1.3 Environmental threats to human health

Literally, the word "environment" refers to whatever surrounds an object or some other entity. Humans experience the environment in which they live as an assemblage of physical, chemical, biological, social, cultural and economic conditions which differ according to local geography, infrastructure, season, time of day and activity undertaken. In this book, however, we focus on the impacts of environmental conditions on health, and on the social and economic conditions that act as "driving forces" and put "pressures" on the environment. We therefore discuss other threats to health such as smoking and poor diet in brief only. This accords with the way in which environment is considered in Agenda 21 (UN, 1993).

The different environmental threats can be divided into "traditional hazards" associated with lack of development, and "modern hazards" associated with unsustainable development (WHO, 1992a). The changing pattern of environmental health hazards and associated health risks - moving from "traditional" to "modern" with time and economic development - has been called the "risk transition" (Box 1.3).

One of the differences between traditional and modern environmental health hazards is that the former are often rather quickly expressed as disease. For example, a villager drinks polluted water today and tomorrow has severe diarrhoea. Diarrhoeal incidence can accordingly be a relatively useful measure of the relevant risk and of our efforts to control it. For many modern environmental health hazards, however, a long period of time may pass before the health effect manifests itself A cancer-causing chemical released into the environment today may not reach a person until it has passed through the food-chain for months or years, for instance, and even then may not cause development of a noticeable tumour for decades. Similarly, environmental change occurring over several decades, such as stratospheric ozone depletion due to chlorofluorocarbon emissions (see Section 4.9), may undermine Earth's life support-systems. So for modern environmental health hazards, understanding the environmental pathways through which the hazards move is particularly important.

"Traditional hazards" related to poverty and "insufficient" development include:

· lack of access to safe drinking-water
· inadequate basic sanitation in the household and the community
· food contamination with pathogens
· indoor air pollution from cooking and heating using coal or biomass fuel
· inadequate solid waste disposal
· occupational injury hazards in agriculture and cottage industries
· natural disasters, including floods, droughts and earthquakes
· disease vectors, mainly insects and rodents.

"Modern hazards" are related to rapid "development" that lacks health-and-environment safeguards, and to unsustainable consumption of natural resources. They include:

· water pollution from populated areas, industry and intensive agriculture

· urban air pollution from motor cars, coal power stations and industry

· solid and hazardous waste accumulation

· chemical and radiation hazards following introduction of industrial and agricultural technologies

· emerging and re-emerging infectious disease hazards

· deforestation, land degradation and other major ecological change at local and regional levels

· climate change, stratospheric ozone depletion and transboundary pollution.