9.quantitative risk assessment

8/13/2019 9.Quantitative Risk Assessment

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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



Introduction

Purpose of risk assessment

Stages of risk assessment› Hazard Identification

› Exposure Assessment

›

Toxicity Assessment› Risk Characterization



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.



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.



Hazard Identification

Exposure Assessment

Toxicity Assessment

Risk Characterization



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.



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.



Further Screening of Chemicals

› Additional considerations include:

Mean concentration Mobility

Frequency of detection

Persistence in the environment

Treatability



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



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



Contaminant Release, Transport, Transfer,and Transformation

Release of contaminants – result from

natural processes.

Important things to consider:

› How they are transported, transferred and

transformed.



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



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



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.



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.



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)



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.



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.



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)]



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.

9.quantitative risk assessment

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