Risk and exposure assessment
- Concept
Risk assessment estimates how much harm a substance or agent can cause, given how many people are exposed and how much.
What it is
Human health risk assessment is a scientific process that estimates the nature and size of an environmental or occupational risk. After a planning phase it has four steps: hazard identification, dose-response assessment, exposure assessment and risk characterisation. Its results feed risk management, which is the decision on what to do, and risk communication.
Worked example
- Data (made up): in a rural area, well water has a metal at 3 times the guideline value; 1 200 people drink it (800 adults, 400 children).
- Hazard: the literature links chronic intake of that metal to skin lesions and cancer.
- Dose-response (linear assumption): at the guideline value the extra lifetime cancer risk is 1 per 100 000 people.
- Exposure: adults receive 3 times the guideline-level dose; children, who drink more per kilo of body weight, 6 times.
- Extra risk: adults 3 per 100 000; children 6 per 100 000 (simplified assumption of sustained exposure).
- Expected extra cases: 800 × 3/100 000 = 0.024 and 400 × 6/100 000 = 0.024; total ≈ 0.05 over this group's lifetime.
- Threshold effect: hazard quotient = 3 in adults and 6 in children; both > 1, so there is cause for concern.
- Reading: the cancer excess is small but avoidable and children are the most exposed; management decides on an alternative water source.
The steps of risk assessment
| Step | Question | Data it uses |
|---|---|---|
| Planning | Who is at risk, from what and by which pathway? | Context, population, sources |
| Hazard identification | Can it harm humans? | Toxicology, animal and human studies |
| Dose-response | How much harm at which dose? | Dose-response curves, reference values |
| Exposure | How much do people receive, for how long and by which route? | Environmental measurements, surveys, biomarkers |
| Characterisation | What is the risk and how sure is the estimate? | Integration of the above and uncertainty |
Markers
- Hazard
- Dose-response
- Exposure
- Characterisation
- Hazard quotient
In practice
- It is used for water and air pollution, hazardous waste, pesticides, occupational exposure and food additives.
- Exposure assessment looks at sensitive subgroups: children, pregnant women and workers with daily exposure.
- An honest characterisation states its uncertainty; if it is large, more data are requested and the cycle repeats.
Common pitfalls
- Confusing hazard (can cause harm) with risk (probability of harm given real exposure).
- Assuming everyone is exposed equally: exposure varies with age, occupation and behaviour.
- Giving a risk figure without its assumptions or uncertainty.
- Mixing the scientific assessment with the management decision.
Test yourself
Think of the answer, then tap the question to see it.
What are the four steps of human health risk assessment?
Hazard identification, dose-response assessment, exposure assessment and risk characterisation, preceded by a planning phase.
What is the difference between hazard and risk?
Hazard is an agent's capacity to cause harm; risk is the probability that the harm occurs in a population given its real exposure.
What does a hazard quotient above 1 indicate?
That the estimated exposure exceeds the reference dose considered without appreciable effect, so there is cause for concern and more analysis or action is needed.
How does risk assessment differ from risk management?
Assessment is the scientific process that estimates the risk; management is the decision on what to do, which also weighs costs, feasibility and social values.
Connections
Educational content on epidemiological and statistical methods; the examples use made-up numbers to teach the calculation. Not a clinical or legal guide: current Colombian rules are in the official sources.
Sources: Conducting a Human Health Risk Assessment (U.S. Environmental Protection Agency, 2026); About Risk Assessment (U.S. Environmental Protection Agency, 2026).
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Representative model, for educational purposes only.