Healthy world, healthy people

Posted: 15 August 2000

Author: Tony McMichael

Author Info: Tony McMichael is Professor of Epidemiology at the London School of Hygiene and Tropical Medicine and author of Planetary Overload. Global Environmental Change and the Health of the Human Species, Canto/Cambridge University Press, 1995, £7.95pb. He chaired the scientific panel that wrote the chapter on potential health impacts for the UN's Intergovernmental Panel on Climate Change second (1996) and third (2001) Assessment Reports.

The many, often insidious, challenges to human health from changes in the physical and social environment of our planet are outlined in this wide-ranging overview by Tony McMichael.

"The environment" is an accommodating term. Minimally, it refers to the physical and chemical conditions in the living space around us, such as the quality of local urban air, freshwater supplies and the concentrations of chemical residues in food. A more liberal definition includes the conditions of the social environment - encompassing everything from housing quality to transport, recreational amenities, population growth, density and mobility, social networks, and political and distributive equity. From even the more restrictive definition of environment flows a long list of health hazards. We are well familiar with the adverse health effects of extreme disasters such as Minamata, Bhopal, Chernobyl and Love Canal. In 1981-82, adulterated cooking oil in Spain caused about 600 deaths and serious illness in 20,000 people. Meanwhile, most of the burden of environmentally-induced poor health and early death arises less obviously. Children playing in the Pasig River, Manila, Philippines, where factories dump their waste© Ron Giling/Panos Pictures

It results from persistent exposures to polluted air (both ambient and - in many poor rural populations - domestic), faecally contaminated drinking water, physical hazards, agricultural pesticides and other noxious agents. Such exposures abound particularly in poor, powerless and under-educated Third World populations. The World Health Organization (WHO), estimates that around two-thirds of diarrhoeal episodes around the world - the cause of three million deaths in young children annually - arise from contaminated food or water.

These exposures are diverse, widespread, and (often) poorly documented. Their health effects are often insidious. Environmental lead exposure, for example, blunts young children's intelligence. Yet that particular public health problem - increasingly evident in traffic-congested cities in developing countries - does not figure in health and vital statistics. There are recent concerns that certain types of other widespread environmental exposures may act in non-specific fashion - for example, the blunting of the immune system response that may result from our accumulating exposure to organic pesticides, or the possible effects upon fertility and reproduction from the accumulation of endocrine-disrupting chemicals in the environment. Research by the World Resources Institute indicates that thousands of men who were exposed to the nematicide dibromochloropropane in Costa Rican banana plantations in the 1970s (well after it was banned in the United States) suffered from reduced fertility. Many such environmental health hazards remain suspected but unconfirmed. There are two reasons why cause-effect relationships may be elusive. First, environmental exposures are typically diffuse, impinging on whole communities and thus are less amenable to the counting-and-scoring methods of epidemiology than are individual-level behavioural, occupational or biomedical factors. Second, although the prevalence of exposure may be very high (indeed universal) within a community, the average level of exposure is often lower and longer-term than those higher-impact exposures associated with extreme acute events or with the occupational environment. Meanwhile, there is a larger environmental challenge; one that entails a seeming paradox. On many counts the environment has manifestly deteriorated both locally and, of increasing concern, globally - yet human life expectancies have increased in recent decades in most countries. However, we must understand that certain types of environmental damage may only impair health when critical thresholds are passed: when the inputs needed to sustain good health become deficient. For this reason, there is no necessary immediacy between environmental change and human health. The population health impacts of forest clearance, land degradation, depletion of aquifers, climate change or loss of biodiversity occur predominantly via pathways that are neither simple nor direct. These pathways thus differ from those of local directly-acting chemical toxins, physical agents (such as radiation) and locally-circulating microbes. For many such "traditional" environmental exposures - whether pesticides in drinking water or particulates in air - we assume that approximately linear threshold-free relationships apply: a little exposure will do some harm; a lot will do more harm. In reality, univariate and linear models are usually inadequate to describe the health risks posed by complex ecological disruptions.

To take full account of how environments affect our health, we must extend our "environmental health" lexicon to include the fundamental long-term role of ecological systems and processes as life-support systems. We are no longer talking only of an increased exposure to specific extraneous hazards as a cause of bad health. We are also recognising the depletion or disruption of natural biophysical processes that are the basic source of sustained good health. This includes the ecosystems that determine, for example, the productivity of food-producing systems on land and sea and the range of infectious (especially vector-borne) disease agents. It includes global systems such as the hydrological cycle and the stratospheric 'ozone shield' against excessive solar ultraviolet irradiation. The considerable recent gains in health and longevity, first in westernised countries and subsequently in others, have depended primarily on reductions in early-life infectious disease mortality. Basic gains in food security, hygiene and water sanitation, supplemented by advances in vaccination, antibiotic treatment and oral rehydration therapy, have changed the profile of infectious disease mortality in most populations. These technical and social improvements have been closely bound up with the processes of urbanization, industrialization and increasing material wealth. They, and the resultant gains in life expectancy, have therefore proceeded in parallel with increasing levels of physical alteration and chemical contamination of our ambient environment.

Dead cattle© Neil Cooper/Panos PicturesWe must now ask ourselves: For how long can we expect to maintain these parallel increasing trends in consumption, life expectancy and environmental impact? At what stage might depletion of the world's ecological and biophysical capital rebound against the health of human populations?

As a species, we humans are uniquely inventive, resourceful and adaptive. The heterogeneity and flexibility of our personal behaviours, local diets and community cultures provides a buffering against many potential adverse environmental exposures. Yet it is becoming increasingly difficult to remain optimistic about our "dominant species" mode stewardship of this planet and our capacity to sustain healthy and happy populations in the coming century.

The shape of the modern global economy is dominated by rapid technological change, acquisitive consumerism, a discounting (or ignorance) of distant and deferred environmental impacts, and a pervasive free-market ethos. Currently, the policy-setting role of national governments is contracting, as trade and financial transactions become globalized, as the balance of power between private and public sectors shifts, and as the resultant cost-cutting competitiveness puts a squeeze on national social expenditures. So, just when co-ordinated, strong and farsighted government is needed to reduce damage to the world's ecological infrastructure, and hence to the sustainability of human health, we are instead entrusting ourselves to the limited-vision rationalism of the market. Some of the environmental consequences are evident enough. As the rich-poor gap in the world persists, indeed widens, so the perennial public health scourges of malnutrition, unclean drinking water, unsafe housing, vector-borne infections and hazardous occupations continue. As the international car industry targets the huge aspiring middle-class markets in India, Southeast Asia, Latin America, China, Eastern Europe and elsewhere, so cities are transformed, air is polluted, and urban life becomes more fragmented and more hazardous. (With Japanese money, the city of Calcutta is about to displace tens of thousands of its slum and streetside dwellers and their pedal-rickshaw breadwinners with a complex of vast concrete fly-overs. This, of course, is a timely investment by a nation that sells cars to the world.) Chemical wastes are increasingly contaminating and affecting fish, bird, reptile and amphibian species. Meanwhile, many vital, life-supporting, components of this closed-system planet are showing signs of systemic stress: arable land, ocean fisheries, freshwater supplies, climatic processes, and biological and genetic diversity everywhere. Some scientists think that we may be seeing early evidence of ecological and health-related impacts of climate change. For example, the recent concurrence of retreating glaciers, upward migration of alpine plant species, and reports of an increased altitudinal range of malaria and dengue in highlands in several continents may be an early signal of the consequences of global warming. Many other components of the apparent worldwide emergence and resurgence of infectious diseases may be due to these multiple, large-scale, ecological, demographic and social disturbances. We thus begin the new century with a mixed and widening agenda of environmental health challenges. Of course, we must continue to seek clean, safe and socially intact living environments. We must respect the vulnerability of local and regional ecosystems - and understand that there are better ways of managing local biological problems (whether plant pests, rodent populations or mosquitoes) than by primary reliance on hazardous and ecotoxic chemicals. We need the imagination to perceive a larger spatial and temporal dimension to the "environment" than we had previously appreciated. Nascent recognition of this dimension was an important difference between the policy frameworks of the Stockholm (1972) and Rio (1992) UN Conferences on the environment.

This enlarged agenda seems daunting. We are beginning to understand the profoundly ecological nature of the larger environment-and-health relationship. In turn, this is helping us to perceive connections between local, regional and global impacts, and to understand that actions taken to prevent future adverse global-change impacts need not detract from tackling today's environmental health problems. These are all parts of a greater whole.

The sheer scale of today's environmental problems will require us to take stock of our priorities and to seek socially and ecologically sustainable ways of living. Time is relatively short, the issues are complex, communities are naturally (and in some ways reassuringly) conservative, and politicians in democratic systems have limited spatial and temporal horizons. Even so, there is evidence that people increasingly and instinctively understand many of these issues and, when thus confronted, will declare a primary preference for security, happiness and health. Hence, there is a growing public resistance to road-building in Britain; to dam-building in India; to logging in various Latin American countries; and to golf course construction in East Asia.

We must look beyond the restricted view of 'environmental health' as a problem of local pollution "a problem amenable to piecemeal and technical management (but often compromised when 'economic growth' is the competing value). Rather, as we acquire a more integrated view of the world's environment, its ecosystems, and their fundamental role in sustaining the health of a growing population, so we must think more radically about how best to manage and sustain these essential life-support systems," while also maintaining the immediate quality and safety of the local environment.