Exposure Science Lab Exposure assessment and biomarkers for health evaluation
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Concept and Process of Exposure Assessment

Exposure assessment is an applied science that describes how an individual or population comes in contact with a risk factor, including quantification of the amount of the risk factor across space and time (Lioy, 1990). It is a key component in studying health effects of exposure (e.g. epidemiological studies) and in controlling exposure to reduce harm (e.g. compliance/routine surveillance and risk assessment) in both occupational and environmental settings.

  1. Important factors to be considered in exposure assessment:

When exposure occurs in a microenvironment, such as a location or an activity, it is determined by exposure intensity, exposure frequency, and exposure duration. In order to quantify exposure, following important aspects need to be considered in exposure assessment: 

Agent(s)

biological, chemical, physical, single agent, multiple agents, mixtures

Source(s)

anthropogenic/non-anthropogenic, area/point, stationary/mobile, indoor/outdoor

Transport/carrier medium

air, water, soil, dust, food, product/item

Exposure pathway(s)

eating contaminated food, breathing contaminated workplace air touching residential surface

Exposure concentration

mg/kg (food), mg/litre (water), μg/m3 (air), μg/cm2 contaminated surface), % by weight, fibres/m3 (air)

Exposure route(s)

inhalation, dermal contact, ingestion, multiple routes

Exposure duration

seconds, minutes, hours, days, weeks, months, years, lifetime

Exposure frequency

continuous, intermittent, cyclic, random, rare

Exposure setting(s)

occupational/non-occupational, residential/non-residential, indoors/outdoors

Exposed population

general population, population subgroups, individuals

Geographic scope

site/source specific, local, regional, national, international, global

Time frame

past, present, future, trends

(Source: https://newonlinecourses.science.psu.edu/stat507/node/31/) 

 

  1. Conceptual Model of Exposure

Establishing a conceptual exposure model is the first step in the process of exposure assessment. It is important to design an exposure assessment strategy according to well-defined exposure scenario and specific assessment objectives. The conceptual model should be defined through a thorough analysis of the exposure pathway, which comprises following five elements:

  1. Source(s);
  2. Environmental transport mechanism;
  3. Point of exposure;
  4. Exposure routes, e.g., inhalation, ingestion, or dermal contact;
  5. Receptors and potential health outcomes.

Issues that should be considered in the design of a study need to be considered in this stage. More information can be found in Public Health Assessment Guidance Manual (2005 Update)(Source: https://www.atsdr.cdc.gov/hac/phamanual/ch6.html).

 

  1. Exposure Data Collection

Exposure data collection is indeed beyond just collecting exposure measurements. Data sources, sample collection methods, and sample size need to be determined based on well-defined exposure assessment objectives. Data can be collected from a variety of sources, such as directly measured, acquired from existing database, collected from questionnaire, or modeled from other data. Measurements can be direct or indirect. Personal sampling and biological monitoring are examples of methods that directly measure personal exposure. Job exposure matrix (JEM) and area minoring combined with questionnaire and time/location/activity diaries are examples of indirect assessment methods that provide personal exposure estimates. Sometimes exposure surrogates are used.   

 

  1. Data Analysis, Exposure Estimates and Exposure Error

Many factors need to be evaluated in this stage. Below are some examples:

  1. Different types of exposure indices can be used to estimated exposure. Their strengths and limitations should be described in the data analysis and results interpretation.
  2. All exposure measurements can result in measurement error, such as exposure measurements determined from samples collected not representing the true exposure. Exposure misclassification can happen as well, particularly when investigating chronic effects. These compose exposure error, which need to be minimized through study design and evaluated in the data analysis stage. For example, systematic and random error should be compared and contrasted, and the potential effects of each type should be described.
  3. Quality assurance/quality control, instrument detection limit and method detection limit need to be assessed in the study design and discussed in data analysis.
  4. Potential confounding need to be minimized and controlled in both study design and analysis phase.
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