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# 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.

Updated Nov 13, 2026

## Key points

- Hazard identification: can this agent cause an adverse effect in humans (cancer, birth defects, organ damage)?
- Dose-response: how the likelihood and severity of the effect change with the amount of exposure; low doses are often extrapolated.
- Exposure assessment: size, frequency and duration, by pathway (air, water, soil, food) and route (ingestion, inhalation, skin).
- Risk characterisation: combines the three steps into an estimate and states assumptions and uncertainties.
- For effects with a threshold a hazard quotient is used (exposure / reference dose); above 1 there is cause for concern.
- Assessing risk (science) differs from managing it (decision): management also weighs costs, feasibility and values.

## 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.

## Memory aid

‘Does it harm? How much? Who gets it? So what?’: hazard, dose-response, exposure and characterisation, in that order.

## 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.

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## Connections

## Related 5

- [Communicating risk and evidence](https://durgical.com/en/epidemiology/communicating-risk-and-evidence/)
- [Attributable risk and attributable fraction](https://durgical.com/en/epidemiology/attributable-risk-and-attributable-fraction/)
- [Epidemiologic triad and chain of infection](https://durgical.com/en/epidemiology/epidemiologic-triad-and-chain-of-infection/)
- [The occupational risk system](https://durgical.com/en/epidemiology/the-occupational-risk-system/)
- [Public health surveillance](https://durgical.com/en/epidemiology/public-health-surveillance/)

[← All of epidemiology](https://durgical.com/en/epidemiology/)

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](https://www.epa.gov/risk/conducting-human-health-risk-assessment) (U.S. Environmental Protection Agency, 2026); [About Risk Assessment](https://www.epa.gov/risk/about-risk-assessment) (U.S. Environmental Protection Agency, 2026).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/epidemiology/risk-and-exposure-assessment/