requesting a few state health departments to provide reports for examination, developing criteria that help to define adequate epidemiologic studies, applying those criteria to selected state studies, and assessing those studies.

Introduction

Most people in the developed and developing worlds endorse environmental protection (Dunlap, 1992). Public concern about the environment and its relation to human health is demonstrated by the public reaction to reports of contamination at places like Love Canal, Times Beach, and Stringfellow Pits in the United States.

The nature of environmental-health concerns differs considerably between the developed and developing worlds (Doll, 1992). In the former, cigarette-smoking constitutes a major cause of illness and death, and occupational hazards, environmental tobacco smoke, lead, and other air pollutants adversely affect public health. Levels of lead thought to be safe a decade ago are now believed to produce permanent damage to children's intellectual potential (ATSDR, 1990).

In the developing world, concern focuses on basic sanitation, pure air, and clean water. The problems are traceable to a large extent to infectious agents, but exposure to toxic substances plays a role. The World Bank estimates that 1 billion people lack safe water, 1.7 billion are without adequate sanitation, 1.3 billion are exposed to unsafe soot and smoke, and 700 million women and children are exposed to severe air pollution from cooking fires (World Bank, 1992).

The incomplete understanding of causes of many common chronic diseases in both developed and developing countries fuels interest in identifying avoidable environmental hazards. Thus, more than 60% of all cases of birth defects are of unknown or poorly understood etiology (NRC, 1989a), as are many cases of degenerative neurologic diseases (NRC, 1992a), adult-onset asthma (NRC, 1992b) and other chronic respiratory diseases (NRC, 1989b), and renal and hepatic diseases. With respect to reproductive health generally, an array of end points are of concern, ranging from effects on offspring to reproductive health in males and females, including sexual maturation, onset of menses, menopause, sexual functioning, and endometriosis. Although these events are often discussed in an atmosphere of high public concern, suspect environmental factors must be studied with strict adherence to scientific canons of independent, verifiable research.

Although genetic predisposition and poor nutrition are important risk factors for many chronic diseases and other adverse health outcomes, the possible contribution of preventable or controllable environmental fac-



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