Human Exposure Assessment Human Health and the Atmospheric Environment

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Human Exposure AssessmentHuman Health and the
Atmospheric Environment

• Stephen Corbett
• Centre for Public Health
• Western Sydney Area Health Service

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Environmental Contamination
Environmental Concentration
Air Water Food
Soil
Exposure
External Exposure Absorbed Dose Target Organ
Dose
Health Effects
Subclinical Effects Morbidity Mortality
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Direct and Indirect Approaches to Measuring
Exposure
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The Lungs
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Inhalation

• The lungs have evolved to absorb and excrete
  gases
• The surface area of the lung epithelium available
  for absorption (1.5m tall) is 100 m2
• Particles reach the bottom of the lungs
  (alveoli) if they are small enough (less than 10
  µm aerodynamic diameter - PM10 fraction)
• Particles such as asbestos fibres and
  crystalline silica can cause lung cancer
• Wood dust can cause nasal and lung cancers
• Inhaled particles larger than the PM 10 fraction
  enter
• the gut either directly after deposition before
• entering the lungs or indirectly in mucus from
  the

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Pharmacokinetic and Pharmacodynamic Models
Toxicokinetics describes the uptake and
distribution of a substance through the
body It includes absorption, distribution,
storage, metabolism and excretion
Toxicodynamic phase covers all aspects of the way
in which a substance causes harm once it reaches
its target in the body
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Direct and Indirect Approaches to Measuring
Exposure
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Personal Monitoring
Measuring personal exposure to an airborne
contaminant
ACTIVE devices A small pump attached to a
filter. Air is drawn at a known rate across
sampling media and a collection
device Advantages Correlates with personal
actual exposure, Can be linked to levels of
activity Limitations Detection Limits, Battery
Life, Disruption of Normal Activity
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Personal Monitoring
Measuring personal exposure to an airborne
contaminant
PASSIVE devices Air is sampled passively due to
natural air movement eg NO2 samplers Advantages U
nobtrusive, Can measure cumulative exposure over
long periods Limitations Unavailable for many
contaminants. Correlation with actual exposure
needs to be ascertained
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Personal Monitoring
Measuring personal exposure to an airborne
contaminant
AREA devices Air is sampled continuously at large
volumes Advantages Sophisticated equipment,
large volumes, continuous operation, Immediate
results Limitations May correlate poorly with
actual exposure
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Personal Monitoring
Air Passive Sampler (Nox, Formaldehyde, SO2)
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Personal Monitoring
Air Passive Sampler (Nox, Formaldehyde, SO2)
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Personal Monitoring
Benzene, Toluene, Xylene (BTEX) Passive Sampler
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Personal Monitoring
BTEX Sampler
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Biological Markers of Exposure
A Biological Marker of Exposure is a measurable
biochemical or physiological alteration in an
organism which has the potential to cause harm
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Environmental Monitoring
Macro- Environmental Measurements
Criteria Pollutants SO2, NOx, CO, Lead,
Ozone,Particulates Most large urban areas
continuously monitor these pollutants Results
usually reported as averages. Maximum or peak
exposures also important eg asthma, mortality
studies Correlates between Ambient and
Personal Exposure substance dependent On a day
to day basis, meteorology is the main determinant
of exposure
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Environmental Monitoring
Micro- Environmental Measurements
Personal Exposure Monitoring - active or passive
can measure total exposure in a home For some
contaminants e.g. indoor allergens, household
lead dust exposure depends on time/activity
patterns in the home
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Modeling Exposure
Modeling is Estimation of exposure as an
alternative to measurement Personal Exposure
can estimated using mathematical formulae based
on data and a knowledge of other
measurements Surrogate measures of exposure
imply the use of a model of exposure
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Modeling Exposure
Examples Simple models Classify exposure to
NO2 by single surrogate variable Gas vs
Electric Stove Classify exposure to airborne
lead by distance from a smelter stack lt 1km
high, 1-2 medium , gt 2 low
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Modeling Exposure
Examples Statistical Models 1. Knowledge
of type of cooking appliance and results of
indoor NO2 concentrations from previous
studies i.e Indoor NO2 Concentration
Outdoor NO2 Concentration a Where a0
with electric stoves and 45 g/m3 when gas is
used 2. Knowledge of factors influencing Blood
Lead in a Smelter Community from previous
studies on individual children Blood Lead
Concentration (Age) (Gender) (Hand Mouth
Behaviour) (House Dust Lead )
(Distance from smelter) (Lead in Air
Concentration)
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Modeling Exposure
Examples Models based on a knowledge of
physics, chemistry and physiology (Deterministic
models) Modeling personal exposure to NO2 from
knowledge of indoor and outdoor NO2
concentrations, and time activity
patterns Personal NO2 Exposure (Outdoor
exposure) (Indoor exposure) (Time
Spent Outdoors) (Time Spent Indoor)

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Modeling Exposure
Why is modeling important in Public
Health Modeling used to forecast likely human
exposures to new point source emissions e.g a
new ventilation stack for a motorway tunnel.
An extension to an existing copper smelting
plant designed to increase production
capacity Understanding the assumptions,
uncertainty and limitations inherent in model
design are critical in assessing public health
impacts Modeling is usually the only source of
information about possible health impacts of
future developments
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Modeling Exposure
Integrated Models combine statistical and
deterministic elements Increasing use of
Physiologically based toxicokinetic models which
take account of the absorption, metabolism,
storage and excretion of a substance in assessing
the effect of a toxic agent on disease
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Plume Modeling of a Chemical Fire
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(No Transcript)
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Calculating Exposure from Airborne Contaminants
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Lung Ventilation Rates at Different Levels of
Activity as a Function of Age
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Direct and Indirect Approaches to Measuring
Exposure
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Questionnaires and Diaries

• Questionnaire data can
• links individual subjects to environmental
  exposure measurement
• determine time and activity patterns
• elicit symptoms which may in turn guide exposure
  measurement
• determine length of exposure e.g time at place
  of residence
• collect information on surrogates for exposure
  e.g odours,
• Diaries record information over longer time
  periods, rather than at one time or at protracted
  intervals. They can recorsd time and activity
  prospectively and records symptoms

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Exposure Models and Pathways
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Household Dust
Combustion
Airborne Lead
Evaporation
Deposition
Inhalation
Wind Borne Particles
Carpet/Floor/ Household Surfaces
Aquatic and Terrestrial Biota
Lead Source
Soil/Dust
Hand Lead
Ingestion (Food)
Sedimentation
Runoff/ Leaching
Human (Children)
Direct Contact (Pica)
Deposition
Ingestion
Excretion
Ingestion (Water)
Leaching/Runoff
Water
Sources and Pathways of Airborne Lead Exposure in
Children
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Surrogate Measures of Exposure
Surrogate measures of exposure correlate with
contaminant concentration. Easier and cheaper to
measure than biological or environmental
measurements
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Time and Place
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Time and Place
Spring attendances for asthma at Tamworth Base
Hospital, 1984 and 1986-90 Recurrent Epidemics
of asthma linked to thunderstorms in 4 years
1984-1990, on or about 1st November Probable
cause Amplification of the number of respirable
rye grass pollen particles caused by thunderstorm
1984
1986
1987
1990
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Exposure Measurement in Epidemiological Studies
Which exposure is to be measured? The choice is
based on an understanding of the transformation
and dispersion of pollutants, and the biological
properties of the agent. Measuring personal
exposure or biomarkers is usually more expensive
than measuring ambient levels of pollutant A
decision to use surrogate or approximate measures
must be done in the knowledge of the correlation
with true measurement
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Exposure Measurement in Epidemiological Studies
Validity and Precision The Validity refers to
the agreement between the chosen measure and the
true exposure. Low Validity is due to systematic
error in exposure measurement. The Precision
of a measure refers to its repeatability. Low
precision is due to random error. Increasing the
number of measurements per subject Estimating
the variability of measurements between and
within subjects is necessary to calculate the
number of measurements needed per person to
optimise precision.
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Resources
Exposure Assessment Exposure Scenarios and
Exposure Settings (2001) http//www.health.gov.au
/pubhlth/publicat/document/env_exposure.pdf Crite
ria Air Pollutants Ozone (1997) PDF file, 268k
http//enhealth.nphp.gov.au/council/pubs/pdf/ozone
.pdf Benzene (1997) PDF file, 108k
http//enhealth.nphp.gov.au/council/pubs/pdf/ozone
.pdf Nitrogen Dioxide (1997) PDF file, 200k
http//enhealth.nphp.gov.au/council/pubs/pdf/nitrd
iox.pdf Sulfur dioxide (1999) http//enhealth.nph
p.gov.au/council/pubs/pdf/suldiox.pdf Risk
Assessment Environmental Health Risk Assessment
- Guidelines for assessing human health risks
from environmental hazards (2002)
http//enhealth.nphp.gov.au/council/pubs/pdf/envh
azards.pdf
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Resources
Environmental Health Criteria http//www.inchem.o
rg International Program on Chemical
Safety Environmental Health Criteria Food
Additives Occupational Health and Safety
Standards International Agency for Research on
Cancer Environmental Health Textbook and
Teaching Resources WHO Introductory Environmental
Health http//www.who.int/docstore/peh/archives/be
h/Behtgtoc2.htm