Exposure Assessment. There are voluntary exposures and involuntary exposures. An example of a voluntary exposure is a person smoking cigarettes. Additionally, while driving a car, there is the voluntary exposure of using a seatbelt to help reduce morbidity and mortality during a potential motor vehicle accident. Involuntary exposures are exposures from things we do not voluntarily expose ourselves to, such as air quality and second-hand smoke exposure. Occupational and environmental exposures tend to be non-voluntary exposures. Exposure assessments are done to identify harmful chemicals and substances (in research settings as well as regulatory and advisory settings) and to determine if the exposure is impacting human health. Exposure assessments are done to determine how well guidelines and standards are followed. Quantifying the exposure considers the concentration and amount of chemical or substance a person or population is exposed to and over what timeframe and frequency the exposure occured. This is called the exposure level. As mentioned, the exposure level considers the amount, duration, and frequency of exposure. The total exposure can be determined once all of the exposure information collected and analyzed. There are various routes of exposure: inhalation, direct exposure from eating a substance, or direct exposures through breastmilk, indirect exposures as may be seen with infants and toddlers who touch lead paint dust on the floor and then ingest the lead paint dust by putting their hands in their mouth, there is exposure from dermal and mucosal absorption, exposure from an injection of a vaccine, for example, in utero fetal exposure, called transplacental exposure, and another form of direct exposure newborns experience during labor and delivery, for example, vertical transmission of H.I.V. to the newborn, and lastly, psychological exposures. Taking all routes of exposure into account, you can get the aggregate exposure. There are also the exposure categories of ecological or population levels and a different category of exposure from personal or individual level exposures. Additionally, there is the concept of the exposome. An exposome is a concept of there being a collective accumulation of all human environmental and occupational exposures. There is the internal exposome which includes oxidative stress markers and components of the inflammatory system that may take a toll on human health over time, increasing the risk of cancer and heart disease, for example. Think of stress hormones, cortisol exposure is part of the internal exposome. External exposures are what we think they are, exposures to chemicals, exposures to infectious agents, and exposures to extremes of hot and cold environments, as a few examples. Lastly, there are psychosocial exposures such as exposure to psychological stress, social interactions, and a given economic situation. The E.P.A. publishes primary and secondary standards, primary standards are legally enforceable, secondary standards are not. Primary standards are to ensure the public's health is protected. The E.P.A. intends its primary standards to protect the general population as well as vulnerable populations (women, children, pregnant people, people with chronic diseases, among others). Secondary standards, which are not enforceable by the federal government, are also intended to protect the public's health. Using drinking water as an example the E.P.A.'s primary standards for clean drinking water include: microorganisms, certain disinfectant byproducts such as chlorite and disinfectants such as chlorine, inorganic chemicals such as arsenic and lead, contaminants such as benzene and toluene, as well as radionuclides such as alpha and beta particles. The E.P.A.'s secondary standards for clean drinking water include things like taste, odor, and fluoride levels. When it comes to making measurements and collecting data for exposure assessments, there is active and passive sampling. Active sampling measures exposures with an instrument where a sample is collected through the mechanism of the sample being pumped into the instrument. Passive sampling does not pump the sample into the instrument, with passive sampling, diffusion brings the exposure of interest into the instrument's sampling zone. When analyzing collected samples, both random error and systemic error should be considered. An example of random error is poor reproducibility of an instrument or poor precision. An inaccurate instrument will also give random error with inaccurate readings. Systematic error would be if the instrument were not calibrated correctly, for example. 

Reference:

Koehler K, Rule AM, Quirós-Alcalá L. Exposures and Their Assessment, Including General and Occupational Environments. In: Boulton ML, Wallace RB. eds. Maxcy-Rosenau-Last Public Health & Preventive Medicine, 16e. McGraw Hill; 2022.