Environmental risk transition is the process by which traditional communities with associated environmental health issues become more economically developed and experience new health issues. In traditional or economically undeveloped regions, people often suffer and die from infectious diseases or malnutrition due to poor food, water, and air quality. As economic development occurs, these environmental problems are reduced or solved, and others begin to arise. This leads to a shift in the nature of environmental hazards and, consequently, in the causes of death and disease.

Risk transition framework: Several transition frameworks have been developed to understand the impacts of socioeconomic development. The oldest and best-known is the demographic transition framework, established in the 1940s; it describes the shift from high fertility and high mortality in underdeveloped societies to lower fertility and mortality rates as development proceeds. Around 1970 the epidemiological transition framework was introduced to characterize changes in population health during development. To categorize causes of death and disease more clearly when studying epidemiological shifts, the following categories were created:
I. Traditional: infectious, nutritional, perinatal, and maternal causes.
II. Modern: cancer, heart disease, neuropsychiatric disorders, chronic lung disease, diabetes, and congenital causes. In 1990, environmental health researcher Kirk R. Smith at the University of California, Berkeley proposed the "risk transition" framework in relation to the demographic and epidemiological transition frameworks. The theory holds that shifts in risk factors precede shifts in causes of death and disease. To emphasize prevention rather than response, the risk transition was further studied and quantified. Figure 1 illustrates how risk, epidemiological, and demographic transitions interact: changes in risk factors alter disease patterns and population health, which in turn affect demographics; demographic shifts also influence risk factors, so the three frameworks mutually impact one another. Smith later developed the "environmental risk transition" framework, which categorizes risks as traditional or modern and considers spatial dimensions. According to this framework, in early stages of development, environmental health problems concentrated in households—such as poor sanitation—are resolved but shifted into the community, producing issues such as urban pollution; these are examples of traditional and modern risks, respectively. As development proceeds, community-level risks decrease while risks shift to the global environment, creating concerns such as increased greenhouse gas emissions. Unlike traditional risks, modern risks tend to accumulate over time and often lack single identifiable causes. These categories were defined because most environmental risks associated with Category I diseases initially appeared at the household level; as development addressed these risks, environmental causes of Category II diseases became more significant at the community level. This concept is illustrated in Figure 2.

Quantifying: Using data from the Global Burden of Disease Study (GBD) and the Comparative Risk Assessment (CRA) managed by the World Health Organization (WHO), empirical data were gathered to test the environmental risk transition framework.

Measuring development: Common metrics of development include income per capita adjusted for purchasing power in 2000 (dollars of gross domestic product per capita, adjusted for purchasing power, $PPP/capita). The Human Development Index (HDI) combines purchasing-power-adjusted income per capita, life expectancy, and education level (in 2000) to measure development in a population. Risk metric:
Risks were quantified as the percentage of the total disease burden (measured in disability-adjusted life years, DALYs) and as burden per capita (DALYs per 1,000 population).

Household:
The following summarizes the three major environmental risks in households with young children, who are most at risk:
- Poor water, sanitation, and hygiene, which significantly contribute to diarrheal disease.
- Use of solid fuels (biomass or coal) for cooking and heating, which emits pollutants that contribute to acute lower respiratory infections, chronic obstructive pulmonary disease, and lung cancer.
- Inadequate household measures—such as lack of screening, pesticides, and bed nets—which contribute to a significant malaria burden.

As development increases—measured by gross domestic product per capita adjusted for purchasing power (PPP, $PPP/capita)—household environmental risks decline considerably. Comparing poor and rich countries by $PPP/capita, household risks decrease by more than two orders of magnitude.

Community:
The major environmental risks at the community level include:
- Urban outdoor air pollution.
- Lead pollution from gasoline and industrial sources.
- Occupational risks, including exposure to carcinogens, injuries, noise, and poor ergonomics.
- Traffic accidents affecting drivers and pedestrians. There are more fluctuations in community risks with development than in household risks; the pattern is more complex and less pronounced. However, traffic accidents and air pollution generally increase with development. Lead and occupational risks, however, varied significantly.

The WHO Comparative Risk Assessment (CRA) analyzed only one global environmental risk: climate change, which has had a relatively small impact on human health to date. No data were collected for other global risks, such as ozone depletion and land-use change. Exposure to climate change is expected to increase, which may amplify risks such as malaria. Results show that climate change–related risks decrease with higher levels of development, indicating that poorer populations are more susceptible to the diseases affected by climate change. This finding contradicts the environmental transition framework because the analysis considers where risks are experienced rather than where they originate. Nevertheless, as development proceeds, the global extent of climate change risk is likely to expand.

Limitations: Many important environmental health risks could not be addressed or analyzed in this study.