A hazard is something that can cause harm, while a risk is the chance that a hazard will cause harm. Environmental risk assessment is the process of estimating potential impacts of hazards like chemicals or climate change on human health. It involves compiling exposure data, reviewing epidemiological evidence on associations between environmental factors and health, and combining exposure and response data. Key steps include specifying the health risk and exposure measures, estimating population exposure, selecting health outcomes and exposure-response relationships, and calculating attributable burdens of disease.

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MPH First Semester, Environmental Health
Lecture Handouts of Mr. Nabin Lamichhane (Faculty Member, PUCMAS)
Hazard and Risk
A hazard is something that can cause harm, e.g. electricity, chemicals, working up a
ladder, noise, a keyboard, a bully at work, stress, etc.
A risk is the chance, high or low, that any hazard will actually cause somebody harm.
For example, working alone away from your office can be a hazard.
For example:
a. Climbing to the ladder- Hazard
b. Falling from ladder- Risk
c. Plane is a hazard
d. Flying in plane/accident - risk
Fig: Understanding Hazard and Risk
Environmental Risk Assessment
Humans interact with the environment constantly. These interactions affect quality of
life, years of healthy life lived, and health disparities.

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Risk assessment is the process of estimating the potential impact of a chemical,
physical, microbiological or psychosocial hazard on a specified human population or
ecological system under a specific set of conditions and for a certain time frame.
Similarly, environmental risk is defined as a catastrophe, pesticide risk or the relative
sustainability of the environment to social and economic activities. Some definitions of
environmental risk include a small number of indicators, while others incorporate a large
number of components.
The scope of environmental health risk assessment (EHRA) can cover health impacts
of:
• Chemical pollutants and contaminants in air, water, soil and food
• Pathogenic microbiological contaminants in food and water
• Radiation sources
• Electromagnetic fields (EMFs)
• Climate and climate change
Environmental risk factors that are considered in the series of guides (WHO 2008):
1. Indoor smoke from solid fuel use
2. Outdoor air pollution
3. Water, sanitation & hygiene
4. Solar ultraviolet radiation
5. Climate change
6. Lead
7. Mercury
8. Occupational carcinogen
9. Occupational airborne particulates
10. Second-hand smoke (in preparation
How to do Environment risk assessment?
Quantitative assessments of health impacts are based on combining exposure data with
exposure-response information. Such assessments require

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(i) the compilation of exposure data,
(ii) a systematic review of evidence from epidemiology and other scientific disciplines
concerning the association between environmental factors and human health, and
(iii) the combination of exposure and exposure -response.
Steps
1. Specify the health risk to be addressed in the impact assessment.
2. Specify the measure of exposure and the range of exposure to be considered.
3. Estimate the population exposure distribution.
4. Select appropriate health outcome(s).
5. Select exposure-response relationship in the population of interest, from the
scientific literature or available guidance.
6. Combine exposure and exposure-response relationship data for each
population group under consideration. (e.g. by age and gender).
7. Calculate the attributable fraction of disease(s) multiplied by the health
statistics associated with the disease(s) under study.
8. Quantify uncertainty of the estimate (range of potential effect).
Measurement
1. Disability adjusted life years (DALYs), or occasionally, number of
cases.
2. Number of hospital admissions.
3. Odd ratio
4. Relative risks
5. Lethal dose
6. Relative risk
7. Air quality monitoring indicators
8. indicators related to water pollution
9. Emission limits

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OECD KEY ENVIRONMENTAL INDICATORS 2008

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For further information:
1. https://www.oecd.org/env/indicators-modelling-outlooks/37551205.pdf
2. Text book of PSM by K. Park
3. PUBMED, Google Scholar