Supercourse

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Supercourse

• Environmental Exposure Assessment And Biomarkers
• Wael Al-Delaimy, MD, PhD

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• Environmental and Occupational Epidemiology
  study the distribution of human health and
  disease in relationship to exposure to agents in
  the general and occupational environment

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• Validity of Environmental Epidemiology
  Occupational Epidemiology depends on Assessment
  of exposure
• Assessment of effects on health
• Bias an error that leads to incorrect
  conclusions
• Accuracy (validity) the capacity of an exposure
  variable to measure the true exposure
• Precision is a measure of the variation in the
  measurement error in the population

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Exposure in the dictionary means

• unmasking (exposure of electoral fraud)
• to light (photography)
• to cold (he died of cold exposure)
• position of a building (a house with western
  exposure)
• to leave unprotected (the metal was left
  exposed in the rain
• to give an experience (expose him to hardship)

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• Exposure in Epidemiology any of a subjects
  attributes or any agent with which the subject
  may come in contact with and that may be relevant
  to health.
• Environmental exposure any contact between a
  potentially harmful agent present in the any
  medium, and a surface of the human body.

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• Types of exposure (time related)
• Instantaneous exposure
• Cumulative exposure
• average exposure
• peak exposure
• Components of exposure
• a target
• an agent
• and contact between both

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Dose

• Definition amount of pollution that actually
  crosses the border between the environment and
  the human body
• Types of Dose of exposure
• potential dose
• applied dose
• absorbed dose
• active dose
• eliminated dose
• net dose
• accumulated dose

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Dose estimation

• Modeling data based physiologically based
• Measurement
• Measurement is the classification of objects and
  events in which assignment of numerals to those
  objects and events are according to rules.
• Measurement method in epidemiology is a procedure
  or set of procedures designed to measure one or
  several of the variables of interest in an
  epidemiological study.

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Exposure Measurement Error

• The measurement error model ZXe
• Differential
• Non-differential
• Berkson error

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Strategies of exposure assessment

• Types of Data
  Approximation
  To actual exposure
• Quantified personal measurements
• Quantified area or ambient measurements
  Best
• In the vicinity of the residence or other sites
• Of activity
• Quantified surrogates of exposure (e.g. estimates
  of
• Of drinking water use)
• Distance from site and duration of residence
• Distance or duration of residence
• Residence or employment in geographic area in
• reasonable proximity to site of exposure..
• Residence or employment in defined geographical
• area (e.g. county) of the site.
  
  
  poorest

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Biological Markers

• Definition
• they are cellular, biochemical, or molecular
  alterations that are measurable in biological
  media ( such as human tissues, cells or fluids).
• Three types of measurements used for biomarkers
• A. The level of the substance itself in
  biological media
• B. The level of products of bio-transformation of
  the substances in the same media
• C. The biological effect that result from contact
  of the external agent with the human body

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Biological Markers

• Advantages
• improve validity and reduce bias
• more individualized measurements of the subjects
• specifically address the effect of one agent on a
  certain tissue in the body
• identify individual susceptibility (e.g.
  genetics)
• allow earlier disease detection (e.g. preventive
  medicine)
• mechanisms of disease occurrence (e.g. cancer)
• intervention trials (e.g. smoke cessation)

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Target tissue and media for biomarkers
Inhalation
Absorption
Ingestion
Exha- lation
Saliva
Respiratory tract
Exfo- liation
GI tract
Skin
Blood
Sweat
Liver
Feces
Kidney
oo
Urine
Hair
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Relation of biomarkers to exposure and disease
Physical
Biological
Chemical
Culture
susceptibility
Altered structure/ function
BED
Disease
Internal dose
Early response
Exposure
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• Interpretation of biomarkers
• Statistical relationships
• biological relationships
• Types of Biomarkers
• Markers of exposure
• Susceptibility Markers
• Markers of disease

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Markers of exposure

• Uses
• Integrate multiple portals of entry
• integrate fluctuating exposure
• relate time of exposure to internal dose
• study acute exposure-outcome association
• detect non-specific exposure hazards
• use innovative biological specimens
• assess real-world exposure using lab experiments
  measurements

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Constraints

• Most biomarkers are experimental
• (need replication in multiple studies, different
  groups of people, various setting, over different
  points in time.)
• Intra and inter individual variability
• issues of accuracy and reliability of laboratory
  assays
• Short 1/2 life
• Intrusive
• costly
• lack of normal population data distribution

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