receptorpopulations.
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Hazard Identification
Exposure Assessment
Toxicity Assessment
Risk Characterization
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Examine the data all contaminantsdetected at site and consolidates the
data to stress the chemical concern. Normally involve clear understanding on:
› What chemicals are present at a site
› Their concentration and spatial distribution
› How they could move in the environmentfrom the site to potential receptor points.
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Initial Screening
› To calculate the ranking of toxicity scores –
indicate which compounds pose thegreatest hazard based solely on theirmaximum concentration and toxicity.
Further Screening of Chemicals
› Further evaluation to consider for eachchemical its ranges of concentration, itsmobility in the environment and other issues.
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Further Screening of Chemicals
› Additional considerations include:
Mean concentration Mobility
Frequency of detection
Persistence in the environment
Treatability
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Consist of estimating the exposure to thechemicals by the populations potentially atrisk.
Considerable attention:› Identification of general and sensitive
populations of current and potential receptors
› Estimation of both short- and long-termexposures in terms of doses by exposure route.
Delineation of thesources & spatial
distribution ofcontaminants at the
site
Analyze how thecontaminants might
be released
Estimate how itmigrate to a
potential receptor
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Environmental Pathways Consist of fate and transport analysis Pathway- the environmental routes by which
chemicals from the site can reach receptors.
Element:› Source
› Chemical release mechanism
› Transport mechanism
› Transfer mechanism
› Transformation mechanism
› Exposure point
› Receptors
› Exposure route
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Contaminant Release, Transport, Transfer,and Transformation
Release of contaminants – result from
natural processes.
Important things to consider:
› How they are transported, transferred and
transformed.
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Potentially Exposed Populations
To determine potentially exposedpopulations.
Include:
› Present population in vicinity of the site
› Future population in vicinity of the site
› Subpopulations of special concern› Potential on-site workers during any
remediation
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Development of Exposure Scenarios To characterize the conditions under which the
populations may be potentially exposed. Involves an evaluation of both current and
reasonable future uses of the site. Then, the specific parameters governing
exposure can be selected. Commonly used exposure scenarios:
› Worker scenario
› Trespasser scenario
› Residential use scenario
› Recreational use scenario
› Construction scenario
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Exposure Point Concentrations
Exposure point-define the locations ofthe receptors for the various scenarios.
May be as close as the sources of wasteat the site itself or at a considerabledistance, particularly for pathways
involving the food chain.
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Receptor Doses
To estimate the doses of the differentchemicals of concern to which receptorsare potentially exposed at the exposurepoint.
Three routes are considered – ingestion,
inhalation and dermal contact. Three types of doses-the administered
dose, the intake dose and target dose.
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Receptor Doses Other factors: life style, frequency and duration of exposure,
the body weight of the receptor.
I = Intake (mg/kg of body weight. day) C= concentration at exposure point (mg/L in water or mg/m3
in air) CR = Contact rate (L/day or m3/day) EF = exposure frequency (days/year) ED = exposure duration (years) BW = body weight (kg) AT = averaging time (days)
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Analyze the uncertainty inherent inthese numbers, and describe how thisuncertainty may affect the estimates
of risk.
For the purpose of quantifying human
health risk, chemicals arecharacterized as carcinogens andnon-carcinogens.
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To estimate risk
Consist in part of calculating quantitativeestimates of both the carcinogenic and
noncarcinogenic risk to receptors for allexposure scenarios considered.
Background risk – is what people are
exposed to in the absence of theparticular source of risk being studies
Incremental risk - is that caused by this
source.
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Carcinogenic Risk
Risk = Ic x SF Where
› Ic = chronic daily intake of carcinogen [mg/(kg.day)]› SF = carcinogen slope factor [(kg.day)/mg]
Noncarcinogenic Risk
HI = IN x RfC Where
› HI = hazard Index (dimensionless)
› IN = Chronic daily intake of noncarcinogen [mg/(kg.day)]
› RfC = references concentration [mg/(kg.day)]
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It is important to keep in mind that riskassessment is an iterative process.
An analysis of the sensitivity of the
magnitude of calculated risk to theseassumptions will indicate whether the riskanalyst should revisit these assumptions
and refine them. Additionally sampling may be required
to fill data gaps or to present a morecredible worst-case assessment.