Transboundary water resources and public health in the U.S.-Mexico border region.

Background: Environment of the Twin Cities of Nogales, Arizona, and Nogales, Sonora

The U.S.-Mexico border region stretches nearly 3,000 kilometers from the Pacific Ocean to the Gulf of Mexico [ILLUSTRATION FOR FIGURE 1 OMITTED]. Metropolitan Nogales, the site of study, lies on the Arizona-Sonora frontier, within the western quarter of the U.S.-Mexico border. The area encompassing the twin cities of Nogales, Arizona, and Nogales, Sonora, (known in Spanish as Ambos Nogales - literally, "Both Nogaleses") shares a common history, culture, and economy. As importantly, the two cities share a physical environment.

As everywhere, this environment, its natural resources, and its dynamic processes do not respect human-created international boundaries. The interdependent nature of transboundary resources is nowhere better illustrated than in the water resources of Ambos Nogales. The Santa Cruz Basin Aquifer, upon which the two cities depend for their water supplies, is bisected by the border at Nogales. The aquifer is fed by the Santa Cruz River that originates in Arizona, loops down into Sonora and back up toward Tucson. A tributary, the Nogales Wash, flows through both cities and joins the Santa Cruz not far from the International Wastewater Treatment Plant that handles the sewage (liquid and solid waste, as opposed to sewerage, a term used throughout this paper to describe a system for removal of sewage) from both communities. Most of the surface flow of the Santa Cruz originates from effluent discharges and results in a rich, restored downstream ri-parian habitat.

The Sonoran Desert, within which the Ambos Nogales communities lie, is an area of relatively low annual rainfall (400 mm or 16 inches) and seasonally hot temperatures. But as in other dry regions, the climate is characterized more by pronounced variation than by averages. Alternating extremes of drought and flooding are not uncommon, and both of these conditions, the present paper will show, can significantly affect public health.

The metropolitan area's topography features steep hillsides that slope downward from south to north, creating a basin in which surface water, groundwater, and air currents migrate to the United States (2). This landscape combined with shallow soils and sparse vegetation on the hillsides render the area prone to flooding when normally dry washes (streamlets) and canyons quickly fill by runoff. Such urban flooding often is accompanied by broken sewer and water lines. Storm runoff mixes with industrial contaminants and household waste, exacerbating pollution problems and threatening public health on both sides of the border (2,3).

In Ambos Nogales, centuries-long human occupation has generated land use patterns dictated by landscape, climate, and social needs. The activities resulting from rapid population growth, changes in habitation patterns from the valley floor to higher elevations, expanding industry, and rising commerce have engendered numerous problems. Among the most common are antiquated and decaying infrastructure, chronic shortages of water supply, rising air and water pollution, soil contamination, and resource depletion.

The "Ambos Nogales Water Project"

The "Ambos Nogales Water Project," the unofficial title for "U.S.-Mexico Transboundary Water Resources Management: Bilateral Issues, Policies, and Strategies in the Nogales Region," represents an interdisciplinary study of transnational water management policy. The project was a joint, binational effort undertaken from 1989 through 1993 by the Udall Center for Studies in Public Policy at the University of Arizona and El Colegio de la Frontera Norte (COLEF) in Tijuana and Nogales, Mexico. Funding was provided by the Ford Foundation, from both its New York City headquarters and Mexico City office. The project's goals were to: 1. survey and characterize the shared physical water resources of the Nogales area; 2. determine the various ways in which water is used and managed in a semiarid, urban environment; and 3. suggest ways in which water-related decisions and policies could be made responsive to local needs and desires. Members of the research team represented several disciplines, including hydrology, geography, regional development and planning, political science, policy analysis, comparative law, public health, anthropology, and history. Throughout the study, the Udall Center and COLEF teams remained sensitive to the concerns of local grassroots organizations and stressed the need for greater communication among local residents, government agencies, and academic institutions.

The authors note that they were not involved in the primary water resources research or sampling surveys that are the background of this paper. They have employed the data generated to discuss previously unaddressed public health aspects of the work.

The project's principal objectives were to: 1. document uses and sources of water for municipal and industrial purposes; 2. investigate the extent and possible severity of surface and groundwater contamination on both sides of the international border; 3. identify institutional structures used to regulate and monitor environmental conditions in both Arizona and Sonora; 4. evaluate the importance of informal transborder networks that link agencies, individuals, and groups; 5. suggest alternative management strategies for efficient use of available water resources; 6. identify future water needs and constraints to meeting those needs; 7. suggest mechanisms for a binational management system; and 8. facilitate dialogue and action.

Water Resources and Public Health

When examining water management, particularly in an urban setting, key issues include quantity (water supply), sewerage (water and waste removal), and quality. All three subjects bear directly on human health, and all are closely interrelated. According to David C. Warner, an authority on border healthcare financing and utilization at the LBJ School of Public Affairs, "there can probably be no improvement in general health unless the more basic problems of the environment, sanitation, and safe drinking water are resolved"(4). The relationships between water management issues and public health in the Ambos Nogales area are discussed below.

Water Supply and Health

In the area that is now metropolitan Nogales, until this century availability of water had been a function primarily of geologic processes and climatic conditions. The mountain ranges surrounding Nogales mostly comprise impermeable Tertiary volcanic materials that cannot store groundwater. The two cities themselves are built atop Quaternary alluvia, a bed that can yield moderate amounts of water at relatively shallow depths. But in the past decades first urbanization, then industrialization have altered the regional water balance. In consequence, growing human demand has been rapidly depleting stores of subsurface water, the only stable source. Given these pressures of population and development, "natural" recharge from mountain-front and stream-channel recharge processes cannot adequately replenish the supply of groundwater (5).

Compounding the effects of overdraft, the deterioration of the delivery system over time, particularly on the Mexican side, has further reduced both the volume and reliability of the water supply (5). In this regard, the spatial distribution of the delivery system mirrors the historical evolution of the inhabited areas. Since the 1960s, maquiladoras (multinational industrial and commercial plants) have mushroomed in communities along the border, with about 70 of them located in Nogales, Sonora, alone. These ventures have attracted large numbers of migrant workers from Mexico's interior who live in colonias, or squatter settlements, that are not generally served by piped water and other infrastructure.

The net effect of these demographic and economic phenomena, especially in the case of Nogales, Sonora, is that entire neighborhoods remain unsupplied or undersupplied with running water. To obtain water, residents of these areas rely on several alternative sources; those who can afford it contract with truck deliverers who fill their rooftop tanks or purchase bottled water. Less affluent residents, especially those living in colonias, walk to distant community spigots or hoses and fill cans and other receptacles.

Water, as is well known, is essential for maintenance of life. It functions in digestion, absorption, circulation, and excretion, and plays a role in maintaining body temperature. Water serves as a building material for growth and repair of the body, and it is part of all body tissues and fluids (6). The water supply situation in the Ambos Nogales area, therefore, holds a number of significant implications for the health of area residents. First, inadequate consumption of water is detrimental to human health and contributes to mortality in developing societies; dehydration will kill faster than starvation. Everywhere special attention to water needs should be given to infants and to the sick, and in hot environments, to all persons (6). Further, chronic water shortages seriously compromise household sanitation and personal hygiene which, in turn, can lead to a variety of health problems, most notably gastrointestinal diseases and parasitic infestations (7,8). A recent comprehensive review of 100 studies evaluating the health impact of improvements in water supplies and sanitation in developing countries found that improvements in water supply alone were associated with a median reduction of 25% in diarrheal morbidity (9). The same study also revealed that, in these same areas, improvements in both water and sanitation have an even greater impact on mortality than on illness, with a median reduction of 60% in deaths from diarrheal diseases. Finally, not less seriously, such shortages indirectly affect health by causing water users to seek substitutes for household delivery. This practice often results in chemical or microorganismic contamination from the alternative source or from the vessels used for storage or transfer. Frequently, water is stored in 55-gallon drums usually scavenged from local industries (10).

Wastewater Collection and Health

Mapping the sewerage system in both Nogaleses revealed that, like water delivery lines, sewer lines were also spatially distributed according to established socioeconomic patterns (11,12). Accordingly, Nogales' colonias remain largely beyond the reach of the city's sewers. Furthermore, the sewers beneath the streets of Nogales, Sonora, are aging and poorly maintained. Thus, not only are entire zones and neighborhoods unserved, but even sewered areas are problematic because of breaks and leaks. These breaches are exacerbated regularly by rushing floodwaters caused by the region's heavy rainfalls, especially during the summer "monsoons."' As a result, during such episodes sewer-line breaks are common and leaks find their way to the aquifer, threatening groundwater quality (10,13,14,15).

Again, the connection between disease and sanitation is clearly established. As development specialists recognize, one need only see an aggregate statistic on a nation's urban sewerage coverage to gauge the overall level of its public health (7). The U.S. Agency for International Development study cited earlier found that improvements in the disposal of excreta were associated with a median reduction of 22% in diarrheal morbidity (9). In Nogales, Sonora, it is difficult to estimate accurately the percentage of households with direct sewer lines. First, even the population figures remain essentially unknowable; the official population is 130,000 according to the latest census, but some estimates place it as high as 200,000. Then, because of shifting, provisional settlements by migrant workers and rapid development of new communities, the number of households fluctuates considerably. Finally, even with reasonable assessments of the coverage, the effectiveness of the city's sewer system is reduced by the high degree of leakage, whose volume remains unquantified. During periods of extreme flooding, moreover, health hazards increase due to open exposure of raw sewage and because post-flood surface accumulations create breeding ground for infectious disease (16, 17) [ILLUSTRATION FOR FIGURE 2 OMITTED].

For the above reasons, residents of Nogales, like those in other border communities, experience many of the health problems associated with inadequate sewerage and the ensuing water contamination, primarily gastrointestinal diseases and hepatitis (18,19,20,21,22,23,24). An evaluation of primary healthcare in Nogales, Sonora, conducted by the Colegio de Sonora from 1989 to 1991, revealed that diarrheal diseases, along with acute respiratory infections, were the principal causes of morbidity among children from birth to four years of age (21). The same study also found that gastroenteritis and other infectious diseases were the seventh leading cause of mortality among the general population (21).

During this same period, an assessment of health status and services in Nogales, Arizona, undertaken by the University of Arizona Southwest Rural Health Research Center in the fall of 1990, found an incidence rate for Hepatitis A of 27 cases per 10,000 people in Nogales, Arizona, and 18.67 cases per 10,000 people in Santa Cruz County. These incidence rates were considerably higher than those for other Arizona border counties in 1990: 4.2 per 10,000 in Yuma County and 3.7 per 10,000 in Cochise County (20). Hepatitis A is contracted through water and food; the virus has an oral/fecal transmission. Of additional concern was the finding of traces of Type I Polio virus in Nogales Wash in 1990. It was determined that the Polio was indeed vaccine. However, the finding suggests that Nogales Wash can support viruses (20).

In view of these concerns, an August 1993 U.S. Environmental Protection Agency (EPA) commissioned report by the agency's Border Public Advisory Committee and prepared by the Udall Center considers wastewater collection and treatment among the most pressing infrastructural problems facing the urbanized portions of the U.S.-Mexico border. But recognizing that it is not just an infrastructural problem, the report states that "its solution would resolve many associated environmental and health problems in the large and small population centers of the region" (25).

Water Quality and Health

Quality of water is as important a determinant of public health as are quantity of water available and disposal of excreta. Partly in view of the significant presence of maquiladora plants and their alleged waste-handling processes, the project decided to collect available information on water quality in both communities-Nogales, Arizona, and Nogales, Sonora. It was apparent to the study team, however, that existing data were insufficient, less than totally reliable, or noncomparably expressed. In the fall of 1990, therefore, the project undertook a small, pilot study of water quality in approximately 20 selected wells on each side of the border. Primarily, the exercise sought to demonstrate that such surveys could be done cooperatively and binationally, and at relatively modest costs. These objectives were easily realized.

More importantly for public health, the pilot study also sought to determine water concentrations of known carcinogenic compounds such as TCE (trichloroethylene, a volatile organic compound or VOC) and nitrates as well as other VOCs, bacteria, inorganic compounds (major cations and anions), and metals. The map shown in Figure 3 is a product of the project's GIS (geographic information system) database; it depicts nitrate levels, sewerage, and distribution of households reporting health effects. Similar maps were created for levels of TCE, others VOCs, and fecal coliforms (26).

Principal findings included the following: 1. Nogales Wash and wells located along Nogales Wash or along wastewater lines in Nogales, Sonora, were generally contaminated by bacteria. The Nogales International Wastewater Treatment Facility reduces, but does not eliminate, bacteriologic contamination caused by wastewater; 2. elevated nitrate levels were found in some wells near Nogales Wash or along wastewater lines in both Sonora and Arizona, but nitrate levels in Arizona groundwater do not exceed state standards. However, the sampling revealed that some Sonoran groundwater nitrate concentrations exceeded Mexican standards; and 3. detectable concentrations of VOCs were found in parts of the shallow alluvial aquifer that underlies Nogales Wash and wastewater lines in Arizona and Sonora. In Arizona, the VOC concentrations were within acceptable limits while three public drinking water supply wells in Sonora contained elevated concentrations of VOCs (5).

Earlier, during the 1980s, Arizona Department of Environmental Quality (ADEQ) and Arizona Department of Health Services (ADHS) monitored various groundwater and surface water sites in the U.S. for VOCs (27). At both groundwater and surface water sites in Arizona, tetrachloroethylene (PCE) generally exceeded the current Arizona Health-Based Guidance Levels (HBGL). TCE was also detected in groundwater at levels exceeding the HBGL and ADEQ's maximum contaminant level (MCL). The HBGL represents the human ingestion level of a chemical that is unlikely, to result in long-term, adverse health effects, and the MCL is the maximum permissible level of a contaminant in water that may be delivered to any user of a public water system.

As a result of the contamination, ADEQ undertook a major monitoring program in June 1990 in Nogales, Arizona, to determine the extent of the chemical and microbiological contamination for both groundwater and surface water. Subsequently, ADHS utilized the ADEQ June 1990 groundwater monitoring data to carry out a human health risk assessment for residents of Nogales, Arizona. It was found that PCE concentrations were in excess of the HBGL at various groundwater sites and in excess of the MCL at a single groundwater well 1.8 km (1.1 miles) north of the U.S.-Mexico border.

At this same well site, TCE was detected at a concentration greater than the HBGL. The concentrations of PCE and TCE were generally high in Nogales, Sonora, exceeding the HBGLs and MCLs, and lower in Nogales, Arizona. The results suggested that the contamination was restricted to an area within 4 miles (6.4 km) of the border. The EPA cancer risk method computes estimates which are the "incremental probability of an individual developing cancer over a lifetime as a result of exposure to the potential carcinogen." In this study, variations in the concentration levels of PCE/TCE were reflected in the potential excess lifetime cancer risk (ELCR). In general, the potential ELCR from all exposure pathways (i.e., inhalation, ingestion, dermal) in adults in Nogales, Arizona, ranged from two to six excess cases per million persons with the exception of a peak in the ELCR of 20 cases per million, observed 1.1 miles (1.8 km) north of the border. Fecal coliform bacteria were also found in Nogales Wash and surrounding groundwater at levels in excess of the state standard for drinking water and surface water (27).

It is important to highlight that a concomitant assessment of health status and services in Nogales, Arizona, in 1990 also revealed high levels of fecal coliform and traces of VOCs, among other contaminants (20). An earlier groundwater study in Nogales, Sonora, conducted by Prescott College in 1988, found fecal coliform levels above the Federal Drinking Water Standard. The standard is 1 count per 100 ml; the study found fecal coliform levels ranging from 17 to 2,400 counts per ml (28). Fecal coliform is not a health hazard per se. However, fecal coliform counts are good indicators of potential health problems, such as amebiasis and hepatitis (28). Similarly, according to the Pan American Health Organization, yearly evaluations of surface water quality in Ambos Nogales from 1988 to 1991 showed contamination with fecal coliforms. Monitoring of surface water held during the same period revealed fecal coliforms and a certain degree of solvent contamination in wells that were not very deep (29).

The results of the "Ambos Nogales Water Project" pilot water sample survey may have played a role in the International Boundary and Water Commission's (IBWC) decision in 1994 to undertake a groundwater monitoring activity in Ambos Nogales. Other likely factors contributing to the IBWC decision include community pressure, expressed concern by the Santa Cruz County Health Department, and repeated flooding patterns in the area. The groundwater monitoring activity was scheduled to begin in early December 1994 with technical assistance provided from the Arizona Department of Environmental Quality (ADEQ) and funding from the EPA. Water samples are to be collected over a 12-month period from a total of 13 monitoring wells located along the Nogales Wash on both sides of the border. Water samples will be analyzed by ADEQ to assess levels of VOCs, trace metals, major cations and anions, total and fecal coliforms, and total petroleum hydrocarbons (TPH) (30).

Also partly driven by the findings of the project's water sample survey, in 1992, the Nogales citizens' group, Living is for Everyone (LIFE), requested assistance from the University of Arizona to investigate possible clusters of multiple myeloma, leukemia, and systemic lupus erythematosus (SLE) in their community (31,32). The affected residents believe the health problems were caused by environmental contamination. Possible environmental exposure sources included drinking water, TCE, and air pollution generated from a frequently burning garbage dump in Nogales, Sonora. Over the next year, University of Arizona staff and members of LIFE collaboratively planned and initiated a volunteer effort to undertake a community survey of the problem. Fourteen incident cases of multiple myeloma and 26 prevalent cases of SLE were documented in Santa Cruz County during the years 1989 to 1993. The expected number of incident cases of multiple myeloma in a population the size of that in Santa Cruz County during that period is five, while the expected number of prevalent cases of SLE is four.

Pursuant to this preliminary effort, in December 1993, Arizona Governor Fife Symington authorized funds to conduct a study of environmental health problems in Nogales and, more broadly, in Santa Cruz County. The Arizona Cancer Center at the University of Arizona was contracted to undertake this effort in collaboration with LIFE and several public health institutions in Tucson, Phoenix, and Nogales. A team of researchers led by epidemiologist Larry C. Clark began implementing the survey in July 1994. The study relied on a sample of 708 individuals (546 residing in Nogales and 162 in a control community in Patagonia, Arizona, outside Nogales). This sample includes all confirmed and available cases of the study diseases, family members of each case, a random sample of Nogales residents, and a random sample of residents from the control community (33,34). The Clark team's survey findings, released in late 1994, present strong evidence that incidences of multiple myeloma and SLE in Nogales, Arizona, have been abnormally high (35).

Conclusion

The "Ambos Nogales Water Project" was a 4-1/2 year undertaking whose purpose was to understand how a critical resource, water, is managed in a transborder setting. As such, the project yielded some important accomplishments. The water sample survey, for example, helped forge an alliance of public agencies, community groups, and academic institutions from Sonora and Arizona. This new alliance joined to investigate water issues that have threatened public health in both communities for several decades. In the process of compiling the results of the survey and evaluating their significance, the project also assembled the region's first genuinely binational geographic information system database on water resources. This database permits the display and analysis of spatial and temporal distributions of infrastructure and industry, population demographic features, water quality test results, and incidence of environment-related health problems, among other uses.

While the primary focus of project activities was the sociopolitical context within which water is distributed and used, public health issues also were identified and addressed given the clearly inseparable linkages between water and human health. As a result, the project yielded insights into the relationships between water management issues and public health issues.

Because metropolitan Nogales in many ways typifies the binational ambience of communities in the U.S.-Mexico border region, these insights and the procedures utilized to unveil them are readily adaptable and extendable to other border communities from California to Texas.

For epidemiologists and health officials, the study delivered another important finding. In the process of researching water and public health relationships in Ambos Nogales, it became apparent that little scientific data exist and few systematic studies have been undertaken on water-related health problems and their causes in the two communities, and indeed throughout the U.S.-Mexico border area. This discovery is particularly notable given that gastrointestinal diseases are among the leading causes of morbidity and mortality, especially in Nogales, Sonora. The paucity of scientific studies and reliable information argue for further study of the nature and magnitude of water-related health problems in Ambos Nogales and elsewhere in the border region.

Finally, pursuant to the adoption of the North American Free Trade Agreement (NAFTA) in late 1993 has come the potential for increased economic development of the U.S.-Mexico border region and, concomitantly, the opportunity to improve and sustain human and ecosystem health in the region. Unlike previous multinational trade accords, NAFTA provides for the establishment of new institutions charged with assuring the financial and environmental well-being of the border region (36). These include the binational (U.S.-Mexico) North American Development Bank (NADBank) and Border Environment Cooperation Commission (BECC). The former institution was created to fund "environmental investments," while the latter will evaluate and certify projects submitted to NADBank for funding. More specifically, the purpose of BECC is to "help preserve, protect and enhance the environment of the border region in order to advance the well-being of the people of the United States and Mexico" (37). Significantly, for those interested in public health, in general, and water-related health problems, in particular, NADBank and BECC have identified water-related problems as their initial priority to improve overall quality of life in the border region. The findings and outputs of the "Ambos Nogales Water Project" clearly support this decision and, more importantly, abet bi-national efforts that address mutual concerns relating to water management issues.

References

1. Udall Center for Studies in Public Policy (1994), The Ambos Nogales Water Resources Project: Summary of Project Outputs, Tucson, Ariz.: Udall Center; and H. Ingram, N.K. Laney, and D.M. Gillilan (1995; forthcoming), Divided Waters: Bridging the U.S.-Mexican Border, Tucson: University of Arizona Press.

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Acknowledgements

The authors thank Helen Ingrain, director of the Udall Center for Studies in Public Policy at the University of Arizona, and principal investigator of the "Arebus Nogales Water Project," whose outputs inform the present essay (1). The authors did not conduct the project's water resources research or sampling surveys, which were accomplished by a technical team led by Simon Ince, with primary contributions by James DuBois, Todd Rassmussen, Dick Kamp, and Irasema Coronado. Roberto Sanchez of El Colegio de la Frontera Norte (COLEF) in Tijuana, Baja California; and Francisco Lara of COLEF in Nogales, Sonora, the project's principal Mexican collaborators, provided invaluable information and ideas to this article. Len Milich, Nancy Laney, and David Gillilan also contributed notably. The authors gratefully acknowledge the financial support of the Ford Foundation for the research upon which this article is based.

Robert G. Varady, Ph.D., Associate Director, Udall Center for Studies in Public Policy, The University of Arizona, 803/811 East First St., Tucson, AZ 85719