3_Exposure_Risk Introduction

Concepts and Terminology of Health Risk Assessment

Mustafa M. Aral

MESL @CEE,GThttp://mesl.ce.gatech.edu/maral@ce.gatech.edu

3_Exposure_Risk Introduction

3_Exposure_Risk Introduction

3_Exposure_Risk Introduction

3_Exposure_Risk Introduction

3_Exposure_Risk Introduction

3_Exposure_Risk Introduction

3_Exposure_Risk Introduction

3_Exposure_Risk Introduction

Health Risk Assessment process:

Hazard identification;

Exposure-dose assessment;

Dose-response assessment; and,

Risk characterization.

3_Exposure_Risk Introduction

Steps Involved in HRA.

3_Exposure_Risk Introduction

Exposure Assessment

1

2 3

4

5

Environmental Health Continuum

Pathway Transport

Epi studies

3_Exposure_Risk Introduction

Continuum For Relating Environmental Contamination With Clinical Disease

S

C

OURCE

ONTAMINATION

T

H

E

OTAL

UMAN

XPOSURE

I

D

NTERNAL

OSE

B

E

D

IOLOGICALLY

FFECTIVE

OSE

E

B

E

ARLY

IOLOGICAL

FFECT

E

T

NVIRONMENTAL

RANSPORT

A

S /

F

LTERED

TRUCTURE

UNCTION

C

D

LINICAL

ISEASE

EC

NV

IRO

NM

EN

TA

LO

NT

AM

I NA

TI O

N

HE

EA

LT

HF

FE

CT

S

(After Lioy, 1990; Johnson and Jones, 1992)

X

3_Exposure_Risk Introduction

Framework for Exposure Assessment

3_Exposure_Risk Introduction

Exposure Assessment Risk Evaluation Process:

Contaminant SourceSource Identification

Environmental ConcentrationAir, surface water and groundwater

ExposureDermal, Ingestion, Inhalation

Exposure Dose

Exposure Risk

Multipathway fate and

transport processes

Multipathway fate and

transport modeling

Human activities and

contactExposure modeling

Intake and uptake Kinetic models

Dose to risk analysisMechanistic, statistical

and uncertainty models

3_Exposure_Risk Introduction

Source to Population Risk Man.

CONTAMINANT

SOURCE

ADVECTIVE ANDDIFFUSIVE

TRANSPORT

CHEMICAL,BIOLOGICAL AND

PHYSICAL FATEPROCESSES

POPULATIONRECEPTORS

Physical Removal

Chemical Removal

Biological Removal

REMEDIATION

Physical Containment

PATHWAY CONTROL

Chemical Containment

Biologic Containment

Risk Assessment

Risk Communication

Exposure-DoseAnalysis

RISK MANAGEMENT

Out flux Prevention

Recycling

Out flux Minimization

SOURCE MANAGEMENT

3_Exposure_Risk Introduction

Exposure Assessment:Historical Perspectives-1

About 3200 B.C.: The Asipu, a group of priests in the Tigris-Euphrates Valley establish a methodology:

Hazard identification;

Generation of alternatives;

Data collection (including signs from the gods) and analysis;

Report creation and documentation.

3_Exposure_Risk Introduction

Exposure Assessment:Historical Perspectives-2

King Edward II had to deal with the problem of smoke in London:

1285: Established a commission to study the problem.

1298: Commission called for voluntary reductions in the use of soft coal.

1307: Royal proclamation banned soft coal, followed by a second commission to study why the proclamation was not being followed.

3_Exposure_Risk Introduction

Exposure Assessment:Historical Perspectives-3

London cholera epidemic of 1854

2,050 people died in one week.

Method of cholera transmission unknown.

Exposure assessment method

Dr. John Snows cholera map

Relation of cholera cases (deaths) to water supply.

3_Exposure_Risk Introduction

Dr. John Snows cholera map

3_Exposure_Risk Introduction

Defining Exposure

Contact of a chemical, physical, or biological agent with the outer boundary of an organism.

3_Exposure_Risk Introduction

Defining Dose

Dose is the amount of a substance available for interaction with metabolic processes or biologically significant receptors aftercrossing the outer boundary of an organism

Exposure is external

Dose is internal

3_Exposure_Risk Introduction

Exposure / Dose

3_Exposure_Risk Introduction

Exposure

Dose

Quantifying Exposure:

Exposure is quantified as the concentration of the agent in the medium in contact, integrated over the time duration of contact

1

0

( , ) ( )t T

t TE c t C t dt

=

=

=

This

Course

3_Exposure_Risk Introduction

Quantifying Dose:

Potential dose for an intake process (dermal, inhalation and ingestion) is the integration of the chemical intake rate (concentration of the chemical in the medium times the intake rate of the medium, C times IR) over time

D C t IR t dtpott

t

= ( ) ( )2

1

3_Exposure_Risk Introduction

This Course

Quantifying Exposure:

Present exposure

Environmental and biologic measurements

Past exposure

Data if available in conjunction with computational models

3_Exposure_Risk Introduction

Quantifying Exposure:

RI/FS

Epidemiologic investigation

Time Present-day

Con

tam

inatio

n

Exposure

Relationship of epidemiologic investigations to remediation activities (RI/FS)

3_Exposure_Risk Introduction

Approaches to Quantification of Exposure

Exposure can also be estimated from dose, which in turn can be reconstructed through internal indicators (biomarkers, body burden, excretion levels, etc.) after the exposure has taken place (reconstruction)

3_Exposure_Risk Introduction

Approaches to Quantification of Exposure

Measure at point of contact while it is taking place, measuring both exposure and time of contact and integrating them (point- of-contact measurement)

Estimated by separately evaluating exposure concentration and time of contact, and then combining the information (scenario evaluation)

3_Exposure_Risk Introduction

Quantifying Exposure:

Typical ConditionDesired Condition

3_Exposure_Risk Introduction

Quantifying Exposure:

Screening level models

ACTS, ISCPC

Complex environmental systems

Groundwater flow and transport models

Water-distribution system models

Atmospheric dispersion models

Uncertainty analysis

Monte Carlo simulation

3_Exposure_Risk Introduction

Dose Terminology

Potential dose

Amount available for ingestion, inhalation, or skin absorption.

Applied dose

Amount of a substance presented to an absorption barrier and available for absorption.

3_Exposure_Risk Introduction

Dose Terminology--continued

Absorbed dose

Amount crossing a specific absorption barrier (exchange boundaries of skin, lung, digestive tract, etc. )

Internal dose

Amount absorbed and associated with internal adverse effect (a more general term )

3_Exposure_Risk Introduction

Toxicology

Zero contaminant discharge in an industrial society is not possible;

It is safe to say that we are being constantly exposed to natural or synthetic chemicals in our ambient environment;

The task of the environmental health scientists is to ensure that the public health is not adversely affected by exposure to these chemicals.

3_Exposure_Risk Introduction

Toxicology

Exposure aspects of environmental health effect studies are commonly considered in epidemiologic investigations.

Adversity or other measures of the effect of exposure is studied in the field of toxicology.

Scientist, who conduct laboratory studies on animals to understand, quantify and estimate health effects of a wide range of toxic substances, are referred to as toxicologist.

Their work traditionally consists of quantifying the effects of one toxicant to a single or multiple animal species.

3_Exposure_Risk Introduction

Toxicology Descriptive toxicology: In this group, scientists work primarily focuses

on the toxicity testing of chemicals. The studies performed in this category are designed to generate toxicity information that can be used to identify the various organ toxicities that the test agent is capable of inducing under a wide range of exposure conditions;

Research/mechanistic toxicology: Under this category, scientists study the toxicant in more detail for the purpose of gaining an understanding of how the toxicant initiates those biochemical orphysiological changes within the cell or tissue that results in toxicity. Thus, the goal here is to understand the chain of biologic or biochemical events a toxicant triggers in a cell to create a toxic outcome; and,

Environmental/applied toxicology: The studies described in the two categories given above are conducted in a laboratory setting. In the applied toxicology category scientists focus