8.3: Risk Assessments
- Page ID
- 237542
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Risk assessment formally measures the potential impact of a known hazard. The results of a risk assessment help decision-makers determine whether action is needed to remediate or mitigate environmental threats and provide the scientific basis for setting regulatory policies and developing public health interventions (Israr et al., 2025). The four steps of risk assessment are (US Environmental Protection Agency, 2025; Basu, n.d.):
- Hazard identification: The first step is to identify a potentially harmful agent in the environment, which can be chemical, biological, or physical.
- Dose-response assessment: This step analyzes the relationship between the amount of exposure to the hazard and the likelihood and severity of health effects.
- Exposure assessment: This involves estimating the frequency, magnitude, and duration of human and ecological exposure to the hazard.
- Risk characterization: In the final step, all information from the previous stages is combined to estimate the probability, nature, and magnitude of adverse effects resulting from exposure.
Factors that Affect the Impact of Exposure
The following factors determine the level at which a substance becomes hazardous to the body (HSI, 2025; Health Canada,2023):
Route of exposure: How a substance enters the body affects its impact. Entry can occur via inhalation, ingestion, or skin absorption.
Substance Dosage and Toxicity Level: Any substance can become toxic to the body at sufficiently high levels, even water. The substance's inherent toxicity significantly affects the likelihood of adverse effects. Research of a substance provides a measuring indicator of toxicity called LD50 (Lethal Dose 50). This is the amount of the substance when 50% of the lab animals die from exposure. Also, the timing of the exposure matters; low-dose exposure may have different effects than short-term, high-dose exposure.
Body's Rate of Removal: Once the substance is in the body, it will be processed and excreted. Excretion happens via feces, urine, sweat, or exhaled air. The quicker the body is able to remove and excrete, the less the chance for adverse effects.
Individual Biological Variation: An individual's biological makeup has a tremendous impact on their health. These include genetic factors, age, gender, physical condition, and the individual's body health. Some people are more sensitive to toxicity than others, for example, children, seniors, pregnant women, and indigenous people. Also, some people may be sensitive to the substance, and even a small amount of exposure may trigger an allergic reaction.
Interaction with other substances: In some cases, the exposure to one chemical can be affected by the presence of another. An example of this, which will be explained in more detail later in the chapter, is the co-occurrence of radon gas and smoking.
Public Health Assessment
A public health assessment is a process for evaluating whether exposure to hazardous substances in the environment, such as those found at waste sites, poses a threat to people's health. These assessments determine the levels of a substance, how people might be exposed to it, and what potential harm it could cause. Based on the findings, recommendations are made to protect public health, such as limiting contact with contaminated soil, restricting consumption of certain foods, or cleaning up the site (Ohio Department of Health, n.d.). A core similarity between risk assessment (discussed in the paragraph above) and public health assessments is their exclusive attention to human health impacts.
Over the years, these risk assessments have been controversial and have often taken many years to complete. Often, it takes time for health consequences to appear in the population. The history of lead's health risks spans from ancient times to the present, with early civilizations documenting lead poisoning and its effects, like colic, anemia, and paralysis. The Romans extensively used lead in pipes, cookware, and wine, which is believed to have caused widespread chronic lead poisoning among the upper classes, leading to symptoms like paralysis, madness, gout, and the cause of abortion. Historians believe Roman emperors were affected by high levels of lead. As we look into the Industrial Revolution, we see that it caused an epidemic of lead exposure and highlighted the dangers of chronic, low-level exposure, leading to the idea that there is no safe threshold for exposure. In the 20th century, the recognition of lead's occupational and environmental toxicity grew, leading to greater public awareness and protective legislation. In the 1970s, it was understood that, due to its bioaccumulative nature, there is no safe threshold for lead exposure. This knowledge led to the gradual removal of lead from products such as paint (1978 in the U.S.) and gasoline (1996 in the U.S.), resulting in a significant drop in exposure levels.
Today, although regulations have reduced risks, lead exposure from sources like old paint and water pipes continues to be a major public health issue, particularly for children, and is linked to a wide range of health problems, including neurological damage, cardiovascular disease, and kidney issues (Rica et al, 2012; Riegelman & Kirkwood, 2025; National Institute of Environmental Health Science, 2025). One well-known lead poisoning incident occurred due to lead in the city's water pipes during the 2014 water crisis in Flint, Michigan. In April 2014, Flint, Michigan, switched its municipal water supply from Lake Huron to the Flint River as a cost-saving measure. The river water was not properly treated, causing aging pipes to corrode and leach lead and other contaminants into the drinking water. Residents immediately reported issues with the water's color and odor, and the lack of corrosion control led to a public health crisis, including elevated blood lead levels in children (Ezell, 2021).
This is a 48-minute documentary about what happened in Flint, Michigan, and the progress made in the 10 years that followed.
YouTube video
Ecological Risk Assessment
Ecological risk assessment evaluates the consequences of environmental exposure on non-human organisms, specifically plants and animals. Plants and animals affect human health. In many cases, the results of a risk assessment determine the cleanup goals needed to adequately protect human health and the natural environment (Department of Environmental Conservation, 2025).
The ecological view of environmental health issues was brought to the forefront by Rachel Carson's Silent Spring, a nonfiction book that exposed the dangers of chemical pesticides, such as DDT, to the environment and human health. It is credited with launching the modern environmental movement and led to the ban of DDT in 1972. The book argues that these pesticides accumulate in the food chain, harming wildlife and potentially causing health issues in humans, while criticizing the chemical industry and government for downplaying the risks (Natural Resources Defense Council, 2015; Riegelman & Kirkwood, 2025 p179).
One example of how ecological risk assessment is conducted and its impact on public health is mercury exposure. The history of mercury poisoning spans millennia, from ancient China, where emperors consumed mercury for an attempt at immortality, to ancient Rome, where cinnabar, a mercury-rich mineral, was identified as a poison, and early forms of personal protective equipment were used by workers. In the 1800s, during the industrial era, the dangers of organic mercury were first documented. In the 20th century, numerous incidents of mass mercury poisoning occurred in parts of the world, such as Iraq and Canada, further highlighting the global nature of the problem, and in 2009, an international agreement to control mercury pollution was reached, marking a significant step in addressing the global mercury crisis (Schultz, 2013).
An example of a United States ecological risk assessment for mercury involves the Great Lakes risk assessment, which evaluates threats to the ecosystem. The goal is primarily to evaluate pollution levels (including mercury) alongside other assessments, such as climate change and invasive species. The risks include chemical contamination from urban and agricultural runoff, habitat destruction, and the negative impacts of invasive species. The assessment considers how these threats can harm the environment and human health (National Oceanic and Atmospheric Administration, 2025).
Reference
Basu A. (n.d.). Lecture notes on environmental health risk assessment. Authorea www.authorea.com
Department of Environmental Conservation. (2025). Human health risk assessment. Division of Spill Prevention and Response. The Great State of Alaska www.dec.alaska.gov
Ezell, J. M. & Chase, E. C. (2021). A population-based assessment of physical symptoms and mental health outcomes among adults following the Flint water Crisis. Journal of Urban Health. Oct;98(5):642-653. doi: 10.1007/s11524-021-00525-2
Health Canada (2023). Exposure and health effects of chemicals. Government of Canada www.canada.ca
HSI (2025). What factors influence toxic exposure levels? HSI www.hsi.com
Israr, M., Jain, A., Adusumilli, S. B. K., & Sharma, A. (2025). Chapter 10 - Risk assessment for environmental health and public health. Developments in Environmental Science. Elsevier Ltd. doi.org/10.1016/B978-0-443-33530-3.00010-4
National Institute of Environmental Health Science. (2025). Lead. NIH www.niehs.nih.gov
National Oceanic and Atmospheric Administration. (2025). Great Lakes ecoregion. US Department of Commerce. NOAA www.noaa.gov
Natural Resources Defense Council. (2015). The story of Silent Spring. NRDC www.nrdc.org
Ohio Department of Health. (n.d.). Public Health Assessments. ODH odh.ohio.gov
Riva ,M.A., Lafranconi, A., D'Orso, M.I., & Cesana, G. (2012). Lead poisoning: historical aspects of a paradigmatic "occupational and environmental disease". Safety and Health at Work. Mar;3(1):11-6. doi: 10.5491/SHAW.2012.3.1.11
Riegelman, R. & Kirkwood, B. (2025). Public health 101: Improving community health (4th ed). Jones & Bartlett Learning, LLC.
Schultz, C. (2023). After millennia of heavy use, mercury gets the boot. Smithsonian magazine www.smithsonianmag.com
US Environmental Protection Agency. (2025). Conducting a human health risk assessment. EPA www.epa.gov