The nature and extent of our interactions with the natural environment have a profound impact on human well-being. Earth science includes the broad subdisciplines of geology, geophysics, geochemistry, geomorphology, soil science, hydrology, mineralogy, remote sensing, mapping, climatology, volcanology, physical geography, and seismology. As such, earth science describes a substantial component of this natural environment, encompassing the key terrestrial materials, associations, and processes that have both beneficial and adverse impacts on public health. Despite this association between public health and the natural environment, geologists, geophysicists, and geochemists have intensively studied the earth for the past two centuries with only passing appreciation for the impacts of the geological substrate, earth materials, and earth processes on human health. Similarly, although health scientists have a rapidly expanding understanding of individual physiology and the epidemiology of human populations on local to global scales, most modern public health practitioners have only limited awareness of the extent to which the earth environment impinges on public health.
Although valuable linkages do currently exist between the earth science and public health communities, the limited extent of interdisciplinary cooperation has restricted the ability of scientists and public health workers to solve a range of complex environmental health problems, with the result that the considerable potential for increased knowledge at the interface of earth science and public health has been only partially realized. The linkage of earth science and public health is not about the relevance of earth science knowledge to health, or vice versa—rather, the
issue addressed here is the generally inadequate appreciation of the potential benefits of this interface and the consequent diminished priority that it is accorded.
NEED FOR COLLABORATIVE RESEARCH
Historically, it was known that some geographic locations were associated with specific diseases in humans and animals. Marco Polo recognized hoof diseases in animals that had consumed certain plants (later determined to be selenium-accumulating plants) and observed physical abnormalities (goiters) that he attributed to the local water supply. Recognition of the role of iodine to alleviate goiter emphasizes the importance of research at the interface of earth science and public health, and in fact iodine deficiency is one of the single most preventable causes of mental retardation (Delange et al., 2001). Similarly, the addition of fluoride to drinking water and toothpaste, based on recognition of the beneficial effects of naturally fluoridated water, has been hailed as one of the top 10 public health achievements of the twentieth century (CDC, 1999). For communities of more than 20,000 people, the cost savings from prevention of dental cavities as a result of water fluoridation has been estimated as 38 times the cost of fluoride addition (Griffin et al., 2001).
Such instances are far outweighed by examples where prior knowledge of earth science and improved understanding of the characteristics of earth materials could have informed the decision-making process and prevented disease. Volcanic aerosols, gases and ash, airborne and waterborne fibrous minerals, and toxic metals in soils and plants are all examples presented later in this report where earth materials have adversely affected human health (see Box 1.1).
In a series of reports more than 20 years ago, National Research Council (NRC) committees described the contemporary understanding of interactions between earth’s geochemical environment and public health (NRC, 1974, 1977, 1978, 1979, 1981). This report presents a broad update describing our understanding of the interactions between earth materials and public health, provides an introduction to successful past cooperative scientific activities at the interface of the earth and health sciences, and suggests future avenues for crossover and integration of research for the common good of humankind.
COMMITTEE CHARGE AND SCOPE OF THE STUDY
Recognizing the current disconnect between research carried out by the earth science and public health communities, the National Science Foundation (NSF), U.S. Geological Survey (USGS), and National Aero-
Arsenic Contamination of Groundwater in Bangladesh
One of the clearest examples of the crossover between the earth sciences and public health is the infamous problem of arsenic in Bangladesh and West Bengal, India. In the 1970s, the United Nations Educational, Scientific and Cultural Organization (UNESCO) funded the digging of simple tube wells (up to 150 m deep) into rapidly deposited, unconsolidated deltaic sediments of the Ganges and Brahmaputra river systems. The goal was to minimize the use of surface waters for domestic use and thereby reduce the devastating effects of cholera and diarrhea, which were responsible for many deaths among the young and the elderly. Water from tube wells, it was thought, would replace the seriously contaminated surface water supply with adequate fresh, pure groundwater. The deltaic sediments, consisting chiefly of mud, silt, and sand, also contain organic matter and trace minerals carried from the upper reaches of the river systems. The iron oxides in these sediments are effective at scavenging arsenic (and other oxyanions such as phosphate), and when the iron oxides are reduced by iron-reducing bacteria (reductive dissolution), the associated ions such as arsenate are mobilized. Consumption and crop irrigation of arsenic-bearing water, in some cases with arsenic contents greater than 500 µg L−1, resulted in widespread arsenic poisoning which was especially prevalent in people at high risk due to poor nutrition. The result was a horrible disease most commonly manifested by skin lesions and cancer. Although the effect of the arsenic varies with the element species (As3+, As5+), it mostly acts through inactivation of enzyme systems, with trivalent arsenic being the most injurious (Ginsburg, and Lotspeich, 1963). In this region, more than 30 million people are drinking water that contains arsenic at concentrations exceeding the Bangladesh drinking water guidance value of 0.05 mg L−1 (i.e., 50 µg L−1) (Rahman et al., 2003), and the number would be considerably greater if the World Health Organization–recommended guideline value of 10 µg L−1 (WHO, 2001) were used. Further, at least 175,000 people have skin lesions caused by arsenic poisoning.1
Statement of Task
A National Research Council ad hoc committee will assess the present status of research at the interface between medicine and earth science, and will advise on the high priority research activities that should be undertaken for optimum societal benefit. The committee will report on the most profitable areas for communication and collaboration between the earth science and medical communities, recognizing both the infectious disease and environmental components. The committee is specifically tasked to:
nautics and Space Administration (NASA) requested that the NRC undertake a study to explore avenues for interdisciplinary research that would further knowledge at the interface between these disciplines (see Box 1.2). The ultimate goal is to encourage collaboration to comprehensively address human health problems in the context of the geological environment.
The committee assembled by the National Academies to address this task held three open, information-gathering meetings, where representatives from federal and state agencies, the academic community, and professional societies provided information and perspectives on the committee’s task. One of these meetings was a three-day workshop, where a combination of presentations and breakout groups allowed for extensive interdisciplinary exchange of data and concepts. During closed sessions, the committee deliberated on the broad issues involved in the integration of disparate disciplinary approaches. Although recognizing that processes linking the solid earth with the biosphere, the oceans, and the atmosphere represent a continuum, the committee concentrated its atten-
tion on the relatively direct geological drivers of human health. Recent NRC reports have described interactions between human health issues and the oceans (NRC, 1999d) and between human health and the atmosphere (NRC, 2001a); accordingly, this committee focused on the continental environment and only considered oceanic and the atmospheric effects on human health through their interactions with on-land geology (e.g., volcanic emanations, particulate matter). The committee excluded the extremely important domain of agriculture as beyond its purview.
The recent publication of two major texts on the earth sciences and health (Skinner and Berger, 2003; Selinus et al., 2005) reflects the increased attention being focused by researchers on important interactions between these fields. Together, these books provide a comprehensive description of current understanding of the relationship between the natural environment and public health, as well as numerous examples describing the connections and interactions between these fields. Rather than attempt to cover the same material, the NRC committee sought to build on these works by focusing its endeavors on understanding the vast array of potential research directions at the interface of earth science and public health and to identify those that it considers to have the highest priority.
The process of identifying the priority research areas presented in this report was based on the discussions and conclusions at the open workshop hosted by the committee. The four workshop breakout groups—in each case coordinated by a committee member and including members of the earth science, public health, and governmental communities—reported back with recommendations that described important research areas for the committee’s consideration. The committee focused on those areas that required full collaboration by both earth science and public health researchers and did not consider the numerous examples of valuable research topics that could be undertaken primarily within one of these research disciplines without requiring significant participation by the other.
When members of two distinct professional communities who have traditionally had little interaction come together on a study committee such as this, it is not surprising that issues of vocabulary and definition rapidly emerge. Recognizing that acceptance of the recommendations contained here by both communities will, to some extent, depend on both being able to easily understand the presentation of the ideas and concepts without either feeling that there is an overlay of technical jargon, the committee has attempted to ensure that such jargon is kept to a minimum throughout the report. In some cases, this has resulted in ideas, concepts, and situations being presented in a somewhat simplistic manner; nevertheless, the committee considers that such simplicity is essential. This approach is reflected in Chapter 2, where basic earth science concepts are
presented for the public health community and basic human physiological concepts are presented for the earth science community.
The committee decided that the report could best highlight the state of knowledge by focusing on the interactions between earth science and public health through the public health reference frame—that is, through human exposure routes. The committee organized these sections of the report into what we breathe (Chapter 3), what we drink (Chapter 4), and what we eat (Chapter 5). Public health interactions with earth perturbations, both natural (e.g., earthquakes, volcanic eruptions) and anthropogenic (e.g., extractive industries), are described in Chapter 6. In these separate sections, the committee employs specific examples to focus on, and highlight, the state of present knowledge. These considerations of cause and health effect resulting from exposure to earth materials give rise to a range of research priorities for each exposure pathway—in each case, those that have been identified by the committee require active collaboration between researchers from both the earth science and the public health communities. The role of geospatial information—geological maps for earth scientists and epidemiological data for public health professionals— is recognized as an essential integrative tool that is fundamental to the activities of both communities (Chapter 7), and a number of suggestions are presented for mechanisms to promote and enhance collaboration (Chapter 8). Finally, the committee presents a series of conclusions and recommendations, based on the opportunities for research collaboration described in Chapters 3 through 7, which are designed to enhance integration of the earth and public health sciences (Chapter 9).