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1. Group Four
1. Abebaw Addisu
2. Teklu Degefa
3. Thomas Ayalew
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December,2018
Jimma University Department of Environmental Health

2. Course Outline
 Introduction
 General Concepts in Exposure Assessment
 Planning an Exposure Assessment
 Gathering and Developing Data for Exposure Assessments
 Using Data to Determine or Estimate Exposure and Dose
 Assessing Uncertainty
 Presenting the Results of the Exposure Assessment
 References
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3. Course Objective
In Exposure Assessment, the following will be covered
• Definition, Terms and Concepts
• Steps & Models in Exposure Assessment
• Consideration in Exposure Assessment
• Reporting Exposure Assessment
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4. 1. Introduction
• Epidemiology is the study of disease occurrence and the causes
of disease, while the exposure assessment deal primarily with
occupational exposure.
• The process of a chemical entering the body can be described in
two steps: contact (exposure), followed by actual entry
(crossing the boundary).
• Absorption, either upon crossing the boundary or subsequently,
leads to the availability of an amount of the chemical to
biologically significant sites within the body.
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5. Cont.
• Although the description of contact with the outer boundary is
simple conceptually, the description of a chemical crossing this
boundary is somewhat more complex.
• The intake rate is the amount of chemical crossing the outer
boundary per unit time, and is the product of the exposure
concentration times the ingestion or inhalation rate.
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6. Cont.
I. Exposure
• The condition of a chemical contacting the outer boundary of a
human is exposure.
• Most of the time, the chemical is contained in air, water, soil, a
product, or a transport or carrier medium; the chemical
concentration at the point of contact is the exposure
concentration.
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7. Cont.
II. Applied Dose and Potential Dose
• Applied dose is the amount of a chemical at the absorption
barrier (skin, lung, gastrointestinal tract) available for
absorption.
• Potential dose is simply the amount of the chemical ingested,
inhaled, or in material applied to the skin.
• The amount of a chemical that has been absorbed and is
available for interaction with biologically significant receptors
is called the internal dose.
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8. 3. PLANNING AN EXPOSURE ASSESSMENT
• The particular purpose for which an exposure assessment will
be used will often have significant implications for the scope,
level of detail, and approach of the assessment.
• Using Exposure Assessments in Epidemiologic Studies
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9. Cont.
I. Using Exposure Assessments in Epidemiologic Studies
• The emphasis is on using the exposure assessment to establish
exposure-incidence (dose effect) relationships
• If the population exposed, personal monitoring or biological
monitoring helpful in establishing exposure or dose levels.
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10. Cont.
• If the exposure took place in the past, biological monitoring may provide
useful data, provided the chemical is amenable to detection without
interference or degradation, and the pharmacokinetics are known.
• For risk assessments, exposure information must be clearly linked to the
hazard identification and dose-response relationship.
• The toxic endpoints (e.g., cancer, reproductive effects, neurotoxic effects)
can vary widely, and along with other aspects of the hazard identification
and dose-response relationships, can have a major effect on how the
exposure information must be collected and analyzed for a risk assessment.
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11. 4. GATHERING & DEVELOPING DATA:
EXPOSURE ASSESSMENTS
There are 4 approach requires for this duty:
A. Measurement Data for Point-of-contact Assessments
B. Obtaining Chemical Concentration Information
C. Estimating Duration of Contact
D. Obtaining Data on Body Burden or Biomarkers
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12. A. Measurement Data for Point-of-contact Assessments
• Chemical concentrations be measured at the interface b/n the
person & media; using personal monitors.
• The chemical concentrations contacted in the media are measured by
sampling the individual’s breathing zone, food, and water.
• It is valuable in evaluating overall population exposure and checking the
credibility of exposure estimates generated by other methods.
Originally developed for OHS monitoring ( U.S. EPA, 1987a)
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13. B. Obtaining Chemical Concentration Information
• Is used to measure the concentration that comes in contact with
the individual(s) at any given time and place using personal
monitoring or Alternative methods.
• Measurements used to determine chemical concentration:
i) Concentration Measurements in Environmental Media
ii) Use of Models for Concentration Estimation
iii) Selection of Models for Environmental Concentrations
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14. i. Concentration Measurements in Environmental Media
• Measured concentration data can be generated for the exposure
assessment by a new field study.
• Media measurements taken close to the point of contact for
certainty and relevance of the data.
• Concentrations can vary considerably from place to place,
seasonally, and over time due to changing emission and use
patterns. See next table-1 & 2 for clarity (U.S. EPA, 1985-87)
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15. Type of
measurement
(sample)
Usually attempts to
characterize
(whole)
Examples Typical information needed to Characterize
exposure
A. FOR USE IN EXPOSURE SCENARIO EVALUATION
Food samples Concentrations of
contaminants in food
supply.
FDA Total Diet Study
Programmemarket basket
studies, shelf studies,
cooked-food diet sampling.
Dietary habits of various age, sex, or cultural
groups. Relationship between food items sampled
and groups (geographic, ethnic, demographic)
studied. Relationships between
concentrations in uncooked versus prepared food.
Drinking
water samples
Concentrations of
pollutants in
drinking water
supply
Ground Water Supply
Survey, Community
Water Supply
Survey,tap water.
Fate and distribution of pollutants from point of
sample to point of consumption. Population served
by specific facilities and consumption rates. For
exposure due to other uses (e.g., cooking and
showering), need to know activity patterns and
volatilization rates.
Breathing
Zone
Measurements
Exposure to airborne
chemicals.
Industrial hygiene studies,
occupational surveys,
indoor air studies.
Location, activities, and time spent relative to
monitoring locations. Protective
measures/avoidance.
Table 1. Examples of types of measurements to characterize exposure-related media
and parameters
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16. Type of measurement
(sample)
Usually attempts to
characterize (whole)
Examples Typical information needed to Characterize
exposure
B. FOR USE IN POINT-OF-CONTACT MEASUREMENT
Air Pump/Particulates
and Vapors
Exposure of an
individual or
population via the air
medium.
TEAM study of carbon
monoxide
Breathing zone
sampling in industrial
settings.
Relationships between individuals and the
population must be established, Relationships
between times sampled and other times for the
same individuals, and Relationships between
sampled individuals and other populations.
Skin Patch Samples Dermal exposure of an
individual or
population.
Pesticide Applicator
Survey
1) Same as above.
2) Skin penetration.
C. FOR USE IN EXPOSURE ESTIMATION FROM RECONSTRUCTED DOSE
Breath Total internal dose for
individuals or population
Measurement of VOCs,
alcohol.
1) Relationship between individuals and
population; exposure history chemical half-
life, possible reservoirs within the body.
2) Relationship between breath content and
body burden.
Blood Total internal dose for
individuals or population
Lead studies, pesticides,
heavy metals
1) Same as above
2) 2) Relationship between blood content and
body burden.
Table 2. Examples of types of measurements to characterize exposure-related media
and parameters
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17. ii. Use of Models for Concentration Estimation
• If concentrations in the media cannot be measured, we can measure using related
measurements and models.
• Source characterization (environmental fate models): determine rate of release of
chemicals to environment from a point of emission e.g. incinerator, landfill,
industrial...
• These measurements are used to estimate emission factors, or a relationship
between releases and facility operations.
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18. iii. Selection of Models for Environmental Concentrations
• Uses for simulation of chemical concentrations.
• There is nor right model; Neither best model.
Consideration in selecting a model:
 Objective of the exposure assessment
 Associated schedule, budget, and other resource constraints
Its ability to simulate site-specific contaminant transport and transformation
processes.
Performance characteristics it used
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19. C. ESTIMATING DURATION OF CONTACT
• The time that the individual is in contact with a chemical would
be observed and recorded, and linked to the concentrations of the
chemical during those time segments.
• When the above fails it will be estimated by using data that may
be somewhat removed from the actual point of contact, and
assumptions must be made as to the relevance of the data.
– largest source of uncertainty is the concentration for a given exposure duration.
– the concentration in the media is known with more certainty than the activities of the individual(s) exposed
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20. i. Observation and Survey Data
• Data collected by Observer at point of contact are location-time
data for individual or a population segment.
• Usual method for obtaining these data for population segments or
populations is survey questionnaires.
• There are several approaches used in activity surveys, including
diaries, respondent or third-party estimates, momentary sampling,
video monitoring, and behavioral meters. (U.S. EPA, 1984b)
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21. Several Approaches In Activity of Survey
Approaches Technic of Surveying Advantage Limitation
Diary forms Respondents report all
their activities and locations
for that period
Most powerful &
less expensive
Validity of time-diary
data
Questionnaires Professionals well-versed in
survey techniques
Direct questions to
collect the basic
data
complex and subtle
process
Respondent
estimates
Respondents are simply asked
to estimate the time they spend
at a particular activity
least expensive
and most
commonly used
Less precise and less
accurate
Momentary(bee
per) sampling
The moment the respondent’s
home
telephone or beeper sounds
Brief reports for a
specific moment
Times at home or carry
beepers with them
Behavioral
meters & Video
monitoring
Measures using development
of equipment by respondent
More Accurate Most expensive
Skill Gap
Respondent refusal to use7/2/2019 21

22. ii. Developing Other Estimates of Duration of Contact
When Survey cannot used-estimated from more indirect data.
– least expensive
– generating estimates of duration of contact;
– least accurate.
But it is only approach assessing the risk to new Chemicals.
Methods used to make these estimates:
a) Time it takes to perform an activity
b) Average duration of contact
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23. D. Obtaining Data on Body Burden or Biomarkers
Biomarkers/Body Burden: data denote the presence of chemicals (Exposome) the
body of exposed individuals(biological media).
Bioindicators :demonstrate biological changes indicative of future
adverse health effects.
Exposome: endogenous and exogenous chemicals that are biomarkers in Biological
media (blood, breath, and urine).
Gene –Environment (“G × E” ): the accumulation of an individual’s environmental
exposures and metabolic responses throughout the person’s lifetime.
(M. Ariel Geer Wallace,2018)
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24. Accessed:J Toxicol Environ Health B Crit Rev. 2016 ; 19(8): 380–409. doi:10.1080/10937404.2016.1215772
Blood-borne biomarkers and bio indicators for linking exposure
to health effects in environmental health science
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25. i. Obtaining Data for Pharmacokinetic Relationships
 The pharmacokinetic data necessary for model development are
usually obtained from laboratory studies with animals.
Comparing risks resulting from different exposure the result of
even be a different toxicological endpoint.
Example: enzymes that normally could metabolize low
concentrations of a chemical may be saturated when the chemical
is absorbed in high doses, resulting in a higher dose delivered to
target tissues.
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26. ii. Obtaining Data on Intake and Uptake
Intake factors included are:
 drinking water consumption rates;
 consumption rates for homegrown fruits, vegetables, beef, and dairy products;
 consumption rates for recreationally caught fish and shellfish;
 incidental soil ingestion rates;
 pulmonary ventilation rates; and
 surface areas of various parts of the human body.
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27. 5.USING DATA TO DETERMINE OR ESTIMATE
EXPOSURE AND DOSE
Once an acceptable data set is available, the assessor can calculate exposure or dose.
• There are several ways to calculate exposure and dose:
• making inferences
• assumptions
• calculations
A. Use of Data in Making Inferences for Exposure Assessments
– generalizations that go beyond the information contained in a data set.
– Professional judgment is usually preferred
– infer more general information about
• exposure concentrations,
• contact times,
• exposures, or doses.
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28. Cont.
B. Dealing With Data Gaps
• Even after supplementing existing measurement data with
model results, there are likely to be gaps
Options:
– New data can be collected: if the new data are quick and easy to
obtain
– The scope of the assessment can be narrowed:T his is unlikely to be
satisfactory if the part of the assessment deleted.7/2/2019

29. C. CALCULATING EXPOSURE AND DOSE
Equations Used for Quantification of Exposure
 General statement
Chemical x Intake x Retention Factor x Length of Exposure
 For Noncarcinogens
Maximum Daily Dose (MDD)
 For Carcinogens=Life time Daily Dose(LADD)
Lifetime Average Daily Dose (LADD)
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30. Dose levels (animal studies)
 NOEL no-observed effect level
 NOAEL no-observed-adverse effect level
LOAEL lowest-observed-adverse effect level
 MTD maximum tolerated dose
 LD50 dose which kills 50% of population
 LC50 concentration which kills 50% of
population
Increasingdose
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31. Reference dose
is an estimate of the daily dose of a chemical that will avoid toxic
effects other than cancer
The animal dose (NOAEL, LOAEL) is adjusted by uncertainty
factors (UF) to allow for differences in sensitivity to chemicals
Human data: UF = 10
Animal data:
UF = 100 (NOAEL), 1000 (LOAEL), 1000 (NOAEL, less data)
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32. Reference dose
RfD = NOAEL/UF
100 mg/kg-day / 100 = 1 mg/kg-day
Use RfD to establish allowed concentrations
 allowed C = RfD x body wt / daily intake
= 1 mg/kg-day x 70 kg / 2 liters/day
= 35 mg/l
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34. 7/2/2019 34

35. 6. ASSESSING UNCERTAINTY
• Exposure assessment uses a wide array of information sources and
techniques.
• Most likely, data will not be available for all aspects of the exposure
assessment.
• Those data that are available may be of questionable or unknown quality.
• The net result will be based on a number of assumptions with varying
degrees of uncertainty.
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36. TYPES OF UNCERTAINTY
Uncertainty in exposure assessment can be classified into three broad
categories:
I. Scenario Uncertainty
 Uncertainty regarding missing or incomplete information needed to fully
define the exposure and dose.
II. parameter uncertainty
 Uncertainty regarding some parameter
III. model uncertainty
 Uncertainty regarding gaps in scientific theory required to make predictions
on the basis of causal inferences.
• Identification of the sources of uncertainty is the first step to reduce that
uncertainty.7/2/2019 36

37. I. Scenario Uncertainty
• The sources of scenario uncertainty include descriptive errors,
aggregation errors, errors in professional judgment, and incomplete
analysis.
A. Descriptive errors include errors in information, such as the
current producers of the chemical and its industrial, commercial,
and consumer uses.
B. Aggregation errors arise as a result of lumping approximations.
Included among these are assumptions of homogeneous
populations, and spatial and temporal approximations such as
assumptions of steady-state conditions.
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38. C. Professional judgment
• Errors in professional judgment also are a source of uncertainty.
• A potentially serious source of uncertainty in exposure assessments arises from
incomplete analysis due to lack of information regarding the use of a chemical in a
particular product.
• The justification for excluding particular exposure scenarios should be described and the
uncertainty in those decisions should be characterized as
» HIGH,
» MEDIUM
» LOW7/2/2019 38

39. II.Parameter Uncertainty
• Sources of parameter uncertainty include measurement errors, sampling errors,
variability, and use of generic or surrogate data.
• Measurement errors can be random or systematic.
• Random error results from imprecision in the measurement process.
• Systematic error is a bias or tendency away from the true value.
• Sampling errors concern sample representativeness.
• Data that generated for another purpose do not represent the exposure being
analyzed.
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40. • The inability to characterize the inherent variability in environmental and exposure
related parameters is a major source of uncertainty.
• For example, meteorological and hydrological conditions may vary seasonally
• human activity patterns can vary substantially depending on age, sex, and geography
• The use of generic or surrogate data is common when site-specific data are not avail.
• Examples include standard emission factors for industrial processes, and data
pertaining to structurally related chemicals as surrogates for the chemical of interest.
• This is an additional source of uncertainty, and should be avoided if actual data can
be obtained.
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41. III. Model Uncertainty
• At a minimum, the exposure assessor should describe in qualitative terms
the rationale for selection of any conceptual and mathematical models.
• Relationship errors and modeling errors are the primary sources of
modeling uncertainty.
• Relationship errors include errors in correlations between chemical
properties, structure reactivity correlations, and environmental fate
models.
• Modeling errors are due to models being simplified representations of
reality, for example approximating a three-dimensional aquifer with a
two-dimensional mathematical model.
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42. Most approaches for analyzing uncertainty have focused on
in parameter values translates into overall uncertainty in the
assessment.
i. Sensitivity analysis is the process of changing one variable while leaving the others
constant and determining the effect on the output.
These results are useful to identify the variables that have the greatest effect on
exposure and to help focus further information gathering.
ii. Analytical uncertainty propagation involves examining how uncertainty in
individual parameters affects the overall uncertainty of the exposure assessment7/2/2019 42
Cont.

43. 7.Presenting and Communicating The Results of The
Exposure Assessment
• One of the most important aspects of the exposure assessment is presenting the
results.
• It is here that the assessment ultimately succeeds or fails in meeting the objectives
laid out in the planning.
• Is more than a simple summary of conclusions
• Is quantitative estimates for the various pathways and routes of exposure.
• Is the overall narrative exposure characterization .
• Should consist of , and
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44. I. Exposure Characterization
• The exposure characterization is the summary explanation of the exposure ass.
• provides a statement of purpose, scope, level of detail, and approach used in the
assessment, including key assumptions;
• presents the estimates of exposure and dose by pathway and route for individuals,
population segments, and populations in a manner appropriate for the intended risk
characterization;
• develop a risk characterization.
• identify key data gaps that can help focus further efforts to reduce uncertainty.
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45. II. Risk Characterization
• Most exposure assessments will be done as part of a risk assessment.
• Risk characterization is the culmination of the risk assessment process.
• Integrates the individual characterizations from the hazard identification, dose
response, and exposure assessments;
• provides an evaluation of the overall quality of the assessment and the degree of
confidence the authors have in the estimates of risk and conclusions drawn;
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46. • Describes risks to individuals and populations in terms of extent and
severity of probable harm; and
• Communicates results of the risk assessment to the risk manager.
• It provides a scientific interpretation of the assessment.
• The risk manager can then use the risk assessment, along with other risk
management elements, to make public health decisions.
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47. References
1. US EPA 1992 Guidelines for Exposure Assessment
2. WHO 2000,Evaluation and use of epidemiological evidence for environmental health risk
assessment guideline document
3. Gehring et al. Environmental Health 2013, 12:8
4. Wallace et al. J Toxicol Environ Health B Crit Rev. Author manuscript; available in PMC 2018
September 20.
5. Grandjean and Bellanger Environmental Health (2017) 16:123
6. S.K. Bopp et al.Environment International 120 (2018) 544–562
7. Budnik et al. Journal of Occupational Medicine and Toxicology (2018) 13:6
8. Bokkers et al. Food Chem Toxicol. 2017 December ; 110: 408–417. doi:10.1016/j.fct.2017.10.038.
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