Urbanization and the environmental risk transition.
Globally, ill health has declined markedly with economic development. As economies develop and economic conditions improve, however, traditional sources of ill health associated with rural poverty trend downward while modern diseases such as cancer and heart disease increase. The transition point may be defined as the level of development at which one has an equal probability of dying by modern and traditional causes, or as the level of development at which life years lost to traditional and modern causes of death are equal. These changes are most rapid and concentrated in cities. Human environmental risks which directly and indirectly affect health are, however, found in urban environments. The Risk Transition framework is discussed as an extension of Abel Omran's 1971 Epidemiologic Transition framework and is used to help explain the dynamics of environmental health risks in developing world cities. While it may be expected that health conditions improve with urbanization, reductions in mortality and morbidity may not be fully realized among those who are most poor and disenfranchised. Poor environmental health conditions and stresses in cities actually make cities primary sources of risk factors leading to modern diseases. A large proportion of death and disease is environmentally related on both sides of the transition and environmental health risks undergo transition as do patterns of overall ill health. It is noted that risk transition patterns vary between cities and that the concept simply provides a useful framework in which to compare and analyze changes in environmental risk between cities. Risk overlap and net risk, as well as urban water problems, air pollution, solid waste, and slums are considered. Costs and benefits of development and urbanization are unequally distributed even if overall risks turn negative. The urban poor are comparatively unfortunate in having to face health risks caused by both poverty and the toxic effluents of industrialization, urbanization, and modernization. With increasingly larger proportions of people living in cities, effective ways to handle the urban environmental risk transition must be identified.